REPORT DOCUMENTATION PAGE

Transcription

1 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (Whan Data Entered; 1 REPORT NUMBER AFGL-TR REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM 2. GOVT ACCESSION NO. 3 RECIPIENT'S CATALOG NUMBER 4 TITLE (and Subline) 5. TYPE OF REPORT ft PERIOD COVEREO AN ANALYSIS OF INFRARED AND VISIBLE Scientific Reprt N. 2 ATMOSPHERIC EXTINCTION COEFFICIENTS MEASURED AT ONE-MINUTE INTERVALS 6 PERFORMING ORG. REPORT NUMBER SIO Ref AUTHOR^; B CONTRACT OR GRANT NUMBERfaJ Janet E. Shields F C PERFORMING ORGANIZATION NAME AND ADDRESS University f Califrnia, San Dieg Visibility Labratry La Jlla, Califrnia II CONTROLLING OFFICE NAME AND AODRESS Air Frce Gephysics Labratry Hanscm AFB, Massachusetts Cntract Mnitr: Lt.Cl. Jhn D. Mill/OPA 10 PROGRAM ELEMENT. PROJECT, TASK AREA ft WORK UNIT NUMBERS 62101F REPORT DATE July 1983 O NUMBER OF PAGES 65 U MONITORING AGENCY NAME ft ADDRESSf/f different frm Cntrlling Office) IS SECURITY CLASS, (f thie reprt; UNCLASSIFIED ISa DECL ASSIFICATION/DOWNGRADING SCHEDULE 16 DISTRIBUTION STATEMENT (f this Reprt) Distributin limited t U.S. Gvernment agencies nly; Freign Infrmatin; 30 September Other requests fr this dcument must be referred t AFGL/OPA, Hanscm AFB, Massachusetts DISTRIBUTION STATEMENT (f the abetract entered In Blck 20, It different frm Reprt) Apprved fr public release; distributin unlimited. 18 SUPPLEMENTARY NOTES 19 KEY WORDS (Cntinue n reveree aide if neceaeary and Identity by blck number) Aersl Extinctin Cefficient Atmspheric Aersls Atmspheric Optical Prperties Atmspheric Extinctin Cefficient Infrared Extinctin Infrared Transmittance 20. ABSTRACT (Cntinue n reveree aide It neceeamry and Identify by blck number) This reprt discusses an analysis f tw ne-mnth data sets cnsisting f measurements f visible and infrared (3-5/1 m and 8-12 /um) extinctin recrded at ne-minute intervals. The data were supplied by the Air Frce Gephysics Labratry, which acquired the data jintly with the Ministry f Defense f the Federal Republic f Germany at the OPAQUE statin near Meppen, FRG. High infrared extinctins f apprximate magnitude 1 km -1 ccur in this data set almst exclusively when the visible extinctin cefficient exceeds 1 km -1 and the relative humidity exceeds 80%. Within a mist and fg bin, defined by pints meeting the abve cnditins, the relatin between the infrared and visible extinctin is fund t be quite variable. DD,^M7, 1473 EOITION OF t NOV 65 IS OBSOLETE S/N UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)

2 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE ftttien Data Entered) 20. ABSTRACT cntinued: Cntinuus mist and fg perids lasting 30 minutes r lnger have been extracted, and the tempral variatins in the extinctins during these perids have been analyzed. It was fund that in sme cases the tempral variatins in the infrared and visible extinctins crrespnded very well. In many cases, the infrared tempral changes were greatly magnified cmpared with the visible extinctin changes. Als, in sme cases the infrared extinctin shwed essentially n variatin when the visible extinctin was less than a certain threshld; when the visible extinctin exceeded that same threshld, the infrared extinctin changed markedly in cnjunctin with visible extinctin changes. The bserved tempral variatins are illustrated and discussed, alng with the scatter plts f the infrared vs visible extinctin fr these perids. Fllwing this analysis, statistics relating t the incidence f high infrared extinctins are illustrated and discussed. Estimates f the prbability f exceeding threshlds are given, as well as estimates f the cnditinal prbability f exceeding threshld given a previus ccurrence f high infrared extinctin r high visible extinctin. Fr this data set, the estimated prbability f exceeding a threshld f 1 km -1 is rughly 5% fr bth infrared wavebands, whereas the cnditinal prbability f exceeding threshld six hurs after the threshld has been exceeded at night is apprximately 30%. The cnditinal prbability fr a lag interval f ne hur at night is apprximately 50%. In the daytime, the cnditinal prbabilities are high nly fr abut an hur. These data and a variety f additinal cnditinal prbabilities are illustrated and discussed in this reprt. UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGEfHTien Data Entered)

3 AFGL-TR SIO Ref AN ANALYSIS OF INFRARED AND VISIBLE ATMOSPHERIC EXTINCTION COEFFICIENTS MEASURED AT ONE-MINUTE INTERVALS Janet E Shields Visibility Labratry University f Califrnia, San Dieg Scripps Institutin f Oceangraphy La Jlla, Califrnia Apprved Apprved Rsvtell W Au^rrfi, Directr William A NierenbergT Directr ^ Visibility Labratry Scripps Institutin f Oceangraphy CONTRACT NO. F C-0060 Prject N Task N Wrk Unit N Scientific Reprt N. 2 July 1983 Cntract Mnitr Lt. Cl. Jhn D. Mill, Atmspheric Optics Branch, Optical Physics Divisin Distributin limited t U.S. Gvernment agencies nly; Freign Infrmatin; 30 September Other requests fr this dcument must be referred t AFGL/OPA, Hanscm AFB, Massachusetts SUBJECT TO EXPORT CONTROL LAWS This dcument cntains infrmatin fr manufacturing r using munitins f war. Exprt f the infrmatin cntained herein, r release t freign natinals within the United States, withut first btaining an exprt license, is a vilatin f the Internatinal Traffic in Arms Regulatins. Such vilatin is subject t a penalty f up t 2 years imprisnment and a fine f $100,000 under 22 U.S.C Prepared fr AIR FORCE GEOPHYSICS LABORATORY AIR FORCE SYSTEMS COMMAND UNITED STATES AIR FORCE HANSCOM AFB, MASSACHUSETTS 01731

4 SUMMARY This reprt discusses an analysis f tw ne-mnth data sets cnsisting f measurements f visible and infrared (3-5/u.w and 8-12/j.m) extinctin recrded at ne-minute intervals. The data were supplied by the Air Frce Gephysics Labratry, which acquired the data jintly with the Ministry f Defense f the Federal Republic f Germany at the OPAQUE statin near Meppen, FRG. High infrared extinctins f apprximate magnitude 1 km -1 ccur in this data set almst exclusively when the visible extinctin cefficient exceeds 1 km -1 and the relative humidity exceeds 80%. Within a mist and fg bin, defined by pints meeting the abve cnditins, the relatin between the infrared and visible extinctin is fund t be quite variable. Cntinuus mist and fg perids lasting 30 minutes r lnger have been extracted, and the tempral variatins in the extinctins during these perids have been analyzed. It was fund that in sme cases the tempral variatins in the infrared and visible extinctins crrespnded very well. In many cases, the infrared tempral changes were greatly magnified cmpared with the visible extinctin changes. Als, in sme cases the infrared extinctin shwed essentially n variatin when the visible extinctin was less than a certain threshld; when the visible extinctin exceeded that same threshld, the infrared extinctin changed markedly in cnjunctin with visible extinctin changes. The bserved tempral variatins are illustrated and discussed, alng with the scatter plts f the infrared vs visible extinctin fr these perids. Fllwing this analysis, statistics relating t the incidence f high infrared extinctins are illustrated and discussed. Estimates f the prbability f exceeding threshlds are given, as well as estimates f the cnditinal prbability f exceeding threshld given a previus ccurrence f high infrared extinctin r high visible extinctin. Fr this data set, the estimated prbability f exceeding a threshld f 1 km -1 is rughly 5% fr bth infrared wavebands, whereas the cnditinal prbability f exceeding threshld six hurs after the threshld has been exceeded at night is apprximately 30%. The cnditinal prbability fr a lag interval f ne hur at night is apprximately 50%. In the daytime, the cnditinal prbabilities are high nly fr abut an hur. These data and a variety f additinal cnditinal prbabilities are illustrated and discussed in this reprt. -v-

5 TABLE OF CONTENTS SUMMARY LIST OF TABLES AND ILLUSTRATIONS v ix 1. INTRODUCTION Theretical Backgrund Descriptin f Data Measurements Data Reductin 3 2. RELATION OF MEASURED INFRARED AND VISIBLE EXTINCTIONS Incidence f High IR Extinctin Values Tempral Behavir f Extinctin During Mist/Fg Episdes IR t Visible Magnitude Relatinship During Mist/Fg Episdes Summary f IR and Visible Extinctin Cmparisns CONDITIONAL PROBABILITY ESTIMATES Cmputatin f Prbability and Persistence Results f Prbability Cmputatins Summary f Prbability Estimate Results CONCLUSION Results f the Analysis Cntinuing Analysis Objectives REFERENCES ACKNOWLEDGEMENTS 26 APPENDIX A: Time Series Plts and Scatter Plts f IR Aersl Extinctin and Visible Extinctin Cefficient 27 APPENDIX B: Plts f Prbability Estimates 42 APPENDIX C: Visibility Labratry Cntracts & Related Publicatins 54 -vii-

6 LIST OF TABLES AND ILLUSTRATIONS Table N. Page Number f Mist/Fg Episdes each Mnth Summary f Tempral Behavir Summary f IR t Visible Extinctin Linearity Standard Deviatin f Extinctin Cmpnents Types f Prbability Estimates Cmparisn f Visible and IR Prbabilities Effect f Visible vs IR Cnditins n Prbability Estimates, September Effect f Visible KS IR Cnditins n Prbability Estimates, March Fig. N Page Near Dawn and Late Afternn Extinctins, IR vs Visible Near Dawn and Late Afternn Extinctins vs RH IR Extinctin, Netherlands Netherlands Mist/Fg Bin Extinctin Ratis Minute Data Mist/Fg Bin Extinctin Ratis Time Series, 6 Sep Time Series, 22 Sep Time Series, 21 Mar Time Series, 28 Sep and 30 Mar Scatter Plts, 14 Sep Scatter Plts. 3 Sep Scatter Plts, 30 Mar Scatter Plts, 12 Mar Visible and IR Prbabilities, March nighttime Visible and IR Prbabilities, March daytime Persistence vs Time Lag, March Prbability Each Hur, Sep. nighttime Results f IR vs Visible Cnditinal Requirements P\a,KU+A)>T\ails(')>\km '1 vs Time Lag P \n/k(t+l\)>t\ans(t)>4km '] vs Time Lag Results f Relative Humidity Cnditinal Requirement Results f Extinctin at Dawn Cnditinal Requirement ix-

7 Frntispiece Meppen Grund Site Tp: Grund view shwing Eltr transmissmeter and meterlgical twer. Center: Grund view shwing meterlgical twer, AEG/FFM Scattered Light Recrder, and trailer with IR receiver. Bttm: Airbrne view f site lcated in triangular area near center f pht. Meterlgical twers maj be lcated by their shadws. -X-

8 AN ANALYSIS OF INFRARED AND VISIBLE ATMOSPHERIC EXTINCTION COEFFICIENTS MEASURED AT ONE-MINUTE INTERVALS Janet E Shields 1.0 INTRODUCTION Fr sme time, electr-ptical instrument systems perating in the infrared regin have been used in a variety f airbrne and grund based applicatins As a cnsequence, there has been cntinued interest in understanding and quantifying the transmittance f infrared radiatin thrugh paths f sight in the atmsphere Investigatrs have researched varius aspects f the prblem, and several mdels have been develped Fr example, the LOWTRAN5 mdel (Kneizys et al (1980)) includes the effects f scattering and absrptin f light by the varius cmpnents f the atmsphere In LOWTRAN5, the infrared extinctin can be cmputed as a functin f wave number ver hrizntal paths r slant-paths in the atmsphere In many f the mdels, including LOWTRAN5, either the visibility r the visible extinctin cefficient is a required input There is cntinued interest in studying atmspheric extinctin, in rder t determine the limitatins f mdels such as LOWTRAN 5 and t imprve such mdels where pssible The infrared extinctin due t aersls is particularly difficult t predict accurately, especially in thick haze, mist, 1 and fg Fr a given wavelength and fg type, the LOWTRAN mdels apprximate the infrared extinctin as a cnstant value fr each value f visible extinctin In mist and fg, measurements shw that fr a given value f visible extinctin, the infrared extinctin in a given waveband may cver a large range f values (Shields (1981)) This variatin in the infrared extinctin relative t the visible extinctin appears t ccur n a time scale which is shrt relative t the length f a mist r fg episde (Shields (1981) and Gimmestad et al (1982)) If this type f variatin ccurs in general at widespread lcatins, it culd have impact n the predictability f the infrared extinctin A set f data acquired during the OPAQUE prgram (Optical Atmspheric Quantities in Eurpe, see Fenn (1978)) frm an excellent data base fr an analysis f the tempral variatin f the infrared extinctin The data base cnsists f measurements f visible extinctin A suspensin f water drplets ccurring in near cndensatin cnditins is defined as fg r mist depending n whether the visibility is less than 1 km r greater than 1 km respectively (Mcintsh (1963) and Prulx (1971)) cefficient and infrared transmittance recrded at ne minute intervals ver a ne year perid The measurements were acquired near Meppen, Federal Republic f Germany, at the NATO statin perated jintly by the U S Air Frce and the Ministry f Defense f the FRG The extracted data, prvided by Air Frce Gephysics Labratry, will be referred t herein as the "minute data" The present reprt is an interim reprt, discussing an analysis f the data frm tw mnths, September 1978 and March 1978 Sectin 1 f the reprt gives the backgrund t the analysis Sectin 2 illustrates the behavir f the infrared and visible extinctin cefficients during the mist and fg episdes The mist episdes are extracted frm the full data base fr each mnth, and time series plts and scatter plts f the data during these episdes are discussed Sectin 3 is directed tward ptentially mre peratinally useful analysis Several sets f estimates f prbability and cnditinal prbability f ccurrence were extracted frm the data, and the results and sample plts are included in Sectin 3 Sectin 4 summarizes the results f the analysis, and discusses the prpsed apprach t the remainder f the year's minute data 1.1 Theretical Backgrund Definitin f Terms In this analysis, the tw terms dealt with mst frequently are aersl extinctin and ttal extinctin The term "aersl extinctin" represents the atmspheric extinctin due t aersl particles, that is, the wet and dry particles suspended in the atmsphere The term "ttal extinctin" indicates the atmspheric extinctin due t all atmspheric cmpnents, that is, the air mlecule cmpnents, the water vapr, and the aersl particles The effective bradband extinctin cefficient apprpriate fr analysis f bradband transmissmeter measurements is defined by where r is the measurement range, and T is the bradband transmittance defined by -1-

9 T=^-p. (1.2) J N K R K dk In this definitin, 7\ is the mnchrmatic transmittance f the atmsphere, N k is the radiance f the surce, and R K is the spectral respnse f the sensr. A mre detailed discussin f these definitins is included in Shields (1981). Typical Prperties f Extinctin The aersl extinctin depends n the relative distributin f particle size, the refractive index distributin, and the number density f the particles. If nly the number density changes, the spectral relatinship f the extinctin cefficients will be fixed. That is, the rati f extinctin cefficient at tw given wavelengths will be cnstant. If the particle size distributin r the refractive index distributin are allwed t change, then the spectral relatinships f the extinctin will change. The visible extinctin shuld be mre strngly affected by the submicrn regin f the particle size distributin, while the infrared extinctin shuld be mre strngly affected by the larger particles in the micrn regin, such as may ccur in mist and fg. When the atmspheric cnditins range frm clear t hazy, aersl extinctins are generally smaller at infrared wavelengths than at visible wavelengths. Under mst hazy cnditins, this will result in better ptical prpagatin within the infrared "windw" regins (abut 3-5/LitTi and 8-12/um) than at visible wavelengths. Hwever, in the presence f large drplets f size abut equal t wavelength (i.e. the micrn range), that nrmally ccur in mist and fg, the infrared aersl extinctin can increase and, in sme cases, becme slightly greater than the visible extinctin. Additinal details f theretical cnsideratins dealing with aersl extinctin are presented in Shettle and Fenn (1979), Nilssn (1979), and ther references discussed in Shields (1981). Recent Backgrund In Shields (1981), an analysis was made f simultaneusly measured visible and infrared extinctins (phtpic, 3-5/xm, and 8-12/j.m). These grund-based measurements were recrded in the Netherlands (Janssen and van Schie (1982)) as part f the OPAQUE prgram. The measurements were recrded at hurly intervals ver three 3-mnth perids. It was fund that essentially all the high infrared extinctins ccurred when the visible extinctin exceeded 1 km -1 and the relative humidity exceeded 94%. The pints meeting these cnditins were defined as the mist bin. Within this bin the infrared extinctin was quite variable: at mderate visible extinctins crrespnding t mist, the infrared extinctin was at times much higher than mdel estimates; and at higher visible extinctins crrespnding t fg, the infrared extinctin was extremely variable, varying frm the high values estimated fr fg t much lwer nes. The general magnitudes were cnsistent with the LOWTRAN and Huschke (1976) mdels, hwever the variatins frm estimated values were quite large. The tempral stability f the infrared extinctin in the mist bin was studied in Shields (1981) by extracting the persistence crrelatin cefficients (Brks and Carruthers (1953)). These persistence calculatins indicated that the variatins in infrared extinctin were ccurring n a relatively fast time scale. That is, the decay in the persistence crrelatin cefficient with time was large ver the time interval f an average mist episde. The decay was typically much greater in the infrared regin than fr visible wavelengths. This gives emphasis t the fact that the predictin f infrared extinctin n the basis f visible extinctin and lng-term parameters such as air mass type r fg type is subject t large uncertainties. With a view tward imprved stchastic methds f infrared extinctin predictin, it is imprtant t explre the behavir f the shrt perid fluctuatins. The persistence analysis f the Netherlands data was limited by the hurly data taking interval. Fr this reasn, the minute data set is f particular interest. Gimmestad et al. (1982) similarly reprt that the relatin between the infrared extinctin cefficient and visible extinctin cefficient may be highly variable within a given fg episde. They shw extinctin measurements taken at minute intervals ver a 3-hur perid in which the relatin between the visible and infrared extinctins is linear fr shrt perids, but nt ver the fg perid as a whle. They state that As the fg frmed, bth infrared and visible extinctin cefficients increased. When the fg dissipated, bth cefficients decreased, but they did nt retrace the path f fg frmatin. As the fg thickened again, the data pints again tk a different path n the lg-lg plt...a linear mdel may be a gd apprximatin fr the dependence f p, R n /J^/s fr any single-fg prcess, but nly if measurements are made n a time scale shrt cmpared with fg lifetimes. In this statement, /3 is the extinctin cefficient. Given that the shrt term tempral variatins may be quite significant in mist and fg cnditins, the minute data set is useful due t its shrt measurement interval f ne minute, and its lng extent f a year. Time series plts may be used in cnjunctin with scatter plts t evaluate the types f tempral variatins which can ccur in mist r fg. Additinally, estimates f cnditinal prbability f ccurrance may be extracted in rder t estimate the effect f these tempral variatins. 1.2 Descriptin f Data Measurements The instruments used at the Meppen statin are described and illustrated in Fenn et al. (1979), which als dcuments the data prcessing used t generate OPAQUE

10 tapes cntaining data at hurly intervals. The minute data set and the hur data set are extracted frm the same riginal data base. The infrared transmittance data were acquired using a 500-meter-baseline Barnes Transmissmeter Mdel The blackbdy surce is maintained at a temperature f apprximately 650 C C. An intercmparisn between the transmissmeters f the varius OPAQUE statins was cnducted in 1978, as described in Shand (1978) and Fenn et al. (1979). The intercmparisn demnstrated that prblems existed with the standard.calibratin prcedure. A different calibratin scheme was evlved, in which the data are searched fr a clear day with lw aersl and water vapr cntent, i.e. preferably a day with meterlgical range ^ 20 km, relative humidity < 80%, and dewpint temperature < 10 C. The beam transmittance measured under clear day cnditins is cmpared with the LOWTRAN calculatin f transmittance in rder t determine a calibratin cnstant. See Shettle and Fenn (1978), Khnle (1979), and Shettle (1980). Uncertainty in the calibratin has little effect n the infrared aersl extinctin in mist and fg. The effects f calibratin uncertainty and ther uncertainties n the extinctin data are discussed in Sectin 5.2 and Appendix C f Shields (1981). The measurement uncertainty is apprximately ±2% transmittance. The uncertainty exceeds 10% fr aersl extinctins greater than abut 10 km -1 r less than abut.1 km -1. The infrared transmittance is recrded in fur spectral regins: 3-5/xm, 8-12^m, /im, and narrw band 4/nm. Recrdings are made every minute, cycling thrugh the fur filters, s that a measurement is recrded fr a given filter every 4 minutes. The 3-5^m and 8-12/xm data have been analyzed fr this reprt. The visible extinctin cefficient was measured in tw ways: with an Eltr transmissmeter (300 meter path length), and an AEG/FFM scattered light recrder. The minute data file includes the Eltr data when it is available, and therwise lists the AEG data. The tw mnths' data analyzed in this reprt included the Eltr data in September and the first third f March, and AEG data in the remainder f March. The Eltr transmissmeter has a relative errr in measured extinctin f less than 10% fr extinctin cefficients between 13 km -1 and.65 km -1. The AEG accuracy is apprximately 10%. The AEG measurement range is apprximately.1 km -1 t 80 km -1. Visible extinctin measurements are given every minute in the minute data file. Since the difference between visible scattering and ttal extinctin is within measurement uncertainty, the tw parameters will nt be distinguished fr the visible band measurements. Meterlgical data are nt included in the minute data base. Standard meterlgical data were recrded at 10 minute intervals, hwever the currently available data base lists data at hurly intervals. Meterlgical data are nt required fr the generatin f the ttal extinctins analyzed in Sectin 3. The aersl extinctins utilized in the analysis fr Sectin 2 are cmputed using the hurly meterlgical data. 1.3 Data Reductin The minute data base was prvided by Air Frce Gephysics Labratry in the frm f tapes cntaining data fr each minute. Each minute's data includes an infrared transmittance, a visible extinctin, the filter number, and time in minutes frm the beginning f the year. The calibratin factrs t be applied t the infrared transmittances are supplied separately. The ttal extinctin is cmputed by dividing the transmittance by the calibratin factr and applying Eq. (1.2). The data are srted and prcessed s that the resulting file cntains recrds at fur-minute intervals f infrared extinctin in ne filter, visible extinctin, mnth, day, and time. The prcessing f aersl extinctin is smewhat mre cmplicated. A file is created, which cntains the minute data, alng with the meterlgical data frm the nearest hur (extracted frm the hurly OPAQUE tape). The prcessing t aersl extinctin is then identical t that discussed in Shields (1981). That is, the mlecular and water vapr transmittances are cmputed frm the temperature and dewpint temperature using the equatins frm Shettle (1978a) and (1978b). The aersl extinctin is then cmputed frm the measured ttal transmittance (crrected by the calibratin factr) by the fllwing equatins: where t is ambient temperature and t d is dewpint temperature. The resulting file cntains recrds at fur minute intervals similar in frmat t the ttal extinctin files. The analysis in Sectin 2 is based n the aersl extinctin files. Fr Sectin 3, the analysis is based n the ttal extinctin files. 2.0 RELATION OF MEASURED INFRARED AND VISIBLE EXTINCTIONS This sectin discusses the relatinship between the measured infrared extinctin cefficients and the measured visible extinctin cefficients. The first sub-sectin (2.1) discusses the incidence f high infrared extinctin values within the full data set-when they ccur, and at what values f visible extinctin. These results are cmpared with the relatinships bserved in the Netherlands data set discussed in Shields (1981). The secnd and third sub-sectins (2.2 and 2.3) discuss the mist and fg episdes, and hw the visible and infrared extinctins vary and interrelate during the episdes. 2.1 Incidence f High Infrared Extinctin Values Full Data Set Characteristics After the initial data quality checks were cmpleted, the aersl extinctins were cmputed and pltted as a -3-

11 functin f visible extinctin cefficient and relative humidity. Since the large size f each mnth's minute data file precludes including all pints frm a mnth n ne plt, the data fr each mnth were srted by hur f the day, and separate plts were generated fr each hur. Sample plts are illustrated in Figs. 2-1 and 2-2. Figure 2-1 illustrates the infrared vs visible extinctin. The near dawn set, at hur 05, is quite typical f the data during the night. During the night, the infrared and visible extinctins cver a large range f values. They are apprximately linearly related; high infrared extinctins tend t ccur with high visible extinctins. The late afternn data, at hur 17, are typical f the daytime data. The infrared and visible extinctins are similar t the data in the night plts, except that the high extinctin values d nt ccur. The plts in Fig. 2-1, alng with thse at ther hurs nt included here, indicate that the infrared aersl extinctin and visible extinctin are related fr this data set, hwever the relatin is nt strng enugh fr the visible extinctin t be an accurate predictr by itself. The squared crrelatin cefficients, r 2, between lg infrared aersl extinctin and lg visible extinctin were apprximately 0.7 at night (i.e., in the hurs near midnight), 0.3 (a) Hur 05, 3-5^m T] i i i i i 1111 i i n n 1 t T I'"T TTT 1 l l I I I I I TIL ' ^ - (b) Hur 05, 8-12/xm ",-, _ z: CJ X LJ ce «D a DD : [ tei i D 1 t-1 X LJ r "_ a i 'J.,1 D D a B CD -7 ~. 1 IM'ITI I I I I ll 1 1 I I I I M VISIBLE EXTINCTION (KM-l! 10' ' 1 " T 1" r i i I I I I III i i i i uir ( VISIBLE EXTINCTION (KM-l) ~ I 1111 T] 1 1 r-ttitt] I I ML (c) Hur 17, 3-5/i m i i i i 11m 1 i i i i i i i IIL (d) Hur 17, 8-12/im,-, CD. I " ^ _ O O.-. O t-< x LJ r r 2- X LJ r i T i i I I i ii ii 1 i i i i i ii 10"' ' VISIBLE EXTINCTION (KM-l) I *> Tl I ll 1 1 I I I I ll 1 1 I I I III 10"' 10 10' 10' VISIBLE EXTINCTION (KM-l) Fig Infrared aersl extinctins vs visible extinctins; near dawn and late afternn; data fr all f September 1978 during given hur. -4-

12 in the mrning, 0.1 in the afternn, and 0.3 in the evening (i.e., in the hurs near sunset) fr the September data. The time dependence has been evaluated by cmparing the varius hurly plts f infrared vs visible extinctin (f which Fig. 2-1 is a sample). It was fund that the very high values f infrared aersl extinctin ccur generally thrughut the night but disappear quickly in the mrning. Fr example, after 08 hurs, the 3-5fim extinctins have a maximum near 2 km -1, whereas befre 8 there are nrmally several pints well abve this value. The magnitude f the highest extinctins is slightly larger after 18 hurs, with very high values near 10 km -1 appearing by 23 hurs. Thus the infrared and visible extinctins f the full data set are smewhat related, and the highest infrared extinctins tend t ccur at night. The plts f infrared aersl extinctin as a functin f relative humidity are shwn in Fig In these plts, as in thse at ther hurs nt shwn, the high extinctin values ccur almst exclusively at the high relative humidity values, but there is therwise little apparent relatinship between the parameters. These relatinships are cnsistent with mdel results, and in fact are very similar t the relatinships RELRTIVE HUMIDITY (7.) RELRTIVE HUMIDITY {'/.) RELATIVE HUMIDITY 17.) RELATIVE HUMIDITY 17.) Fig Infrared aersl extinctins vs relative humidity; near dawn and late afternn; data fr all f September 1978 during given hur. -5-

13 bserved in the Netherlands data discussed in Shields (1981). Figure 2-3 shws sample plts frm Shields (1981). These data are recrded at hur intervals. The data at all hurs fr a three mnth perid are shwn in Fig The hrizntal line shwn in these plts is the median mlecular and water vapr extinctin, included fr cmparisn with the aersl extinctin values. Mist Bin Characteristics With the Netherlands data, it was fund that an "upper bin" culd be defined which included all the high infrared extinctin values. This upper bin cnsisted f all the pints with visible extinctin greater than 1 km -1 and relative humidity greater than 94%. This categry was designated the "mist bin", since the threshlds are cnsistent with the definitin f mist, the cnditin in which particles f size greater than 1/nm begin t ccur. This is the cnditin in which infrared extinctin might be expected t becme large. The bin includes bth mist and fg cases. Any cases with visible extinctin avis > 3 km - ' are defined t be fg, based n definitins in Mcintsh (1963). With the minute data set, the high infrared extinctin values similarly ccur under cnditins f high visible 10 2 ta) 3-5^m extinctin vs visible extinctin (b)8 12/xm extinctin vs visible extinctin. 10' E a. 10' z t) 10 ; H X UJ UJ < a M1 + HjO lo- 10-' 10 10' 10 2 VISUAL SCATTERING COEFFICIENT (km" 1 ) Z z H X w 06 UJ < 06 10" 10"' VISUAL SCATTERING COEFFICIENT (km" 1 ) 10 2 (c) 3-5/im extinctin vs relative humidity (d) 8-12/^m extinctin ra relative humidity. 'g 10' a. 10' z g 10" z H X UJ _1 i-' 06 UJ < 06 Z 10 p z p X u -I gi-h 06 UJ <, t. * *. *. * i-» * y 10" i- -t* RELATIVE HUMIDITY (Percent) RELATIVE HUMIDITY (Percent) Fig Infrared aersl extinctin plts frm Shields (1981), Netherlands data; cmbined data fr three mnths, at hurly intervals, Summer

14 extinctin and high relative humidity The high infrared extinctins ccur when the visible extinctin is greater than 1 km -1, and the relative humidity is greater than at least 80%, and generally 90% Thus a "mist bin" can be defined as the set f pints with visible extinctin greater than 1 0 km -1, and relative humidity greater than 80% This relative humidity threshld, which is set t include a large majrity f the high infrared extinctins in the bin, is lwer than was required fr the Netherlands data set As befre, this bin includes bth mist and fg cnditins (the designatin "mist bin" is used nly fr cnvenience) Als, unlike the Netherlands data analysis, the minute data analysis included bth rain and nn-rain data in the mist bin, since measurements f rain rate were nt available in the September minute data set Within the Netherlands data, it was fund that in the mist bin, the infrared extinctins were quite variable The general magnitudes f the infrared extinctins were cnsistent with LOWTRAN mdel estimates, hwever the variatin abut these estimates was quite large In particular, when the visible extinctin was in the range apprpriate fr fg (abut 4 km -1 ), the rati f infrared aersl t visible extinctin varied frm the high ratis predicted fr fg t lw ratis predicted fr haze Figure 2-4 illustrates plts f these ratis, taken frm Shields (1981) It was further fund that the variatin in the extinctin appeared t be ccurring n a time scale which was shrt relative t the duratin f the mist r fg events The minute data extinctin ratis were similarly pltted fr the mist bin These ratis are illustrated in Fig 1 9 (a) 3-5jim 19 (b) 8-12 M m c UJ w> a O 1 E u. UJ Z u n u z O z t 06 UJ UJ _J E «O i/i u U1 -i < 06 UJ 1 5 I ia'.i*.t. '-*-' ' I0 2 VISUAL SCATTERING COEFFICIENT (km- 1 ) T E OO UL w UJ z O <-> 11 h z p 06 H UJ w t 07 -j ** O -J u 06 UJ < < 3 CO 06 > \&**'\*J,St * ' 10 2 VISUAL SCATTERING COEFFICIENT (km" 1 ) Fig Netherlands data mist/fg bin, rati f infrared aersl extinctin t visible extinctin, frm Shields (1981), data fr three mnths, Summer 1977 OJ- 1 1 i i I I (b) 8-12 M m x LJ CD i i > f-i X. LJ \n D O " a X * LJ CO > D B l-i -1 5ftr J D a S X LJ DC wfc k ^» D in 5«3B^D " ^L VISIBLE EXTINCTION (KM-l) O D * mmm\ «, i ' 10' VISIBLE EXTINCTION (KM-l) Fig September 1978 minute data mist/fg bin, rati f infrared aersl extinctin t visible extinctin -7-

15 2-5. These plts are quite similar t thse extracted frm Shields (1981). The ratis ften apprach 1 r mre when the extinctin is high, as predicted by LOWTRAN. Hwever, there are a great many lw ratis even at the highest visible extinctins. Althugh this result is nt particularly desirable frm a mdelers viewpint, it des indicate that the features discussed in Shields (1981) are nt just a lcally ccurring phenmena. Als, it means that the Meppen minute data set can be used t address sme f the questins prpsed in Shields (1981). That is, are the variatins truly shrt term; is the infrared t visible relatinship changing within mist and fg episdes. If variatins are shrt term, can ccurrence f the ccasinal high values be predicted. As a first step, the mist/fg episdes lasting cntinuusly fr 30 minutes r lnger were extracted frm the minute data, and time series plts f these episdes were generated. The next sectin discusses the analysis f these cntinuus mist perids. 2.2 Tempral Behavir f Extinctin During Mist and Fg Episdes Extractin f Mist and Fg Episdes In rder t extract the mist and fg episde data, a mist episde (r perid) was defined as any unbrken interval f 30 minutes r mre during which the data were assigned t the mist bin (defined abve). Shrt intervals in which the infrared data were ffscale r in which there were n infrared data recrded were included if they ccurred within a mist perid. In this cntext, the term mist episde shuld be understd t imply mist and/r fg, since the resulting data set will include fg perids. There were a surprisingly large number f cntinuus mist perids within each mnth. The results f the srting are listed in Table 2.1. In this table, the results are listed by filter, e.g. 3-5/xm data set. The srting is based n visible rather than infrared data, hwever the visible extinctin measurements assciated with the 3-5/xm data may differ slightly frm the visible data assciated with the 8-12/y.m data. Fr example, when the infrared data fr ne filter are ffscale, the crrespnding visible data are nt reprted. As a cnsequence, the srting results differ slightly in the tw filters. Out f the apprximately 10,500 data pints per filter each mnth, there were abut 1400 mist bin pints in September, and abut 2700 in March. There were apprximately 10 perids f mist lasting 3 hurs r mre each mnth. It shuld be pinted ut that any perids which were abve the visible extinctin and relative humidity threshlds fr mst f the perid and nly briefly drpped dwn wuld nt be included here. In rder t avid this bias, all the data, and nt just the cntinuus perids, were included in the statistical analysis f Sectin 3. The visible extinctins and infrared aersl extinctins were pltted as a functin f time fr the cntinuus mist perids. These are illustrated in Appendix A, in Figs. A-l thrugh A-6. These plts were generated with a cnstant scale, fr cnvenient inter-cmparisn. Observed Tempral Behavir The eighteen mist episdes illustrated in Appendix A reveal a variety f tempral behavirs. The types f behavir are summarized in Table 2.2. The descriptins in Table 2.2 are apprximate, since in sme Table 2.1. Occurrance f mist episdes each mnth. Occurrence September March Statistics 3-5/j.m 8-12>i.m 3-5/im 8-12 M m Data Set Data Set Data Set Data Set Ttal number f pints in data file Pints with valid a vis anc ' RH data fr threshld check Mist data pints*, le pints abve a vi$ and RH threshld Number f cntinuus mist perids Lasting ^ 30 min Lasting ^ 3 hrs Includes bth cntinuus perids and intermittent pints -8-

16 Table 2.2. Summary f tempral behavir Mnth Day Time Behavir Descriptin (see text) Vis Ext (km- 1 )* Duratin Hur min Sep Sep Sep Sep Sep Sep Sep Sep Sep Sep Mar Mar Mar Mar Mar Mar Mar Mar (Offscale) Threshld Threshld Threshld Well related Unrelated Mixed Well related Steady Unrelated Threshld Well related Well related Threshld Threshld Well related Unrelated Mixed Behavir Type Thresh Well Rel Unrel Other Ttal Cunts * Apprximate extinctin threshld is listed in "Threshld" cases, therwise extinctin range is listed cases the mist episdes had elements f mre than ne Table 2.3. Summary f infrared behavir. The number f cases listed in Tables 2.2 and t visible extinctin linearity 2.3 differ smewhat frm the number f cases in Table during mist episdes 2.1, fr reasns discussed in Appendix A. Descriptin f Linearity Mnth Day Time (see text) Sep (Offscale) Sep rughly linear Sep partly nn-linear Sep rughly linear Sep mstly linear Sep nn-linear Sep mstly linear Sep mstly linear Mar mstly linear Mar mstly linear Mar nn-linear Mar mstly linear Mar nn-linear Mar nn-linear Mar nn-linear Mar nn-linear Linearity Type Mstly lin Rughly lin Nn-hn Ttal Cunts Threshld. One f the mre cmmn types f behavir is what we will call "threshld behavir". An example f this is the September mist starting n day 6 at The time plts fr this mist are shwn in Fig Figure 2-6(b) shws a 4-hur prtin f this episde with an amplified time scale. In this mist, the infrared aersl extinctin is near 0 except when the visible extinctin exceeds apprximately 3-4 km -1. When the visible extinctin exceeds this value, the infrared aersl extinctin changes almst abruptly frm values f less than.1 km -1 t values between 1 and 10 km -1. The small time scale variatins in the visible extinctin abve 3 km -1 are assciated with crrespnding variatins in the infrared extinctin, hwever the infrared variatin is much mre extreme in the magnitude swings. The swings abve and belw the 3-4 km -1 visible threshld ccur several times during the episde. The 3-4 km -1 threshld is apprximate; that is, the pint at which the infrared extinctin changes abruptly varies smewhat during the episde. One might summarize this behavir as threshld effectbelw a given visible threshld, the infrared extinctin is quite lw, but abve this visible threshld the infrared extinctin is quite variable and clsely related t small variatins in visible extinctin. -9-

17 Fig Time series plts illustrating "threshld" behavir Mist episde starting 6 Sep ' , 3-5/nm (O =«ra O = a m ) This threshld-type behavir may be bserved in several f the mist episdes illustrated in Appendix A, as listed in Table 2 2 Althugh the threshld behavir was bserved in 6 f the 18 mists illustrated in Appendix A, the visible threshld at which the infrared extinctin became respnsive varied smewhat frm ne episde t the next, ranging frm abut 2 km -1 t 5 km -1 Nte that this is abut the magnitude assciated with the defined mist-t-fg transitin pint (visibility = 1 km) Well Related The next mst cmmn type f behavir was the "well related" categry As listed in Table 2 2, there were several mist episdes in which the infrared and visible extinctin were very well related In many f these cases, the visible extinctin was clse t r lwer than the threshld values nted in the threshldtype plts That is, fr example, in the "threshld" case n 6 September at 2120, the extinctins were well related nly when the visible extinctin was ver abut 3 km -1 But in the "well related" case n 14 September at 0858, the extinctins were well related even thugh the visible extinctin was near 1-2 km -1, which is well belw the mist-t-fg threshld A sample mist which has been classified as "well related" in Table 2 2 is illustrated in Fig 2-7 Nte that even the small excursins in the visible extinctin are clsely fllwed by excursins in the infrared extinctin In this particular episde, the visible extinctin changes are greatly magnified by the infrared extinctin changes In sme ther cases, the changes are f similar magnitude in the tw spectral regins Figure 2-8 illustrates ne such example In Fig 2-8, the trends n an hurly scale are quite similar in the tw spectral bands, althugh the minute-by-minute variatins d nt crrespnd clsely Nte that even thugh the visible extinctin values and variatins are f abut the same magnitude in Figs 2-7 and 2-8, the infrared aersl extinctin varies much mre in the frmer plt Unrelated. In sme cases the behavir was characterized as "unrelated", since the infrared aersl and visible extinctin appear t be ttally unrelated Figure 2-9(a) illustrates ne such example In this plt, the visible extinctin is quite stable, yet the infrared extinctin varies in an apparently unrelated manner Mixed A few f the mists shw "mixed" characteristics Fr example, the mist shwn in Fig 2-9(b) has a small peak in the visible extinctin near minute 80 (minutes since episde start) which des nt appear in the infrared extinctin Near 420 minutes and 520 minutes, the infrared extinctin increases fr shrt perids, with little crrespnding variatin in the visible extinctin Yet the variatins during the perid frm 600 minutes t 800 minutes are reasnably matched in the tw spectral regins Measurement Effects In tw cases, measurement limitatins affect the data The mist starting 5 September at 2320 has infrared extinctins which are nearly cnstant, because they are at the lw transmittance end f the instrument's measurement range The values crrespnd t a measured transmittance less than 1% In the mist starting 10 Mar at 0740, there is a sudden change in the visible extinctin abut 16 hurs after the episde beginning, which is the result f a change in the instrument used The recrded visible extinctin data are Eltr data fr the first part f the episde, and AEG data fr the remainder f the episde Evaluatin All f these bserved behavirs are reasnable behavirs t expect t see, because the large and small drplets can be affected by different physical mechanisms Fr example, if the air reaches saturatin, the large drplets can grw quickly, resulting in a large change in infrared extinctin This culd accunt fr the "threshld type behavir" In fact, rain may pssibly cntribute t this behavir Wave mtin in the mist layers, -10-

18 I 1 1 (a) Cmplete mist episde 0.0 -l 1 1 = i r Fig Time series plts illustrating "well related" behavir Mist episde starting 22 Sep ' , 3 5/nm ( = a ra O = a /R ). i x IAJ CO a z cc ^^A^ker^b '^VwvA, i i Fig Time series plt illustrating "well related" behavir. Mist episde starting 21 Mar ' , 3-5/um (D =a V i S O = a, R ). i. (a) "Unrelateted" behavir, episde starting 28 Sep ' T T (b) "Mixed" behavir, episde starting 30 Mar ' , minutes ^ - X LLJ Q z CE r ' yv^^^y^ 7 Q-A,.f\ T -r Fig Time series plts illustrating "unrelated" and "mixed" behavir. 3-5/im ( =atvis O = aj R )

19 which results in the raising and lwering f the altitude f individual layers, culd cnceivably lead t "well related" variatins in the tw extinctins Lss f large drplets by preferential gravitatinal settling culd cntribute t "unrelated" variatins in the tw extinctins There are a number f mechanisms which can affect the large drplets and the small drplets differently and therefre result in varying infrared t visible relatinships The time series plts shw that a variety f types f tempral behavir d in fact ccur It wuld thus be difficult t quantify the infrared-visible relatinship under these cnditins It may be pssible t relate the type f behavir ccurring in a mist/fg episde t parameters such as fg type It wuld be particularly wrthwhile t determine which episdes are assciated with rain Rain data is available fr the March data set, as well as perhaps ther mnths in the year's data base 2.3 Infrared t Visible Magnitude Relatinship During Mist/Fg Episdes Since the relatinship f the infrared aersl extinctin t the visible extinctin is quite varied within the mist bin, it is f interest t determine whether the relatinship is well defined within the individual mist episdes (As befre, the terms "mist" bin and "mist" episde r perid, represent data sets which may include bth mist and fg) The infrared aersl extinctins were pltted as a functin f visible extinctin fr each cntinuus mist perid Mst f these plts are included in Appendix A The relatinships illustrated in these plts have been classified as either mstly linear, nly apprximately r rughly linear, r nn-linear These classificatins are listed in Table 2 3 Apprximately half f the plts shw mstly "linear" relatinships Figure 2-10 illustrates ne f the mre linear plts Nte frm cmparisn f the scatter plt (a) with the tempral plt (b) that the linear relatinship remained nearly cnstant even thugh the extinctins increased and decreased several times during the perid f apprximately 3 hurs Anther interesting example f the mstly linear relatinship is illustrated in Fig 2-11 In this set f plts, the infrared t visible relatinship is extremely linear ver a large range f extinctins, except fr the pints n the lw visible extinctin side f the curve, which appear in plt (a) f Fig 2-11 These nn-linear pints ccurred near the beginning f the episde, during which time the extinctin did nt vary smthly with time Thrughut the mist t fg episde, the extinctin increased and decreased several times, yet a nearly cnstant linear relatinship was maintained (The pints in plt (c) which appear t be nn-linear are an artifact f the measurement, the measurements were at the lw transmittance end f the measurement range ) At the ther extreme are several mist episdes which exhibit essentially n linearity in the infrared t visible relatinship Figure 2-12 illustrates ne example In this episde, the tempral plt illustrated in Fig 2-12(b) shws little relatin between the infrared and visible extinctin variatins, s the pr relatin illustrated n Fig 2-12(a) is nt unexpected Figure 2-13, n the ther hand, illustrates a mist perid in which the infrared and visible extinctins varied in a very similar manner n a tempral scale, and yet the verall relatinship is extremely nn-linear In Fig 2-13(c), the data pints have been cnnected sequentially The resulting pattern is very nn-systematic, indicating a pr infrared t visible relatinship even n a shrt time scale As nted in Sectin 1, Gimmestad et al discuss the questin f infrared vs visible extinctin linearity during fg On the basis f measurements at ne minute intervals during ne fg episde, they indicate that althugh the infrared t visible extinctin relatinship was nt linear ver the fg episde as a whle, the relatinship was linear ver several perids lasting frm 38 t 76 i 1 i i i i i i i i 11. (a) Infrared aersl vs visible extinctin w 10' VISIBLE EXTINCTION (KM-l) O. 1 - r 1 l i i.. (b) Infrared and visible extinctin vs time - 1 (D =a V S 0 = a IR ) - sz ^ ~_. i - 1 z 4 - t-> _ X UJ I - t Vv_ fw - > a a - -1 fl z az a:» i \ ' r t \ 1 I I I I 1.C Fig Scatter plt illustrating "linear" relatinship, with assciated time plt Mist episde starting 14 Sep ' /um

20 -I 1 1 I I I I I I I 1 1 I Mil. (a) a R Ma VIS, min i i i i i i i 1 1 I i I I 10' 10' VISIBLE EXTINCTION (KM-l) '( i r i i i i i i 111 i 1 i i i i 11. (c) a )R vs a V S, mm 1 i i i i i i i 1 1 i i i i i i J VISIBLE EXTINCTION (KM-l) Y '" i ' 1 ' r " 10' 10' VISIBLE EXTINCTION (KM-l) -i r Fig Scatter plts and time plts fr mist episde starting 3 Sep ' , 3-5/nm Time duratins shwn are frm start time (In plts (b), (d), and (f), D=a ;;jo = a tr ) -13-

21 I I I I I I Iff I I I I TTTT (a) Infrared aersl vs visible extinctin 1 I I I TT~ I I I I r 10' VISIBLE EXTINCTION (KM-l) 10' "i r Fig Scatter plt illustrating "nn-linear" relatinship, with assciated time plt. Mist episde starting 30 Mar ' , minutes 0-800, 3-5,um I l I l I I I i l r~~i i i i i I. (a) Infrared aersl vs visible extinctin i i i I i i i 1 1 i r r 10" 10' VISIBLE EXTINCTION (KM-l) 10' 1 H ^r : i i i i i r : - (b) Infrared and visible extinctin vs time -_ (D =a VIS 0 = a )R ). '. CJ,-, - z : i i - _ e-< X r'y Jb/l_ VJl /WV-, v- CJJ _ (T> _ ~J x^jv ^ *^-^ vn^ i _ X S-^^^t > O O z : ~ en ; _ \ " ai \ f*\ - \ ^ \ I " VI) 1 II (c) Infrared aersl vs visible extinctin, pints cnnected serially I zz e x LJ 10 u 10' VISIBLE EXTINCTION (KM-l: Fig Scatter plts and time plt fr episde starting 12 Mar ' , 3-5/xm. -14-

22 minutes. They pint ut that their measurements at frequent intervals yield well crrelated infrared vs visible extinctin cefficients, whereas measurements at lnger intervals may nt. Several f the episdes pltted here, such as Fig. 2-11, shw behavir similar t that bserved by Gimmestad. Hwever, in cntrast t his example, we als bserve cases such as Fig. 2-13, in which the data are nn-linear even ver shrt time intervals. (The data range in Fig. 2-13, rughly 10 t 10 1 fr visible and lo -1 t 10 fr infrared, was well within the bserved ranges f Fig and f Gimmestad's example.) Thus, even n a neminute time scale, the infrared t visible relatinship need nt be linear. 2.4 Summary f Infrared and Visible Extinctin Cmparisn Althugh a well defined linear relatinship between the infrared and visible extinctin cefficients wuld be extremely desirable frm a mdeling pint f view, past and current analysis f measured extinctins shws that in the mist t fg regime, such relatinships ften d nt ccur. The time series plts and scatter plts in the preceding sectins illustrate the srt f relatinships which can ccur. In sme cases, the infrared and visible extinctins vary in a similar manner as a functin f time, but ften they d nt. In many cases, the fluctuatins in.the visible extinctin are nt assciated with variatins in the infrared extinctin until quite high values f visible extinctin are reached. At this pint, the infrared extinctin frequently exhibits the same type f variatins as the visible extinctin, nly greatly magnified. This variety in the types f bserved behavirs helps shw why the infrared extinctin can be difficult t predict n the basis f visible extinctin alne. 3.0 CONDITIONAL PROBABILITY ESTIMATES Like the OPAQUE hur interval data base, the minute data base can be used t extract the prbability that the infrared extinctin will exceed given threshlds. Additinally, the minute data base is uniquely apprpriate fr extractin f cnditinal prbability estimates such as the cnditinal prbability that the infrared extinctin will exceed the threshld a given number f minutes after it was knwn t initially exceed the threshld. One can als extract ther prbabilities, such as the cnditinal prbability that the infrared extinctin will exceed threshld a given number f minutes after it was knwn that the visible extinctin exceeded sme threshld. These site-specific statistics can be useful fr peratinal purpses. Fr example, if an aircraft missin has been delayed because it is fggy and the infrared transmittance cnditins are t pr, it culd be useful t knw the prbability that the infrared transmittance will be acceptable in anther hur. This may differ frm the prbability that the fg will dissipate. Additinally, statistics f this srt can help indicate which parameters are mre accurate predictrs. One might wish t knw, fr example, whether a predicted visibility at deplyment time r a measured infrared extinctin three hurs befre deplyment time is the mre accurate predictr. This sectin cntains the results f several estimates f cnditinal prbability which were extracted frm the tw ne-mnth samples f minute data. 3.1 Cmputatin f Prbability and Persistence The cnditinal prbabilities were cmputed frm the ttal extinctin, rather than aersl extinctin. This was dne partly because the ttal extinctins are mre easily generated, and partly because the ttal extinctin is f mre interest peratinally. The variance in the ttal extinctin shuld be mstly due t variance in aersl extinctin, except under clear cnditins, when the ttal extinctin nearly equals the mlecular extinctin. The statistics are cmputed fr threshlds which are high enugh t avid the clear cnditins. The standard deviatins f the cmpnents f the ttal extinctin were extracted fr the September data, and are listed in Table 3.1. The variance in the mlecular and water vapr cmpnent includes the effect f uncertainties in measurement f temperature and dewpint temperature, which d nt affect the ttal extinctin. The variance in the aersl extinctin includes the effect f measured transmittance uncertainties, which d affect the ttal extinctin. This effect is minimal in the mist and fg regimes. Table 3.1. Standard deviatin f extinctin cmpnents, September 1978 minute data. Extinctin Data Set a aer * a " data ' a aer data < 1 km"' a aer data > 1 km -1 Observed STD in km /itn ^m a H 2 0+M/ The standard deviatin in the mlecular and water vapr cmpnent, rw 4, is 1 t 2 rders f magnitude less than the standard deviatin in the aersl extinctin. Bth the set f aersl extinctins greater than 1 km -1 and the set f aersl extinctins less than 1 km -1 have much larger standard deviatins than the mlecular plus water vapr extinctins. Thus, Table 3.1 shws that fr the range f extinctins f interest in this reprt, the variance in the ttal extinctin is indeed primarily due t aersl extinctin variatins. Prbability Cmputatin The prbability estimates were cmputed using the cmplete data base fr each mnth, rather than just the -15-

23 mist and fg data. Data assciated with rainfall culd nt be deleted, because rain rate measurements were nt available with the September data. Table 3.2 cntains a list f the types f cnditinal prbability estimates which were extracted. Each type f prbability estimate was cmputed fr ten threshlds and ten time lags. Estimates invlving the infrared extinctins were cmputed separately fr the 3-5/j.m data and the 8-12/j,m data. The daytime prbabilities were cmputed separately frm the nighttime prbabilities, since the nighttime data may be expected t shw different behavir frm that f the daytime data. The data were categrized as night r day using the sunrise and sunset time fr each day. A summary f a sample prbability cmputatin may be helpful. The prbability that 3-5/xm IR extinctin exceeds threshld fr each hur at night, P[a m (hr)> T], was determined by srting the data frm ne mnth int ne f three categries: daytime (i.e. after sunrise and befre sunset), nighttime but n data recrded, r nighttime with valid data. Thse data which fall in the third categry are then cunted as abve r belw threshld, fr each f 10 threshlds. The desired prbability fr a given hur hr is then the rati f the number abve t the number belw threshld fr thse cases ccurring between hur hr and hr+ 1. A flw chart illustrating the general lgic is included in Appendix B, as Fig. B-10. The cnditinal prbabilities are smewhat mre cmplicated. The night cnditinal prbability P [a ir (t + A)> T a m (t)> T], is cmputed as fllws. The data fr each minute is srted int ne f the abve categries. If the data fr a given minute is in the "night abve threshld" categry fr a given threshld, then the data fr minutes which ccur at set intervals (r lags) after that given minute are investigated t see which f the categries they fall int. The cunts assciated with the lagged data are stred as a functin f lag and threshld. The cnditinal prbability fr each lag is then the rati f the abve and belw threshld cunts in the lagged categries. The resulting cnditinal prbabilities are given fr each lag and threshld. These calculatins are made fr 10 lags ranging frm 10 minutes up t 6 hurs. This prcedure is illustrated in a flw chart in Fig. B-l 1 In the plts in the fllwing sectin, PI always refers t an uncnditinal prbability, fr example the prbability that the IR extinctin exceeds threshld. P2 refers t cnditinal prbabilities, fr example the cnditinal prbability that IR extinctin exceeds threshld given that it als did a time interval earlier. Fr cases in which bth P1 and P2 are cmputed, ne wuld expect P2 t be higher than PI if there is persistence. Fr example, fr the September /xm night data, fr a threshld f 1 km -1, PI was 0.06, indicating a lw prbability f exceeding threshld, but P2 fr a lag f ne hur was That is, having exceeded threshld, the prbability f exceeding threshld an hur later is quite high. Nrmally, P2 may be expected t decrease as the time lag increases. Table 3.2. Types f prbability estimates extracted frm September 1978 and March 1978 minute data. P[a lr >T]. NIGHT Prbability that IR extinctin exceeds threshld T Pla, R (t+b)>t\a IR (t)>t]. Cnditinal prbability that IR extinctin at time f+a exceeds threshld T, given that IR extinctin at time t exceeds threshld T P{a lr (hr)>t]. Prbability that IR extinctin exceeds threshld T, cmputed as a functin f hur f the day Pla lr (t+b)>t\a m (t)>vt]. Cnditinal prbability that IR extinctin at time /+A exceeds threshld 7\ given that visible extinctin at time I exceeds threshld VT (cmputed fr visible threshlds 1km -1 and 4 km -1 ) when A=0 this becmes Pla IR (i)>tia yls (r)>vt] P[ay /S > T]. Prbability that visible extinctin exceeds threshld T Pla y i S (t+\)>t\a v[s (t)>t). Cnditinal prbability that visible extinctin at time r+a exceeds threshld T given that visible extinctin at time i exceeds threshld T P[a IR (t+&)>t\ay, s (.t)>l km -1 it R//(/)>80%). Cnditinal prbability that IR extinctin at time ;+A exceeds threshld 7", given that visible extinctin at time ; exceeds 1 km -1 and relative humidity at time I exceeds 80% When A=0 this becmes P[a IR U)>T\a m (i)>\ km- l &RH(r)>Sm) P\RH> T\. Prbability that relative humidity exceeds threshld 7" P\RH(t+\)>T\RH(t)>T]. Cnditinal prbability that relative humidity at time (+A exceeds threshld T, given that relative humidity at time I exceeds threshld T DAY P\f* lr > 71. Prbability that IR extinctin exceeds threshld T P{a lr (t+\)>t\a IR {t)>t]. Cnditinal prbability that IR extinctin at time r+a exceeds threshld T given that IR extinctin at time / exceeds threshld T Pla IR (hr)>t]. Prbability that IR extinctin exceeds threshld 7", cmputed as a functin f hur f the day P[a, R (hr)>t\a IR (t-dawn)>t]. Cnditinal prbability that IR extinctin exceeds threshld T fr each hur, given that IR extinctin exceeds threshld T at dawn (using average extinctin fr first 20 minutes after sunrise) Pla lr (l+ L)>T\ty ls (t)> VT]. Cnditinal prbability that IR extinctin at time f+a exceeds threshld T, given that visible extinctin at time I exceeds threshld VT (cmputed fr visible threshlds 1km" 1 and 2 km -1 ) When A=0 this becmes P\t IR (t)>t\a vls (t)>vt] P[<x VIS > 71. Prbability that visible extinctin exceeds threshld T Platy IS (t+b)>t\a yls (t)>t]. Cnditinal prbability that visible extinctin at time t+^ exceeds threshld 7\ given that visible extinctin at time i exceeds threshld T Persistence Cmputatin A nice measure f the cmparisn between PI and P2 is the "persistence cefficient" (Brks and Carruthers (1953)) defined by r(ar)~l- '-«<*.n 2 (31) -16-

24 where A is time lag, and T is threshld This cefficient ranges frm +1 t Ttal persistence implies that nce an event ccurs it will definitely ccur at the later time, thus PI wuld be less than 1, P2 wuld equal 1, and r wuld equal 1 N persistence is when the ccurrence f an event has n effect n the prbability f ccurrence after the interval In this case, P2 wuld equal PI, s r wuld be 0 Negative persistence results frm the case where nce an event ccurs, it is less likely t ccur after the interval In the extreme case, P2 wuld equal 0, and r wuld be a large negative number with magnitude depending n PI, the larger the PI value, the mre negative r wuld be Our use f the persistence cefficient is slightly different frm the classical use Persistence nrmally requires that the event ccur cntinuusly during any prescribed time interval In ur cmputatins, P2 is the prbability that the event ccurs again Our P2 includes the cases in which the event was persistent (/ e cntinuus), intermittent, and recurrent (/ e ccurred again fr the first time at the end f the interval) Unfrtunately, there appears t be n term which classically implies exactly this prbability Reccurrence might be the best term t use, althugh it is nt defined statistically Fr the purpses f this reprt we will use the terms reccurrence and persistence interchangeably t describe the statistics we have extracted Plts f persistence cefficient were generated fr bth the visible data and the infrared data as a functin f threshld and lag Appendix B cntains plts f mst f the prbability types listed in Table 3 2 The prbability plts are discussed in the next sectin In the next sectin, general statements regarding the interpretatin f the statistics are intended t apply t this data set The extent t which these bservatins apply t ther mnths and lcatins is largely unknwn 3.2 Results f Prbability Cmputatins Visible Extinctin-Occurrence and Reccurrence As nted in Sectin II, mists and fgs ccurred frequently within the tw mnths, where mist/fg is defined n the basis f visible extinctin and relative humidity data Cnsequently, visible extinctin prbability estimates are fairly high The visible extinctin prbabilities are illustrated in Fig B-5 (in Appendix B) and Figs 3-1(a) and 3-2(a) As an example, in the March nighttime data illustrated in Fig 3-1(a), curve PI representing the uncnditinal prbabilities shws a 32% prbability f exceeding 1 km -1 (the threshld used in srting the mist cases) Table 3 3 lists the uncnditinal prbabilities fr threshld 1 km -1 fr the visible and infrared data, as well as the persistence cefficients fr a 3 hur lag As shwn in Table 3 3, the prbability f ccurrence fr the visible data range frm abut 16 r 32 fr a threshld f 1 km" 1 Thus, mist cnditins ccurred frequently in this data set The persistence is quite high in the visible, that is, the cnditinal prbabilities are significantly higher than the uncnditinal prbabilities Fr example, the persistence cefficients fr visible data fr a threshld f 1 km -1 and a lag f 3 hurs (listed in Table 3 3) fall near 9 in 3 f the 4 cases tabulated (The maximum pssible is 1 0) In this example, the assciated cnditinal prbabilities fr a lag f 3 hurs and visible extinctin abve 1 km -1 are near 75% Thus the visible data illustrate that visible extinctin was ften high, and that the persistence ver a few hurs was quite high In vernacular terms, the mists ccur fairly ften, and nce ccurring, tend t stick arund fr a few hurs Infrared Extinctin-Occurrence and Reccurrence The infrared extinctin behavir is f mre interest, since the infrared extinctin is nt always high during the mist episdes The infrared extinctin plts are given in Figs B-2 and B-7 (Appendix B), and summarized in Figs 3-1 (b) and 3-2(b), and Table 3 3 The uncnditinal prbabilities fr the infrared data are much lwer than the uncnditinal prbabilities fr the visible data The infrared extinctins exceeded 1 km -1 less than 10% f the time at night During the daylight hurs, the percentage is apprximately 5% r less Nte in Table 3 3 that the infrared prbability values are much lwer than the visible prbability values fr all mnths and filters Thus, even thugh mist cnditins ccur frequently, the infrared extinctin is nt frequently high Table 3.3. Cmparisn f visible and infrared prbability estimates fr threshld T = 1 km ' and lag A =3 hurs 1- P2 1- PI 2 Pl~P\a>T] P2 ~ P[a(t + b)>t \a(t)>t] r=la) Visible Data b) 3 5/xm Data c) 8-12/xm Data Night Day Night Day Night Day Sep Mar Sep Mar Sep Mar Sep Mar Sep Mar Sep Mar PI P2 r PI P2 r PI P2 r ' "Apprximate estimate due t lw cunts -17-

25 Althugh the prbability f the infrared extinctin exceeding a high threshld is quite lw, the prbability f reccurrence nce such an event ccurs (P2), abut 50% at night, which is quite high (see Fig 3-1) The persistence cefficients given in Table 3 3 range frm 4 t 8 fr the night infrared data Althugh these values are nt as high as bserved in the visible data, they d yield fairly high cnditinal prbabilities, as shwn in the P2 curves f Fig 3-Kb) Thus, at night, nce the infrared extinctin is high, it is likely t be high a few hurs later als The day infrared statistics (see Fig 3-2) are quite different frm the night statistics As nted earlier, the prbability f ccurrence fr 1 km -1 is much lwer during the day The night and day prbabilities differ the mst at the higher threshlds, s that the higher threshld values are much mre likely t ccur at night Als, the reccurrence prbabilities are very lw during the daytime The day persistence cefficients in Table 3 3 are apprximately 1, with assciated cnditinal prbabilities f reccurrence f abut 5-10% fr the daytime infrared data During the daytime, therefre, the infrared extinctin is unlikely t becme high, and if it des becme high, it is unlikely t remain high Nte in Fig 3-2 (b), that the P2 values fr a 6 hur lag even fall belw the PI values at high threshlds If a high extinctin ccurs, it is generally mrning r evening, s the statistics fr 6 hurs later will be afternn, when a high extinctin is unlikely, r night, when the data will nt be included Thus P2 is less than PI fr this case, crrespnding t negative persistence At night, the persistence cefficients d nt depend strngly n the time lag, as illustrated in Fig 3-3 As a result, the cnditinal prbabilities are much greater than the uncnditinal prbabilities fr all lags tested, i e up t 6 hurs lag That is, the extinctin six hurs after a high extinctin event is nearly as likely t be high as an extinctin ne hur after the high extinctin event During the daytime, the persistence values are strngly lag dependent, and the cnditinal prbabilities were significantly greater than the uncnditinal prbabilities nly fr lags f an hur r less Thus the prbability f ccurrence is higher than nrmal fr nly abut an hur after a high daytime extinctin Thus these data shw that even thugh mists are ccurring frequently, the infrared extinctin is nt ften CO 06 0_ O O 06 O e CD CC 03 O 06 - PI - P2(lflB 16) - P2ILH8 60) - P2tlP,S 1B0) - P2ILP.G THRESHOLD EXTINCTION Fig. 3-1 Visible prbability estimates, PI = P[a yls > T] P2 =P[a vls (f+a)> 7"], and infrared 3-5^m prbability estimates, PI =P[a, R >T),P2 =*P[a, R (t+a)>t \a IR (t)>t] March 1978, nighttime data CD O 06 CD O C 0_ O 06 O CO <n CO r 0_ (a) Visible extinctin - PI - P2IIA8 16) A - P2ILP.8 60) + - P2ILH6 180) X - P2ILH8 360) THRESHOLD EXTINCTION 1 2 KM-l) 0_ tr CQ cc (b) 3 5^im extinctin D - PI - P2ILHB 16) A - P2ILBS 60) + - P2ILHG 1B0) x - P2ILRS 360) T" i C THRESHOLD EXTINCTION (KM-l) 1 6 Fig Visible prbability estimates, PI =P[a yls >T], P2 = P[a y, s (t+b)>t], and infrared 3-5/u.m prbability estimates, PI =P[a, R > T], P2 =P[a, R (M-A)> T a lr (t)> T] March 1978, daytime data THRESHOLD EXTINCTION (K.M- -18-

26 \ LJ O LJ z t LJ LJ O CJ CJ z LJ e CO t en LJ Q_ 1 r - (b) Daytime data. T-0.7 T-0.9 T-1.0 T-1.1 T-1.3 T-l.S I LAG IN MINUTES i Fig Persistence cefficients as a functin f time lag, March /j.m, where r = 1 - [(1 andp2 =P[ai R (t+b)>t \a, R (t)>t]. CO LAG IN MINUTES P2)I(\-P1)V\ PI = Pla, R >T) very high. Once it becmes high, it persists well at night, but very little during the day. The resulting cnditinal prbabilities are much higher at night than during the day. The uncnditinal prbabilities fr the infrared data were srted as a functin f hur f the day and are shwn in Appendix Figs. B-l and B-6. Fr the threshlds f interest, the prbabilities tend t be quite lw during the daylight hurs, then rise slightly during the night. The prbabilities tend t be highest near dawn. Dawn ccurred during the 05 hur in September, and the 05 and 06 hur during March. The September data shw a definite increase in prbability f ccurrence during the befre-dawn data at hur 04 and the after-dawn data during hur 05, while the March data have increased prbability values in the befre-dawn data during hur 06. A sample f the plts is shwn in Fig Nte in Fig. 3-4(a) the rise at hur 04. The pre-dawn maximum is illustrated in Fig. 3-4(b) by the curve fr hur 04, which lies abve the curves fr the ther hurs at all threshlds. Infrared Extinctin Occurrence After a Visible Event Since the infrared extinctin is related t the visible extinctin as shwn in Sectin II, it is desirable t try using the visible extinctin as a predictr. This kind f infrmatin is particularly useful, since visible extinctins in the frm f visibility estimates are s readily available in the field. Fr this reasn, estimates were extracted f the cnditinal prbability that the infrared extinctin exceed threshld, given that the visible extinctin exceeds a given threshld. These estimates were extracted using the visible extinctin threshlds f 1 km -1 and 4 km" 1 during the night, fr a range f infrared extinctin threshlds. During the daytime, there were nt enugh ccurrences f 4 km -1 visible extinctins t yield reliable statistics, s visible extinctin threshlds f 1 km -1 and 2 km -1 were used. The resulting plts are shwn in Appendix Figs. B-3, B-4, B-8, and B-9. These figures shw that the cnditinal prbability f ccurrence, given the visible extinctin exceeds 1 km -1, is higher than the uncnditinal prbability f ccurrence. Figure 3-5 shws an example f this. Cmparing the cnditinal prbabilities P[a /R 0+A)> T \a m (t)>\ km -1 ], plts (c) and (d), with the uncnditinal prbabilities Pla/R > T ], which are the PI curves in plts (a) and (b), ne can see that a high infrared extinctin is mre likely t ccur if the visible extinctin has recently exceeded 1 km" 1. > ( > X T f 1 x LJ rn < i 0_ n z «(a) Uncnditinal prbability vs hur. O- T T-0.9 a- T T-1.1 X- T T-l.S ID O X CE» CO X CO HOUR THRESHOLD EXTINCTION Fig Uncnditinal prbability each hur, P[a IR (hr)> 71. September 1978, 3-5/*m nighttime. 19-

27 CO ce D- PI O- P2ILRB 16) a - P2(lflG P2ILHG 180 X - P2ILRB 360) I -r- I r~ I THRESHOLD EXTINCTION (a) Nighttime PI = Pla /R >T\ P2 = P{a IR (.t+b)>t (KM-1) \a IR U)>T) 1.6 m x CO Q_ D - PI - P2ILAG 16) i - P21LRG 60) + - P2IIRG 180) x - P2ILRG THRESHOLD EXTINCTION (b) Daytime PI = P[a IR >T] P2 = P[a IR U+CL)>T (KM-1) \a, R U)>T) x THRESHOLD EXTINCTION (c) Nighttime P[a IR (r+a)> T a yls U)> 1 km -1 ] (d) Daytime P[a, R (t+a)>t \ a vls U)> \ km - P2ILR6 0) - P2ILAS 16) - P2ILRG 60) - P2IIRG 1B0) 03 " O - LRG-0 - LRG LRG-60 UJ + - LAG-180 (_) "? X - LflG-360 It U- n «* s ( > 0.0 I (e) Nighttime P\t/ R ('+A)> 7" a y /s U)> 4 km (f) Daytime Pk*i R ('+A)> T I a y fs (i)> 2 km - Fig Cmparisn f cnditinal prbabilities resulting frm IR extinctin cnditins with thse resulting frm visible extinctin cnditins September 1978, 3-5^m Tables 3.4 and 3.5 illustrate these results fr the infrared extinctin threshld 1 km -1. Cmparing the uncnditinal prbabilities in the first rw with the cnditinal prbabilities in rws 4 and 5, ne can see that the cnditinal prbabilities given that the visible extinctin exceeded 1 km ' are smewhat higher than the uncnditinal prbabilities, fr bth seasns and filters. Interestingly, these cnditinal prbabilities d nt depend strngly n the time lag at night, up t lags f at -20-

28 least 6 hurs. This effect is simply the result f the high persistence in the visible extinctin. During the daytime, the cnditinal prbabilities are strngly lag dependent. The dependence n lag is illustrated in Fig Whereas the cnditinal prbability P[a, R (r+a)> T avi S {t)> 1 km -1 ] is greater than the uncnditinal prbability P[a /R > T ], we find that at night it is much lwer than the P[ a, R (f+a)> T \a, R (t)>t] cnditinal prbabilities discussed earlier. This may be seen frm a cmparisn f rws 2 and 3 with rws 4 and 5 f Tables 3.4 and 3.5, r frm a cmparisn f the P2 curves f plt (a) with the curves f plt (c) in Fig Nte that at night an infrared event 6 hurs in advance is assciated with higher cnditinal prbabilities than even a simultaneus visible event. Fr the daytime data, the P[a, R 0+A)> T \aw S (t)>\ km -1 ] cnditinal prbabilities are cmparable in magnitude t the P[a, R (r+a) > T \a, R (t)>t] cnditinal prbabilities fr A values f mre than an hur. That is, the cnditinal prbabilities assciated with an earlier visible extinctin event are abut equal t the cnditinal prbabilities assciated with an earlier infrared event during the day, if the lag is mre than an hur. Only fr a time lag f an hur r less is the P[a /R (f+a) > T a tr U)>T] cnditinal prbability significantly greater. Thus, the infrared extinctin lis mre likely t exceed threshld if the visible extinctin exceeds threshld 1 km -1 simultaneusly r earlier. That is, the cnditinal prbabilities are higher than the uncnditinal prbabilities. And at night it is even mre likely t exceed Table 3.4. Effect f visible vs infrared cnditins n prbability estimates, fr threshld 7"=1 krrr 1 September 1978 data Table 3.5. Effect f visible vs infrared cnditins n prbability estimates fr threshld 7*= 1 krrr 1, March 1978 data Prbability Type Nighl Day 3-5^ Mm 3-5/im 8-12Mm Prbability Type Nighl Day 3-5^m 8-l2Mm 3-5nm 8-l2Mm Uncnditinal P1 a /R > T1 Uncnditinal P1 a [R > T1 T - 1 km - ' T = 1 km"' Cnditinal n Infrared P\aIR(t+b)>T \air{i)>t] Cnditinal n Infrared />ta/w(h-a)>7" \airu)>t] T~ 1 km -1, A - 6hr T= 1 km" 1. A = 6hr < 015 T- 1 km" 1. A - 1 hr T= 1 km"', A = 1 hr Cnditinal n Visible PlaIRU+b)>T T-\ km" 1 \a lsu)>vt\, Cnditinal n Visible / > U/R(f+A)>r \amu)> VT]. T=\ km" 1 VT- 1 km -1, A - 6hr VT = 1 km" 1, A = 6hr VT- 1 km -1, A VT = 1 km"'. A = VT- 4 r 2* km -1, A - 3 hr VT- 4 r 2* km -1. A = 3 hr VT - 4 r 2* km"', A VT = 4 r 2* km"'. A = Used 4 fr nighl, 2 fr day Used 4 fr nighl, 2 fr day 03 O a: 1k^ ae-e r (a) Nighttime data, Sep 3-5/j.m D- T T-0.9 a - T-l.O + - T-l.l X - T-l T-l.S CD O r _ a a CJ -i r (b) Daytime data, Sep 3-5/* m LRG IN MINUTES LAG IN MINUTES Fig Cnditinal prbabilities, P\a ir 0+A)> T I a m d)> l km -1 ], as a functin f time lag September 1978, 3-5/im -21-

29 threshld if the infrared extinctin exceeds threshld even as much as 6 hurs earlier. When the visible extinctin threshld used in the cnditinal requirement is increased, the cnditinal prbabilities are significantly increased. Plts (e) and (f) f Fig. 3-5 shw the cnditinal prbabilities P[a IR 0+A) >T a vls (t)>4 km -1 ] fr nighttime and P[a, R (t+\) >T ayis(t)>2 km -1 ] fr daytime, respectively. Als see rws 6 and 7 f Tables 3.4 and 3.5. The prbabilities are quite high, being cmparable t the P[a, R 0+A) >T amu)>t ] prbabilities fr a lag f 16 minutes. The daytime data prbabilities were extracted fr visual threshld 2 km -1 rather than 4 km -1 due t lack f data. These cnditinal prbabilities are much higher than thse fr visible extinctin threshld 1 km -1, being similar in magnitude t the P[a, R (t+&)> T \a IR (t)>t] prbabilities in plt (b). The P[a, R (t+a)>t a ra 0)>4km-'] prbabilities d nt depend strngly n lag during the night, as shwn in Fig The daytime P[a IR (t + A)> T I avi S (t)>2 km -1 ] prbabilities are strngly lag dependent. T summarize, if ne is trying t predict whether the infrared extinctin is ging t exceed threshld, knwing that the visible extinctin is quite high, say > 4 km -1, is a gd indicatr. Hwever, when the visible extinctin is smewhat lwer hwever, fr example near 1 km -1, then a measurement f the infrared extinctin prvides a better indicatr than a measurement f visible extinctin. Knwing that the infrared extinctin is high is a gd indicatr fr several-hur frecasts at night. Additinal Prbability Estimates The data were als used t extract the cnditinal prbability f exceeding threshld given that the visible extinctin exceeded 1 km" 1 and the relative humidity exceeded 80%. These cnditinal prbabilities, P[a IR U+A)>T \a m (t)>\ km" 1 & RH(t)>80%], are quite similar t the cnditinal prbabilities given visible extinctin > 1 km -1, P[a, R (/+A)> T\a y, s (t)> 1 km" 1 ]. A typical sample f the effect f the relative humidity cnditin is illustrated in Fig In this figure, the plt (b), which shws P[a, R (t+a)>t \ ay, s (t) >lkm-'c5 RH(.t)>&0%] is nearly identical t plt (a), which shws P[a, R 0+A)> T a ra 0)> 1 kirr 1 ]. Sme similarity is t be expected, because the relative humidity nrmally exceeds 80% when a VIS exceeds 1 km -1 ; rughly } A f the cases with a ra > 1 km -1 als have RH> 80%. The majr cause f the similarity in the statistics, hwever, is the high persistence f the relative humidity values. Plt (c) shws the cnditinal prbabilities fr relative humidity, P[RH(t+A)> T \ RH(t)> T]. Fr relative humidity values f 80%, the persistence is very high, being.98 fr a six hur lag in September at night. This high persistence is the reasn that impsitin f the relative humidity cnditin has little additinal effect. Higher relative humidity values persist abut 4 hurs. There are additinal prbability estimates which wuld be f interest, hwever with a ne mnth data sample, lack f data can becme a prblem. Each additinal cnditin which is impsed n the data eliminates additinal data cases and thus lwers the number f values cnsidered. In particular, an attempt was made t extract the cnditinal prbability that the infrared extinctin wuld exceed threshld given that the infrared extinctin exceeded threshld at dawn. Figure 3-9 shws a sample cmparisn f the effects f adding the dawn cnditinal requirement. Althugh the cnditinal prbabilities in plt (b) are higher than the uncnditinal prbabilities in plt (a), there were t few data pints t yield accurate estimates. Fr example, fr hur 12, threshld 1.0 km -1, the abve and belw threshld cunts are 16 and 385 respectively fr plt (a), and 2 and 43 respectively fr plt (b). This lack f data is apparent in the increased scatter f plt (b). 3.3 Summary f Prbability Estimate Results In general, the behavir f the extinctin values, as indicated by the prbability estimates, is quite different at nighttime and at daytime. The tw mnths f data which CO r Q. Q z CJ T-0.7 T-0.9 T-1.0 T-1.1 T-1.3 T-1.5 (b) Daytime data IN MINUTES LAG IN MINUTES Fig Cnditinal prbabilities as a functin f time lag Pla IR (H-A)> T a y/s (/)> 4 km"" 1 ] at nighttime, P[a, R (t+a)>t a vls (t)> 2 km -1 ] during daytime March 1978, 3-5fxm

30 f- CQ CC : _ CC' < - P2ILA0 0) - P2[LflS 16) 4 - P2ILAB 60) + - P2ILRB 180) X - P2ILRB 360) (r+a)>r \ayi S (l)> 1 km CO cc CD "> CC "' _ cc «D- P2ILHS 0) >a- P2(LflB 16) n - P2IUW 60) + - P2tlflB 180) X- P2ILP.B 360) (b) Pla, R (t+b)>t \c,y ls (l)> 1 km" &RH{l)> 80%] 2 O CJ CJ I I THRESHOLD REL HUM ("/.) Fig Effect f adding a relative humidity cnditinal requirement. September 1978, 3-5/Lim, nighttime. r O X X en >- t (a) P[a IR(hr)>T] a - T T-0.9 & T ~ T-1.1 x - T-1.3 T-l.S ~* l 1 i i 1 i i I I I ^» (b) Pic, m Uir)>T\alR(dawn)>T] O <=" ~ X a T-0.9 O "> CC a- Ul CD O f a - T T-1.1 X- T-1.3»- T-l.S CQ CC CO ; a. a CJ a /S f f HOUR T T 1 r 0.0 * 2.0 f * 4.0 t M.O HOUR Fig Effect f adding the cnditinal requirement that extinctin exceed threshld at dawn. September 1978, 3-5/xm, daytime. were extracted yielded values which were quite similar in behavir, althugh smewhat different in magnitude in sme cases. In this data set, the verall prbability f having high extinctin values was fairly high in the visible regin, but quite lw in bth infrared bands. The persistence is very high in the visible regin. In the infrared bands, the persistence at night is high, althugh nt quite s high as in the visible. The resulting cnditinal prbabilities at night are high, fr lags up t at least 6 hurs. During the day, the persistence is high nly fr a lag f abut an hur r less. After an hur, the cnditinal prbabilities in the infrared regins becme very lw during the day. Cnditinal prbabilities based n the visible extinctin as a cnditinal requirement were als cmputed. The resulting cnditinal prbabilities P[a m (t+a)> T \ay/su)>\ km -1 ] were in general nt as high as the P[a /R 0+A)> T a, R 0)> T ] cnditinal prbabilities. -23-

31 In the rare cases when the visible extinctin exceeded 4 km -1, hwever, infrared cnditinal prbabilities became very high. It is nt clear yet whether it will eventually be pssible t parameterize these relatinships in an peratinally useful way. The general behavir f the tw mnths' data is s similar that there is reasn t try t quantify these relatinships. An additinal 10 mnths f data is currently underging prcessing. These additinal data will allw us t investigate the mnth-t-mnth changes, as well as intrduce additinal cnditinal requirements. Fr example, air mass type, predicted fg type, the number f hurs the mist has already persisted, and the rate f temperature drp are additinal predictrs which culd perhaps be evaluated with the larger data base. It wuld be particularly useful if the data yield cnsistent cnditinal prbability data as a functin f the visible extinctin, since predicted visible extinctins are ften available in the field. 4.0 CONCLUSION This reprt discusses an analysis f atmspheric extinctin cefficients measured simultaneusly in the visible and infrared (3-5/j,m and 8-12^m) regins. The measurements, taken in Meppen Germany, were recrded at ne minute intervals. Of the year's data base which is currently available, this reprt discusses the analysis f tw mnths f data. The analysis was designed t evaluate the shrt term tempral variatins in the infrared extinctin cefficient, particularly during mist and fg episdes. Previus research based n hurly interval data indicates that the relatin between the infrared and visible extinctin can be quite variable under these cnditins. The variatins in the hurly data appear t be ccurring n a time scale which is shrt relative t the length f the mist episdes. The minute data were analyzed because they are uniquely suitable fr studying the nature f the shrt term tempral variatins and fr extracting statistics relating t the prbability that the infrared extinctin will becme high and remain high. 4.1 Results f the Analysis Mist Bin It was fund that the high infrared aersl extinctins in the minute data set tend t ccur nly when the visible extinctin exceeds 1 km -1 and the relative humidity exceeds 80%. The set f pints meeting these cnditins were defined as the mist bin. Within this mist bin, which includes bth mist and fg, the infrared extinctin data are quite variable. The rati f infrared aersl t visible extinctin was fund t cver a large range f values, even at the high visible extinctin values nrmally assciated with fg (abut 4 km -1 r mre). Extinctin Relatins During Mist Episdes In rder t understand the nature f this variatin, cntinuus mist r fg perids lasting 30 minutes r mre were extracted and studied in mre detail. Plts f the infrared aersl extinctin and visible extinctin as a functin f time during the mist episdes were generated, alng with plts f infrared aersl extinctin as a functin f visible extinctin. During sme mist episdes, tempral variatins in the infrared aersl extinctin crrespnded very well t the variatins in the visible extinctin. In a few episdes, the infrared and visible extinctins appeared t be unrelated. In many cases, the infrared extinctin variatins crrespnded well t the visible extinctin variatins, except that they were very much magnified. That is, a small change in visible extinctin ften was assciated with a very large change in infrared aersl extinctin. Als, in many cases the infrared extinctin had essentially n variatin as lng as the visible extinctin was belw a certain threshld value; when the visible extinctin was abve that threshld value, the infrared extinctin shwed very large excursins in cnjunctin with the visible extinctin changes. The visible threshld at which this behavir ccurred tended t vary frm ne episde t the next. Althugh this threshld-type behavir ccurred during several mist episdes, there were several ther mist episdes, with similar values f visible extinctin, which did nt shw any threshld-type behavir. During the mist episdes, the infrared aersl extinctins were related t the visible extinctins in a nearly linear manner during apprximately half the episdes. Thus it was fund that althugh sme f the variability in the infrared t visible relatinship in the mist bin is due t differences between the individual mist episdes, much f the variability may be attributed t variatin in the infrared-visible relatinship within individual mist episdes. The magnified changes in the infrared extinctin ccurring within a mist episde in cnjunctin with relatively small visible extinctin changes (discussed in the previus paragraph) particularly cntributes t this variatin in the infrared-visible relatinship. Prbability Results Fllwing the abve analysis f mist and fg perids, statistics relating t the prbability f a high infrared extinctin ccurring were discussed. Fr this analysis, the cmplete data base fr each f the tw mnths was used, rather than just the mist bin, and the ttal extinctin rather than the aersl extinctin was used. It was fund that althugh the visible extinctin exceeded threshlds n the rder f 1 km -1 fairly ften, the infrared extinctin exceeded such threshlds nly rarely. Fr the higher threshlds, the infrared extinctin was particularly unlikely t exceed threshld during the daylight hurs. Althugh high extinctin events were infrequent, it was fund that nce a high infrared extinctin ccurred, it was quite likely t remain high, particularly during the night hurs. That is, the cnditinal prbability that the infrared extinctin will exceed threshld a given interval after it has nce exceeded threshld was quite high, fr intervals up t at least 6 hurs at night. The assciated -24-

32 persistence cefficients were therefre high. During the daylight hurs, the persistence and assciated cnditinal prbabilities were high nly fr an interval f apprximately an hur. After an hur, the cnditinal prbabilities were quite lw. Althugh the infrared extinctin persistence was high at night, it was nt as high as the nighttime persistence in the visible extinctin cefficient. That is, the high infrared extinctin values were less stable than the high visible extinctin values. It was als fund that nce a high visible extinctin ccurs, a high infrared extinctin is smewhat mre likely t ccur. That is, the cnditinal prbability that the infrared extinctin will exceed threshld a given interval after the visible extinctin has exceeded sme threshld is smewhat higher than the uncnditinal prbability that the infrared extinctin will exceed threshld. This effect is nearly lag (r interval) independent, fr intervals f at least 6 hurs. When the visible extinctin used in the cnditinal requirement is increased, the cnditinal prbabilities fr high infrared extinctin increase cnsiderably. In summary, the prbability estimates shw that if a high infrared extinctin ccurs, the infrared extinctin has a fairly large prbability f exceeding threshld in subsequent hurs, particularly at night. Als, if a high visible extinctin ccurs, the infrared extinctin has a mre than nrmal prbability f exceeding threshld in subsequent hurs--in fact the prbability becmes fairly large if the cnditinal visible extinctin is increased. In general, hwever, the verall prbability f a large infrared extinctin ccurring is quite lw. Althugh the magnitudes f the extracted prbability estimates differed smewhat n the tw mnths, the general character f the prbability curves was quite similar. The behavir f the night data differed cnsiderably frm the behavir f the day data. 4.2 Cntinuing Analysis Objectives The additinal 10 mnths f minute data are currently underging prcessing and initial quality evaluatin. With this larger data base, it shuld be pssible t intrduce additinal predictrs and cnditinal requirements n. the data. Althugh the exact apprach t the data analysis has nt yet been established, there are several appraches which are being cnsidered. Depending n data availability, it may be pssible t srt the data and determine cnditinal prbabilities fr different air mass types, and/r fr different fg types. Anther srting criteria f interest is the length f time that the high extinctin has already persisted, and perhaps the rate at which the temperature drpped. Mnths will prbably be cmbined seasnally fr this analysis. The hpe is that if the imprtant predictrs can be determined, it may be pssible t yield repeatable prbability estimates. That is, if the data are srted n the basis f seasn and fg type, fr example, r perhaps visibility predicted by the weather service, it may be that independent data sets, say in tw different mnths, will yield cnsistent cnditinal prbability estimates. If this were the case, these relatinships culd perhaps be parameterized fr frecasting. On the ther hand, if the real wrld data fall shrt f this hpe, it culd be peratinally useful t determine the general data relatinships, and hw these relatinships vary frm mnth t mnth. In additin t further analysis f prbability estimates, mentined abve, cntinuing analysis f the mist and fg episde data is planned. As nted in Sectin 2, the infrared extinctin is smetimes stable and/r well related t visible extinctin during the mist episdes, and smetimes it is extremely variable. The ability t predict which type f behavir will ccur in an nging mist r fg episde wuld be peratinally imprtant. With this gal in mind, we particularly wish t investigate rain data and aersl particle distributin measurements when they are available during mist perids. 5.0 REFERENCES Brks, C.E.P., and N. Carruthers (1953), Handbk f Statistical Methds in Meterlgy, Air Ministry, Meterlgical Office, Her Majesty's Statinary Office, Lndn. Fenn, R.W. (1978), "OPAQUE - A Measurement Prgram n Optical Atmspheric Prperties in Eurpe, Vl. I. The NATO OPAQUE Prgram", Special Reprts N. 211, AFGL-TR , ADB L. Fenn, R.W., T.S. Cress, Dr. DeHart, R. Dirkman, J.D. Essex, K. Lichtenberg, V.A. Marcell, J.E. Pwers, E.P. Shettle, H. Srn, J. Sullivan, F.P. Suprin, R.B. Tlin, V.D. Turner, F.E. Vlz (1979), "OPAQUE - A Measurement Prgram n Optical Atmspheric Quantities in Eurpe, Vl. II - The US/German OPAQUE Statin Near Meppen, Federal Republic f Germany", Special Reprts N. 222, AFGL-TR , ADB L. Gimmestad, G.G., L.W. Winchester, Jr., W.K. Chi, and S.M. Lee (1982), "Crrelatin Between the Infrared and Visible Extinctin Cefficients f Fg", Optics Letters, Vl. 7, N. 10, Huschke, R.E. (1976), "Atmspheric Visual and Infrared Transmissin Deduced frm Surface Weather Observatins: Weather and Warplanes VI", Reprt R PR RAND, Santa Mnica. Janssen, L.H. and J. van Schie (1982), "Frequencies f Occurrance f Transmittances in Several Wavelength Regins during Three Years", Appl. Opt., Vl. 21, N. 12, Kneizys, F.X., E.P. Shettle, W.O. Gallery, J.H. Cherwynd, Jr., L.W. Abreu, J.E.A. Selby, R.W. Fenn, and R.A. McClatchey (1980), "Atmspheric Transmittance- Radiance Cmputer Cde LOWTRAN5", AFGL- TR , ADA Khnle, A. (1979), "Barnes Calibratin via LOWTRAN, sme Aspects", Frschunginstitut fur Optik, Tubingen, OPAQUE AN-N/GE

33 Mcintsh, D.H. (1963), Meterlgical Glssary, Meterlgical Office, Her Majesty's Statinary Office, Lndn. Nilssn, B. (1979), "Meterlgical Influence n Aersl Extinctin in the /XWJ Wavelength Range", Appl. Opt., Vl. 18, N. 20, Prulx, G.J. (1971), Standard Dictinary f Meterlgical Sciences, Scientific and Technical Divisin, Department f the Secretary f State, Ottawa, Canada, McGill-Queen's University Press. Shand, W.A. Ed. (1978), "Barnes Intercmparisn Trial- Pershre. September 1977", RSRE(C) Christchurch, Drsett, England, OPAQUE R7804. Shettle, E.P. (1978a), "Theretical Transmittances fr the OPAQUE Barnes Transmissmeters", Air Frce Gephysics Labratry, Bedfrd, Mass., OPAQUE N/US Shettle, E.P. (1978b), "Analytic Expressins fr the Atmspheric Water Vapr Cntent", Air Frce Gephysics Labratry, Bedfrd, Mass., OPAQUE N/US Shettle, E.P. (1980), "Prcedure fr Calibratin f the OPAQUE IR Transmissmeters via LOWTRAN Calculatins", Air Frce Gephysics Labratry, Bedfrd, Mass., OPAQUE N/US Shettle, E.P. and R.W. Fenn (1978), "IR-Transmissmeter Calibratin, Cmparisn with LOWTRAN', Air Frce Gephysics Labratry, Bedfrd, Mass., OPAQUE N/US Shettle, E.P. and R.W. Fenn (1979), "Mdels fr the Aersls f the Lwer Atmsphere and the Effects f Humidity Variatins n Their Optical Prperties", AFGL-TR , ADA Shields, J.E. (1981), "An Analysis f Infrared and Visible Atmspheric Extinctin Measurements in Eurpe", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 82-4, AFGL-TR , ADA ACKNOWLEDGEMENTS This reprt has been prepared fr the Air Frce Gephysics Labratry under Cntract N. F I wish t thank the members f the Atmspheric Optical Physics Optics Branch f the Air Frce Gephysics Labratry, wh supplied the data, and prvided technical supprt. Special thanks t Mr. Eric Shettle fr his help with the data quality evaluatins. Credit is due t the Air Frce Gephysics Labratry, Mr. K. Lichtenberg and persnnel frm the Meppen Artillery Test Range, Meppen Germany, wh were jintly respnsible fr the measurement prgram. Several members f the Visibility Labratry staff have been mst helpful. I appreciate the assistance f the fllwing individuals: Mr. Richard W. Jhnsn and Mr. Wayne S. Hering, fr their valuable discussins during the analysis stages; Ms. Miriam K. Oleinik, fr advice and assistance with the cmputer prgram develpment stages; Ms. Alicia G. Hill, Mr. Jhn C. Brwn, and Mr. James Rdriguez fr careful dcument preparatin; and Mr. Jhn S. Fx fr assistance with cmputer prcessing. -26-

34 APPENDIX A Time Series Plts and Scatter '. and Visible Ex This appendix cntains mst f the time series plts and scatter plts which were generated fr the analysis in Sectin 2. Figures A-l thrugh A-6 illustrate the infrared aersl extinctin cefficients and the visible extinctin cefficients fr each mist episde, pltted as a functin f time since the beginning f the episde. Only the simultaneus visible extinctins at 4 minute intervals were pltted. The episde start times are indicated in the figure captins. Plts such as A-4 (c) and (d), which are a cntinuatin f the previus plt, begin 800 min and 1600 min after the episde start. Figures A-7 thrugh A-14 illustrate the plts f infrared aersl extinctin cefficient pltted as a functin f visible extinctin cefficient fr each mist episde. Plts were generated if there were at least 40 data pints within an episde. In sme cases the plts have nt been included in this appendix because the infrared data are belw the pltting scale minimum f.01 km -1. As a cnsequence, the number f plts included in this appendix is nt exactly the same as the number f 3 hur f Infrared Aersl Extinctin in Cefficient episdes listed in Table 2.1. Tw episdes included in the time series plts (A-l thrugh A-6) are deleted frm the scatter plt figures (A-7 thrugh A-14) because the numbers are mstly ffscale in ne case, and nearly cnstant in the ther. The srting prgram requires that the visible extinctin and relative humidity be valid and abve threshld thrughut the whle episde. (The nly exceptin t this rule is the case in which the visible data were nt reprted because the IR data were ffscale.) In the mist episde f Fig. A-2(g,h) the visible extinctin drpped belw 1 km -1 during ne 8-12^/w measurement at 1612, but remained abve threshld during the 3-5/xw measurements. As a cnsequence, the 8-12^im data srt yielded a mist starting at 1616, whereas the 3-5/AW data srt yielded an earlier start time, In tw ther cases, A-l(a,b) and A-3(a,b) the mist start times differ fr the tw filters due t a mmentary lss f visible extinctin data in ne filter's data set.

35 (a) 5 Sep 2320, 3-5/im (b) 5 Sep 2345, 8-12^m (c) 6 Sep 2110, 3-5/im (d) 6 Sep 2112, 8-12/*"! (e) 7 Sep 1830, 3-5/im : (0 7 Sep 1836, 8-12/xm u en ^r^» L * 1 J _ I 1 i r" (g) 9 Sep 0226, 3-5^ (h) 9 Sep 0228, 8-12/xm Fig. A-l. September 1978, aersl extinctin vs time (D =<*VIS 0=0: IR)- -28-

36 (a) 14Sep0858, 3-5Mm '. _ 1 (b) 14 Sep 0900, 8-12/im T 1 EXTINC (KM 10' *. Q : 2 cr a; '. "-I (e) 20 Sep 2230, 3-5 M m 7 1 EXTINC (KM 10' <n (d) 20 Sep 2236, 8-12 M m O ~- : -z. c 1 ' ii i ^ i (e) 22 Sep 0234, 3-5 M m J (f) 22 Sep 0228, 8-12 M m.vw : (g) 22 Sep 1534, 3-5/x m EXTINC (KM 10' IR AND VIS 10 \ p Hz 1 '. 1 I, (U,,,, X CJJ tr> > 'a. a ': z. a: ; r ' J\K rw/mi (h) 22 Sep 1616, 8-12/in Fig. A-2. September 1978, aersl extinctin vs time ( = avts 0=a tr^ -29-

37 (a) 23 Sep 2332, i-sfim -: (b) 24Sep0038, 8-12Mm V,01 ON 11X3 S. a a *: CE '»^y r& -g^0' A.-C- ^v^^-^^-g^e"-** ^"^ (c) 28 Sep 2334, 3-5Mm (d) 28 Sep 2332, 8-12^ m v^ja.ft B Fig. A-3. September 1978, aersl extinctin vs time (D =av,so=ir) -30-

38 (a) 3 Mar 0935, i-5tim (b) 3 Mar 0929, 8-12Mm MINJTES SINCE EPISODE STPRT (c) 3 Mar 0935, 3-5Mm cnt. (d) 3 Mar 0929, 8-12^ m cnt (e) 3 Mar 0935, 3-5jim cnt (0 3 Mar 0929, 8-12Mm cnt D 2 r (g) 5 Mar 0025, 3-5^ (h) 5 Mar 0019, 8-12Mm Fig. A-4. March 1978, aersl extinctin vs time (D *vis k MR' -31-

39 (a) 7 Mar 1733, 3-5/xm (b) 7 Mar 1735, 8-12/xm UJ (n r - i (c) 10 Mar 0740, 3-5/xm (d) 10 Mar 0742, 8-12/xm V~*~ (e) 10 Mar 0740, 3-5/xm cnt (f) 10 Mar 0742, 8-12/xm cnt (g) 12 Mar 1533, 3-5/xm (h) 12 Mar 1531, 8-12/xm Fig. A-5. March 1978, aersl extinctin vs time ( =avis =a ir^ -32-

40 ~ : 2% i X UJ R AND VIS!0 (a) 21 Mar 0149, 3-5/xm 3 - : (b) 21 Mar 0151, 8-12Mm i sr Z~ -. z t -J Q - *: : a: '. ^^~^«^J^ '. -^-f (c) 25 Mar 0011, 3-5/xm (d) 25 Mar 0009, 8-12/xm -I 1 ""I (e) 30 Mar 0140, 3-5/xm (f) 30Mar0138, 8-12Mm 2-= -< LJ CO /UV^V^^-^VA MINUTES SINCE EPiSOJL STPRT z en AAA\ ML., (g) 30 Mar 0140, 3-5/xm cnt (h) 30 Mar 0138, 8-12/xm cnt Fig. A-6. March 1978, aersl extinctin vs time ( =a VIS 0=a m ) -33-

41 (a) 5Sep2320, 3-5Mm (b) 5 Sep 2345, 8-12/xm 1 1 i i i i i i i I'Ti-q 10" 10' ' 10" (c) 6 Sep 2110, 3-5/xm (d) 6 Sep /xm ft ft% at «_,rp D - -. D D % B % D I TT ^ I 111] 10 10' 10 J VISIBLE EXTINCTION IKM-1) % D,P "1 D D a M 10" 10" 10' (e) 7 Sep 1830, 3-5M m \ (f) 7 Sep 1836, 8-12Mm - D ; D : D a a OO" D a 1»9 i i i i i i 1 i i M i i n 1 1 i rrtrn VISIBLE EXTINCTION (KM"1) (g) 9 Sep 0226, 3-5/xm (h) 9 Sep 0228, 8-12/xm - i i i i 1111 HI 10" ' ^ I I t r i i i ] r 1 i i I I I I) 10 10' 10' Fig. A-7. September 1978, infrared aersl extinctin vs visible extinctin. -34-

42 (a) 14 Sep /xm (b) 14 Sep 0900, 8-12/xm 10" 10' " 10' 10' (c) 22 Sep 0234, 3-5/xm (d) 22 Sep 0228, 8-12/xm 10" 10' 10 1 T i i i i i i i i i i r 10" 10' 10" (e) 22 Sep 1534, 3-5/xm (f) 22 Sep 1616, 8-12/xm 10" 10' 10' '-,* 10'!0' VISIBLE EXTINCTION (KM-i: (g) 28 Sep /xm (h) 28 Sep 2332, 8-12/xm ' r T I I I I I T T T 1 10" 10' 10 2 i 1 i i i i 111 i " 10' 10' Fig. A-8. September 1978, infrared aersl extinctin vs visible extinctin -35-

43 5"b UJ «}f 1 T I I I I I I I I 1 I I 10 10' 10 1 i i i i i i i i i ' 10 2 (a) 3-5/xm = 6 Sep 0639 O = 10 Sep 0602 A = 13 Sep = 13 Sep 1630 x = 13 Sep 2030 (b) 8-12/xm D = 6 Sep 0637 O =» 13 Sep I I I I I I I 10" 10' J* I' TTI I 1 r ~ 1 rtttttl 10" 10' 10 a (c) 3-5/xm D = 17 Sep 0430 O = 30 Sep 2203 (d) 8-12/xm D = 17 Sep 0432 O = 22 Sep 1532 A = 27 Sep = 30 Sep 2145 Fig. A-9. September 1978, infrared aersl extinctin vs visible extinctin. -36-

44 " (a) 3 Mar 0935, 3-5/xm.-, - ; (b) 3 Mar 0929, 8-1 2M m - a. 0 «a ' D fl2 " Mf &jf. a cf_jn -^ Jr? #,, T i t i 11 i 1 i r-rr-rn 10 10' 10' i 71 - \c _ : z: *-> z t a x _ D R) CC ; ^ ffd * r.us'r " D fipfift ID n * D D ' (c) 3 Mar 0935, 3-5/xm cnt 3 ' (d) 3 Mar 0929, 8-12/xm cnt > 1 f -i f ri-it 1 1 i i i i T ' 10 1 M 0. D M O'jjjfl 0 Aj«_> e z \ f 0 x 0. CC ' a a flf an '_ T T 1 n r i-rrn 10" 10' 10 2 (e) 3 Mar 0935, 3-5/xm cnt (f) 3 Mar 0929, 8-12/xm cm " 10' ^Sr T&T r-i-rrr 1 ' ' '''' I 10 10' 10 2 (g) 5 Mar 0025, 3-5/xm (h) 5 Mar 0019, 8-12/xm r _ T' T'l I 1 I 1 r-t~ttt 10" 10' " 10' 10 2 Fig. A-10. March 1978, infrared aersl extinctin vs visible extinctin -37-

45 (a) 7 Mar 1733, 3-5/xm (b) 7 Mar 1735, 8-12Mm EXTINCTION CC 10 (all data ffscale) fa r Jf ^ i i I I i I 1 1 i t r 10 10' 10' '_ 10 10' 10 2 (c) 10 Mar 0740, 3-5/xm (d) 10 Mar 0742, 8-12/xm \ ~' i i' i i i 11 i i r- i u r n 10" 10' 10' 10 ~ ' ' i i 11 n 1 1 i i i i i r i 10' 10 2 (e) 0 Mar 0740, 3-5/xm cnt (f) 10 Mar 0742, 8-12/xm cnt ; f r q9 $» m - jr - i i i 10" I I i i 10' 10 2 V ^" I I I I I I M 1 1 I I I 11] 10" 10' 10 2 (g) 12 Mar 1533, 3-5/xm (h) 12 Mar 1531, 8-12/xm a u -»*l 10" 10' 10 2 jb<3 ffl. 1 ' ' I, i i ' r-t-rtt) 10" 10' 10 2 Fig. A-ll. March 1978, infrared aersl extinctin vs visible extinctin. -38-

46 (a) 21 Mar 0149, 3-5/xm (b) 21 Mar0151,8-12Mm TION (KM 1 z X 10' LJ : CC '- Pg -1 1 i i 1 i i, i i i, W&E), 1 i i,ii,,) i0" 10' 10 2 (c) 25 Mar 0011, 3-5/xm (d) 25 Mar 0009, 8-12/xm i, i 11 M 1 i i i i 11 M 10" " 10' 10 2 (e) 30 Mar 0140, 3-5/xm (f) 30 Mar 0138, 8-12/xm 10" 10' 10 J VISIBLE EXTINCTION (KM-!) (g) 30 Mar 0140, 3-5/xm cm ~ 2Z _ z '- t z x: LJ r- (h) 30 Mar 0138, 8-12Mmcnt Srffitf - Wm _ i 1 i, i i i i i 1 1 n 10" 10' 10' '_ " I I I l~t~tt Fig. A-12. March 1978, infrared aersl extinctin vs visible extinctin -39-

47 J + + t - -i l^fa : A 10 i 1 i i i rit 10' T i i i r i 1 r i 10 2 OH i, i i i i i 1 T i I r i 11 10" 10' 10 2 (a) 3-5/xm Q = 3 Mar 0459 O = 3 Mar 0839 A = 4 Mar = 5 Mar 0857 X = 7 Mar 1137 (b) 8-12/xm D = 3 Mar 0449 O = 3 Mar 0841 A = 4 Mar = 5 Mar " 10' \m, 10 a i i i i M, 1 1 I, (c) 3-5/xm D = 7 Mar 1533 O = 8 Mar 1033 A = 10 Mar = 12 Mar 1233 x = 13 Mar 2231 (d) 8-12/xm = 9 Mar 1535 O = 12 Mar 1231 A = 13 Mar = 13 Mar 2345 Fig. A-13. March 1978, infrared aersl extinctin vs visible extinctin -40-

48 i r-i-ttn ' r i i i " 10' 10 2 J 2-*r 10" 10' VISIBLE EXTINCTION (KM-1) 10' (a) 3-5/xm (b) 8-12/x m D = 14 Mar 0243 O - 19 Mar 1859 A = 19 Mar = 22 Mar 0848 X = 22 Mar 2132 a = 19 Mar Mar 2233 A 22 Mar Mar D,-n 10 VISIBLE EXTINCTION (KM-1) " 10' VISIBLE EXTINCTION (KM-1) 10' (c) 3-5/xm (d) 8-12/xm D = 27 Mar 1515 = 27 Mar 2347 A = 28 Mar = 28 Mar 1504 X = 30 Mar 2136 = 27 Mar 1517 O = 27 Mar 2345 A = 28 Mar = 28 Mar 1402 X = 28 Mar = 30 Mar 2134 Fig. A-14. March 1978, infrared aersl extinctin vs visible extinctin -41-

49 APPENDIX B Plts f Prb This appendix cntains mst f the prbability plts which were generated fr the analysis in Sectin 3. All f the types f prbability estimates listed in Table 3.2 were cmputed and pltted. The resulting plts are included here except as fllws. Plts f P[ai R U+A)>T\a v,su)>l km" 1 & RH(t)>80%] are nt included because the results are nearly identical t plts f P[a /R (t+a) > T Vis(t)> 1 km~ n. The cmpanin plts P[RH>T] and P[RH(t+A)>T \ RH(t)>T], which were used t y Estimates analyze the abve, are als nt included. Sample plts f these data are included in Fig Als, the plts f P[a /R (hr)> T \a /R (t = dawn)> T] are excluded since there were insufficient data t prvide an accurate estimate. A sample plt is included in Fig Fllwing these plts are tw flwcharts illustrating sample prbability cmputatins as discussed in Sectin 3.1. These flwcharts indicate the cnceptual flw. The actual prgrams accmplished equivalent prcedures in smewhat different rder, fr efficiency.

50 D-HOUR-00 "HOUR-02 a -HOUR HOUR-20 X -HOUR-22 I -HOUR-00 -HOUR-02 A -HOUR-Oi + -HOUR-20 X -HOUR (a) Sep '78 3-5/xm, Prb vs Thresh (b) Sep ' /xm, Prb vs Thresh -HOUR-00 -HOUR-02 A -HOUR-Oi + -HOUR-20 X -HOUR-22 CC a X 21 CJ a: LJ >-, -" a ~ d~ \ \\ "HOUR-00 \fl -HOUR-02 W A -HOUR-04 1\ + -HOUR-20 1\ X -HOUR (c) Mar '78 3-5/xm, Prb. vs Thresh CD a: CD O CC Q_ CM d" d» ft I 1 1 T -f 9 = T- =a (d) Mar' /xm, Prb vs Thresh» 9= d - T T-0.9 «- T T-1.1 X- T T-1.5 ***w -i r HOUR (e) Sep '78 3-5/xm, Prb vs Hur - T-0.3 O - T-0.S A - T-.a * - T-1.0 X - T T-l *4 a ffi^ HOUR (f) Sep ' /xm, Prb vs Hur D- T T-0.9 a- T T-1.1 X- T T T T T T-1.0 X- T T-1.5 ~l ?? i.o HOUR (g) Mar '78 3-5/xm, Prb vs Hur HOUR (h) Mar ' /xm, Prb vs Hur Fig. B-l. Night Prbability vs Hur /> = P[a, R (hr) > T ] -43-

51 SYMEOLS - pi - P2UJW 16) «- P2ime 60) + - P21LH6 1BO) X - P21LIW 3601 P2[U» 16) P2ILAS 60) P2ILA6 ISO) P2ILH0 360) (a) Sep '78 3-5>im, Prb vs Thresh THRESHOLD EXTINCTION 1 2 (KM-1) (b) Sep ' ^m, Prb vs Thresh >~ ^ (c) Mar'78 3-5/im, Prb vs Thresh I (d) Mar ' /* m, Prb vs Thresh _ *$5fc«v "^==== * "» T T-0 9 A - T-l T-l 1 X " T-l 3 - T-l LAG IN MINUTES (e) Sep '78 3 5^m, Pers vs Lag LAG IN MINUTES (f) Sep' (um Pers vs Lag LAG IN MINUTES (g) Mar '78 3-5/im, Pers vs Lag LAG IN MINUTES (h) Mar ' /xm, Pers vs Lag Fig. B-2. Night Prbabilities PI = P[a IR > T ], P2 = P[a, R (H-A) >T\a, R (t)>t) -44-

52 n- P2IUW 01 - P2IUW 16) a - P2IUW 60) + - P2IUW ISO) X- P2IUS 360) - P2[Lfltf O) O- P2IUW 16) 4- P2US P2ILA8 160) X - P2ILA8 360) O.B (a) Sep '78 3-5Mm, Prb. vs Thresh (b) Sep ' /nm, Prb. vs Thresh. D- P2ILA8 0) - P2IUW 16) 4- P2ILA8 60) + - P2CUW 160) X - P2IUIB 360) n - P2ILR8 0) - P2ILAC 16) A - P2ilflB 60) + - P2(Lflfl 1B0) X - P2ILA8 360) (c) Mar '78 3 5jim, Prb. vs Thresh (d) Mar ' /um, Prb. vs Thresh. a- T «- T I-I.l X- T-l T-I.S - " a r-.s 4- I-O.B»- r-i. X r-i.s LUG IN MINUTES (e) Sep '78 3 5/iin, Prb. vs Lag ;^^^ 1 i i l LAG IN MINUTES (f) Sep ' /tm, Prb. vs Lag ) LAG IN MINUTES (g) Mar '78 3-5/im, Prb. vs Lag Fig. B-3. Night Prbabilities P LAG IN MINUTES (h) Mar ' )nm, Prb. vs Lag P[a, R (t+b)>t \a m (t)> 1 km-']. -45-

53 D - P2ILP.B 0) - P21LAC 16) A - P21LP.G 60) + - P21LP.G 160) (a) Sep '78 3-5/im, Prb vs Thresh (b) Sep ' ^m, Prb vs Thresh > H r "1 CD 1 \ m (T rn \ i ** a. O " O - P21LAC 0) O 0 - P2ILAB 16) A - P2ILAC 60) rvj + - P21LAC 160) n X n (c) Mar '78 3-5/im, Prb vs Thresh D- P2ILP.8 0) - P2ILAG 16) A - P2ILA8 60) + - P2ILAB 160) X- P21Ufl8 360) THRESHOLD EXTINCTION (KM-1) (d) Mar' M m Prb vs Thresh ~ [^ ^7C \ \ - T-0 3 \ - T-0 5 \ - H I \ LAG IN MINUTES (e) Sep '78 3-5/im, Prb vs Lag LAG IN MINUTES (f) Sep ' /ixm, Prb vs Lag D - T T T-l T-l 1 X - T-l 3» - T-l LAG IN MINUTES (g) Mar '78 3-5/i.m, Prb vs Lag LAG IN MINUTES Fig. B-4. Night Prbabilities P (h) Mar' /im Prb vs Lag P[a IR (t+a) > T \a vls (t) >4km-'] -46-

54 E=fe 3- PI 3- P2IL6C 16) i - P2ILP.8 60) - P2ILHS 160) < - P2H.P.S 360) THRESHOLD EXTINCTION 1 2 (KM-1) (a) Sep 78 Night, Prb vs Thresh THRESHOLD EXTINCTION (KM-1) (b) Mar '78 Night Prb vs Thresh T-0 7 T-0 9 T-l 0 T-l LAG IN MINUTES (c) Sep '78 Night, Pers vs Lag ISO LAG IN MINUTES (d) Mar '78 Night, Pers vs Lag e e e * D- PI - P2ILAB 16)»- P2ILH8 60) + - P21LA8 1B0) X - P2(me 360) - pi - P21LA8 16) 4 - P2ILA8 60) + - P21LAB 160) X - P2CLAB 360) (e) Sep '78 Day Prb vs Thresh THRESHOLD EXTINCTION 1 2 (KM-1) (f) Mar 78 Day Prb vs Thresh ^^ V^C^^N^ T T- 9 \w ^* ^fcr - ^ - - ^ ^ ^^^-t A T-l 0 ^^J^^^--^ ^ + ~ T-l 1 ^ ^ S J L ^""-- ^ x T-l 3 ^^^s:^^ ^""--.f - T-l 5 ^^"^^^s^x LAG IN MINUTES (g) Sep '78 Day Pers vs Lag LAG IN MINUTES (h) Mar '78 Day, Pers vs Lag Fig. B-S. Night & Day Prbabilities PI = P[a vls > T ], P2 = Pla m b+a) > T \a m d) > T 1-47-

55 HOUR-06 HOUR-09 HOUR-12 HOUR-15 HOUR J D- HOUR HOUR HOUR HOUR-IS 1 X - HOUR (a) Sep'78 3-5/im Prb vs Thresh (b) Sep ' /xm, Prb vs Thresh - HOUR-06 - HOUR HOUR-12 * - HOUR-15 X- HOUR-18 O- HOUR-06 O- HOUR HOUR-12 - HOUR-15 X - HOUR-16 -I (c) Mar '78 3-5/im, Prb vs Thresh (d) Mar ' /im, Prb vs Thresh D - T T-0 9 A ~ T-l 0 + ~ T-l 1 x T-l 3 T-l HOUR (e) Sep '78 3-5/xm, Prb vs Hur ir ID O 31 T r t (T -1 <D SYM D - T T-0 5 T-0 6 LJ O" 0 >- f _) Q - m u CD fm <r Q_ O HOUR (f) Sep ' /im, Prb vs Hur n- T T T-l 0 * - T-l 1 X - T-l 3» - T-l 5 - T T T-0 B + - T-l 0 X- T-l T-l HOUR (g) Mar '78 3-5/im, Prb vs Hur IB HOUR (h) Mar ' /im, Prb vs Hur Fig. B-6. Day Prbability vs Hur P = P[a m (hr) > T ] -48-

56 - P2ll.R0 16) 4 - P2ILRG 60) + - P2ILP.S 180) X - P2ILPB 360) (a) Sep '78 3-5^111, Prb vs Thresh (b) Sep ' Mm, Prb vs Thresh - P2(LP.G 16) 4 - P2ILP.B 60) + - P2II.P.G 160) X - P21LP.C 360) a - pi - P2IIR8 16) 4 - P2H.RB 60) + - P2ILR6 1BO) X - P2ILP.G 360) OB 10 THRESHOLD EXTINCTION (KM-1) (c) Mar '78 3-5/im, Prb vs Thresh OB (d) Mar ' /im, Prb vs Thresh a - T T T-l T-] LAG IN MINUTES (e) Sep '78 3-5/im, Pers vs Lag LAG IN MINUTES (f) Sep ' /im, Pers vs Lag a - T-0 3 O - T T-0 8 t X- T-l 2»- W S ' LAG IN MINUTES (g) Mar '78 3-5/im, Pers vs Lag ISO LAG IN MINUTES (h) Mar ' ju.m, Pers vs Lag Fig. B-7. Day Prbabilities PI = Pi a, R > T], P2 = P[ a, R (/+A)> T a IR (r) > 7"] -49-

57 LP.G-0 LPrS-16 LRB-60 LRB-160 LRC (a) Sep '78 3-5/xm, Prb. vs Thresh (b) Sep ' /im, Prb. vs Thresh. D - LRO-0 - LR me Lfl-ie X - LflB (c) Mar '78 3-5/im, Prb. vs Thresh (d) Mar ' /im, Prb. vs Thresh LAG IN MINUTES (e) Sep '78 3-5/1"!, Prb. vs Lag B LAG IN MINUTES (f) Sep ' /im, Prb. vs Lag - T T T T-1.0 X- T-l.2 - T-l LAG IN MINUTES (g) Mar '78 3-5/xm, Prb. vs Lag Fig. B-8. Day Prbabilities P P[a m (t+a) LAG IN MINUTES (h) Mar ' /im, Prb. vs Lag > T a ra (f)>lkm-']. -50-

58 a - LfiO-0 O- LB LRS-tO + - LR8-160 LflO THRESHOLD EXTINCTION IKM-1) (a) Sep'78 3-5/im Prb vs Thresh (b) Sep' /im Prb vs Thresh CD O D- UW-0 - LH LflS Lfts-ie X - LR8-360 Q 2 O (c) Mar '78 3-5/xm, Prb vs Thresh (d) Mar' /im Prb vs Thresh z T-0 7 T-0 9 T-l 0 T-l 1 T-l 3 T-l S LAG IN MINUTES (e) Sep '78 3-5/im Prb vs Lag IB LAG IN MINUTES (f) Sep ' /im, Prb vs Lag I LAG IN MINUTES (g) Mar '78 3-5/xm, Prb vs Lag Fig. B-9. Day Prbabilities P Pla lr (i+a)>t LAG IN MINUTES 'h) Mar ' /xm, Prb vs Lag a ra (f)>2krrr'] -51-

59 start g t next min. data recrd read data fr 1 min. fr each hr and T(J),P = "abve" / "belw" cunt as "sunlit" print results cunt as "n data" END fr hur = hr cunt "belw" threshld TU) fr hur = hr cunt "abve" threshld T(J) J = J+l Fig. B-10. Flw chart illustrating cmputatin f sample prbability estimate, P[a m (hr)>t] at night. -52-

60 subchart 7=1 cunt as "sunlit" r as "lag-sunlit" fr lag K - cunt as "n data" r "lag-n data" fr lag K - Start read first 6 hurs f data apply sub-chart i I t I first minute ' J 1 mve 6 hur interval dwn l recrd (4 mm) fr each TU) PI = "abve" / "belw" fr TU), cunt as "belw" r "lag-belw" fr lag K K = l ' fr each TU) and lag, P2 - "lag-abvd' "lag-belv)' yes fr 7V), cunt as abve" r" lag-abve" fr lag K apply sub-chart t min at lag A( K ) I ~l fr each TU) and lag, r = 1- P PI K = lc n yes J = J+l yes print results end Fig. B-ll. Flw chart illustrating cmputatin f sample prbability estimate, P[a U+&)> T a (r)> T]

61 APPENDIX C VISIBILITY LABORATORY CONTRACTS AND RELATED PUBLICATIONS Previus Related Cntracts: F C-0013, F C-0004 PUBLICATIONS: Duntley, S.Q., R.W. Jhnsn, J.I. Grdn, and A. R. Bileau, "Airbrne Measurements f Optical Atmspheric Prperties at Night", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 70-7, AFCRL , NTIS N. AD (1970). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties in Suthern Germany", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL , NTIS N. AD (1972a). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne and Grund-Based Measurements f Optical Atmspheric Prperties in Central New Mexic", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL , NTIS N. AD (1972b). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties, Summary and Review", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL , NTIS N. AD (1972c). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties in Suthern Illinis", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL-TR , NTIS N. AD (1973). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne and Grund-Based Measurements f Optical Atmspheric Prperties in Suthern Illinis", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL-TR , NTIS N. ADA (1974). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties in Western Washingtn", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL-TR , NTIS N. ADA (1975a). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties, Summary and Review If, University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFCRL-TR , NTIS N. ADA (1975b). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties in Nrthern Germany", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFGL-TR , NTIS N. ADA (1976). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Atmspheric Vlume Scattering Cefficients in Nrthern Eurpe, Spring 1976", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 77-8, AFGL-TR , NTIS N. ADA (1977). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Atmspheric Vlume Scattering Cefficients in Nrthern Eurpe, Fall 1976", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 78-3, AFGL-TR , NTIS N. ADA (1978a). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Atmspheric Vlume Scattering Cefficients in Nrthern Eurpe, Summer 1977', University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFGL-TR , NTIS N. ADA (1978b). Duntley, S.Q., R.W. Jhnsn, and J.I. Grdn, "Airbrne Measurements f Optical Atmspheric Prperties, Summary and Review III", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 79-5, AFGL-TR , NTIS N. ADA (1978c). Fitch, B.W. and T.S. Cress, "Measurements f Aersl Size Distributin in the Lwer Trpsphere ver Nrthern Eurpe", J. Appl. Met. 20, N. 10, , als University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFGL-TR , NTIS N. ADA (1981). Grdn, J.I., C. F. Edgertn, and S.Q. Duntley, "Signal- Light Nmgram", J. Opt. Sc. Am. 65, (1975). Grdn, J.I., J. L. Harris, Sr., and S.Q. Duntley, "Measuring Earth-t-Space Cntrast Transmittance frm Grund Statins", Appl. Opt. 12, (1973). Grdn, J.I., "Mdel fr a Clear Atmsphere", J. Opt. Sc. Am. 59, (1969). Grdn, J.I., "Daytime Visibility, A Cnceptual Review", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref. 80-1, AFGL-TR , NTIS N. ADA (1979). Grdn, J.I., "Implicatins f the Equatin f Transfer Within the Visible and Infrared Spectrum", University f Califrnia, San Dieg, Scripps Institutin f Oceangraphy, Visibility Labratry, SIO Ref , AFGL-TR (1983). Hering, W. S., "An Operatinal Technique fr Estimating Visible Spectrum Cntrast Transmittance", Univer- -54-