NASA Cold Land Processes Experiment (CLPX 2002/03): Local Scale Observation Site

Transcription

1 1434 J O U R N A L O F H Y D R O M E T E O R O L O G Y VOLUME 9 NASA Cold Land Pocesses Expeiment (CLPX 2002/03): Local Scale Obsevation Site JANET HARDY,* ROBERT DAVIS,* YEOHOON KOH,* DON CLINE, KELLY ELDER, # RICHARD HANS-PETER THOMAS PAINTER, & GILLES CASTRES SAINT-MARTIN,** ROGER DEROO,** KAMAL SARABANDI,** TOBIAS GRAF, TOSHIO KOIKE, AND KYLE MCDONALD ## * Cold Regions Reseach and Engineeing Laboatoy, Enginee Reseach and Development Cente, U.S. Amy Cops of Enginees, Hanove, New Hampshie NOAA/NWS/National Opeational Hydologic Remote Sensing Cente, Chanhassen, Minnesota # USDA Foest Sevice, Fot Collins, Univesity of Coloado, Boulde, Coloado & Univesity of Utah, Salt Lake City, Utah ** Univesity of Michigan, Ann Abo, Michigan Univesity of Tokyo, Tokyo, Japan ## NASA Jet Populsion Laboatoy, Califonia Institute of Technology, Pasadena, Califonia (Manuscipt eceived 12 Januay 2007, in final fom 19 Mach 2008) ABSTRACT The local scale obsevation site (LSOS) is the smallest study site (0.8 ha) of the 2002/03 Cold Land Pocesses Expeiment (CLPX) and is located within the Fase mesocell study aea. It was the most intensively measued site of the CLPX, and measuements hee had the geatest tempoal component of all CLPX sites. Measuements made at the LSOS wee designed to poduce a compehensive assessment of the snow, soil, and vegetation chaacteistics viewed by the gound-based emote sensing instuments. The objective of the gound-based micowave emote sensing was to collect time seies of active and passive micowave spectal signatues ove snow, soil, and foest, which is coincident with the intensive physical chaacteization of these featues. Gound-based emote sensing instuments included fequency modulated continuous wave (FMCW) adas opeating ove multiple micowave bandwidths; the Gound-Based Micowave Radiomete (GBMR-7) opeating at channels 18.7, 23.8, 36.5, and 89 GHz; and in 2003, an L-, C-, X- and Ku-band scatteomete ada system. Snow and soil measuements included standad snow physical popeties, snow wetness, snow depth tansects, and soil moistue. The stem and canopy tempeatue and xylem sap flux of seveal tees wee monitoed continuously. Five micometeoological towes monitoed ambient conditions and povided focing datasets fo 1D snow and soil models. Aays of pyanometes (0.3 3 m) and a scanning themal adiomete (8 12 m) chaacteized the vaiability of adiative eceipt in the foests. A field spectoadiomete measued the hypespectal hemispheical-diectional eflectance of the snow suface. These measuements, togethe with the gound-based emote sensing, povide the famewok fo evaluating and impoving micowave adiative tansfe models and coupling them to land suface models. The dataset is achived at the National Snow and Ice Data Cente (NSIDC) in Boulde, Coloado. 1. Intoduction The local scale obsevation site (LSOS) is the smallest study site of the Cold Land Pocesses Expeiment (CLPX; D. Cline et al. 2008, unpublished manuscipt) and Coesponding autho addess: Janet P. Hady, CRREL, Enginee Reseach and Development Cente, U.S. Amy Cops of Enginees, 72 Lyme Road, Hanove, NH janet.p.hady@usace.amy.mil is located within the Fase mesocell study aea (MSA), nea the Fase Expeimental Foest headquates facility in Fase, Coloado [ N, W; 2780 m asl (metes above sea level); Fig. 1]. The 0.8-ha tiangula site consists of a small cleaing, a managed unifom pine canopy, and a discontinuous, mixed age canopy (Fig. 2). The LSOS was the most intensively measued site in the CLPX, whee the measuement detail fa exceeded simila measuements at the lage scales. The data collected at the LSOS allows fo a DOI: /2008JHM Ameican Meteoological Society

2 DECEMBER 2008 H A R D Y E T A L A netwok of footpaths was established thoughout the LSOS to pevent the disuption of the specific measuement sites. 2. Summay of collected data paametes FIG. 1. The LSOS ( ) elative to the thee Fase ISAs and Fase, CO. complete and detailed chaacteization of the local snow conditions, soil popeties, vegetation, and enegy balance chaacteistics. Additionally, measued goundbased micowave emote sensing (active and passive) at the LSOS povided data to elate to the measued snow and canopy popeties as well as emote sensing signatues. The dataset is achived at the National Snow and Ice Data Cente (NSIDC) in Boulde, Coloado (available online at The pupose of the LSOS measuements was to allow scaling between gound-based and aibone- and satellite-based instuments. The detailed measuements allow full chaacteization of the test site and can be used to validate small-scale models and futhe extapolate and test algoithms at lage scales. The gound-based emote sensos viewed a homogeneous snow-coveed cleaing and a small foest stand. Snow scattes the micowave emissions fom the soil, and the amount of this scatte is elated to the snow popeties, including snow wate equivalent (SWE), gain size, wetness, depth, and density. Suface enegetics dive the enegy balance components that influence these snowpack physical popeties, which in tun affect the signal eceived by the gound-based sensos. The measuement appoach within the LSOS consisted of a high sampling density within elatively unifom aeas of the LSOS to facilitate a compaison of micowave emote sensing data, adiative tansfe models, detailed physical models of the snow and the undelying soil, and gound obsevations. a. Canopy chaacteization In the fall of 2001, Cold Regions Reseach and Engineeing Laboatoy (CRREL) scientists of the Enginee Reseach and Development Cente (ERDC) defined and extensively mapped the canopy in the LSOS. The aea was divided into seventy-eight 10 m 10 m plots (Fig. 2), and the canopy in each plot was chaacteized using hemispheic photogaphy. The individual tee locations in 62 plots wee mapped and linked to thei physical measuements (tee height, cown height, diamete at beast height, and cown diamete). The LSOS was gouped into thee main canopy types: unifom pine canopy, discontinuous pine canopy, and small cleaing. b. Snowpack physical popeties Snow pits at the LSOS consist of thee snow pits pe day duing all intensive obsevation peiods (IOPs): one in each of the two canopy types and one in the cleaing. The potocol fom all the physical measuements used in the intensive study aeas (ISAs) (Elde et al. 2009a) wee used fo all the LSOS measuements to ensue data compatibility and to facilitate modeling and compaisons acoss scales. In addition to the standad potocol, we measued snow wetness duing the sping IOPs at 10-cm depth intevals including the snow suface using the Denoth snow wetness mete. Additionally, scientists opeating the Gound-Based Micowave Radiomete (GBMR-7) measued the snow popeties outside the IOPs to suppot thei adiomete measuements. c. Snow suveys Systematic measuements of snow depth and snow wate equivalent (SWE) wee made duing each IOP in each of the thee canopy types. Snow depth was measued to the neaest centimete using a calibated snow pobe inseted into the snow each mete along the paths. In 2003 only, SWE and density measuements wee made appoximately evey 5 10 m along the paths using the Canadian ESC-30 sample. d. Subcanopy enegetics Standad meteoological data collected at the LSOS anged fom subcanopy tempeatue, elative humidity,

3 1436 J O U R N A L O F H Y D R O M E T E O R O L O G Y VOLUME 9 FIG. 2. Map showing the layout of the LSOS with appoximate locations of instumentation. The unifom pine canopy is southeast of the cleaing. The discontinuous pine canopy is nothwest of the cleaing. and wind speed measued in the unifom canopy in 2002 to five full weathe stations (unifom canopy, cleaing, two in discontinuous canopy, and one appoximately 500 m west of the LSOS) and an eddy covaiance (EC) system in 2003 (Maks et al. 2008). The measued meteoological data included sola and longwave downwad adiation, snow, soil and ai tempeatue, elative humidity, wind speed and diection, pecipitation, soil heat flux, and soil moistue. Aays of ten sola and two longwave adiometes sampled enegy beneath the unifom conifeous canopy and the discontinuous canopy. The U.S. Foest Sevice measued the above-canopy adiation as well as othe meteoological components at the LSOS (Elde et al. 2009b). Spatial vaiations in the longwave adiation emitted wee compaed between the tee tunks, snow, and gound foliage using a themal infaed imaging adiomete (8 12 m). The measuements of the hypespectal hemispheical diectional eflectance facto (HDRF) of the snow suface (wavelength ange m), using a field spectoadiomete, povided calibation data fo the optical aibone and spacebone imaging spectometes and the multispectal images used in the CLPX. These measuements will also be compaed with field micowave measuements fo synthesizing the models snow popeties, including gain size, albedo, and suface liquid wate content. e. Micowave adiomete systems The Univesity of Michigan Radiation Laboatoy managed a passive micowave adiomete system that opeated at 1.4, 6.7, 19, and 37 GHz. These systems measued adiometic bightness in vetical (V) and hoizontal (H) polaizations. The 19- and 37-GHz systems have beamwidths of 10 each, while the 1.4 and 6.7-GHz systems have beamwidths of 22 each. These systems wee mounted on the end of a 10-m telescoping boom and allowed fo incidence angle vaiation fom nadi (0 ) to zenith (180 ; Fischman 2001). The adiomete systems wee configued to opeate continuously duing IOP3 and IOP4, with an objective to chaacteize micowave emission fom the snow cove and adjacent tees. The 6.7-, 19-, and 37-GHz systems collected micowave bightness data of a snow field at 54 incidence angle. Altenate tagets wee measued seveal times pe day: 1) a scan in elevation fom 0 to 65 of upwelling bightness fom the snow field, 2) a scan in azimuth of upwelling bightness at 54 fom shot tees to the southwest of the adiometes, 3) a scan in azimuth of upwelling bightness at 54 fom the sides of

4 DECEMBER 2008 H A R D Y E T A L snowpack popeties. The adiomete was mounted on a flexible positioning system, which allowed fo vaiety in the obsevation diection and incident angle. Two obsevation aeas have been used fo the expeiment: 1) the snowpack notheast of the adiomete (Fig. 2) was undistubed duing the winte and egulaly scanned with vaying incident angles (between 30 and 70 ), and 2) the nothen aea was used fo obseving bae soil (afte emoving snow) and new snow on the gound. Both taget aeas wee scanned seveal times a day duing the IOPs. FIG. 3. Photo of the GBMR-7 in opeation at the LSOS. tees talle than the tuck boom to the noth and nothwest, and 4) a scan in elevation fom 90 to 135 of the downwelling bightness fom the same tall tees (De Roo et al. 2007). f. Gound-based micowave adiomete The Univesity of Tokyo opeated the GBMR-7 Advanced Micowave Scanning Radiomete (AMSR) simulato (Fig. 3), which obseved the bightness tempeatue at 18.7, 23.8, 36.5, and 89 GHz (Kazama et al. 1999). The objectives of this passive micowave adiomete wee to 1) obseve the influence of snowpack metamophism and the melting efeezing cycle on the bightness tempeatue of the snow cove, and 2) develop a scheme, which couples a adiative tansfe model with a physical-based snow model using data assimilation. To develop and validate the assimilation scheme, a vey detailed dataset was collected, which compised focing data, adiomete obsevations, and g. L- and K u -band scatteomete The Univesity of Michigan opeated a scatteomete, a ada system capable of measuing the amplitude and phase of the backscatteed signal, in the lage cleaing in the LSOS. The system opeated at L-band ( GHz) and Ku-band ( GHz; Tassoudji et al. 1989). The measuements wee taken fom thee diffeent incidence angles (20, 35, and 50 fom nadi). A total of 401 fequency points wee ecoded ove the bandwidth fo both scatteometes, and data collection was pefomed ove 60 independent spatial samples at 20, and 30 independent spatial samples at 35 and 50. The measued data wee calibated using a metallic 36-cm diamete sphee and the single taget calibation technique (STCT; Saabandi and Ulaby 1990) algoithm. The polaimetic scatteing data afte calibation was fomatted in Muelle matix fom and stoed. h. Fequency modulated continuous wave adas The CRREL/ERDC and the Univesity of Coloado obtained ada gound measuements using FMCW adas in thee fequency bands [2 6 GHz (C-band), 8 12 GHz (X-band), and GHz (Ku-band)] as well as naow-band measuements (bandwidth 1 GHz and 100 MHz) centeed in each fequency ange (Stove 1992). Metal eflectos placed on the suface and in the TABLE 1. Tempoal esolution of measued data. Refe to specific datasets fo moe details. PeIOPs IOP Inteim IOPs IOP IOP Inteim IOPs IOP Canopy chaacteization Snow popeties and snow suveys Subcanopy enegetics Micowave adiomete GBMR-7 adiomete * Scatteomete FMCW ada Biophysical popeties Ongoing, beginning with IOP1 * Data only fo 25 Ma 2003.

5 1438 J O U R N A L O F H Y D R O M E T E O R O L O G Y VOLUME 9 TABLE 2. Measued micowave fequencies (GHz) of vaious instuments. Hee, indicates bandwidths Micowave adiomete GBMR-7 adiomete Scatteomete FMCW ada bands snowpack allowed fo calibation and attenuation calculations. These ada measuements simulated satellite and aibone measuements. This multifequency appoach fo ada emote sensing was designed to suppot the investigation of snowpack paametes such as density, depth, and wetness. As the ada fequency inceases, the effect of snow gain size becomes moe impotant. Radas opeating in the Ku-band contain the most infomation about the intenal featues of a dy snowpack; howeve, in a wet snowpack, the suface eflection dominates and gound etun is insignificant. Radas opeating at lowe fequencies (C-band) ae pefeable fo achieving the necessay penetation though a wet snowpack. i. Biophysical activity in tees The NASA Jet Populsion Laboatoy (JPL) monitoed biophysical activity in six selected tees with instuments that included themistos implanted in the soil and in the hydoactive tissues of the tee tunks, xylem sap flow sensos, and dielectic pobes. Xylem flux was monitoed using a constant enegy input method (Ganie 1987). The micowave dielectic constant of the hydoactive stem tissue was monitoed with an automated dielectic monitoing system (McDonald et al. 1999). Data acquied by these instuments chaacteized the themal egime within the tees and soil, and the wate consumed by the plant. Two goals of this eseach wee to detemine the wate conductive state of the tees duing spingtime thaw and to elate this infomation to measuements acquied with micowave emote sensing instuments. The genealized tempoal esolution of all collected data is summaized in Table 1. The peiop was conducted fom 2 to 6 Novembe 2001, IOP1 fom 17 to 24 Febuay 2002, IOP2 fom 24 to 30 Mach 2002, IOP3 fom 17 to 25 Febuay 2003, and IOP4 fom 25 Mach though 1 Apil Table 2 summaizes the measued micowave fequencies of all adas and adiometes opeating at the LSOS. 3. Example esults The data volume fom the LSOS is too lage fo full pesentation. To explain the esults fom the LSOS, we FIG. 4. Patial meteoological data fom the discontinuous pine site on 25 Ma Sola and longwave iadiance data ae fom two pyanometes (PSP 3-tee well and PSP 10-canopy gap) and one pygeomete (PIR 1-tee well). pesent a sample of data collected fom most sensos on one day of IOP4: 25 Mach Data included snow and meteoological obsevations, gound-based micowave adiomete data, gound-based ada data, and biophysical measuements. a. Snow and meteoological data On 25 Mach 2003, the sky was clea, midday ai tempeatues climbed above feezing, and the measued daily total incoming sola iadiance beneath the discontinuous pine site vaied between a minimum of 6.5 MJ m 2 (nea a tee tunk) to a maximum of 20.6 MJ m 2 (canopy gap; Fig. 4). Hemispheical diectional eflectance facto specta data of the snow suface in FIG. 5. HDRF specta measued with a field spectoadiomete on 25 Ma 2003 at 1230 local time (LT). The sola zenith and azimuth angles wee 38 and 188, espectively. Each of the thee lines epesents a diffeent measue of the specta.

6 DECEMBER 2008 H A R D Y E T A L TABLE 3. Snowpack popeties in the cleaing on 25 Ma 2003 at 1300 LT. UTM is Univesal Tansvese Mecato. Pit: LSOS_2a Date: UTM-E UTM-N Total Depth 107 Time: 1300 Location (UTM) Hit above gound Top Bottom Mean density kg m 3 Snow wetness % Height above gound Snow tempeatue C Hit above gound Top Bottom Gain size (mm) Sm Med Lg Snow suface n/a n/a 7 0 Snowpack mean: * ounded gains. Gain type* Comments Wet snow Had cust Satuated laye Depth hoa Depth hoa the cleaing ae pesented in Fig. 5. Snow pit data collected fom the cleaing at midday showed an isothemal snowpack of 1.07-m depth with ounded gains and a mean snowpack density of 284 kg m 3 (Table 3). Of paticula inteest fo intepetation of the adiomete and ada data was the measued statigaphy and snow wetness data showing a wet snow laye at the suface and a midpack satuated laye height of m. Snow depths in the discontinuous pine site wee moe vaiable than in the unifom pine site with a mean LSOS depth of 0.91 m (n 275; Fig. 6). snow wetness elationships on 25 Mach 2003 (Figs. 7 and 8). In Fig. 7, the Univesity of Michigan measued inceases in the 19-GHz bightness tempeatues at midday and again aound 0200 LT on 26 Mach 2003, coinciding with ising ai tempeatues. Similaly, the GBMR-7, opeated by the Univesity of Tokyo, showed an incease in bightness tempeatue fom moning though midaftenoon on 25 Mach, coesponding with an incease in snow wetness (Fig. 8a). Because of the unique micowave spectal signatue of snow, the diffeence in bightness tempeatue between b. Micowave adiomete systems Micowave adiomete data fom two sepaate sensos show bightness tempeatue, ai tempeatue, and FIG. 6. Snow depth tansect though both foest types. Each measued data point is 1 m apat. FIG. 7. Relationship between ai tempeatue and snow suface bightness tempeatue as measued at 19 GHz by Univesity of Michigan s micowave adiomete on 25 Ma 2003.

7 1440 J O U R N A L O F H Y D R O M E T E O R O L O G Y VOLUME 9 FIG. 8. (a) Influence of wet snow on the bightness tempeatue as measued by the GBMR-7 with hoizontal and vetical polaization. (b) Estimated SWE based on the bightness tempeatue diffeence. Because of the wet snow suface, note that (b) incoectly indicates the snowpack melted out completely afte 1200 LT on 25 Ma the lowe (e.g., 18.7 GHz) and the highe (e.g., 36.5 GHz) fequencies povides an indication of the SWE (Schmugge et al. 2002). Howeve, this elationship is only valid fo a completely dy snowpack and will fail at the pesence of liquid wate. Fo example, in Fig. 8b, the SWE is calculated using an algoithm based on the wok of Chang et al. (1987), SWE 4.77 TB 18.7H TB 36.5H, whee SWE epesents the snow wate equivalent (in millimetes), and TB 18.7H and TB 36.5H ae epesenting the bightness tempeatue obsevations at 18.7 GHz and 36.5 GHz (hoizontal polaization). Figue 8b also povides a good example of the effect of a wet snowpack. The low SWE in the moning was caused by the wet midlaye snowpack (see Table 3). Duing late obsevations, the bightness tempeatue diffeences deceases because of an inceasing snow suface wetness. Coespondingly, the estimated SWE deceases, and the obsevation afte 1200 LT incoectly suggests the absence of snow on the gound. c. Scatteomete and FMCW ada Figue 9 shows a epesentative set of polaimetic backscatteing coefficients collected on 26 Mach 2003 by the Univesity of Michigan s ada at Ku-band ( GHz). The data show simila copolaized backscatteing coefficients, which indicates that the snow volume entiely dominated the scatteing. This esult is also evident fom the copolaized atio to the coss-polaized atio ( 9 db), which is mainly caused by the multiple scatteing within the snow medium. CRREL/ERDC and the Univesity of Coloado s multiband ada pofile fo the wet snow of 25 Mach (Figs. 10a and 10b) showed the pesence of a small amount of wate affected ada inteaction with the snowpack. C-band (2 8 GHz) measuements (Fig. 10a) esolved the lowe layes in the snowpack; howeve, at the Ku-band (14 18 GHz) fequencies (Fig. 10b), the suface eflection was the dominant effect in the wet snow, and gound etun was insignificant. Fo this wet snowpack, adas opeating at lowe fequencies wee pefeable to achieve necessay penetation. These esults suggest that a dual-fequency appoach fo ada emote sensing is necessay to etieve snowpack paametes such as density, depth, and wetness. d. Biophysical activity in tees An example of the NASA JPL dataset fom one of the six tees continuously monitoed fo two yeas shows snow, soil, and stem tempeatues below feezing on 25 Mach 2003 (Fig. 11). These data change damatically late in the sping as ai, soil, and stem tempeatues incease and sap flow begins. This change is used FIG. 9. Time seies of backscatteing coefficients as a function of the incidence angle fo the Ku-band scatteomete on 26 Ma The backscatteing coefficient is the atio of the ada coss section of the taget to its aeal extent, expessed in decibels.

8 DECEMBER 2008 H A R D Y E T A L FIG. 10. (a) C-band and (b) Ku-band data fom the FMCW ada on 25 Ma Black indicates stong eflection, and white indicates no eflection. Note that the C-band measuement penetates to the gound in this wet snowpack and shows eflections fom midpack layes. The Ku-band measuement has a vey stong suface eflection as a esult of the moistue content and shows midpack eflections, but it is attenuated befoe eaching the snow gound inteface. to detemine the onset of the gowing season fo LSOS conife tees. These data will augment and suppot the intepetation of the measuements acquied with micowave emote sensing instuments. 4. Summay Data wee collected at the local scale obsevation site ove a peiod of two yeas and by seveal coopeating institutions and numeous people. The data pesented hee wee intended to show the contents of the lage database. This database povides details of fully chaacteized snow, soil, canopy, enegy balance, and micowave popeties. Using this database, physically based models, emote sensing etieval algoithms, and theoies can be confidently evaluated with minimal ambiguity. Scaling execises, in conjunction with the full CLPX dataset, will test the pefomance of these algoithms and models at the 1- and 25-km scales (ISA and MSA, espectively), and the egional scale. Acknowledgments. This wok was funded though coopeation of many agencies and oganizations including the National Aeonautics and Space Administation (NASA), the U.S. Amy Cops of Enginees Civil Woks Remote Sensing Reseach Pogam, the U.S. Amy Basic Reseach Pogam, the Japan Aeospace Exploation Agency (JAXA), the Japan Science and Technology Agency, and the National Assembly fo Wales, Stategic Reseach Investment Fund, Cadiff. A potion of this wok was conducted at the Jet Populsion Laboatoy at the Califonia Institute of Technology, unde contact to NASA. Many individuals contibuted to the success of the data collection effot at the LSOS. Ou gatitude is extended to H. Boyne, M. J. Bodzik, T. England, R. Essey, R. Foeste, H. Fujii, G. Koenig, T. Link, D. Maks, M. Matinez, R. Melloh, N. Mulhein, E. Podest, J. Pomeoy, A. Rowlands, A. Twombly, and othe staff at the U.S. Foest Sevice, Fase Expeimental Foest. REFERENCES FIG. 11. Stem tempeatue monitoed at 1.5-m height and at the stem base of one lodgepole pine tee on 25 Ma Snowpack tempeatue at 0.1 m above the gound suface, and soil tempeatue at the gound suface and at 0.1-m depth. Chang, A. T. C., J. L. Foste, and D. K. Hall, 1987: Nimbus-7 SMMR deived global snow cove paametes. Ann. Glaciol., 9, De Roo, R. D., A. R. Chang, and A. W. England, 2007: Radiobightness at 6.7-, 19-, and 37-GHz downwelling fom matue evegeen tees obseved duing the Cold Lands Pocesses Expeiment in Coloado. IEEE Tans. Geosci. Remote Sens., 45, Elde, K., D. Cline, A. Goodbody, P. House, G. Liston, L. Maht, and N. Rutte, 2009a: NASA Cold Land Pocesses Expeiment (CLPX 2002/03): Gound-based and nea-suface meteoological obsevations. J. Hydometeo., in pess.,, G. Liston, and R. Amstong, 2009b: NASA Cold

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