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1 RD-R64 S24 NOLECULAR ABSORPTON OF ATNOSPNERC SPECESCU) DUKE L/1 UNV DURHAM NC F C DE LUCA 17 DEC 85 RRO-21?56. 1-PH DAA29-84-K-6S73 UNCLASSFED F/S 4/1 ML m.'.

2 .. % 11111W.O 25 Lu LA MCROCOPY RESOLUTON TEST CHART i J NA, 196, A

3 icotyclassvcaton OF THS PAGE (Wi.. Doesa Entored) REPORT DOCUMENTATON PAGE - ~ READ STRUCTONS 14. TTLE (end Stle). s. TYPE or REPORT & PEROD COVERED Final Molecular Absorption of Atmospheric species 7 May 84 - Sep 85 S. PERFORMNG ORG. REPORT NUMBER 7. AUTHOR(s) S.CONTRACT OR GRANT NUMEER(a) Frank C. De Lucia DAAG29-84-K-73 ~J- ~ %.' e 3. PERFORMNG ORGANZATON NAME AND ADDRESS 1. PROGRAM ELEMENT. PROJECT. TASK AREA & WORK UNT NUMBERS Duke University Durham, NC CONTROLLNG OFFCE NARE AND ADDRESS 12. REPORT DATE U. S. Army Research Office 12/17/85 Post Office Box NUERPAS 14. MOTRG AGNY15AE&AOESdleri rmcnrltjofc). SECURTY CLASS. (of this report) ) 16. DSTRBUTON STATEMENT (of this Report) Approved for public release; distribution unlimited. S&. Unclassified DECL ASS FCATON/ DOWNGADNG SCHEDULE E ' S. SPPLEMNTARENOTE The view, opinions, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so * 13. KE~Y WJOS(Continu onvee ide f necessary and identify by block niubor) Microwaves Millimeterwaves * C.) Propagation * Lj A Ar canm wie~r e bt narseamy sid identify by block mtmbr) 7The propagation of microwaves and millimeterwaves through the disturbed atmosphere is affected by molecular absorption that can be significantly different than the absorption in the ambient atmosphere. This is due to two - factors. First, the constituents of the ambient atmosphere will exhibit significantly different electromagnetic properties at elevated temperatures. Second, many additional species that are strong absorbers of microwaves, such as Sa D "D" W 3 EDON OF NOV 65 SOBOLETE ucasfe SECURTY CLASSFCATON OF TS PAGE (Shun D414 Ented)

4 mucvmtv OF T1418 Dole Sows V 2 MO. 1,NhK-ifo, and Wq-O. are present n the disturbed 2O.muNC,3f, Ts fwork addresse& both of these issues. A preliminary version of a code that utilized the previously available molecular data base was written in a form that would be cmoptible with NORSE. This code was turned over to PRi (the keeper of the NORSE code) and is currently being intergrated into it. n addition, measurements to 1K were made on one transition of H'O as a check on the extrapolation to higher teiperature that was used in this code. *.7 V

5 7.r4~W. i-f"-. MOLECULAR ABSORPTON OF ATMOSPHERC SPECES Final Report Frank C.De Ucia :1 December 15, 1985 U. S. Army Research Office DAAG29-84-K-73 Duke University Approved for Publ ic Release; Distribution Unflimited

6 ** ABSTRACT,.., ~.t.'.. i.* '.. " The propagation of microwaves and millimeterwaves through the - disturbed atmosphere is affected by molecular absorption that can be -.: significantly different than the absorption in the ambient atmosphere. This is due to two factors. First, the constituents of the ambient atmosphere will exhibit significantly different electromagnetic properties at elevated temperatures. Second, many additional species that are strong absorbers of microwaves, such as HNO'& HNO 2, 3, NO 2-122, OH, and N 2. are present in the disturbed atmosphere. This work addressed both of these issues. A preliminary version of a code that utilized the previously available molecular data base was written in a form that would be compatible with NORSE. This code was turned over to PRi (the keeper of the NORSE code) and is currently being integrated into it. n addition, measurements to 1K were made on one transition of H 2 as a check on the extrapolation to higher temperature that was used in this code. Acce7sion or - NTS CRA& DTC TAB E Unannou ced ] Justification Di.Bb Distr ibution Availability Codes Special P, ii

7 N N The propagation of microwaves and millimeterwaves (mw/mmw) through the disturbed atmosphere is affected by molecular absorption. The small molecules present n the ambient atmosphere (excluding N 2 ) absorb microwaves because their rotational energy level spacing correspond to microwave frequencies. n addition, theoretical calculations show that._- -r most of the small molecules that can be made by rearranging the atoms n 2, N 2, and H 2 are present in the disturbed atmosphere. n general, these molecules are much stronger absorbers of mw/mmw radiation than the normal constituents, but their much lower abundance significantly reduces this effect. n order to test system and other concepts, large codes have been written that simulate the disturbed atmosphere. These codes nclude pressure and shock wave effects, the extinction due to dust, calculate --.. chemical effects and temperature profiles. etc. However, the current version, NORSE, does not include any effects due to molecular absorption, including effects due to the constituents of the ambient atmosphere, which are known to be large in the millimeter wave region As a result, it s our understanding that the NORSE code s currently "locked aoainst use above 1 ''-- A n the first part of our work we have written a preliminary version of a code that can be integrated nto NORSE to account for these effects. We have designed it so that as additional molecular parameters become available, no significant changes will be required, especially in ts interface with NORSE. There are substantial amount of molecular physics involved in these calculation that will not be detailed here. We refer the interested reader to the literature and note that much of the work on which these.::: - 2..:.-

8 calculations are based resulted from earlier support of our laboratory by the Armyg Research Off ce. Figure shows a block diagram or the code n ts stand alone form n which the output is set directly to a plotter rather than returned to a larger code. The scenario inputs required from the main code are the temperature and the molecular abundances. This is required to specify the physical and chemical conditions. t should be noted that this is a very small amount of nformation and can be easily passed from the larger code. For technical reasons the ambient atmosphere is calculated separately from the contributions due to the trace species, but both require the nput from the molecular data files. These store the molecular nformation at the most fundamental level (. e. transition frequency, transition strength, and absolute energy) and as a result a wide variety of scenarios can be calculated from them. These files suffer from two short comings. First, there are many scenarios, especially at higher temperatures that require information about states and collision processes that is not currently knowr This is primarily because the rather large effort that has been put into understanding mw/mmw propagation has been directed almost entirely to understanding the temperature region between 2-3 K. Secondly. they are rather large. although by no means prohibitive by the standards of codes like NORSE. This is because the information at the most fundamental level must literally deal with,1,+ transitions. t would be possible to preprocess this data to very significantly reduce the size of both the calculation and storage at the expense of generality. f the basic physics and spectroscopy of the situation were carefully considered, t should be possible to do this and to not have this compression be a significant contributor to the error budget of the :3: 6*, i:::i--.

9 iin c im at at.

10 calculation This information s then convoluted with liresha e functions in a procedure that n mar cases uses an estimate of the linshape parameter. This estimate is necessary because at present marvj of these are poorly known in this spectral region Finally. the output s sent to a plotter. When,,.. this code is used as a subroutine in a larger code, this calculation s dorm,--..." manyj times along the sight path and contributes an additional term at each "/: point to the overall attenuation. A tape that contains both the code and the molecular parameters has been turned over to Physical Research ncorporated of Huntsville, Alabama for integration into the NORSE code. Although this is a preliminary versior, its form will require little or no modification to its interface with NORSE as it is updated. Examples of its output in graphical form are shown in Figs t should be emphasized that the code is still preliminary and that as soon as the first cut integration into NORSE is completed, a number of straightforward "tunings m should be done before it is used. t is our judgment that the most significant uncertainty in the code (except for the possibilities of "blunders" that still must be checked for as part of a verification process) are the effects of temperature on the molecular parameters. This is especially true for linewidth parameters because the theory of collisions is too complex to allow reliable *first principle" calculations. As a result we have carried out a check of the temperature dependence used for the width of the H 2 absorption at 183 GHz over the temperature range 3-1K. The code uses Av(MHz) = 3.76 Pa [T/3.., o **~* *...,.

11 ~ ~A ~J a.4,. S S o 4. < 4a' o ai a' 4.' o SC) o c '.4 o * i N~ fa o * - U. i...! * S S S S rngup V ~ -..,. -

12 '".-,,..X.~ * * % V S C o *.- -. V -. ~ 4 * '4 4 C o Can o N p o 4 o.aj 4?.1 S S r* C,' S _ hl S S S S m)/9p S 7 ~ g...~.' ~.e ~-~*--- * * ~?. * -...* ~.J.J d

13 C! in C 4 -d 4 r. "4 4 O V1 m- gu 4) *4 r4 %:k

14 where Pa is the pressure of the dry air (Torr) and T(Kelvln) is the temperature, for the llnewldth contribution due to oxygen and nitrogen and - Ai(MHz) =18.4 Pw [T/31' ', where Pw is the partial pressure of water, as the lirwwidth contribution from water. n Figs. 5 and 6 we plot these function against our experimental measurement and find generally good agreement.

15 4%. A 1) 4.. Pressure Browaeng Parameter 4.5. dueto waer - air cofl 1is 3.15 broadening3. (flhz/torr) Temperature Figure 5. Comparison of experimental (solid) and theoretical (open) linewidth parameters. The experimental point at 925 K is believed to be spurious. -4 1

16 V 1 18 Pressure Broadening Parameter 2 duetowater - war collisions 16 L 14S Broadening 1 lieit prmt rs uebodigprmtr,',,.? Figure 6. Comparison of experimental (solid) and theoretical (open) 7 o -

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