mmm mn - DTIC · 2018-11-08 · data presented in this report consisted of the following basic units: A Czerny-Turner l/2 meter grating spectrometer, a biaxial pointing control or

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ATMOSPHERIC ABSORPTIONS OVER uONG SLANT PATHS IN THE STRATOSPHERE

David G. Murcray, Frank H, Murcray and

Walter J. WiUiams

Department of Physics University of Denver

Denver, Colorado

Contract AF 19(628)-5202

Project 8662

Task 866201

Scientific Report No. 4

October 1966

This re&oarch was sponsored by the Advanced Research Projects Agency under ARPA Order No. 363

Prepared for

Air Force Cambridge Research Laboratories Office of Aerospace Research

Urn ed States Air Force Bedford, Massachusetts

D D C

H JAN 24 1967

B

Distribution of this Document is Unlimited

mmm mn

AFCRL-66-812

ATMOSPHERIC ABSORPTIONS OVER LONG SLANT PATHS IN THE STRATOSPHERE

David G. Marcray, Frank H. Murcray and

Walter J. Williams . ■■

Department of Physics '• University of Denver

Denver, Colorado

Contract AF 19(628)-52C

Project 8662

Task 866201


October 1966

This research was sponsored by the Advanced Research Projects Agency under ARPA Order No. 363

Prepared for

Air Force Cambridge Research Laboratories Office of Aerospace Research

United States Air Force Bedford, Massachusetts

Distribution of this Document is Unlimited

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TABLE OF CONTENTS

Page

VI ABSTRACT

1. INTRODUCTION 1

2. INSTRUMENTATION . . 2

3. FLIGHT DETAILS 3

4. RESULTS 4

5. DISCUSSION 5

6. ACKNOWLEDGMENTS 10

7. REFERENCES 11

IV

LIST OF FIGURES

Figure No. Page

1 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3890- 3740 cm"1, Rec. 12-53 12


3 Atmospheric transmittance versus wavenumber as observed at various altitudes Tor the region 3800- 3670 cm"1, Rec. 31-39 16

i Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3680- 3540 cm"1, Rec. 31-39 18


6 Atme spheric transmittance versus wavenumber as observed at various altitudes for the region 3800- 3670 cm"1, Rec. 46-51 22

7 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3690- 3560 cm'1. Rec 46-51 24

8 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3920- 3790 cm'1, Rec. 54-70 26


10 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3680- 3540 cm"1. Rec. 54-70 30


LIST OF FIGURES (Cont.)

Figure No. Page

12 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3800- 3670 cm-1, Rec. 12-18 34

13 Atmospheiic transmittance versus wavenumber as observed at various altitudes for the region 3680- 3550 cm"1. Rec. 12-18 36


15 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3800- 3670 cm"1, Rec, 19-28 40

16 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3690- 3560 cm-1. Rec. 19-28 42


18 Atmospheric transmittance versus wavenumber as observed at various altitudes for the region 3800- 3690 cm-1, Rec. 37-43 46

19 Comparison of the transmittance observed with the transmittance predicted by Plass in the 3800 cm" to 3730 cm"1 region 48

20 Comparison of the transmittance observed with the transmittance predicted by Plass4 in the 3800 cm-* to 3730 cm-1 region 48

21 "Water vapor mixing ratio profile as determined from the variation of the infrared absorption with altitude 49

vi

ABSTRACT

The variation of the infrared solar spectrum with altitude was observed during a series of balloon flights made from Fairbanks, Alaska. Spectra were obtained at various altitudes with solar zenith angles ranging from 49° to 92°. These spectra were used to determine the atmospheric transmittance to be expected at high altitudes and particularly over very long slant paths in the stratosphere. The trar mit- tance data are presented in this report.

The spectral region scanned during these flights covered the 2. 7\i region. The major atmospheric absorptions in this region are due to carbon dioxide and water vapor. The paths traversed by the solar radiation in reaching the spectrometer when the solar zenith angle is greater than 90° are such that a major portion of the air mass traversed by the radiation is traversed xn a relatively narrow altitude interval close to the minimum height of the ray. Thus these long paths provide a method of sampling the absorption to be expected in relatively narrow layers. The water -'apor absorptions obtained under these conditions have been used to determine the amount of water vapor present in these layers in the stratosphere. These datu. are compared with the mixing ratios determined on the basis of the change in these absorptions during a flight with small solar zenith angle. The agreement is within the accuracy of the measurement and shows no indication that the data of the normal flight are inaccurate due to contamination. The profile indicates the increased mixing ratio above the tropopause noted on other flights at other geographic locations.

JL INTRODUCTION

In previous reports ' we have presented data ähowing the spectral transmittance of the earth's atmosphere at high altitudes. These data have been obtained during a series of balloon flights made with a balloon-borne spectrometer system flown in conjunction with a biaxial pointing control which orients a telescope such that the solar image is formed on the spectrometer entrance slit. Due to the prob- lems associated with flying balloons, these flights are launched close to sunrise and the flights terminated before sunset in order to imple- ment recovery of the equipment. Thus most of the spectra are obtained with the sun high in the sky and the optical air mass traversed by the solar radiation at high altitudes is small. In order to obtain data pertinent to the transmittance over long slant paths at high altitudes, using the sun as a source, it is necessary to obtain data ^'Uh the sun low :n the sky, i. e. , sunrise or sunset. The period during which such data can be obtained is limited at the lower latitudes; however, in the high Northern latitudes during June and July the sun never sets at balloon altitudes and there is a period of several hours when spectra can be obtained with solar zenith angles of 90° or more. In order to obtain transmittance data over such paths, and also to obtain data at geographic 1ocations other than the normal mid-latitude sites, a series of balloon flights was made from Fairbanks, Alaska, during the summer of 1964. The data obtained during these flights are presented in this report.

2. INSTRUMENTATION

The balloon-borne instrumentation employed in obtaining the data presented in this report consisted of the following basic units: A Czerny-Turner l/2 meter grating spectrometer, a biaxial pointing control or "sun seeker, " an on-board digital magnetic tape recorder, an on-board FM-analog magnetic tape recorder, an FM/FM telemetry system, power supplies for operating the various units, a balloon command package, and a gondola in which the units are mounted and which protects the equipment when it is returned to the ground via parachute , The units are described in detail in an article to be published in the February 1967 issue of Applied Optics.3

For these flights two magnetic tape recording systems were used for on-board recording. The primary system was a digital system described in the referenced article. Since this unit was being used for the first time, the analog FM recorder used on previous flights was flown as backup. This unit is a 4-channel unit, also designed and constructed by project personnel for balloon use.

The rectified detector output voltage was recorded in 4 channels of the digital recorder and on one channel of '■.he FM recorder. The ac signal from the detector was also recorded on one channel of the FM recorder. The other channels were used to record auxiliary data pertinent to the experiment and to monitor the performance of various units.

The balloon instrumentation used in this study represented a considerable investment in time and money, hence recovery of the instrumentation was essential. Since upper wind information is generally sparse and balloon ascent rates quite often differ from predicted, it is very difficult to predict accurately where the balloon will be with respect to the ground at any particular time. It is quite often necessary, there- fore, to change flight plans as the flight trajectory develops. A real time readout of the performance of the instrumentation is of great value in making such decisions. An FM/FM telemetry system was also included as part of the balloon instrumentation to provide this real time information. It was also used as a further backup recording of the primary data. The airborne system consisted of 4 standard IRIG voltage-controlled sub-carrier oscillators which fed a 4 watt FM trans- mitter operated at 249. 9 megacycles. The data from this system was •ecorded on the ground in multiplex form on magnetic tape. In addition

one channel of the multiplexed signal was'also fed to a discriminator

and the output of the discriminator was recorded using a visicorder. The channel monitored in this fashion had the ac signal from the spectrometer as its input. This channel was chosen since it provided an excellent evaluation of the overall system performance.

3. FLIGHT DETAILS

3. I Balloon Flight of July 7-8 (Al)

The first flight of this series was launched at 21ZO AST1 July 7, 1964, elfter a two hour delay due to surface winds. At the time the balloon was launched the sun had set on the ground. The balloon ascended with an average ascent rate of 150 m/m.n and reached a floating altitude of 29 km at 0035 AST July 8. The balloon was allowed to float until 0436 AST. The equipment impacted at 15104r W longitude, 65o01, N latitude, and was recovered by helicopter.

3. 2 Balloon Flight of July 13-14 (A2)

After renovation the equipment v/as launched the second time at 1904 AST July 13 and ascended with an average ascent rate of 200 m/ min until the balloon reached approximately 10 km. At this time the ascent rate started decreasing and at an altitude of 13 km the balloon had stopped ascending. Ballast was released by radio command, but the ascent rate achieved during the remainder of the flight was less than 100 m/min. The flight was terminated at 0210 AST July 14. The equipment impacted at 149029l W longitude, 640ll, N latitude. Recovery was accomplished by helicopter.

3. 3 Balloon Flight of July 21 (A3)

The final flight cf the series was launched at 1352 AST July 21, 1964. The balloon ascent rate was normal and an overall ascent rate of 200 m/min was achieved. The balloon reached a floating altitude of 31 km. The flight was terminated at 1803 AST to facilitate recovery. The equipment impacted at 147031l W longitude, 64°39' N latitude, and was recovered using a helicopter. Impact on all flights was soft and no damage was incurred due to impact.

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4. RESULTS

The digital magnetic data tapes were played back into a computer, and selected spectra from each flight were plotted. Examination of these spectra revealed that they all contained many false absorptions thz. ./.re not present in the ac data. It was determined that these were the result of momentary loss of synchronization in the synchronous rectification system, caused by <-he tines of the tuning fork chopper bumping together. This bumping occurred at altitudes in excess of ZO, 000 feet and was due to the fact that the oscillation was air damped. As the air density decreased the amplitude increased until at altitudes above 20, 000 feet the tines started bumping. While this affected the synchronous rectification the ac data were not affected. In view of this the ac data weie used in the data reduction.

Although the analog spectra as recorded contain considerable information, it is necessary, for purposes of quantitative analysis, to convert the data to % transmittance versus wavelength. In order to do this it is necessary to determine whrt the voltage from the detector wou^d have been if the absorpt:'")n were not present, i. e. , the so-called vacuum envelope. This is generally determined on the basis of the spectra recorded at altitude when the absorptions are minimal. On the first flight of this series the overall signal level from the infrared detector was significantly less than on the other two flights. This appears to have been due to the scattering of the solar radiation in traversing the long slant path in the atmosphere. While this relatively non-selective attenuation is of interest the primary concern of this study was with the selective absorption. In view of this the vacuum envelope was determined on the basis of signal recorded in the windov/ regions between groups of absorption lines. Thus the data represent the attenuation due to molecular absorption, and does not include that due to scattering. Once the envelopes had been determined the analog records were digitized and the percent transmission was determined as a function of wavenumber using a digital computer. Selected plots of the spectral transmitt?.nce versus wavemmber, as observed under various conditions during the three flights, are given in Figures 1 through 18.

5. DISCUSSION

As mentioned above the purpose of these flights was to gather data concerning the attenuation of infrared radiation in traversing long slant paths in the earth's atmosphere. The type of path traversed by the radiation when the sun is low in the sky is illustrated below. For obvious reasons the drawing is not to scale.

Balloon Tc Sun

Earth's Surface

Hb is the height of balloon. HQ is the minimum height of

the optical path, is the height of an inter- mediate point on th? optical path. is the radius of the eartn.

Since the plane parallel atmosphere approximation is not valid in this case it is necessary to trace the ray through the atmosphere and

oo

calculate f p(h)dh along the ray in order to determine the amount of

H

absorbing material traversed by the radiation. In performing the ray tracing calculations refraction effects must be taken into account; however, in the cases where the path lies wholly in the stratosphere,

the effects of refraction are small and for purposes of the following discussion can be neglected. Neglecting refraction the length of the path L from H0 to an arbitrary poin^ a distance H above the earth's surface is given by

L = si (RTH)2 - (R+H0)2 = N/ 2RH+H2 - 2H0R-H0

2

L = si [2(R+Ho) + H-Ho] [(H-HQ)]

or neglecting H-H0 with -espect to 2(R+H0) one has

L = si 2(R+Ho)(H-H0)

If one splits the atmosphere into layers, the length i, in the layer is given by

£ = N) 2(R+H0) [ N/ (Hi+1 -H0) - «7 Hi - H0 ]

and the mass of air traversed by the radiation can be determined from

m = 2 sj 2(R+H0) fsl H^ -H0 - sj Hi-uA^

v/here "pi ^s the average density in the i layer, and the summation is performed over the layers from the balloon down to the minimum, height HQ and then from H0 out to the point where the density has fallen off to where any further contribution can be neglected. Ii one calculates the air mass tr versed in a typical path of this type for balloon altitudes, the air mass traversed by the radiation from balloon altitude down to minimum altitude H0 and back to balloon altitude is quite often considerably more than half of the total air mass traversrd by the radiation. The pressure at balloon altitude is sufficiently large that over the lower part of the path the Lorentz line shape predominates. In this case the absorption depends on the /P dw along the path. The inclusion of the pressure weights the lower altitude layers so that this dependence of the absorption on the lo'-'er layers is further enhanced. Thus this type of path pro/ides an excellent method of studying the variation with altitude of the absorbing constituents. The extent of this affect in the spectra obtained during the first and second flights is evident in the data given in Table I. In this table the air mass traversed by the radiation in that portion of the path from the balloon down to the minimum altitude and back up to the balloon altitude is given, along

with the total air mass traversed by the radiation. Once the solar zenith angle becomes much greater than 906 the air mass traversed in this layer becomes more than half of the total air mass.

The solar spectra obtained during the first two flights of this series indicate the transmittance to be expected in this wavelength region over long slant paths in the stratosphere. If one compares these spectra with solar spectra taken at lower altitude but high sun, one finds greater transmittance at the higher altitudes, even though the air masses traversed during these flights are considerably greater (approximately 8 air masses in the case of record 37 on the July 7, flight compared with 1. 5 air masses in a normal ground record). The increase in transmittance at the higher altitude is the result of two factors. Fir^t, the absorptions in this spectral region are pressure dependent, and the reduced atmospheric pressure at the higher altitudes reduces the absorption due to equivalent amounts of absorbing material. Second, the amount of water vapor present per unit air mass is considerably less at the higher altitudes. Thus the observed transmittances are in quantitative agreement with what one would predict on a theoretical basis.

All evidence currently available indicates that carbon dioxide is uniformly distributed in ihe earth's atmosphere. Assuming that this is the case, and that its abundance is ~0. 03% by volume, it is possible to compare the transmittance observed over these long stratospheric paths with the transmittances predicted by Plass. 4 Previous comparisons between his predicted transmittances and our observed transmittances had indicated relatively good agreement for carbon dioxide absorptions. The major carbon dioxide a -sorptions in this region are due to the two bands centered at 3716 cm" and 3609 cm" , The transmittances in the vicinity of the 3716 cm"1 band observed during the flight made July 7, (spectrum number 37) are compared with those given by Plass for 2000 atm-cm of C02 at a temperature of 200oK and pressures of 0. 1 atm and 0. 2 atm in Figure 19. As pointed out above, the major portion of the absorption in this type of path occurs in the layer between the balloon and the minimum height of the ray Thus for record 37 the radiation had traversed approximately 2000 atm-cm of C02, the majority of which is at a pressure of approximately . 07 atm. At first sight it would appear that the theoretical transmittance curve does not fall off as rapidly as it should as one approaches the band center; however, it should be remembered that the t1- joretical curves are for CO? absorption only, while the experi- mental are the result of-absorptions by C02 and H2O. H20 has a group of strong lines in the vicinity of 3750 cm"1. The absorptions in the region from 3800 to 3760 cm-1 are also due to H20.

Figure 20 shows a similar comparison for spectrum number 53. In this case the radiation had traversed approximately 750 atm-cm of CO2, the majority of which was at a pressure of 0. 03 atm. If one makes allowance for the fact that the observed absorptions are Jar to H20 as well as C02, the agreement between the theoretical predictions and the observations is satisfactory.

Water vapor absorptions occur throughout the region scanned during these flights. The absorptions occurring between 3 791 cm"1 and 3860 cm" , in particular, are due mainly to a series of strong water vapor lines. The distribution of water vapor above 13 km is currently the subject of controversy. The opinions concerning the distribution range from the view that the water vapor is uniformly mixed above the tropopause with a constant relatively "dry" mixing ratio of 2- i0"6 g/g to the view that the mixing ratio above the tropopause is variable and often relatively wet, i.e., mixing ratios of approximately 10" g/g at various altitudes. The water vapor absorptions observed during the various balloon flights made previously have been characterized by a very rapid fall-off in absorption as the balloon approaches the tropopause followed by a very slow decrease in absorption above the tropopause and a sig- nificant residual absorption at altitude. Using these absorptions to determine a water vapor mixing ratio profile, one obtains a profile which decreases to a low value (~ 2- 10" g/g) in the lower stratosphere with an increase in the mixing ratio above 20 km, and an average mixing ratio above the balloon of between 10"5 g/g and 10"4 g/g. The results of these measurements have been questioned on the basis that if the balloon or fhe instrumentation is outgassing water vapor, then part of the mea- sured mixing ratio would be due to contamination. The solar spectra obtained during the first two flights are characterized by the fact that the radiation has traversed long paths in the stratosphere and relatively large air masses. As a result, any contamination which might be present becomes insignificant in comparison with the absorptions due to the atmospheric water vapor. Houghton and Seeley give a series of curves of growth for the water vapor absorptions in the region from 3 791 cm"1

to 3860 cm'1. These curves relate N/UP/PQ with the integrated absorption over the region from 3791 - 3811 cm"1, 3811 - 3830 cm"', 3830- 3847 cm"1, and 3847- 3860 cm . The integrated absorptions over these regions were determined for the various spectra obtained during the first two flights and the absorptions were used to determine the values for \l uP/P0. The values of V UP/PQ determined for each spectrum were compared. If the values were in good agreement the values were averaged, and the average value was used to determine the amount of water vapor and the mixing ra';io. This quantit* is really the integral of the water

vapor content times the pressure over the tc/;al path. Since the water vapor distribution is not known this integral cannot be determined. It has been pointed out above that the major portion of the optical path occurs in the layer between the balloor and the minimum point along the path. In determining the mixing ratio the assumption was made that the water vapor is all concentrated in this layer. This has the effect of reaucing the overall amount of water vapor required to account for the observed absorptions by placing it all in the higher pressure environ- ment. In determining mixing ratio the total air mass traversed by the radiation was assumed to be concentrated in this layer. Thus all mixing ratios determined from these spectra are too "dry", i. e. , they are biased toward low mixing ratios. The mixing ratios determined in this fashion are given in Table II. Unfortunately, because of the low ascent rates achieved during these flights, no data were obtained where the minimum altitude along the path was higher than 21. 6 km, and the average height of the layer was about 22-23 km.

The third flight of the series was launched when the sun was relatively high in the sky and the solar zenith angles encountered during the flight were characteristic of those encountered during flights made at low latitude launch sites. During this type of flight the absorptions decrease as the balloon ascends, and it is possible to determine a water vapor mixing ratio profile on the basis of the change in absorption with altitude. A profile was determined on the basis of the variation with altitude of the region from 3847 - 3860 cm"1. The profile determined in this fashion is giyen in Figure 21. Comparison of the results with those determined from the long path absorptions indicates that they agree reasonably well, and the mixing ratio profile determined on the basis of a normal daytime ascent is not significantly contaminated. In comparing the results, one must keep in mind the uncertainties in the curves of growth of '■he absorptions and in the air mass traversed by the radiation in the long path case. Thus the long path data confirm the fact that the mixing ratio increases at altitudes in excess of 20 kms.

10

ACKNOWLEDGEMENT S

The authors want to express their appreciation for the excellent support received from the Air Force Cambridge Research Laboratories Balloon Group who performed the launch of the balloons and the recovery of the instrumentation on these flights, and to the ü. S. Army Arctic Test Center for their support of the operation. Our than ts also to Jim Brooks, Warren Cochran, John Kosters and Steve Smith for their as- sistance in performing the flight and to Charles Garwood and Marie Working for assisting in the data reduction.

11

REFERENCES

1. Murcray, D. G. , F. H. Murcray and W. J. Williams, Scientific Report No. 1, Contract AF 19(628)-5202.

2. Murcray, D, G. , F. H. Murcray and W. J. Williams. Scientific Report No. 3, Contract AF 19(628)-5202.

3. Murcray, D. G. , F. H. Murcray and W. J. Williams, "A Balloon Borne Grating Spectrometer," to be published in Applied Optics, February 1967.

4. Plass, G. N. , V. R. Stull and P. J. Wyatt, Final Report, Vol. Ill, Contract AF 04(695)-96.

5. Houghton, J. T. and J. S. Seeley, Quarterly Journal of the Royal Meteorological Society ^6, p. 358 (I960).

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Mixing Ratio (gKjO/gAir)

Figure 21. Water vapor mixing ratio profile as determined from the variation of the infrared absorption with altitude. The curve marked A-3 was determined from data obtained during the Alaskan flight. The curve marked H-25 was determined from data obtained during flight made from Holloman AFB, New Mexico.

50

TABI.E I

Air Mass Traversed by Solar Radiation

Air Mass Air Mass* Flight No. Record No. kg/cm kg/cm2

Al 12 10.426 3.096

Al 23 9.931 5.989

Al 37 7.958 7.006

53 3.072 2,689

49 2.240 0.452

A2 50 2. 283 0.700

A2 51 2. 288 0,904

A2 54 2.420 1.469

A2 57 2.746 1.989

A2 58 2. 856 2. 192

A2 63 4.219 3. 887

A2 70 4.845 4.497

*The air mass indicated in this column is that traversed by the radiation along the path from the balloon down to the minimum height HQ and back up to the height of the balloon.

51

TAB LE II

Mixing Ratio as Determined from Long Path Absorptions

Av. Ht. Mixing Ratio

Flight No. Record No. km g/g

Al 23 14.0 4.8.10"6

Al 37 16. 3 3. 2.1^"6

Al 53 22. 5 4.4.10-6

A2 54 22.6 6. MO-6

A2 57 22. 2 4.8-10-6

A2 58 22. 2 4. 7-10"6

A2 68 20. 3 3. 0-10-6

JJnclassifipH Security Classification

DOCUMENT CONTROL DATA - R&D fS»Curi»y ^l»»tillemtion at till*, body ol absltact and indexini annolalion must be enlerod when Ihe overall report is class,lied)

1 ORIGINATING ACTIVITY fCorpo«(» «utfior; ^ " '

Department of Physics. University of Denver Denver, Coloardo 80210

2a REPORT SECURITY CLASSIFICATION

Unclassified 2b CROUP

3 REPORT TITLE

Atmospheric Absorptions Over Long Slant Paths in the Stratosphere

4 DESCRIPTIVE NOTES (Typ* ol report and inc/uaiva dales)

Scientific Report Interim 5 AUTHOR^ (Lmat nun,. Unt name, initial)

Murcray, David G. . Murcray, Frank H. . Williams, Walter J.

8 REPORT DATE

October 1966 AkPA OkDER No. 363

7« TOT*. NO OF PACE! 76 NO OF REFS

5 • a. CONTRACT OR GRANT NO.

AF 19(628)-5202 6. PROJECT NO.

9«. ORIGINATOR'S REPORT NOMSERCSJ


8662-01

6250301R 96 OTHER REPORT NOfS) (Any other numbers that may be assigned

this npc-0

AFCRL-66-812 10. A VA IU ABILITY/LIMITATION NOTICES

Distribution of this document is unlimited

H. SUPPLEMENTARY NOTES

Kq. AFCRL, OAR (CRO) United States Air Force T..G. Hanscom Field, Bedford, Mass,

12 SPONSORING MILITARY ACTIVITY

Advanced Research Projects Agency

13 ABSTRACT

Hi The variation of the infrared solar spectrum with altitude was observed during a series

of balloon flights made from Fairbanks, Alaska. Spectra were obtained at various altitudes with solar zenith angles ranging from 49° to 92°. These spectra were used to determine the atmospheric transmittance to be expected at high altitudes and particularly over very long slant paths in the stratosphere. The transmittance data are presented in this report.

The spectral region scanned during this flight covered the 2.7 u region. The major atmospheric absorptions in this region are due tc car! on dioxide and water vapor. The paths traversed by the solar radiation in reaching the spectrometer when the solar zenith angle is greater than 90° arc such tha. a major portion of the air mass traversed by the radiation is traversed in a relatively narrow altitude interval close to the minimum height of i.he ray. Thus these long paths provide i method of sampling the absorption to be expected in relatively narrow layers. The water \'apjr absorptions obtained under these conditions have been used to determine the amount of water vapor present in these layers in the stratosphere. These data are compared with the mixing ratios determined on the basis of the change in these absorptions during a flight with small solar zenith angle. The agreement is within the a-curacy of the measurement and shows no indicaticn that the data of the normal flight are inaccurate due to contamination. The profile indicates the increased mixing .-atio above the tropopause noted on other flights at other geographic locations.

DD Ä 1473 Unclassified Security Classification

^Unclassified Security Classification

KEV WORDS

Solar Spectrum

Infrared Spectrum

Telluric Transmittance

Stratospheric Water Vapor

INSTRUCTIONS

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