C 5 
 
 NOAA TR NESS 64 
 
 A UNITED STATES 
 DEPARTMENT OF 
 COMMERCE 
 PUBLICATION 
 
 **<* TOr c, 
 
 V 
 
 
 NOAA Technical Report NESS 64 
 
 U.S. DEPARTMENT OF COMMERCE 
 
 National Oceanic and Atmospheric Administration 
 
 National Environmental Satellite Service 
 
 Radiometric Techniques for 
 Observing the Atmosphere 
 From Aircraft 
 
 WILLIAM L. SMITH and WARREN J. JACOB 
 
 
 APR A 01973 
 
 
 
 '/), 
 
 WASHINGTON, D.C. 
 January 1973 
 
NOAA TECHNICAL REPORTS 
 
 National Environmental Satellite Service Series 
 
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 ESSA Technical Reports 
 
 38 Angular Distribution of Solar Fadiation Reflected From Clouds as Determined From TIROS IV Radi- 
 ometer Measurements. I. Ruff, R. Koffler, S. Fritz, J. S. Winston, and P. K. Rao, March 1967 
 (PB-174-729) 
 
 39 Motions in the Upper Troposphere as Revealed by Satellite Observed Cirrus Formations. H. 
 McClure Johnson, October 1966. (PB-173-996) 
 
 NESC 40 Clou-1 Measurements Using Aircraft Time-Lapse Photography. Linwood F. Whitney, Jr., and E. Paul. 
 McClain, April 1967. (PB-174-728) 
 
 NESC 41 The SINAP Problem: Present Status and Future Prospects; Proceedings of a Conference Held at 
 the National Environmental Satellite Center, Suitland, Maryland, January 18-20, 1967. E. Paul 
 McClain, October 1967. (PB-176-570) 
 
 NESC 42 Operational Processing of Low Resolution Infrared (LRIR) Data From ESSA Satellites. Louis 
 Rubin, February 1968. (PB-178-123) 
 
 NESC 43 Atlas of World Maps of Long-Wave Radiation and Albedo — for Seasons and Months Based on Measure- 
 ments From TIROS IV and TIROS VII. J. S. Winston and V. Ray Taylor, September 1967. (PB-176- 
 569) 
 
 NESC 44 Processing and Display Experiments Using Digitized ATS-1 Spin Scan Camera Data. M. B. Whitney, 
 R. C. Doolittle, and B. Goddard, April 1968. (PB-178-424) 
 
 NESC 45 The Nature of Intermediate-Scale Cloud Spirals. Linwood F. Whitney, Jr., and Leroy D. Herman, 
 May 1968. (AD-673-681) 
 
 NESC 46 Monthly and Seasonal Mean Global Charts of Brightness From ESSA 3 and ESSA 5 Digitized Pic- 
 tures, February 1967-February 1968. V. Ray Taylor and Jay S. Winston, November 1968. (PB-180- 
 717) 
 
 NESC 47 A Polynomial Representation of Carbon Dioxide and Water Vapor Transmission. William L. Smith, 
 February 1969. (PB-183-296) 
 
 Statistical Estimation of the Atmosphere's Geopotential Height Distribution From Satellite 
 Radiation Measurements. William L. Smith, February 1969. (PB-183-297) 
 
 49 Synoptic/Dynamic Diagnosis of a Developing Low-Level Cyclone and Its Satellite-Viewed Cloud 
 Patterns. Harold J. Brodrick and E. Paul McClain, May 1969. (PB-184-612) 
 
 Estimati urn Wind Speed of Tropical Storms From High Resolution Infrared Data. L. F. 
 Hubert, A. Timchalk, and S. Fritz, May 1969. (PB-184-611) 
 
 (Continued on inside back cover) 
 
dD ATMOSp^ 
 
 r ^ENT Of 
 
 U.S. DEPARTMENT OF COMMERCE 
 Peter G. Peterson, Secretary 
 
 NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 
 Robert M. White, Administrator 
 
 NATIONAL ENVIRONMENTAL SATELLITE SERVICE 
 David S. Johnson, Director 
 
 O 
 
 ft 
 •o 
 
 c 
 
 n 
 
 o 
 
 NOAA Technical Report NESS 64 
 
 Radiometric Techniques for 
 Observing the Atmosphere 
 From Aircraft 
 
 William L. Smith and Warren J. Jacob 
 
 WASHINGTON, D.C. 
 JANUARY 1973 
 
 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 
 Price: 35 cents domestic postpaid, or 25 cents GPO Bookstore Stock Number 0317-00123 
 
UDC 551.507.352:551.508.21:551.501.7 
 
 551.5 Meteorology 
 
 .501 Methods of observation and computation 
 
 .7 Upper air observation methods 
 
 .507 Instrument carriers 
 
 .352 Aircraft observation 
 
 .508 Instruments 
 
 .21 Radiometers 
 
 Mention of a commercial company or product does not constitute 
 an endorsement by the NOAA National Environmental Satellite Ser- 
 vice. Use for publicity or advertising purposes of information 
 from this publication concerning proprietary products or the 
 tests of such products is not authorized. 
 
 li 
 
CONTENTS 
 
 Abstract 1 
 
 1. Introduction 1 
 
 2. The airborne ITPR 2 
 
 3. Radiance specification of atmospheric variables 2 
 
 A. Atmospheric temperature profiles 2 
 
 B. Total precipitable water 4 
 
 C. Clear column radiance 5 
 
 D. Cloud height 7 
 
 E. Effective cloud amount 8 
 
 4. Results 8 
 
 5. Conclusion 11 
 
 Acknowledgments 11 
 
 References 12 
 
 in 
 
RADIOMETRIC TECHNIQUES EOR OBSERyiNG 
 THE ATMOSPHERE FROM AIRCRAFT" 
 
 William L. Smith and Warren J. Jacob 
 National Environmental Satellite Service 
 National Oceanic and Atmospheric Administration 
 Washington, D. C. 
 
 ABSTRACT. Radiometric observations have been made from 
 aircraft with spacecraft prototype instruments to test 
 satellite remote sensing techniques. At the same time 
 these observations have been used to study the problem 
 of remote sensing from aircraft because of its own 
 particular value in providing data in the support of 
 sub-synoptic scale meteorological experiments such as 
 the forthcoming GARP Atlantic Tropical Experiment. 
 
 This paper describes aircraft radiometric methods of 
 obtaining clear column radiances, vertical temperature 
 profiles, total precipitable water, and cloud heights 
 and amounts. Questions regarding vertical resolution 
 and accuracy specification as a function of aircraft 
 altitudes are answered. Results obtained using obser- 
 vations made during June 1970 with prototype versions of 
 the Nimbus-E ITPR aboard the NASA CV-990 are presented 
 and discussed. It is concluded that multi-spectral 
 radiometers aboard an aircraft can be effective 
 meteorological observing tools . 
 
 1. INTRODUCTION 
 
 In this paper we present methods of making meteorological inferences using 
 multi-spectral infrared radiance observations made from an aircraft. In 
 
 particular, methods are given for obtaining: (l) clear column radiances, 
 (2) the vertical temperature profile from aircraft altitude to the earth's 
 surface, (3) the total precipitable water beneath the aircraft, and (4) the 
 height and amount of any clouds below the aircraft flight level. The 
 techniques are tested using radiance observations obtained by a brassboard 
 version of the Infrared Temperature Profile Radiometer (ITPR) from the NASA 
 Convair 990 aircraft during June 1970. Results presented were obtained from 
 observations during a flight over the Pacific Ocean (from Fairbanks, Alaska 
 to San Francisco, California) in which a cold front was encountered near 
 weather ship "Papa" (50°N, 145°W). These results demonstrate that spectral 
 radiometric measurements are very useful for obtaining a detailed depiction 
 of the atmosphere's meteorological state from an aircraft observation 
 platform . 
 
 "Presented at the Conference on Atmospheric Radiation, 
 Ft. Collins, Colorado, August 7-9, 1972. 
 
2. THE AIRBORNE ITPR 
 
 The 1970 airborne ITPR experiment has already been discussed in detail by 
 Smith et al., (1972). Briefly, the ITPR measured the upwelling radiance from 
 the underlying earth and atmosphere in five different spectral regions; one 
 in the rotational water vapor band near 19um, three in the 15-um CO2 band, 
 and one in the atmospheric window at Hum. The detailed spectral response 
 characteristics of the ITPR channels are presented in figure 1. 
 
 Oi 1 1 1 1 1 1 v/V— 1 1 1 1 1 1 — 1 1 J — v^A" 
 
 LU 
 
 z 
 < 
 
 z 
 < 
 
 ex. 
 
 1000 950 900 850 r 770 750 730 710 690 550 50C 
 
 Figure 1 
 
 WAVE NUMBER (cm -1 ) 
 
 -Measured transmittances of the spectral filters in 
 ITPR channels 1 through 5 
 
 3. RADIANCE SPECIFICATION OF ATMOSPHERIC VARIABLES 
 
 A. Atmospheric Temperature Profiles 
 
 The radiance measured by the ITPR, I v (p a ), is related to the atmospheric 
 temperature profile through the radiative transfer equation 
 
 MPa )=I VPo )T v(Pa 
 
 /Po 
 Pa 
 
 B v (p) dT v ( Pa'P ) 
 dp 
 
 dp. 
 
 (1) 
 
B (p) is the Planck radiance given by 
 
 B v (p)=C lV 3 / r e xp(C 2 v/T(p))-ll , (2) 
 
 where C^ and C2 are constants of the Planck function, and T(p) is the 
 temperature at pressure p. t v (p ,p) is the transmittance of the atmosphere 
 between the pressure p and the aircraft pressure level p a , and p Q denotes the 
 surface pressure. 
 
 The solution of (1) for T(p) has been discussed by numerous authors and 
 most of the viable methods have been recently summarized by Fleming and Snrth 
 (1972). For the aircraft inference problem the "statistical regression" 
 solution has been adopted. In this solution 
 
 n 
 
 B r (p)=B r (p)+ J2 a i<Pa>P) [ R i(Pa)-Ri(Pa>] > < 3 > 
 
 i=l 
 
 where B r (p) is the Planck radiance corresponding to a reference frequency r, 
 chosen to be intermediate to the observation frequency range, and R^(p a ) is 
 the measured radiance for the i th frequency 1^ , normalized to the reference 
 frequency by using the relation 
 
 R i = C l r3 ' [" ex P (C 2 r / T?)" 1 ] > (4) 
 
 where the brightness temperature T? i s given by the inverse Planck function 
 
 T? = C 2 v £ / In ["(^ Vi 3 / I.) +1 
 
 (5) 
 
 The barred quantities denote the means of the statistical sample used to de- 
 rive the regression coefficients ai (p a ,p). Once Bp(p) is determined, the 
 temperature profile is calculated using the inverse Planck function in the 
 form 
 
 T(p) = C 2 r/ In j (Cjr 3 / B r (p)) + ll 
 
 (6) 
 
 In this study the regression coefficients were determined from radiances cal- 
 culated for the heterogeneous sample of 106 atmospheres given by Wark et al. 
 (1962). The transmittance functions needed to calculate the ITPR radiances 
 were taken from Smith et al. (1972). Random errors on the order of 0.25% 
 were added to the calculated radiances to simulate actual radiance observations. 
 The regression coefficients were obtained for aircraft pressure-altitudes of 
 950 mb to 200 mb in increments of 50 mb. For each aircraft pressure-altitude, 
 regression coefficients relating the aircraft-level temperatures and the 
 "observed" radiances to the temperatures of various levels were determined, 
 using the standard least-squares solution. 
 
 Figure 2 shows the resulting standard error of estimate associated with the 
 
£ 
 
 £ 500 
 
 
 
 1000 
 
 "i 1 r 
 
 n | I | 1 1 1 1 1 1 1 1 r- 
 
 RMS T(p) Error As A 
 Function Of Aircraft Flight Level 
 
 ~r^ — r 
 
 -i 1 r 
 
 2.8 
 
 Figure 2. --Standard error of estimate of radiance derived temperature 
 profiles as a function of aircraft flight level 
 
 vertical temperature profiles for the dependent sample as a function of the 
 aircraft flight level. As expected, the standard error of estimate for the 
 temperature of a particular pressure level beneath the aircraft decreases 
 with decreasing aircraft altitude (increasing pressure-altitude), especially 
 for the pressure levels near the aircraft pressure-altitude. The standard 
 errors of estimate are largest in the lower troposphere (800-950 mb) where 
 surface inversions occur, and above 300 mb where the tropopause usually 
 exists. The temperature errors are a minimum at the aircraft flight level 
 because the measurement at this level is direct, and are also minimal at the 
 earth's surface because the window channel provides a nearly unique observa- 
 tion of the surface temperature. 
 
 B. Total Precipitable Water 
 
 To estimate the total precipitable water vapor, U Q , from the 19- urn water 
 
 vapor channel radiance, I, the standard iterative equation 
 
 UJ+1= rji + 
 o o 
 
 U j - U j " 1 
 o o 
 
 ft _ £ j-i 
 
 (I 
 
 $ 
 
 (7) 
 
 A 
 
 is used. In (7) I denotes a calculated radiance and the superscript denotes 
 the iterative step. The precipitable water vapor profile required to 
 
calculate the radiance at each Iterative step is given by 
 
 o 
 ' ' o 
 
 where A is used at its climatological value of 3.0 (Smith 1966). 
 
 C. Clear Column Radiance 
 
 When clouds exist, the radiance propagating from the clear air columns 
 must be specified from the measured radiance distribution before soundings 
 down to the earth's surface can be calculated. From an aircraft, one may 
 measure many spatially independent radiances over a short distance along the 
 flight track. Consequently, the variation of the observed radiance over this 
 short distance will be due mainly to variations in the cloudiness within the 
 instrument field of view rather than to variations in atmospheric temperature. 
 If the cloud height is constant over the distance traversed, so that the 
 radiance variations are due to variations in cloud amount, the spatial 
 variation of the radiance in any spectral channel will be linear with respect 
 to the variation of the radiance in any other simultaneously observed spectral 
 channel. This linear function can be used to specify the clear column radi- 
 ances from the observed cloud contaminated radiance distribution (Smith 1968, 
 Luebbe 1971). 
 
 To show this, consider the following equation governing the measured 
 radiance I(v) when a cloud fills the fraction N of the instrument's field of 
 view: 
 
 I(v) = NI cd (v)+(l-N)I c (v) (9) 
 
 Here s l c( j (v) is the total radiance propagating from all of the cloudy columns 
 of air and I c (v) is the radiance arising from all of the cloudless columns 
 of air within the instrument field of view. Differentiating (9) with 
 respect to the spatial coordinate, S, assuming I C( j (v) and I c (v) are 
 constant yields 
 
 dl(v) f "I dN 
 
 _=Ll cd (v)-I c (v)j_ . (10) 
 
 Thus it follows that the relation between the radiances observed simultaneous- 
 ly, at two different spectral frequencies, v^ and Vj , is 
 
 A^Vj.Vj) = W v i> - MV = dI ^ , (ID 
 
 I ,(v.) - I (v.) dl(v.) 
 
 cd ] c ] j 
 
 where A, (v., v.) is a constant. Integrating (11) gives 
 
 Kv.) = A Q (v i ,v j ) + A 1 (v 1 ,v j ) I(v.) (12) 
 
The coefficients A and A, can be determined from a set of simultaneous 
 observations by standard least-squares regression techniques. Then, given 
 clear column radiance for any spectral channel v- the clear column radiance 
 for any other spectral channel v^ can be predicted from (12). 
 
 In practice, the clear column radiance for the window channel is used to 
 predict the clear column radiance for the water vapor and CO2 channels (see 
 fig. 3). The clear column radiance for the window channel can be obtained 
 from statistical histogram analyses of the window radiance observations 
 (Smith, Rao, Koffler and Curtis 1970) if a sufficient number of cloudless 
 fields of view exist. If no completely cloud-free fields of view are avail- 
 able, the clear column radiance can be specified by horizontal interpolation 
 or from an estimate of the surface temperature, i.e. 9 I c = B (T ~ ) + small 
 atmospheric correction. 
 
 Figure 4 shows the mean and the range (maximum and minimum) of radiances 
 observed from about 35,000 feet within 50 n.mi. sections of an Alaska-to- 
 California flight. Each section consists of 100 spatially independent 
 observations. The clear column radiance profile for the window channel 
 (899 cm - -'-) was obtained by spatial interpolation of the window radiances 
 obtained from cloud-free fields of view because the horizontal variation is 
 small over the sea. The clear column radiances for the water vapor and 
 carbon dioxide absorption channels were then calculated for each leg using 
 the regression procedure outlined above. These clear column radiances were 
 then used to calculate the temperature and water vapor profiles (shown later) 
 
 100 
 
 90- 
 
 85 - 
 
 80 - 
 
 60 
 
 55 
 
 50 
 
 Regression Line 
 
 Aircraft ITPR Measurements 
 Near 50°N, 145°W, June 12,1970 
 
 I, (899) 
 
 J L 
 
 _L 
 
 55 60 65 70 75 80 85 90 95 100 
 
 Window Channel Radiance (mw/m str cm"' ) 
 
 Figure 3. — ITPR measured radiances over a cloudv region. Data for CO2 
 
 channel (750 cm" 1 ) are plotted as a function of data measured in a 
 
 w 
 
 indow channel (899 cm 1 ) 
 
June 12 - 13, 1970 
 
 Aircraft ITPR Measured Radiances and 
 Calculated Clear Column Radiances 
 
 1930Z 2000 2030 2100 2130 2200 2330 0000 0030 0100Z 
 120f 
 
 100 
 
 80 
 
 60 
 100 
 
 "i i^=J C^zn r 
 
 T J Ch 1 - 532.5 cm ' 
 
 _ 80- 
 
 7 e 60- 
 ' 40- 
 
 W/ 
 
 ~T¥=¥^ : fP f ^T 
 
 Ch 2 - 899.0 cm 
 
 E 100 
 I 80 
 
 *8 60 
 
 C 
 
 o 
 
 ^ 40 
 
 
 85 
 
 65 
 
 45 
 85 
 
 65 
 
 45 
 
 Calc. Clr. Col. Rad. 
 
 I Range of Rad. 
 Mean of Rad. 
 
 Ch 3 - 747.0 cm" 1 
 
 Wy 
 
 Wy Ch 4 - 732.0 cm" 1 [ l 
 
 TO^f- 
 
 X 
 
 Ch 5 - 708.0 cm 
 
 l i l 
 
 63N 60N 57N 53N 51N 49N 47N 45N 41N 38N 
 
 145W 150W 150W 150W U8W 142W 135W 130W 127W 123W 
 
 Flight Track 
 
 Figure 4.--ITPR measured radiances and calculated clear column radiances 
 
 from flight over Pacific Ocean, June 12, 1970. The heavy dashed 
 line represents interpolated values between data at first point 
 and at 2030 Z. 
 
 D. Cloud Height 
 
 Assuming zero cloud reflectivity for the frequency v., it can be shown that 
 
 I ,(v) = 
 
 cd 
 
 ( v ) i Bcd (v) + ]_i- e (v) 
 
 I (v) 
 
 (13) 
 
 where E (v) is the emissivity of the cloud. The "black" cloud radiance is 
 
 I Bcd (v)=B v (p c )T v (p, s pJ - f B v (p) d V P a' p) 
 
 a c 
 
 / 
 
 dp 
 
 (14) 
 
 dp 
 
 where p is the effective cloud pressure. Substituting (13) into (11) gives 
 
 dl(v ± ) 
 
 dl(v ) 
 
 (v.) 
 
 (V) 
 
 I R ,(v.)-I (v.) 
 
 Bed i c i 
 
 U ,(v )-l (v ) 
 
 Bed ] c ] 
 
 (15) 
 
 If we choose two frequencies which have approximately the same cloud 
 emissivity (e.g., channels in the wing of the 15-ym C0 9 band) then it follows 
 that 
 
A 1 (v i ,v ,,p c ) = I Bcd (v i-Pc ) - I c (v i ) 
 
 I ,(v.,p ) - I (v.) 
 
 Bed J c c 3 
 
 (16) 
 
 Given the ^temperature profile, as calculated from the clear column radiances, 
 
 I , and I can be calculated using (1M-) as a function of cloud pressure. 
 Bed c to v 
 
 Hence, using (16), the radiance slope Aj_ (p c ) can be calculated as a function 
 
 of cloud pressure. Then the actual cloud pressure can be specified from the 
 
 observed slope A, (v., v.) using the iterative solution 
 
 ^ +1 3 p j 
 c ^c 
 
 P . - 4- 1 
 
 Ai(p c )-Al(Pc _1 ) 
 
 A (v.,V.)-A (pD 
 
 1 1 2 1 c 
 
 !'] 
 
 (17) 
 
 which converges for Aj_(v£,v-:) f 0. Also, the pressure of a cloud within the 
 field of view of a single observation, within the sample used to determine 
 the clear column radiances, can be specified by letting 
 
 I(v i } - I c ( vj ) 
 
 vvy = Kv.) . 1 ( v.) 
 
 (18) 
 
 E. Effective Cloud Amount 
 
 The effective amount of cloud, N (equal to N£(v)), within the instrument 
 field of view can then be specified from one of the two channels used to 
 calculate the cloud pressure using the equation 
 
 N" = N£(v) = 
 
 I(v)-I c (v) 
 
 (19) 
 
 where I (v) is either the mean of a sample of observations or an individual 
 observation, depending upon which was used to specify p c and consequently 
 
 ^cd^)- 
 
 4, 
 
 RESULTS 
 
 Figure 5 shows a cross-section of atmospheric temperature obtained while 
 flying at 33,000 feet over a Pacific cold front. The temperature profiles 
 were obtained from the clear column radiances shown in figure 4, using the 
 statistical regression solution presented earlier. The isolines represent 
 departures from the level-mean-values. As shown, the variation of temper- 
 ature across the front could be diagnosed in this case because there were 
 sufficient breaks in the cloudiness associated with the front. 
 
 Figure 6 compares the 1000- to 500-mb and the 500- to 250-mb thickness 
 values obtained from the infrared derived temperature profiles with thickness 
 values derived from simultaneous microwave measurements (NEMS) by Rosenkranz 
 et al. (1971) and observed by the Weather Ship "4YP" (Papa) radiosonde. As 
 
21002 
 
 E 
 
 i i i i i i 1 1 r 
 
 Cross Section of Aircraft ITPR Deduced Temperature 
 over Pacific Cold Front, June 12, 1970 
 
 2200Z 
 
 53N 53N 52N 51 N 51 N 51 N 50N SON 50N 49N 49N 
 I50W 150W 150W 149W 149W U8W 147W 145W U4W 143W 142W 
 
 Flight Track 
 
 Figure 5. — Cross section of ITPR deduced temperature profiles over Pacific 
 
 cold front. Isolines show the departure from the level-mean-values. 
 
 5000 
 
 I 4950 
 a 
 
 -S 4900 
 
 -c 
 
 _Q 
 
 E 4850 
 o 
 
 8 4800 
 4750 
 
 Time 
 2130Z 
 
 ~- 1 1 1 1 1 
 
 Aircraft ITPR and NEMS Deduced Data 
 
 over Pacific Cold Front 
 
 June 12, 1970 ,''' 
 
 2200Z 
 
 5650 
 
 £ 5450 
 
 53 N 
 
 53N 
 
 52N 
 
 51 N 
 
 51 N 51 N 
 
 150W 
 
 150W 
 
 150W 
 
 149W 
 
 149W U8W 
 Flight Track 
 
 50N 50N 50N 49N 
 148W 147W 145W U4W U3W 
 
 49N 
 142W 
 
 Figure 6. — Thickness values (1000- to 500-mb and 500-mb) , derived from infra- 
 red measurements, microwave measurements, and 4YP radiosonde data, 
 
10 
 
 shown, there is relatively good agreement between the infrared and the micro- 
 wave data, although both display some minor discrepancies with the conventional 
 radiosonde data at the location of the weather ship. 
 
 Figure 7 compares the total precipitable water vapor derived from the infra- 
 red water vapor channel radiance data with that obtained from microwave and 
 radiosonde data. Here we see large discrepancies between the total precipit- 
 able water vapor estimates. The systematic discrepancies between the two 
 estimates are clearly related to the temperature discrepancies shown, in 
 figure 6. These result because an over estimate (or an under estimate) of 
 temperature requires an over estimate (or under estimate) of water vapor to 
 satisfy a given water vapor channel radiance measurement. The differences in 
 the relative variations through the frontal zone probably are due to the fact 
 that the infrared estimate is only for the clear air column while the micro- 
 wave estimate includes the water vapor contained within the clouds. This is 
 verified by the two "Papa" raob values , one of which was observed in cloud- 
 less air while the other was observed during an ascent through the frontal 
 clouds. The inability of an infrared sensor to sound through clouds is a 
 severe limitation in the sensing of total precipitable water. 
 
 Figure 8 shows cloud heights and amounts estimated using two CO2 channels 
 (as outlined above) and those determined directly from window radiance 
 measurements (i.e., the pressure at which the air temperature was equal to the 
 window channel brightness temperature), and the comparison of both with visual 
 observations. The comparison of the two estimates shows that the window 
 temperature deduced heights are consistently lower, and exhibit a large degree 
 
 2100Z 
 
 Time 
 2130Z 
 
 2200Z 
 
 53N 
 150W 
 
 
 5.0 
 
 4.5 
 
 1 1 1 1 1 1 
 Aircraft ITPR and NEMS Deduced Data 
 
 1 
 
 1 1 
 
 
 4 
 3 5 
 3 
 
 over Pacific Cold Front 
 June 12, 1970 
 
 A 
 
 A 
 
 / - 
 / 
 
 I 
 
 1 
 
 / _ 
 / 
 
 f 
 
 B 
 
 Q. 
 
 NEMS 
 
 A 4YP RAOB, 1200 GMT 
 A 4YP RAOB, 2300 GMT 
 
 o w 
 
 X 
 ~D 
 
 
 
 2 5 
 2 
 
 
 "~'V 
 
 \ 
 
 1 
 
 
 1 5 
 
 
 
 - 
 
 
 1.0 
 
 5 
 
 
 
 -^\ 
 
 
 
 
 
 
 1 l 1 1 1 1 
 
 1 
 
 1 1 
 
 53N 
 150W 
 
 52N 
 150W 
 
 51 N 
 149W 
 
 51 N 
 149W 
 
 51 N 
 148W 
 
 Flight Track 
 
 50N 
 147W 
 
 50N 
 145W 
 
 50N 
 144W 
 
 49N 
 143W 
 
 49N 
 142W 
 
 Figure 7. — Total precipitable water vapor derived from infrared, microwave, 
 and 4YP radiosonde data. 
 
11 
 
 300 
 
 !£ 
 
 < 
 
 500 
 
 700 
 
 1000 
 100 
 
 80 
 
 60 
 
 40 
 19 
 
 P c (732 cm ' /750 cm ' CO, Channels) 
 P Range (Window Channel) 
 
 40 
 
 1950 
 
 2000 
 
 2010 
 
 2020 
 
 2030 
 
 2040 
 
 Time (GMT) 
 
 Figure 8. --Estimated cloud top pressure determined from ITPR measured radi- 
 
 ,-1 
 
 -1 
 
 ances using 732 cm"- 1 - and 750 cm - - 1 - C0 2 channel observations (solid 
 curve), "window" channel radiance (solid bar) and visual observations 
 (symbols). Shown below is the estimated cloud amount derived from 
 radiances measured in the 732 cm -1 and 750 cm-1 channels. 
 
 of variability even in totally overcast situations. This variability 
 apparently is due to variations in the opacity of the cloud. The measurements 
 in the CO2 band, on the other hand, provide qualitatively good estimates of 
 the cloud heights, in comparison with corresponding visual observations, even 
 when the field of view is not completely filled with cloud. This is demon- 
 strated by the estimates obtained near the beginning of this flight track. In 
 thick overcast regions , the CO2 channel estimates display agreement with the 
 maximum heights obtained from window radiances. 
 
 5. CONCLUSION 
 
 This study shows that multi-spectral infrared radiometers aboard aircraft 
 can be a very effective meteorological observing tool. We propose that this 
 observing capability be used to augment conventional observations for future 
 sub-synoptic scale meteorological research programs, such as the forthcoming 
 GARP Atlantic Tropical Experiment. 
 
 ACKNOWLEDGEMENTS 
 
 We are grateful for the assistance of L. Mannello, P, 
 R. Ryan in the reduction and analysis of the data. 
 
 Pellegrino, and 
 
12 
 
 REFERENCES 
 
 Fleming, H. E., and Smith, W. L. , "Inversion Techniques for Remote Sensing 
 of Atmospheric Temperature Profiles," presented at the Proceedings of 
 the Fifth Symposium on Temperature, Its Measurement and Control in 
 Science and Industry, Washington, D.C., June 21-24, 1971 , to be pub- 
 lished 1972. 
 
 Luebbe, R. C, NOAA/National Environmental Satellite Service, 1971, 
 (unpublished notes). 
 
 Rosenkranz, P. W. , Staelin, D. H. , Barath, F. T. , Blinn III, J. C. and 
 
 Johnson, E. J., "Indirect Sensing of Atmospheric Temperature and Water 
 Vapor Using Microwaves," Proceedings of the Seventh International 
 Symposium on Remote Sensing of Environment , U. of Mich., Vol. Ill, 1971, 
 pp. 1739-1748. 
 
 Smith, W. L. , "Note on the Relationship Between Total Precipitable Water and 
 Surface Dew Point," Journal of Applied Meteorology , Vol. 5, No. 5, Oct. 
 1966, pp. 726-727. 
 
 Smith, W. L. , "An Improved Method for Calculating Tropospheric Temperature 
 and Moisture from Satellite Radiometer Measurements," Monthly Weather 
 Review , Vol. 96, No. 6, June 1968, pp. 387-396. 
 
 Smith, W. L., Rao, P. K. , Koffler, R. , and Curtis, W. R. , "The Determination 
 of Sea-Surface Temperature From Satellite High Resolution Infrared 
 Window Radiation Measurement," Monthly Weather Review , Vol. 98, No. 8, 
 Aug. 1970, pp. 604-611. 
 
 Smith, W. L., Hilleary, D. T. , Baldwin, E. C. , Jacob, W. R. , Jacobowitz, H. , 
 Nelson, C, Soules, S. D. , and Wark, D. Q. , "The Airborne ITPR Brass- 
 board Experiment," NOAA Technical Report NESS 58, Mar. 1972, 74 pp. 
 (Available from the National Technical Information Service.) 
 
 Wark, D. Q. , Yamamoto, G., and Lienesch, J., "Methods of Estimating Infrared 
 Flux and Surface Temperature from Meteorological Satellites," Journal 
 of the Atmospheric Sciences , Vol. 19, No. 5, Sept. 1962, pp. 369-384. 
 
 U. S. GOVERNMENT PRINTING OFFICE : 1973 O - 495-152 
 
(Continued from inside front cover) 
 
 NESC 51 Application of Meteorological Satellite Data in Analysis and Forecasting. Ralph K. Anderson, 
 Jerome P. Ashman, Fred Bittner, Golden R. Farr, Edward W. Ferguson, Vincent J. Oliver, and 
 Arthur H. Smith, September 1969. Price $1.75 (AD-697-033) Supplement price $0.65 (AD-740- 
 017) 
 
 NESC 52 Data Reduction Processes for Spinning Flat-Plate Satellite-Borne Radiometers. Torrence H. 
 MacDonald, July 1970. Price $0.50 (COM-71-00132) 
 
 NESC 53 Archiving and Climatological Applications of Meteorological Satellite Data. John A. Leese, 
 Arthur L. Booth, and Frederick A. Godshall, July 1970. Price $1.25 (COM-71-00076) 
 
 NESC 54 Estimating Cloud Amount and Height From Satellite Infrared Radiation Data. P. Krishna Rao, 
 July 1970. Price $0.25 (PB-194-685) 
 
 NESC 56 Time-Longitude Sections of Tropical Cloudiness (December 1966-November 1967). J. M. Wallace, 
 July 1970. Price $0.50 (COM-71-00131) 
 
 NOAA Technical Reports 
 
 NESS 55 The Use of Satellite-Observed Cloud Patterns in Northern Hemisphere 500-mb Numerical Analysis. 
 Roland E. Nagle and Christopher M. Hayden, April 1971. Price $0.55 
 
 NESS 57 Table of Scattering Function of Infrared Radiation for Water Clouds. Giichi Yamamoto, 
 Masayuki Tanaka, and Shoji Asano, April 1971. Price $1.00 (COM-71-50312) 
 
 NESS 58 The Airborne ITPR Brassboard Experiment. W. L. Smith, D. T. Hilleary, E. C. Baldwin, W. Jacob, 
 H. Jacobowitz, G. Nelson, S. Soules , and D. Q. Wark, March 1972. Price $1.25 (COM-72-10557) 
 
 NESS 59 Temperature Sounding From Satellites. S. Fritz, D. Q. Wark, H. E. Fleming, W. L. Smith, H. 
 Jacobowitz, D. T. Hilleary, and J. C. Alishouse, July 1972. Price $0.55 (COM-72-50963) 
 
 NESS 60 Satellite Measurements of Aerosol Backscattered Radiation From the Nimbus F Earth Radiation Ex- 
 periment. H. Jacobowitz, W. L. Smith, and A. J. Drummond, August 1972. Price $0.25 (COM-72- 
 51031) 
 
 NESS 61 The Measurement of Atmospheric Transmittance From Sun and Sky With an Infrared Vertical 
 Sounder. W. L. Smith and H. B. Howell, September 1972. Price $0.30. (COM-73-50020) 
 
 NESS 62 Proposed Calibration Target for the Visible Channel of a Satellite Radiometer. K. L. Coulson 
 and H. Jacobowitz, October 1972. Price $0.35 
 
 NESS 63 Verification of Operational SIRS B Temperature Retrievals. Harold Brodrick. January 1973. 
 
PENN STATE UNIVERSITY LIBRARIES 
 
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