The TM multispectral scanner system was calibrated in an absolute manner before launch. To determine the temporal changes of the absolute radiometric calibration of the entire system, spectroradiometric measurements of the ground and the atmosphere were made simultaneously with TM collections over White Sands, New Mexico. By entering the measured values in an atmospheric radiative transfer program, the radiance levels of the in four of the spectral bands of the TM were determined. Tables show values for the reflectance of snow at White Sands measured by a modular 8 channel radiometer, and values for exoatmospheric irradiance within the TM passbands, calculated for the Earth-Sun distance using a solar radiometer

Castle, K. R.

Dinguirard, M.

Ezra, C. E.

Holm, R. G.

Jackson, R. D.

Kastner, C. J.

Palmer, J. M.

Savage, R. K.

Slater, P. N.

English

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https://ntrs.nasa.gov/search.jsp?R=19840005569 2020-03-21T01:48:25+00:00Z
11-FLIGHT ABSOLUTE RADIOMETRIC CALIBRATION OF THE THEMATIC MAPPER
84 "' 10 C
K.R. Castle, R.G. Holm, C.J. Kastner, J.M. Palmer, and P.N. Slater
Optical Sciences Center
University of Arizona
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Center d'Etudes et de Recherches de Toulouse
	
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2, Avenue Edouard-Belin
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C.E. Ezra and R.D. Jackson
Agricultural Research Service
U.S. Department of Agriculture
Phoenix, AZ 85040, USA
R. Savage
Atmospheric Sciences Laboratory
White Sands Missile Range, NM 88002, USA
	(Eb4— 10044) IN —FLIGIVI ABSCLUTE 8aDIGMETRIC 	 M84-13637
CALIBRATION of THE THEMATIC MAPPER (Arizona
Univ., Tucson-) 10 P HC 8U1/MF AO! CSCL 08B
Unclas
G3/43 00044
J.
2The Thematic Mapper (TM) multispectral scanner system was placed
into earth orbit on July 16, 1982 as part of NASA's Landsat-4 payload.
The entire system was calibrated in an absolute sense at Santa Barbara
Research Center before launch. 192 During flight, an internal calibration
system is used to monitor the calibration of the focal plane. 3 In order
to determine temporal changes of the absolute radiometric calibration of
the entire system in flight, we initiated a program at White Sands, New
Mexico, on January 3, 1983, to make spectroradiometric measurements of
the ground and the atmosphere simultaneously with TM image collections
over that area .4 By entering the measured values in an atmospheric
radiative transfer program,5 the radiance levels in four of the spectral
_	 bFnds of the TM were determined, ban' . 0.45-0.52um, band 2: 0.53-0.61µm,
band 3: 0.62-0.70pm and band 4: 0.78-0.91um. These levels were compared
to the output digital counts from tie detectors that sampled the
radiometrically measured ground area, thus providing an absolute
radiometric calibration of the entire TM system utilizing those
detectors.
On 3 January 1983, an 80 mm layer of two-day-old snow covered the
flat gypsum surface at the White Sands Missile Range. The reflectance
of the snow was measured by reference to a 1.2 m square barium sulfate
panel using a Barnes Modular Multispectral 8-Channel. Radiometer, that
collected radiant flux simultaneously in all the TM spectral bands ever
a total field angle of 15% The instrument was mounted on a rotatable
boom 2.5 m above the -snow to allow an average reflectance value to be
determined for an area of about 0.5 x 5 m. The measurements were made
at 10.08 hours coinciding with the overpass of the TM and a solar zenith
angle of 60°. When ratioed to the reflectance of the barium sulfate
3panel at 60% the reflectance of the snow in TM bands 1 to 4 was found
to be 0.769, 0.761, 0.756 and 0.732 respectively, with an Yms uncertainty
of ±0.023 in all cases.
A solar radiometer 6
 using nine 10-nm spectral bands in the visible
and near it was used to determine the total spectral optical depths T T
at these nine wavelengths. The measured barometric pressure of 889.5 mB
allowed the Rayleigh spectral optical depth T Ray to be determined. From
these data the Hie and oa:one spectral optical depths were determined.
In bands 1, 2, and 3, the component of T T due to molecular
absorption, Tabs, is :ntirely due to ozone. Water vapor and CO 2
 are
present in addition to ozone in band 4. Their effects have been included
in Table 1 which lists the values of the various atmospheric
constituents in bands 1 through 4.
Table 1. Atmospheric values.
Band a c (um) T, THie -	 T Rsy Tabs
1 0.485 0.2913 0.1475 0.1424 0.0014
2 0.57 0.2177 0.1382 0.0736 0.0059
3 0.66 0.1716 0.1282 0.0406 0.0030
4 0.84 0.1344 0.1099 0.0153 0.0092
Using the data in Table 1 as input to the radiative transfer code, the
following quantities were calculated:
ED,Dir" the direct solar irradiance at the ground - cosG z exp(- T T sect z)
ED,Dif: the diffuse solar irradiance at the ground
LDir: the direct radiance at the TM due to ED,Dir + ED,Dif
Lp: the path radiance at the TM - L T
 - (ED,Dir + ED,Dif) 2- exp(-T T sec5°)
LT: the total radiance at the TM
4Table
	 2.	 Irradiancea and	 radiances (normalized to	 unity solar
exoatmospheric	 irradiance).
Solar
Zenith
Band	 Angle ED,Dir	 ED,Dif LDir Lp LT
1	 550 0.345	 0.185 0.097 0.033 0.1301
650 0.212	 0.152 0.067 0.025 0.092
2	 550	 0.392	 0.145	 0.105	 0.024	 0.129
65 0 	 .253	 0.122	 0.043	 0.019	 0.092
r	3 	 550	 0.425	 0.122	 0.111	 0.019	 0.130
650 	 .282	 0.104	 0.078	 0.015	 0.093
4	 55°	 0.454	 0.095	 0.112	 0.014	 0.126
65 0 	 .308	 0.082	 0.079	 0.011	 0.090
s
Using the equivalent passband technique of Palmer and Tomasko7
and the exoatmospheric solar spectral irradiance values of Neckel and
Labs,8 the values for the exoatmospheric irradiances within the TM
passbands (ExW, were calculated for the earth-sun distance on
January 3. The required values of LT for the solar zenith angle of
60° were found by interpolating between the 55° and 65° data from
Table 2. These, when multiplied by their corresponding Ex4a values,
gave the radiances in mW/cm2 -sr in the TM passbands listed in Table 3.
t
r5
Table 3. Exoatmospheric irradiances and the radiances at the TM in
the TM passbands.
Equivalent Ex6 a LT
Band bandwidth in µm mW/cm2 mW/cm2 - sr
1 0.0712 12.2 1.36
2 0.0884 13.8 1.52
3 0.0773 10.7 1.19
4 0.1345 13.7 1.47
By identifying our site on the raw image data, we determined
which detectors scanned the area and how many samples each collected.
Detectors 1, 2, 3, 15 and 16 collected 5, 3, 1, 2, and 4 samples
respectively. We found the average digital count for each detector,
then calculated the average detector spectral radiance using offset
and gain values reported by Barker et al. l
 These spectral radiances
were multiplied by the number of samples for each detector. The
resultant products were added and then divided by the total number of
samples, 15. Thus we derived a value for the average spectral
radiance of our site as measured by the TM, proportionally weighted
according to the number of samples per detector.
The final step in the calculation was to multiply the average
spectral radiance at the TM by the equivalent passband to determine
the radiance within each TM band (Table 3). These values are compared
in Tables 4, 5 and 6.
P^PF
0+1
6
Table 4. Calculation of radiance in TM band 2 from preflight
calibration data l and comparison with inflight White Sands data.
Average
Average Spectral
Detector Count Radiance Gain Offset
3 139.0 17.04 8.014 2.41
2 143.7 17.42 8.117 2.33
1 146.2 17.52 8.174 2.99
15 141.5 17.43 7.979 2.43
14 147.5 17.71 8.195 2.83
Weighted average - 17.47 mW cm- 2
 sr-1 Om-1
Equivalent band radiance from weighted average - 1.537 mW cm-2 sr-1
Equivalent band radiance from Table 3 - 1.52 mW cm-2 sr-1
Agreement - -1.0% and +2.5% with reference to preflight calibration
and December 8, 1982 inflight data2 respectively.
Table	 5.	 Calculation of radiance in TM	 band 3	 from preflight
calibration d:ta l and comparison with inflight White Sands data.
Average
Average Spectral
Detector Count Radiance Gain Offset
3 165.0 15.4.0 10.590 1.89
2 169.7 15.86 10.602 1.57
1 171.6 15.73 10.777 2.13
16 167.8 15.85 10.484 1.63
15 172.5 15.88 10.769 1.53
Weighted average - 15.78 mW cm- 2
 Fr' 1 14 M,
Equivalent band radiance from weighted average - 1.215 mW cm -2 sr-1
Equivalent band radiance from Table 3 - 1.19 mW cm -2
 3r-1
Agreement - -1.87. and 3.0%	 with reference to preflight and December
8, 1982 inflight data 2
 respectively.
i
7Table 6. Calculation of radiance in TM band 4 from preflight
calibration data l
 and comparison with inflight White Sands data.
Average
Average Spectral
Detector Count Radiance Gain Offset
3 133.0 11.89 11.019 1.96
2 132.0 12.02 10.817 1.94
1 134.2 12.00 10.972 2.53
16 132.0 12.01 10.828 2.00
15 131.5 12.05 10.771 1.69
Weighted average - 12.01 mWcm- 2
 sr-1 U m'1
Equivalent band radiance from weighted average - 1.609 mWcm' 2 or'1
Equivalent band radiance from Table 3 - 1.47 mWcm' 2 sr'l
Agreement - -8.5 % and -5.6 % with reference to preflight and December
8, 1982 inflight data 2 respectively.
Because of the limitations of the instruments used on January 3,
Tabs in band 4 due to water vapor and CO 2 could not be measured.
Instead, the LOWMAN code was used to compute the water vapor and CO2
transmittances across band 4 at 5 cm -1
 intervals. The water vapor
transmittance was scaled, to account for the 44% relative humidity
measured at White Sands on January 3, then averaged to find TH2O+CO2.
Finally, the measured value of T Oz - 0.0003 was added to provide Tabs•
The effect of an error in this estimate can be judged by noting that
the inclusion of water vapor and CO 2 lowered the predicted radiance
level at the TM by only 2%.
Band 1 saturated over the snow field at White Sands. Pre-flight,
data l indicate that a saturation level of 255 counts corresponds to a
radiance at the sensor of 1.14 mWcm' 2 sr' l in TM band 1. Our estimate
v8
is that the snowfield provided a radiance level of 1.36 mWcm' 2 5r -1 at
the sensor.
The estimated uncertainty in the results of this first
measurement is t5%, while the estimated uncertainty in the preflight
calibration is no better than t 6 X 1 o9 We are encouraged that our
results for TM bands 2, 3 and 4 fall between 1% and 8.5% of the
preflight measurements and between 2.5% and 5.6% of the December 8,
1982 inf light data.
We are presently fabricating field equipment to provide more
V detailed and accurate measurements of the surface and atmosphere at
White Sands. Our goal is to reduce the uncertainty in sensor absolute
calibration to less than t3%. We plan to continue the work described
here to include the inflight absolute radiometric calibration of the
second TM and the SystIme Probatoire d'Observation de la Terre, Haute
Rlsolution Visible (SPOT/HRV) systems.
We wish to thank B.M. Herman for the use of his radiative
transfer cone and J.A. Reagan for the use of his solar radiometer. The
University of Arizona authors wish to acknowledge support from NASA
contract number NAS5-27382, J.L. Barker, Science Representative, and
the USDA, broadform contract number 12-14-5001-38.
•9
RRZERINCRS
1. Barker, J. L., D. L. Ball, K. C. Leung, and J. A. Walker, "Prelaunch
absolute radiometric calibration of the reflective bands on the
Landsat-4 protoflight thematic mapper." Proceedings of the
Landsat-4 Early Results Symposium, NASA Goddard Space Flight
Center, in press, (1983).
2. Barker, J. L., R. B. Abrams, D. L. Ball, and K. C. Leung.
"Characterization of Radiometric Calibration of Landsat-4 TM
reflective bands," Proceedings of the Landsat-4 Early Results
Symposium. NASA Goddard space Flight Center, in press, (1983).
3. Slater, P. N., "A review of radiometric calibration problems." Proc.
Intl Coll. on spectral signatures of objects in remote sensing,
Bordeaux, France. In press. (1983).
4. Kastner, C. J. and P. N. Slater, 'in-flight radiometric calibration
of advanced remote sensing systems." Proc. SPIE Symposium, Field
Measurement and Calibration Using Electro-Optical Equipment:
Issues and Requirements 356, pp. 158-165, (1982).
5. Herman, B. M. and S. R. Browning, "The effect of aerosols on the
earth-atmosphere albedo." J. Atmos. Sci, 32, 1430, (1975).
6. Shaw, G. E., J. A. Reagan, B. M. Herman, "Investigations of
atmospheric extinction using direct solar radiation measurements
made with a multiple wavelength radiometer." J. Appl. Meteor, 12,
374, (1973).
I
7. Palmer, J. M. and M. G. Tomasko, "Broadband radiometry with
i
spectrally selective detectors." Optics Lettars, 5, pp. 206-210
	 !
(1980).	 1
i
1+0
10
8. Neckel, N. and D. Labs, "Improved data of solar spectral irradiance
from 0.33 '0 1.25 um." Solar Phys. 74, 231 (1981).
9. Norwood, V. T. and J. C. Lansing, Jr., "Electro-optical imaging
sensors." Cbapter 8 in Manual of Remote Sensing, 2nd od., ad. R. N.
Colwell, 367, (1983).
i


In-flight absolute radiometric calibration of the thematic mapper

In-flight absolute radiometric calibration of the thematic mapper

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