In order to determine temporal changes of the absolute radiometric calibration of the entire TM system in flight spectroradiometric measurements of the ground and the atmosphere were made simultaneously with TM image collections over the White Sands, New Mexico area. By entering the measured values in an atmospheric radiative transfer program, the radiance levels in four of the spectral bands of the TM were determined, band 1:0.45 to 0.52 micrometers, band 2:0.53 to 0.61 micrometers band 3:0.62 to 0.70 micrometers and 4:0.78 to 0.91 micrometers. These levels were compared to the output digital counts from the detectors that sampled the radiometrically measured ground area, thus providing an absolute radiometric calibration of the entire TM system utilizing those detectors

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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rc	 ,
IN-FLIGHT ABSOLUTE RADIONETRIC CALIBRATION OF THE THEMATIC MAPPER
K.R. Castle, R.G. Holm, C.J. Kastner, J.M. Palmer, and P.N. Slater
Optical Sciences Center
University of Arizona
Tucson, Arizona 85721, USA
M. Dinguirard
Center d'Etudes et de Recherches de Toulouse
2, Avenue Edouard-Bolin
31055 Toulouse, Cedex, FRANCE
C.E. Ezra and R.D. Jackson
Agricultural Research Service
U.S. Department of Agriculture
Phoenix, AZ 85040, USA
R. Savage
	
t
Atmospheric Sciences Laboratory	 ►-
White Sands Missile Range, NM 88002, USA
(E84- 10064) Iii-FLIGHT ABSCLUTE RADIOMETRIC 	 N84-15633
CALIBRATION OF THE THEMATIC MAPPER (AriZOna
Univ., Tucson.1 10 p HC A02/tlF A01 CSCL 14A
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The Thematic Mapper (TM) multispectral scanner system was placed
into earth orbit on July 16, 1982 as part of NASA's Landsat-4 payload.
T!!e entire system was calibrated in an absolute sense at Santa Barbara
Research Center before launch. 102
 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
bands of the TM were determined, band 1: 0.45-0.52um, band 2: 0.53-0.6lum,
band 3: 0.62-0.701im and band 4: O.i:-J.91um. These levels were compared
to the output digital counts from the 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 over
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
M3
gel at 60', the reflectance of the snow in TM bands 1 to 4 was found
be 0.769, 0.761, 0.756 and 0.732 respectively, with an Yms uncertainty
±0.023 in all cases.
A solar radiometer6
 using nine 10-nm spectral bands in the visible
near it was used to determine the total spectral optical depths TT
these nine wavelengths. The measured barometric pressure of 889.5 mB
allowed the Rayleigh spectral optical depth TRay to be determined. From
these data the Hie and ozone spectral optical depths were determined.
In bands 1, :., and 3, the component of TT due to molecular
absorption, Tabs, is entirely due to ozone. Water vapor and CO 2
 are
present in add'tion 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 I (P M) TT THie TRay Tabs
1 0.485 0.2913 0.1475 0.1424 0.0014
2 0.57 0.2177 0.1382 0.073E 0.0059
3 0.66 0.1)L8 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 a cos6 z exp( -T T sec6 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 - LT
 - (ED,Dir + ED,Dif ) n eXP('TT sec5')
LT: the total radiance at the TM
4Table	 2.	 Irradiances and radiances (normalized to unity solar
exoatmospheric	 irradiance).
Solar
Zenith
Band
	 Angle ED,Dir ED,Dif LDir Lp LT
1	 556 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
650 	 .253	 0.122	 0.043	 0.019	 0.092
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
650 	 .308	 0.082	 0.079	 0.011	 0.090
Using the equivalent passband technique of Palmer and Toma3ko7
and the exoatmospheric solar spectral irradiance values of Neckel and
Labs,8 the values for the exoatmospheric irradiances within the TM
passbands (ExAA), 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 0 and 65° data from
Table 2. These, when multiplied by their corresponding Ex6a values,
gave the radiances in mW/cm 2-sr in the TM passbands listed in Table 3.
.A
5Table 3. Exoatmospheric irradiances and the radiances at the TM in
the TM passbauds.
Equivalent ExNa LT
Band bandwidth in {tm 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 a1. 1
 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 fins'. step in the calculation was to multiply the average
spectral radiance at the TM by the equivalent pessband to determine
the radiance within each TM band (Table 3). These values are compared
in Tables 4, 5 and 6.
Lr-	 ^	 T
6r
Table 4. Calculation of radiance in TM band 2 from preflight
calibration data l and comparison with inflight White Sands data.
P 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
16 141.5 17.43 7.979 2.43
r-	 15 147.5 17.71 8.195 2.83
Weighted average 17.47 mW cm-2 ar" 1 UM -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 data l and comparison with inflight White Sands data.
Average ?-°
Average
	
Spectral -t
Detector Count	 Radiance Gain Offset	 S
3 165.0	 15.40 10.590 1.89
2 169.7	 15.86 10.602 1.57
1
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	 I
Weighted average 15.78 mW cm- 2 sr- 1
 11 m-
f
a^
Equivalent band radiance from weighted average - 1.215 mW cm -2 sr- 1 	4
Equivalent band radiance from Table 3 - 1.19 mW cm -2 sr-1
Agreement - - 1.8 % and 3.0 E 	with reference to preflight and December
8, 1982 inflight data 2 respectively.
7Table 6. Calculation cf radiance to 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 i+ m"1
Equivalent band radiance from weighted average - 1.609 mWcm-2 ar-1
Equivalent band radiance from Table 3 - 1.47 mWcm" 2 ar-1
Agreement - -8.5 % and -5.6 % with reference to preflight and December
8, 1982 inflight data 2
 respectively. 3
s
Because of the liuitations of the instruments used on January 3, k_,
Tabs in band 4 due Lo water vapor and CO2 could not be measured. ;tea
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 442	 relative humidity
measured at White Sands on January 3, then averaged to find TH2O02•
i
Finally, the measured value of T oz - 0.0003 was added to provide T abs • j
The effect of an error in this estimate can be judged by noting that
t
i
the inclusion of water vapor and CO 2 lowered the predicted radiance
level at the TM by only 2%.
t
Band 1 saturated over the snow field at White Sands.	 Pre-flight
data' indicate that a saturation level of 255 counts corresponds to a
t;
radiance at the sensor of 1.14 mWcm" 2 ar-1 in TM band 1.	 Our estimate
q
1 -
8is that the snowfield provided a radiance Level of 1.36 mWcm' 2 3r-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 t6%1 99 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
detailed and aLnurate 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 Systame °robatoire d'Gbservation de la Terre, Haute
RIsolution Visible (SPOT/HRV) systems.
We wish to thank B.M. Herman for the use of his radiative
transfer code 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.
I
f
a
r;
hM
9Rzynamus
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.
Int'l 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 Usiug Electro-Optical Equipment:
Issues and Requirements 356, pp. 158-165, (1982).
5. Herman, B. M. and S. R. Browning, "Phe effect of aerosols ou 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).
7. Palmer, J. M. and M. G. Tomasko, "Broadband radiometry with
spectrally selective detectors." Optics Letters, 5, pp. 208-210
(1980).
8. Neckel, H. and D. Labs, 'Improved data of solar spectral irradiance
from 0.33 to 1.25 um." Solar phys. 74, 231 ( 1981).
9. Norwood, V. T. and J. C. Lansing, Jr., "Electro -optical imaging
sensors." Chapter 8 in Manual of Remote Sensing, 2nd ad., ad. R. N.
Colwell, 367, ( 1983).
W4
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In-flight absolute radiometric calibration of the thematic mapper

In-flight absolute radiometric calibration of the thematic mapper

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