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Produced by the NASA Center for Aerospace Information (CASI)
( f.ti4 -1 00utJ ) A A~AL.i ' 1 Cl' N Ij TE Ii l ' S 8 - 19957 

t ~ lJ:' Jt.ETf.I<_ CH LCTIlJ N Or LANDS A -q 

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G3/43 00086 
E ReM DDI ~STE s, 

10300 GREENBELT ROA D, SUITE 206, LANHAM, MARYLAND 20706 (301) 390-6100 

An Analysis of New Teehniques for 

Radiometrie Correction of LAN DSA T-4 

Tbematie Mapper Images 

" Made available under 

,n ~e interest of e3r/ NAS4 spOn~orshl, semination of Earth Y and wide disProgram informat' Resources Survey 

for any use made '~~'e:;o~. ~ithout lia bility 

c. 
An Analysis of New Techniques for 

Radiometric Correction of LANDSAT-4 

Thematic Mapper Images 

Prepared For 

National Aeronautics and Space Administration 

Goddard Space Fligbt Center 

Greenbelt, Maryland 20'171 

UNDER 

Contract NO. : NAS 5-27371 

October 20, 1983 

Prepared By 

John KClgUt 

Eliane Larduinat 

Maureen Fitzgerald 

Rese8l'ch and Data Systems, Inc. 

10300 Greenbelt Rd. 

Lanham, MD 20706 

I 

1 

I 

~ .. 
One of the primary objectives of this task is to investigate the utility of neVi 

methods for generating TM RLUTS which will improve the quality of the resultant 

images. Toward that end, various techniques for reducing detector to detector 

striping, and forward and reverse scan bahding which were observl)d in early TM 

images WHe investigated. These investigations for the most part centered upon 

understanc.ing the behavior of the TM calibration procedure, and in particular how 

the data ta~.en when the detectors viewed thr,! TM calibration lamps alld shutter 

could be uset.' to improve the operational 'Algorithms for computing detector gains 

and biases. 

The contents of the TM CCT-ADDS tape were changed for data processed 

after April 27, 1983 to take into account the new collection window for the 

calibration data. For all tapes received after that date the shutter and calibration 

data are formatt~d as follows: 

A ra w video scan contains scene data, data from when the detectors see the 

shutter, dat"l from the shutter when the DC restore circuits are working, more 

shutter data, data from when the detectors view the calibration lamps, and then 

more shutter data. The amount of each type of data for forward and reverse sca:1S 

is arranged as follows: 

Forward (odd numbered) scans 

148 Pixels of lamp data (CAL) 

24 Pixels of shutter data before DC restorp. (B) 

28 Pixels of shutter data after DC restore (A) 

Reverse (even numbered) scans 

148 Pixels of lamp data (CAL) 

24 Pixels of shutter data after DC restore (A) 

28 Pixels of shutter data before DC restore (B) 

Figure 1 shows a schematic of this data format. 

The calibr.ation file contains 32000 byte physical records, with each physical 

record containing 844 byte quad records. Each quad record contains a 4 byte field 

and 4 records at 210 bytes each. The residual bytes in the physical record are 

""I> 

. I filled with a hex value of 4E. -i"-c 

1 
~ v 

CAL CAL 

N FORWARD REVERSE FORWARD 

DC DC 

B A B A 

FIGURE 1 - DATA COLLECTION FORMAT FOR THE CCT-ADDS 

~ 
Several scenes with data in this format have been analyzed in order to 

evaluate the utility of the radiometric corrections operationally applied to the 

image data, and to investigate several techniques for reducing striping in the 

images. 

January 6, 1983; Terrebonne Bay, LA Scene (W022040) 

Band 1 

Analysis of tre Calibration Data 

Printer plots of the TM shutter data were produced and detector statistics 

were compiled and plotted. These statistics included various combinations of the 

average shutter COW)ts for each scan before (SB) ancJ after (SA) DC restore for 

forward (ODD) and reverse (EV EN) scans. 

The main conclusions of this anal~7sis were: 

1. The absolute value of the average shutter counts before and after DC restore 

seem to be correlated with the brightness of the image for that band. 

2. For detectors 4 and 12 both SA and SB averages appear to be locked into 

states about 1'1 and -1 count above and below the scene average. This effect is 

also observeci to a lesser extent (0.5 count) for detectors 8 and 10. This 

observation is consistent with those reported by others (1). 

3. The ave.-age value for detector 1 is consistently higher than for the rest of 

the detectors, and SA is consistently larger than SB. 

Appendix A gives details of this analysis. 

Intrusions of the image into the calibr.ation data were observed for detectors 

15 and 16, and to a lesser degree for detector 14. They occurred at the beginning 

of the calibration window for forward scans and at the end for reverse scans. They 

were generally limited to less than 10 observation points. When data which 

contained these intrusions was used in subsequent analyses, the image intrusion 

data was screened out. 

3 
Radiometric Correction Analy.,!:? 

O~(jUil\l.4.1.. ~ •• ~~:,; ~a 

OF POOR QUALITY 

A number of mehods fel' d~creasing image striping were investigated and 

applied to this scene, including: 

o All detector gains set equal to 1.0 and scan dependent biases 

o Scan dependent gains and biases 

o Prelaunch gains, and scan dependent biases 

The technique which produced the best results is described below. 

Methodology 

For a given region of N pixels in a TM raw image let: 

(1) 

Where 

The digital value for pixel i, scan j, detector d. 

The bias for scan j, detector d. 

GeL ::: The scan independent gain for detector d. 

If we rewrite (1) as 

(2) 

which is the ratio of the true gains for any two detectors d and e, then we can 

assume that: 

(3) 

4 
". - r .,j 

, . t.' ~ ',. .... ~ if 

If we define the gain for detector 9 as being 1.0 then 

Get =- LI: [ M~dA- BM~> ] 

tV M,?~{l- Be)q 

(4) 

the quan tity 

is the average value over the homogeneous region of the ratio of detector d to 

detector 9 for an image corrected with the biases BJ,cl , and constant gains equal to 

l.00 for all detectors. The biases for each detector are computed for each scan in 

the scene from the shutter dat~ before and after DC restore. 

Algorithm for Radiometric Correction 

1. The raw TM image is corrected using a constant gain equal to 1.0, and scan 

dependent biases which for scan j and detector dis: 

(5) 

2. Using the DCOPY program, an ime.5e is made for each detector 2n a 

homogeneous test region. The ratio of each detector to detector 9 is computed 

using the DIVPIC program. The average detector ratio over the test region is 

computed using program LIST. These average ratios are then taken as the gain for 

each detector. 

3. New support files are produced using the scene dependent gains and the scan 

dependent biases. 

4. The RADCOR program is used to produce a radiometrically corrected image 

1 ~ from the raw images and the gains and biases computed above. 

5 
,.1 '.4 

The Band 1 part of Figure 2 shows the average detector data numbers for a 

homogeneous water window of this scene when the gains and biases are computed 

using this method. As can be seen, the difference among all detectors is less than 

0.25 counts. 

B ... nd 6 

Several methods of performing radiometric correction to minimize striping 

were investigated for Band 6. All the methods involved determining differences in 

the Band 6 geometric correction factors (~d.) by analyzing homogeneous regions of 

n41'httime thermal TM scenes. The method which produced the best results is given 

below. 

Methodology 

Differences in gain between detectors were attributed to different 

geometrical scaling factors (fu) for each detector. In order to evaluate 

~cl for each detector the gain and bias for Band 6 are given as: 

Where: 

FBB~d. = interne1 gain for scan j, detector d 

CS~)ct = Shutter counts for scan j, detector d 

6 

(6) 

(7) 
z 

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7 
'I 

r.1 

N1, N2 = Spectral radiances at the limits of the 

detector's response 

If MA,~~ is the digital value for pixel i, scan j, and detector d for the raw image, 

then: 

(8) 

Df\h ,.\..::. i 255" tM.c,a1cJ... CS~A. +(O.QNS -O.l9\} 2S~ /'J i 

10) ~clNZ.-tJJ. FBB cl \ ') N'C.-tJi (9) Jo) 

If we assume that FBBJcl is scene dependent and equal to the average over the 

entire scene, and that CS is essentially constant, then over a large region R of 

the image the average counts measured by all detectors will be roughly equal, that 

is: 

over the large region of interest. 

Then: 

and 

(M~<\pl > -CScl 

+ O.'1";S - O • .1.Cf 

~cl _ f~Bcl. 

~e. <M-<:'6Je > -C Se 

FBBe t O. q tV S - O. 1 '1 

8 

(10) 

(12) 
The ~ coefficients are cnlculated as follows: 

Detector 2 Is taken as the standard and Its ~ value [s set to 0.725 

The average shutter count (C~) and Internal gain (Fi3Bct) are computed for each 

detector over the entire scene. 

The average digital value measured by each detector <~l~ over a large region 

of the scene (256 x 5632 pixels) is computed for the raw image using programs 

DCOPY, DIV PIC, and LIST. 

Using t.his technique the ~ values for thL., image were found to be: 

DET B 

1 0.713135 

2 0.725000 

3 0.714003 

4 0.722340 

Tre radiometric corrections to the image were made as follows: 

The average internal gain FBBd" for each detector was calculated as the average 

over all scans of FBB:?tA .. 

(13) 

Where 

9 
ORIGINAL P/l ~r;: is 

OF POQR QUf.·,l I ('{ 

The gains and biases for each detector are calculated from: 

where: 

c .s .. ,.4 ::: i (S A .• _ ~ .J 4- .s n d .!) 0'-'" 2. '1<l' -Iq °d'I"\ 

The average digital values measured by each detector were calculated 

for the large test region of the image using the gains and biases computed 

this way and are given in the Band 6 part of Figure 2. 

(16) 

U7) 

(18) 

(19) 

Differences between the average detector values for forward and reverse 

scans which are observed here, and which appear greater in other scenes are the 

subject of further investigation. 

January 14, 1983 Grand Bahamas Scene (W014042) 

10 
,{ . q 

ORIGINAL ~\~::;': ::~ 

OF POOR QUj~Ln "'I 

The procedure used for Band 1 in the Terrebonne Bay Scene was tested for all 

the reflective bands for this l::cene. It worked well for Bands 1 through 4, but for 

Bands 5 and 7 the digital counts in the scene are small (of the order of 5 counts 

with many zeros) so that the DIVPIC program could not be used to compute the 

gains for these bands. For bands 5 and 7 then, the detector biases were computed 

liS in the other reflective bands. But the gains were calculated using data taken 

when the detectors viewed the calibration lamps. 

Using this method the gain for any detector is given as 

7 

~s S IG<l.,~ / L~ 

t L~Vdl~ ~:: .J. 

where: 

SIGd,R = The sum over all scans in calibration lamp level of the average 

calibration peak count minus the bias for that scan. 

LEVr!,~ = 'i'he expfj~ted digital count for lamp state and detector .Q J d.. . 

L ~ = The number of scans in lamp state ~ • 

For Band 6 the procedure was identical as that used for the Terrebonne 

Bay Scene, including using the same ~ coefficients. 

The gains which were calculated for all bands for this scene are given 

in Table 1. 

11 

(20) 
TAdLE I 

COMPUTED GAIN FOR THE GRAND BAHAMAS SCENE 

GAINS POR THE REFLECTIVE BANDS 

DET BAND 1 BAND 2 BAND 3 BAND 4 BAND 5 BAND 7 

1 1.005 0.983 0.987 0.990 0.925 0.946 

2 1.015 0.993 1.002 0.994 0.933 0.969 

3 1.020 0.990 0.988 0.984 1.000 0.951 

4 1.021 1.128 0.996 0.989 0.921 0.962 

5 1.012 1.015 0,399 0.962 0.914 0.935 

6 1.005 1.005 0.996 1.010 0.936 0.963 

7 0.995 0.998 0.994 0.985 0.934 0.965 

8 1.006 0.994 0.974 0.937 0.940 0.947 

9 1.000 1.000 1.000 1.000 0.930 0.951 

10 1.011 0.992 0.999 1.033 0.923 0.961 

11 1.005 0.996 0.983 1.007 0.940 0.950 

12 1.011 0.985 1.001 0.949 0.950 0.965 

13 1.011 1.005 0.990 0.967 0.929 0.954 

14 1.013 1..003 0.984 0.951 0.937 0.948 f 

, 

15 1.023 1.010 0.99\ 0.932 0.924 0.944 

16 1.026 0.989 0.985 0.978 0.950 0.975 

Band 6 Geometrical Scaling P actor ~ and A verage Internal Gain PBB 

DET {3 PBB 

1 0.7131 284.940 

2 0.7250 292.346 

3 0.7140 280.984 

4 0.7223 296.132 

(I ' 

12 
'I: 

rIt·, 

New support files for all seven TM bands were prodtweQ for this scene using 

the procedures outlined above for the reflective and thermal bands. The resulting 

support files were applied to the B data for this image by replacing the operational 

fJCROUNGE procedure TMHIST, RLUT, and RADIOM programs with the RADCOR 

prograJIl. This ne w procedure for producing a radiometrically correct image was 

called PSEUDO-SCROUN GE. 

Although the gains for this scene wel'e computed from the image data using 

the DIVPIC program, Table II shows that they are very close to the gains calculated 

for the Terrebonne Bay Scene. The maximum difference between the two sets of 

gains is about 0.5% which translates into a difference of less than I count for image 

pixel values of 200. The fact that the difference between Band 1 gliins computed 

independently for the two scenes were small indicates that it will be possible to 

apply one set of gains to subsequent scenes and not have to recompute new gains 

for each new scene. 

The radiometrica.1~.y corrected images for all bands were analyzed for the 

Grand Bahamas Scene and the preliminary conclusions were as follows: 

1. Detector to detector striping was generally reduced for bands 1,2,4, and 6. 

2. The detector striping in Band 3 was reduced overall, however a crosshr:tching 

pa ttern with pixel values about 2 counts higher than neighboring detectors was 

observed for detector 1. 

3. Computing the gains for Bands 5 and 7 using the method outlined above 

resulted in a more striped final image. Because of this, it was decided that for 

future PSE U DO SCRO UN GE runs the detector gains and offsets which are 

computed by TIPS will be :Jsed for Bands 5 and 7. 

An anomalous scan to scan banding which occurred near large bright targets 

was observed in Bands 1,2,3,and 4 for this scene. It appeared that after the 

detectors had viewed a large cloud, the brightness for the subsequent pixels in the 

scan was lower than for the corresponding pixels in the scans before and after. 

Several regions of the radiometrically corrected image were examined in detail 

and the general pattern which was observed is shown i, -"""ure 3. In addition, the 

follcwi:tg features of this phenomenon were observed: 

13 
TABLE IJ 

COMPARISON OF THE GAINS FOR BAND 1 CALCULATED INDEPENDENTLY FOR 

THE Tr.RREBONNE SA Y AND GRAND BAHAMAS SCENES 

DET TERREBONNE BAY GRAND BAH.A MAS % DIFFERENCE 

1 1.00841:; 1.00473 0.37 

2 1.01838 1.01432 0.34 

3 1.02318 1.02029 0.28 

4 1.0i529 1.02080 0.54 

5 1.01425 1.01192 0.23 

6 1.00759 1..00499 0.26 

7 0.99696 0.99502 0.19 

8 1.00754 1.00625 0.13 

9 1.00000 1.00000 0.00 

10 1.01127 1.01098 0.03 

11 1.00677 1.00503 0.17 

12 1.00791 1.01089 0.29 

13 1.01210 1.01072 0.14 

14 1.01495 1.01330 0.16 

15 1.02584 1.02265 0.31 

16 1.02745 1.02654 0.09 

14 
1. The difference in pixel values between a bright scan and the following dark 

scan is of usually between 2 to 4 counts. 

2. The lower pixel brightness is discernable for up to about 1000 pixels after 

the bright tal'get region has last been viewed. 

3. Data taken during the period when the detectors view the TM shutter seem to 

be affected by the presence of bright targets, with thE' noisiest areas of the shutter 

data corresponding to portions of the image which contain large bright targets such 

as clouds. 

These observations indicate that this striping is caused by the detectors 

becoming saturated when they view a bright cloud, and depress the DC restore 

level. This reduces the bias for scans containing a bright cloud, and striping 

occurs. 

15 

, 
....... 

0' 

BRIGHT 

TARGET 

--. -- -

~ 

-

BRIGHTER DARKER 

FORWARO Sr:I~N 

BRIGHTER 

REVERSE SCAN 

FIGURE 3 - BRIGHT TARGET SCAN TO SCAN BANDING 
References 

1. Study of Spectral/Radiometric Characteristics of the Thematic MapPClr for 

Land Use Applications, W.A. Malila, and M.D. Metz:er, BRIM Report NO. 

164000-3-T, June 30, 1983. 

17 
APPENDIX A 

ANALYSIS OF THE NEW SHUTTER DATA FOR SEVERAL TM SCENES 

Statistics for various combinations of TM shutter or backgrollnd data from 

the new collection window are computed by the BACH software. Twelve seperate 

parameters are computed for each detector and scan in a TM scene, as well as 

scene statistics for each detector. The shutter average, S, is computed as the 

mean of the 16 points before (SB) or the 16 points aiter (SA) the DC restore 

window. Different combinations of odd (forward) scan, SOB, SOA; and even 

(reverse) scan SEB, SEA shutter data averages were combined to form the shutter 

data parameters. 

Printer plots of the 12 shutter data parameters are produced from BACH and 

give every parameter for each scan, or scan pair. In addition BACH computes, for 

every detector and every parameter, the scene average, standard deviation, the 

minimum and maximum. and where they Recurred, and the parameter range. 

January 6, 1983 TERREBONNE BA Y, LA SCENE (W022040) 

Shutter data for TM Band 1 and Band 6 for the January 6, 1983 Terrebonne 

Bay, LA scene were analyzed using BACH. 

Band 1 

Inspection of the printer plots of the 12 shutter data parameters for this 

scene indicated the following: 

o The values of SOB, SOA, SEA; and the SB, SA sequence seem to show 

variations as a function of scan which follow the brightness of the 

image data for this scene. 

o For a number of Scb..'1~ in the scene the shutter counts for detectors 4 

and 12 B"e about 2 counts higher than the average for the rest (If the 

scene. The same pattern of this "noise" is also seen for detectors 8 and 

10, but the magnitude is only about 0.5 counts. 

Figures A-I and A-2 show the average of each of the shutter parameters for 

each detector for this scene. The X axis in each graph is detector number and the 

y axis is average counts. These plots show that for Band 1: 

o Detector 1 is consistently about 0.5 counts higher than the other 

detectors. 

A-I 
I)F PGUK ~\ 'f. J 0",' 

FIGURE A-I - BAND I AVERAGE SHUTTER PARAMETERS JAN 6, 1983 TERREBONNE BAY SCENE ~.OT---~------~--~---r--~--~--~--~~--r---~~~--~--~--~---r~-r--~ 

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OF POOR OUALln' FIGURE A-2 - BAND 1 AVERAGE SHUTTER PARAMETER~ JAN 6, 1983 TERREBONNE BAY SCENE 

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~.O L-~2~~4---b~~8~-'~O---1~2--+'4~-,~o---l.-~~~~--~~---L---l.---~~L-~ 

1)5., A-3 
o Systematic differences in shutter counts between odd and even 

detectors are visible. The difference between odd and even detectors 

appears to become greater with increasing detector number. 

The droop over forward scans (SEA - SOB) averages to about 1 count, 

and droop over reverse scans SOA - SEB averages to about 0 8 count. 

Scan to scan droop over reverse scans appears to inC!rease with detector 

number, but this may be related tl'l the detectors viewing the 

calibration lamps between the time SOA and SEB are measured. 

o For both odd and even scans the average of the shutter counts after the 

D(;; restore region, SA, is greater than the average before, SB. For 

even scans the mean difference is about 0.8 counts, and for odd scans 

the mean difference is about 0.9 counts. 

A-4 

t 

, 
Band 6 

inspection of the printer plots of the shutter parameters show that there is a 

variation in the shutter parameters that is smaller than that in Band 1, but which is 

also a function of the scan number in the scene; and which may reflect the image 

data in the scene. Figures A-3 and A-4 show the plots ' ~ the detector averages of 

the shutter parameters for Band 6. These plots indicate: 

o The difference between the shutter values for detector 1 and the 

average of the other 3 detectors is usually considerably grea ter than 

the differences among detector 2, 3, and 4. That is, detector 1 seems 

to be behaving differentJy from the other three. 

o Scan to scan droop for forward scans averages to about -0.01 counts, 

but the droop for detector 1 is to +0.02 counts And the average for 

dete"tor 2, 3, and 4 is -0.02 counts. The mean d.'oop for reverse scans 

is -0.12 counts. 

o For even scans the difference is shutter counts before and after the DC 

restore period is about 0.11 counts for even scans. For odd scans this 

average difference is +0.18 counts. The average difference for 

detectors 2, 3, and 4 is +0.29 counts While the difference for detector 1 

is nega ti vee 

A-5 
FIGURE A-3 - BAND 6 AVERAGE SHUTTER PARAMETERS JAN 6, 1983 TERREBONNE BAY SCENE 

, I SB I="'A ; auE~\' S~AN! : I : O.'S:,::., : ,-- t2 ... ;~. /- .. -~-........... ····-t···· .. · .-:--. "":'- .+- ~ ... 'jrvl\'~f~B~S .5~ .... ".t- ..••••... 

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+ t, I. . ~:..J. .. ~ V:.,~ ;., ~ ...: ! : 

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1 : " . . .. , dlRIGINAL PAGE :lS.. !o,l!~~~ ~.L 1- '. t·sC~ ._ ... ,.. .L .. ~ IX ;, C)F POOR QUALl1'Y:;: . Oz . ~ 

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2. '3. 4 

l"IFT A-6 
I 

FIGURE A-4 - BAND 6 AVERAGE SHUTTER PARAMETERS JAN 6, 1983 TERREBONNE BAY SCENE 

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'-"-L: • I I i 'I' I! · I ii, I 
Scene Shutter Data Analysis 

Plots of the average shutter data before (SB) and after (SA) the DC restore 

period for each TM scan were produced and evaluated for three scenes for which 

the new images have not yet bee!1 produced. These are images of San Francisco, 

Norman, AR ; and the Atlantic off Virginia. A brief description of the preliminary 

analysis of this data for the reflective bands follows: 

Band 1: 

The shutter counts for detectors 4 and 12 appear to be locked into two 

separate states about 2 counts apart for both SB and SA. This effect was observed 

previously for the Terrebonne Bay Scene, but was not present in the Grand 

Bahamas Scene. The same effect is observed in detE!ctors 8 and 10 but the states 

are about 1 count apart. Detector 1 is higher on average than the other detectors 

by about 0.5 count, and SA is consistantly about 1 count higher than 58 for all 

detectors. Also, even numbered detectors generally have a higher average count 

than odd numbered detectors. 

Band 2: 

Detector 1 is noisi~r and measures an average shutter count value about 0.6 

counts higher than the rest of the detectors for both SB and SA, The value of SA is 

about 0.25 counts higher than both SB and SA. The value of SA is about 0.25 counts 

higher than SB for all detectors, and even detectors are generally higher than odd 

d~tectors for both SB and SA. 

Band 3.~ 

Detectors 16 is the noisiest for both SB and SA, and detector 1 measures the 

highest shutter counts about 0.5 counts above the rest of the detectors. SA is 

about 0.25 counts higher than SB for all detectors, and even detectors measure 

higher than the rest of the detectors. 

A-8 
-

Band 4: 

SA is higher than SB by about a quarter count for all detectors, and even 

detectors are higher than odd for both SB and SA. Detector 1 measures the highest 

shutter values, between 0.25 and 0.5 counts higher than the rest of the detectors. 

Band 5: 

The average values for SA and SB are practically identical except that 

in detectors 1,2,15, and 16 SA is slightly higher than SB. Detector 10 shows the 

most noise. 

Band 7: 

SA and SB are practicRlly identical except for detectors 1 and 16, where 

SA is slightly higher than SB. Detector 7 is the noisies'~ for both SB and SA. 

A-9