70 
DC restore (ADC) from the previous scan, and the average calculated before DC restore (BDC) from the current scan, a linear 
interpolation was performed to determine and remove the bias at each pixel location on the current scan. The first scan of an 
image was processed with the original technique and window w6 since no previous scan data was available. 
Notethatthe beginning of each darkshutter window does not occur simultaneously for every detector. Because of the shutter 
mechanism's configuration, detector one "sees" the dark shutter before detector sixteen in reverse scans. Inthat case window 
placement must be shifted slightly in time for each detector to obtain the proper, corresponding shutter values. Table 1 
presents the locations of the final extraction windows chosen for Landsat 5. 
  
  
  
  
SHUTTER EXTRACTION WINDOWS 
DI ANN BEFORE DC RESTORE START | AFTER DC RESTORE START NO. OF MINOR 
MINOR FRAME MINOR FRAME FRAMES 
Forward 109 538 52 
Reverse 342 728 (Det. 1) - 781 (Det. 16) 52 
  
  
  
  
  
  
Table 1. Final Landsat 5 TM shutter extraction parameters 
6. RESULTS 
The previous processing scheme was tested on the following Landsat 5 images. 
WRS Path=188 Row=041 Libyan Desert collections: 
8 September, 1984 
29 August, 1986 
1 September, 1987 
9 September, 1990 
27 August, 1991 
WRS Path = 033 Row = 033 Colorado Springs: 27 July, 1985 
WRS Path = 172 Row = 066 Zambia: 20 June, 1984 
WRS Path = 172 Row = 071 Zambia: 20 June, 1984 
WRS Path = 172 Row = 072 Zambia/Zimbabwe: 20 June, 1984 
WRS Path = 172 Row = 076 Botswana: 20 June, 1984 
Unfortunately, the pre-1991 Libyan Desert images provided shutter data that was pre-averaged over the window designated 
in the Landsat 5 Long Term Parameter File, thus making a analysis of those images with the new window impossible. 
However, it was still possible to evaluate the impact of the newly calculated gain coefficients on levels of streaking in all of the 
images. The new detector gain coefficients calculated from the earlier1984 Zambian image can be found in Table 2. Figure 3 
provides a sample comparison of the relative detector gains provided in the Long Term Parameter file with the image, to the 
detector gains determined fromthe equalization procedure withthe 1991 Libyan desert scene and the 1984 scene of Zambia. 
The 1984 and 1991 equalization values are virtually identical while the Long Term Parameter values are clearly different 
graphically indicating the reason for the streaking in images produced with the Long Term Parameter gains and that the 
relative gains of the detectors have been extremely stable over many years. 
Streaking performance was consistently good across all years and for all of the reflective bands exceptband 5, notbecause of 
an inherent deficiency in the process, but because data were unavailable for determining new coefficients for band 5 since it 
saturated in the 1991 image. A quantitative determination of streaking (here defined as the difference between the average 
value of one line from one detector and the average value from the two surrounding lines from two adjacent detectors) was 
sometimes difficult to establish because of scene content. However, residual streaking values varied from a high of less than 
0.5DNtoalowof 0.015 DN. Band 2 consistently provided the highest amount of residual streaking. More variation of residual 
streaking was seen from band to band than from image to image. 
Itwas also discovered during the study that residual streaking levels were so small that the quantization of the final pixel values 
to 8 bits (256 gray levels) from the calculated real numbers was actually serving to increase visible streaking. An along track 
profile through a lake in the Colorado Springs image is presented in Figure 4 quantized to 8 bits and 15 bits. The additional, 
stairstep variations displayed in the 8 bit quantized profile clearly serve to exacerbate small differences and cause streaking 
and striping. 
Since striping compensation was calculated on a scan by scan basis using only dark shutter data, its magnitude is virtually 
independent of the equalization process. With very little uniform image data accompanied by raw shutter data, residual 
striping has also been very difficult to quantify. Using 15 bit quantization, the only way to effectively judge the degree of residual 
striping is by visual softcopy inspection and a contrast stretch of from 20 to 80 times (i.e. mapping 8 DN into 256 gray levels). 
The best estimates of performance with these procedures placed striping (which was defined simply as the average difference 
between two adjacent scans) at an average of approximately 0.15 DN, with a maximum of about 0.5 DN. Striping levels after 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop “From Pixels to Sequences”, Zurich, March 22-24 1995 
  
  
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