62
on
563
(3) Scan-direction Radiance Difference and Relative Radiometric Correction
Visual inspection of raw TM image indicates the existance of average
difference between the forward and reverse scans. The cases of (a) Chicago,
Oct 25, 82 and (b) Washington, Nov 2, 82 are shown in Fig. 6 for Band 4 in
terms of mean and S.D. values of respective image histogram of forward and
reverse scans. From the similar analysis with other scenes, it is known that
the image statistics difference due to scan direction has scene dependence.
The cause of the phenomenon is not known well.
Above mentioned difference in radiometric characteristics due to scan
direction indicates the necessity of separate radiometric correction for forward
and reverse scan data. Such an exeperiment was made using data of Chicago,
Oct 25, 82. Enlarged resultant images are shown in Fig. 7
(a) is the image corrected by conventional method, in which forward and reverse
scan data are handled equally for each detector, while (5) is the image which
was applied with a scan-direction separate radiometric Correction, i.e. applying
radiometric corrections to forward and reverse scan data separately using
the forward and reverse scan data statistics, respectively.
The effect of removing scan-direction average radiance by scan-direction separate
radiometric correction is clearly shown. It turned out that the scan-direction
separate radiometric correction is effective for all bands.
Differaice (F-R) (12.0) >
0.2r BAND 4 ;
Washington a
Nov 2, 82
0.1} |
Washington, Nov 2, 82 = 16.57 fe
o. dg S (11.5)
oO uv
ooo??? o
SC ~ Ld
0.0 > e
oO = e
oO E Li
= bod = 2 Chi
e (11.0 icago_
mpd? 2 ei^ Oct 25,8
-0.1f ° à > AR
? . e
Chicago, Oct 25, 82 15.5 : j s
-0.2- 15.5 16.0 18.5
(11.0) (11.5) (12.01
Detecta No. 2 4 6 8 10 12 ]4 I8
FOWARD SCAN
Fig.6 Scan-direction radiance difference for Band 4 detectors
Left: Mean difference, Right: Standard Deviation
(a) Conventional correction (b) Scan-direction separate correction
Fig.7 Relative radiometric correction (8and 4, enlarged)