regions, and the edge lines of boundaries are still pre- 
served. By the use of Cy and Cmaxz in the Gamma 
MAP filter, the image becomes unclear due to the over 
smoothing effect. The theoretical estimates Cy and 
Cmaz are apparently higher compared with Fig. “1. 
The filtered 3-look image shown in Fig. 3(b) was also 
obtained by the same algorithm as that in Fig. 2(b). 
Though the speckle in the image is reduced, the spa- 
tial resolution is reduced as compared with the 1-look 
image. 
5. CONCLUSIONS 
The two thresholds of Cy and C,,,, in reducing 
speckle for 1-look, 2-look, and 3-look of JERS-1/SAR 
images have been estimated for the first time in the 
present report. Then, the filtered images of 1-look, 
2-look, and 3-look processes by use of these thresh- 
olds were obtained and the speckle was successfully 
reduced. The thresholds estimated from the Gamma 
MAP filter have been applied to ERS-1/SAR and C- 
SAR images so far. 
The theoretical estimates of the thresholds for JESR- 
1/SAR images are apparently high. The discrepancy 
between the theoretical and the observed estimates for 
JERS-1/SAR may be due to the assumption of the 
Gamma MAP filtering. The speckle and the radar 
reflectivity are both assumed to be a Gamma distri- 
bution in the Gamma MAP filter. However, the dis- 
tribution of the coefficient of variation C(t) of JERS- 
1/SAR could be estimated as a Gaussian distribtion 
from Fig. 1(a), (b). 
265 
6. ACKNOWLEDGMENTS 
The present work was partially supported by a 
Grant-in-Aid for Science Research (C) [1995-1996, 
No.07680497] from the Ministry of Education of 
Japan. 
7. REFERENCES 
kuan, D.T., Sawchuk, A.A., Strand, T.C., and 
Chavel, P., 1985, Adaptive noise smoothing filter for 
images with signal-dependent noise, IEEE Trans. Pat- 
tern Anal. Machine Intell., Vol.PAMI-7, pp.165-177. 
Lopes, A., Touzi, R., and Nezry, E., 1090, Adaptive 
Speckle Filters and Scene Heterogeneity, IEEE Trans. 
Geosci. Remote Sensing, Vol.GE-28, No.6, pp.992- 
1000. 
Lopes, A., Nezry, E., Touzi, R., and Laur, H., 1993, 
Structure Detection and Statistical Adaptive Speckle 
Filtering in SAR Images, Int. J. Remote Sensing, 
Vol.14, No.9, pp.1735-1758. 
Nezry, E., Lopes, A. and Touzi, R., 1991, Detection 
of Structural and Textural Features for SAR. Images 
Filtering, Proceedings of IGARSS ’91, pp.2169-2172. 
Touzi, R., Lopes, A. and Bousquest, P., 1988, A Sta- 
tistical and Geometrical Edge Detector for SAR Im- 
ages, IEEE Trans. Geosci. Remote Sensing, Vol. GE- 
26, pp. 764-773. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996