| Research Abstract |
Unzen/Fugen volcanic disaster in Shimabara region Japan, is precisely analized by Synthetic Aperture Radar (SAR) sensor of, JERS-1 by NASDA.The volcanic cone of Unzen/Fugen is observed by various methods and sensors to examine an activity of the volcano. By the previous examination on lava domes, it is known that a lava dome will grow up and collapse within a few days. However, it is quite difficult to observe a volcanic cone precisely by optical sensors such as previous satellite ones and airborne ones because of much wet weather and deep volcanic fumes. On the otherhand, the observation by SAR sensor is possible in any day.
We obtained various CCT of this area (PATH-080, ROW-246, LEVEL=0/RAW-DATA), including scenes before the eruption and after that. The spacial resolution of a reproduced image by JERS-1/SAR sensor is 12.5m, which is sufficient to observe a lava dome in the volcanic cone. In order to obtain clearer a SAR image, we complete raw data (level=0) processing system.
SAR images by JERS-1 have been enhanced in several processes of obtaining complete image from raw data (level=0). It seems that image qualities by JERS-1/SAR are different from those by EERS-1/SAR.Several window weighting functions are tried to SAR images to suppress sidelobe in range and azimuth compression procedures, respectively, which include a Kasier, Hamming, Hanning, general Hanning, and rectangular windows. The best SAR image quality is obtained by the Hamming window.
The Maximum A Posteriori (MAP) filter with 11x11 window by Lopes et al.is applied to obtained images for the speckle noise reduction. Two thresholds, Cu and Cmax, on the coefficient of variation value in the revaluating process are examined, especially Cmax. It is found that the image qualities obtained are particularly depend on Cmax.
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