The observation system for Unzen/Fugen by JRRS-1

利用日本宇宙开发事业团JERS-1的合成孔径雷达（SAR）传感器对日本岛原地区的云仙/富源火山灾害进行了精确分析。通过各种方法和传感器对云仙/富源火山锥进行了观测，以检查火山活动。通过以前对熔岩穹丘的研究，我们知道熔岩穹丘会在几天内长大并坍塌。然而，由于气候潮湿，火山烟雾较深，用以往的卫星和机载光学传感器精确观测火山锥是相当困难的。另一方面，SAR传感器的观测可以在任何一天进行，我们获得了该地区的各种CCT（PATH-080，ROW-246，LEVEL=0/RAW-DATA），包括火山爆发前和火山爆发后的场景。JERS-1/SAR遥感器再现图像的空间分辨率为12.5m，足以观测火山锥内的熔岩穹丘。为了得到更清晰的SAR图像，我们完成了原始数据（level=0）处理系统，并对JERS-1 SAR图像进行了增强处理，从原始数据（level=0）得到完整的图像。针对JERS-1/SAR图像与EERS-1/SAR图像在距离向和方位向压缩过程中的旁瓣抑制问题，分别采用了Kasier窗、Hamming窗、Hanning窗、广义Hanning窗和矩形窗等窗加权函数。采用Hamming窗可以获得最佳的SAR图像质量，采用Lopes等提出的11 × 11窗的最大后验（MAP）滤波al.isSAR图像进行相干斑噪声抑制。对重定过程中变异系数值的两个阈值Cu和Cmax进行了检验，尤其是Cmax。发现所获得的图像质量特别依赖于Cmax。

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.