The observation system for Unzen/Fugen by JRRS-1

利用NASDA的JERS-1型合成孔径雷达（SAR）传感器对日本岛原地区的云仙/富根火山灾害进行了精确分析。通过各种方法和传感器观察云禅/富根的火山锥，以检查火山的活动。通过之前对熔岩穹窿的考察，我们知道熔岩穹窿会在几天内形成并坍塌。然而，由于天气潮湿，火山烟雾深，以往卫星和机载的光学传感器很难对火山锥进行精确观测。另一方面，SAR传感器可以在任何一天进行观测。我们获得了该地区的各种CCT (PATH-080, ROW-246， LEVEL=0/RAW-DATA)，包括喷发前和喷发后的场景。由JERS-1/SAR传感器重建的图像空间分辨率为12.5m，足以观测火山锥内的熔岩穹丘。为了获得更清晰的SAR图像，我们完成了原始数据（level=0）处理系统。JERS-1的SAR图像在原始数据获得完整图像的几个过程中进行了增强（水平=0）。JERS-1/SAR的图像质量与ers -1/SAR的图像质量存在差异。在距离和方位角压缩过程中，分别尝试了几种窗口加权函数来抑制SAR图像的副瓣，其中包括Kasier， Hamming, Hanning， general Hanning和矩形窗口。采用汉明窗获得的SAR图像质量最好。利用Lopes等人设计的11x11窗口的MAP （Maximum A Posteriori）滤波器对得到的图像进行散斑降噪。考察了重估过程中变异系数值的两个阈值Cu和Cmax，特别是Cmax。结果表明，所获得的图像质量与Cmax的关系尤为密切。

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.