The observation system for Unzen/Fugen by JRRS-1

利用日本NASDA公司的合成孔径雷达(SAR)传感器JERS-1对日本岛原地区的未增/富根火山灾害进行了精确的分析。通过各种方法和传感器观测未增/富根火山锥，以检测火山的活动性。通过之前对熔岩穹顶的检查，人们知道熔岩穹顶会在几天内长大并坍塌。然而，由于多潮湿的天气和深厚的火山烟雾，利用以前的卫星和机载光学传感器等光学传感器很难精确观测到火山锥。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(路径-080，行-246，Level=0/原始数据)，包括喷发前和喷发后的场景。JERS-1/SAR传感器再现的图像的空间分辨率为12.5m，足以观测到火山锥中的熔岩穹顶。为了得到更清晰的合成孔径雷达图像，我们完成了原始数据(Level=0)处理系统，对JERS-1的SAR图像进行了多次增强处理，从原始数据(Level=0)获得完整图像。JERS-1/SAR的图像质量似乎与EERS-1/SAR的有所不同。我们尝试了几种窗口加权函数来抑制SAR图像的距离和方位旁瓣，其中包括Kasier窗、Hamming窗、Hning窗、一般Hning窗和矩形窗。通过汉明窗获得最佳的合成孔径雷达图像质量，并利用Lope等人提出的11×11窗的最大后验概率(MAP)滤波法对得到的图像进行相干斑噪声抑制。考察了重估过程中变异系数的两个临界值，特别是Cmax。结果表明，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.