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Synthetic aperture radar (SAR) aboard a satellite irradiates observation microwave pulse toward the earth and the microwave pulse arriving at the earth's surface scatters every direction. The backward scattering component of it is received on the antenna of the satellite. The satellite SAR allows us to observe the earth during 24 hours without being influenced by the weather because of this observation principle. On the other hand, since the satellite needs to irradiate the earth's surface not vertically downward but obliquely downward with the observation microwave pulse, radar-shadow area, at which the observation microwave pulse does not arrive due to obstruction of the other higher place, appears depending on geographical features. However, since the observation data of the satellite SAR is recorded in order of arrival at the receiver, in other words in order of distance from the emitter, it is quite difficult to extract the radar-shadow area directly from the observation data. Therefore, when we use the satellite SAR image to detect occurrence of a natural disaster, we might carry out useless calculation about a steep valley bottom region which has a higher possibility of occurrence of the land slide. This is because the steep valley bottom region is often included in the radar-shadow area, that is the no-data area. If we can know about the radar-shadow area corresponding to the latest observation data, improvement of the estimation precision of occurrence of a natural disaster by using satellite SAR image can be expected. Furthermore, since the SAR satellite flies on a fixed orbit, the information of the radar-shadow area is suitable to construct its database for permanent use. In this paper, we propose a method for efficiently constructing a database for radar-shadow cast by ALOS-2/PALSAR- 2 (a satellite operated by JAXA) by using high resolution (5 meters mesh) DEM data as a pre-process.
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