Development of a New Detection Technique for the Ground Deformations associated with Volcanic Activity

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Fundamental aim of this project is to demonstrate the efficiency and quickness of a new detection technique utilizing the Airborne Repeat-Pass Differential Interferometric Synthetic Apature Radar (Airborne RP D-INSAR) for obtaining an accurate detection of group deformations associated with volcanic activity, especially in case of anticipated activity changes during an eruption sequence. In principle, using the Airborne RP D-INSAR,the detection method is quite similar to the one in the satellite D-INSAR.There are, however, several additional requirements to realize the Airborne RP D-INSAR in comparison to the ones in satellite D-INSAR :(1) an accuracy of repeat-pass orbit must typically be within ten meters for the X-band SAR system due to the limitation of the interferometric baseline condition,(2) very precise antenna motion data, typically within a few millimeters accuracy in every seconds, are required for the INSAR processing, and so on.In addition, a relatively small aircraft is … More required to realize the capability of quick response for data acquisition and to make inexpensive system for the case of on-going eruptive activity, as well as other geological events such as the occurrence of earthquakes, unstable slope, upheaval and subsidence of the ground, and so on.In order to overcome these requirements, the differential GPS navigation system adding to the conventional GPS and INS (inertial navigation system) is installed for more accurate repeat-pass flight control and corner reflectors are distributed in the target area for obtaining the sufficient antenna motion compensation data.Results at the Okegawa test site near the local airport, Saitama prefecture, indicate that this system is accurate enough, if it were appropriate wether conditions (moderate wind speed and without rain).Another test site was chosen near the frank of Azuma volcano, Fukushima prefecture, where temporal GPS measurements have shown the movements of kilometer-size blocks of about a few centimeters per day. Results for this experiment showed that the repeat-pass orbit control is accurate enough, although it needs additional ground control points by adding several corner reflectors in the target area.This project has shown, for the first time in the world, the efficient applicability of using a small (propeller) aircraft for the Airborne RP D-INSAR,although the experiments made in this project were only performed in the moderate wether conditions and one or two day's interval.Although considerable problems would, however, remain in every procedure to demonstrate more clearly the efficiency of this method, the essential problems have overcome and results are enough to proceed to the next step, i.e., this method needs to apply to the actually deforming field such as east Izu peninsula and now erupting volcanoes. Less