Japanese L‐Band Radar Improves Surface Deformation Monitoring

Abstract

The termination of the Japanese Earth Resources Satellite (JERS 1) in October 1998 and the subsequent delay of the launch of its successor, the Advanced Land Observing Satellite (ALOS), caused a troublesome interruption in the availability of L‐band synthetic aperture radar (SAR) data to the several research institutions and government agencies in Japan that had been studying surface deformation by SAR techniques since the Japan Aerospace Exploration Agency (JAXA, formerly the National Space Development Agency of Japan) launched JERS 1 in 1992.SAR is an all‐weather type of sensor that is suitable for the derivation of disaster mitigation information, and—as shown, for example, by Massonnet and Feigl [1998]—interferometric SAR (InSAR) techniques can be used to derive precise ground surface deformation maps associated with earthquakes, volcanism, landslides, and slow tectonic motions, as well as with oil pumping and water withdrawal, with fine spatial accuracy. The electromagnetic similarity (coherence) between two SAR images acquired over the same area before and after an event—for instance, an earthquake—is measured, and where appropriately high coherence is achieved, the change in the distance between SAR and the ground target can be derived with fine (centimeter) precision. Both airborne and spaceborne SAR systems are commonly used, although the latter often are preferred due to their long‐term monitoring capacity and global coverage.