SAR interferometry using ALOS-2 PALSAR-2 data for the Mw 7.8 Gorkha, Nepal earthquake

Ryo Natsuaki,Takeo Tadono,Hiroto Nagai,Masanobu Shimada,Takeshi Motohka,Shinichi Suzuki,Masato Ohki,Manabu Watanabe,Rajesh B Thapa

doi:10.1186/s40623-016-0394-4

Abstract

The Advanced Land Observing Satellite-2 (ALOS-2, “DAICHI-2”) has been observing Nepal with the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) in response to an emergency request from Sentinel Asia related to the Mw 7.8 Gorkha earthquake on April 25, 2015. PALSAR-2 successfully detected not only avalanches and local crustal displacements but also continental-scale deformation. Especially, by the use of the ScanSAR mode, we are able to make interferograms that cover the entire displacement area of the earthquake. However, we did encounter some fundamental problems with the ScanSAR and incorrect settings of PALSAR-2 operation that have now been fixed. They include (1) burst overlap misalignment between two ScanSAR observations, which limits the number of pairs available and the quality of the interferogram, (2) non-crustal fringes which are derived from co-registration error and/or ionospheric effect and, (3) incorrect setting of the center frequency in the Stripmap beam F2-6. In this paper, we describe their problems and solutions. The number of interferometric pairs are limited by (1) and (3). The accuracy of the interferograms are limited by (2) and (3). The experimental results showed that current solutions for (2) and (3) work appropriately.

Highlights

Interferometric Synthetic Aperture Radar (InSAR) becomes one of the essential technologies for rapid analysis of ground displacements (Boerner 2003)
The Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard the Advanced Land Observing Satellite-2 (ALOS-2, “DAICHI-2”) is the latest L-band spaceborne SAR operated by the Japan Aerospace Exploration Agency (JAXA) (Arikawa et al 2014; Shimada and Osawa 2012)
ScanSAR-ScanSAR interferometry we report the performance of PALSAR-2 ScanSAR-ScanSAR interferometry for the monitoring of the Mw 7.8 Gorkha, Nepal earthquake on April 25, 2015 (USGS 2016a)

Summary

Introduction

Interferometric Synthetic Aperture Radar (InSAR) becomes one of the essential technologies for rapid analysis of ground displacements (Boerner 2003). Combined with real-time GPS monitoring, it enables us to observe and assess the ground displacement over large areas. The ALOS-2 has worldwide observation scenarios for various missions, e.g., detection of deformation, monitoring forest change, and monitoring sea ice. Its precise orbit control and the gallium nitride (GaN) high-power transmitter/receiver enable accurate analyses in high spatial resolution. Once a large disaster occurred, ALOS-2 is so planned to observe the affected area in every revisit cycle for specific duration. As a duty of the disaster response mission, ALOS-2 was used to observe the area affected by the Mw 7.8 Gorkha, Nepal earthquake and its aftershocks. These results were provided to Nepal through, for example, the International Charter on Space and Major Disasters, Sentinel Asia, and International

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Conclusion