Detection of traces of pyroclastic flows and lahars with satellite synthetic aperture radars

Abstract

To assist volcanic hazard mitigation, detection of traces of pyroclastic flows and lahars were attempted by using satellite synthetic aperture radars (SAR). If such information can be obtained rapidly, it can help early warnings of the next pyroclastic flows and lahars because these flows often occur repeatedly at similar locations. Using three analytical approaches, two satellite SAR data, namely, the L‐band SAR of the Japanese Earth Resource Satellite (JERS‐1) and the C‐band SAR of the European Remote Sensing Satellite (ERS‐1), were tested. These approaches include subtraction of SAR backscatter coefficients, SAR coherence, and SAR interferometry (InSAR). These approaches were validated in the Unzen Volcano with digital elevation model (DEM) subtraction images created from aerial photographs. As a result, it was found that the coherence approach with JERS‐1 SAR was highly capable of detecting the traces of the pyroclastic flows and lahars. The traces appeared as either one of two characteristics on the coherence images: low coherence caused by the new traces formed in between a pair of observations or high coherence caused by the recent traces formed before a pair of observations. In contrast, we could not validate applicability of the backscatter approach or the InSAR approach.

Acknowledgments

The JERS‐1 SAR data used in this study were provided by the National Space Development Agency of Japan (NASDA) and the ERS‐1 SAR data were provided by the European Space Agency (copyright ESA 1996) via Remote Sensing Technology Center of Japan (RESTEC). The DEM data and the aerial photograph were provided by the Unzen Restoration Office of the Ministry of Land, Infrastructure and Transport of Japan. The authors are grateful for the useful comments and suggestions from Dr Kuniaki Miyamoto of the University of Tsukuba and Dr Takao Yamakoshi of the Public Works Research Institute of Japan. This study was supported by the Subsidy for Research and Development (1999) of Sabo Technical Center, Japan.

Notes

Note: Only major events are presented.

E: eruption; L: lahar; P: pyroclastic flow; AV: Akamatsu Valley; MR: Mizunashi River; NR: Nakao River; OV: Oshiga Valley.

All the images have been registered as path 80 and row 246.

InSAR: interferometry; Level 2.1: backscatter image; SLC: single look complex image.