Variations in the Microwave Backscatter From the Ocean Surface Induced by the 2004 Sumatra-Andaman Tsunami
Abstract
A timely and dependable assessment of a tsunami threat requires detection of the tsunami wave in the open ocean, where its amplitude is much smaller than it is close to shore. By complementing traditional seismic data and point measurements of hydrostatic pressure at the ocean bottom as provided by the Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys network, wide-area satellite observations of tsunami manifestations can potentially improve the accuracy and timeliness of tsunami forecasts, increase the lead time of tsunami warnings, decrease the probability of false alarms, and help to avoid unnecessary evacuations. The first detailed measurements of the tsunami effect on sea surface height and radar backscattering strength in the open ocean were obtained from satellite altimeters during passage of the 2004 Sumatra- Andaman tsunami. Of the tsunami manifestations in the deep ocean, variations in ocean surface roughness are most relevant to early tsunami detection from space provided these can be revealed by microwave sensors, which have broad surface coverage across the satellite ground track. However, there remains considerable uncertainty regarding the physical mechanisms and magnitude of tsunami-induced roughness variations and the possibility of their detection against the background of potentially stronger roughness variation due to other geophysical processes. In this study, we concurrently employ radar backscattering strength and sea surface height data obtained by the Jason-1 altimetric satellite. Through statistical analyses of multiple years of satellite altimeter observations, we demonstrate that the Sumatra-Andaman tsunami induced distinctive variations in ocean surface roughness, which are measurable with microwave sensors already in orbit. Statistical confidence of this conclusion is found to be better than 99.9%. The magnitude and spatial structure of the observed variations in radar backscattering strength are consistent with hydrodynamic models predicting variations in the near-surface wind across the tsunami wave front. Our results provide insights into the physics of wave- wind interaction and methods for retrieval of a tsunami signal in radar backscattering data. While further research is required to demonstrate tsunami detection with side-looking radars and scanning microwave radiometers, our findings suggest that such sensors may be an important element in a future global system for tsunami detection and warning.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS43D1320G
- Keywords:
-
- 4504 Air/sea interactions (0312;
- 3339);
- 4564 Tsunamis and storm surges