Using satellite radar interferometry to delineate burn area and detect sediment accumulation, 2018 Montecito disaster, California

Abstract

The Thomas Fire burned slopes above Montecito, California in December 2017, setting the stage for debris flows and flash floods in response to precipitation that exceeded a threshold intensity and duration. A narrow cold frontal rainband storm occurred on January 9, 2018, that exceeded the threshold and caused a disaster in Montecito, killing 23 people, injuring many others, destroying residential buildings, and community infrastructure. The Geotechnical Extreme Event Reconnaissance (GEER) Association mobilized a team to document the damage and geomorphic effects. The potential value of the European Space Agency Copernicus Sentinel Synthetic Aperture Radar Satellite to detect and quantify erosion and deposition was recognized and an environmental scientist skilled with satellite radar interferometry therefore accompanied the GEER team. The Sentinel satellite data were obtained from satellite passes in late November, late December, and late January, which permitted constructions of interferograms that showed the effect of the fire before the January 9 storm and the effects of the storm. The interferometric results display an exact boundary compared to the burn perimeter determined by fire response teams. An interferometric change model constructed using post-fire pre-storm and post-storm Sentinel synthetic aperture radar scenes shows areas interpreted to be possible deposition and erosion. The immediate post-disaster search, rescue, and recovery activities resulted in substantial sediment removal from deposition areas which could not be captured by the available radar coverage.