Effects of ash layers of the 2004 Grímsvötn eruption on SAR backscatter in the accumulation area of Vatnajökull

Abstract

AbstractThe applicability of volcanic ash deposits on Vatnajökull ice cap, Iceland, as a time reference marker for measuring accumulation by the analysis of time sequential SAR backscatter data was investigated. A volcanic eruption at Grímsvötn caldera, a subglacial volcanic system beneath Vatnajökull, deposited an ash layer north of the vent in early November 2004. This ash layer covered a V-shaped area of ∽88km2 on the glacier surface. The ash fall, which was subsequently buried by snow, reveals a distinct backscatter signal in SAR images. In total, the σ0 backscatter values of 40 ENVISAT-ASAR images were analyzed, covering two post-eruption accumulation periods (4 November 2004 to 31 March 2005 and 25 October 2006 to 14 March 2006). Significant differences over time were observed in the SAR backscatter signals over the deposited ash, which appear to be related to the snow accumulation history. The backscatter signals were compared to meteorological conditions at the time of SAR acquisition and to accumulation data derived from two snow pits, one located within the ash fall. A linear regression analysis between the accumulation data and the SAR backscattering coefficient results in high R2 confidence values (>0.8), indicating that the SAR data can be used for estimating the areal accumulation distribution in areas with an existing ash layer.