Moving from Temporal Coherence to Decorrelation Time of Interferometric Measurements Exploiting ESA?s SAR Archive

Abstract

Interferometric coherence can be considered as an expression of temporal decorrelation. It is understood that interferometric coherence decreases with time between SAR acquisitions because of changes in surface reflectivity, reducing the quality of SAR phase measurements. This is an intrinsic characteristic of the design of SAR systems that has a significant contribution at longer time scales. Although in the past there was not sufficient amount of SAR data to extract robust statistical metrics for decorrelation, in the present study it is demonstrated that tailored analysis of interferometric coherence exploiting the large SAR archive available by the European Space Agency (ESA), enables the accurate quantification of temporal decorrelation. A methodology to translate the observed rate of coherence loss into decorrelation times over a volcanic landscape, namely the Santorini volcanic complex is the subject treated in this study. Specifically, a sensitivity analysis was performed on a large data stack of interferometric pairs to quantify at a pixel level the time beyond which the interferometric phase becomes practically unusable due to the effect of decorrelation. Though the dependence of decorrelation on various land cover/use types is already documented the provision of additional information regarding the expected time of decorrelation is of practical use especially when EO data are utilized in operational activities. The performed analysis is viewed within the improved capacity of current and future SAR systems, while underlining the necessity for exploitation of archive data.