Towards monitoring groundwater‐dependent ecosystems using synthetic aperture radar imagery.

Mapping of groundwater‐dependent ecosystems (GDEs) relies largely on assumption‐laden evaporation models, and few global, direct, and real‐time monitoring techniques exist. We propose a new synthetic aperture radar imagery‐derived index, SARGDE, to identify and monitor these ecosystems across Australia. The index captures vegetation reliance on groundwater during dry periods by estimating the relative stability of foliage and branch structure from the vertical/horizontal cross‐polarized band and InSAR coherence. SARGDE is tested over two contrasting study sites in Australia. To build and verify the index, a total of 90 Sentinel‐1 interferometric wide images are processed and stacked in two data‐cubes. GDE response to the SAR signal is explored using a non‐linear dimension reduction algorithm. Relevant statistical parameters are derived from data‐cubes and combined to form the index. As the index relies on a 1‐year time series of globally, freely available, and cloud‐insensitive SAR imagery, SARGDE offers unprecedented capabilities for large‐scale, annual monitoring of GDEs. Such monitoring will aid reconciliation of human and ecosystem groundwater needs by acting as a systematic monitoring tool, helping policy makers to assure ecosystem sustainability where impacts related to mining, agriculture, or climate change may occur. [ABSTRACT FROM AUTHOR]