How far can be SAR considered a tool for mountain hydrology?

摘要

Accurate information about soil moisture content (SMC) in mountain catchments is of great importance in hydrological applications, agriculture and climate change impact analysis. In the last two decades microwave remote sensing sensors such as Synthetic Aperture Radar (SAR) have been deeply exploited for surface SMC estimation. However, obtaining reliable predictions of fine-scale spatial and temporal patterns of SMC in mountain areas is still challenging due to the extreme variability in topography, soil and vegetation properties. In this contribution we analyze the spatial and temporal dynamic of surface SMC of alpine meadows and pastures with different techniques: (Ⅰ) a network of fixed stations; (Ⅱ) field campaigns with mobile ground sensors; (Ⅲ) SMC retrieval from RADARSAT2 SAR images; (Ⅳ) simulations using the GEOtop 2.0 hydrological model. The strength and the weaknesses of the different estimation techniques are evaluated and the physical controls of the observed SMC patterns are analyzed. Results show that SAR SMC estimation corresponds well to the spatial ground surveys, but shows different patterns with respect to the model, especially for irrigated meadows. In fact, SAR patterns reflect vegetation, soil type and topography. Model output is in agreement with fixed stations observations, but it shows less spatial variability compared to SAR. Differences are likely due to the difficulties to know with sufficient spatial detail model parameters and irrigation amount. Therefore, results suggest that SAR products have a good ability to reproduce small-scale SMC patterns in mountain regions, thus complementing the ability of the hydrological model to predict temporal variations of SMC.