remote sensing Article Detection and Quantification of Irrigation Water Amounts at 500 m Using Sentinel-1 Surface Soil Moisture Luca Zappa 1,* , Stefan Schlaffer 1 , Bernhard Bauer-Marschallinger 1 , Claas Nendel 2 , Beate Zimmerman 3 and Wouter Dorigo 1 1 Department of Geodesy and Geoinformation, TU Wien, Wiedner Hauptstrasse 8, 1040 Vienna, Austria;
[email protected] (S.S.);
[email protected] (B.B.-M.);
[email protected] (W.D.) 2 Research Platform Data Analysis and Simulation, Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalderstrasse 84, 15374 Muencheberg, Germany;
[email protected] 3 Forschungsinstitut für Bergbaufolgelandschaften e.V., Brauhausweg 2, 03238 Finsterwalde, Germany; b.zimmermann@fib-ev.de * Correspondence:
[email protected]; Tel.: +43-1-58801-12289 Abstract: Detailed information about irrigation timing and water use at a high spatial resolution is critical for monitoring and improving agricultural water use efficiency. However, neither statistical surveys nor remote sensing-based approaches can currently accommodate this need. To address this gap, we propose a novel approach based on the TU Wien Sentinel-1 Surface Soil Moisture product, characterized by a spatial sampling of 500 m and a revisit time of 1.5–4 days over Europe. Spatiotemporal patterns of soil moisture are used to identify individual irrigation events and estimate irrigation water amounts. To retrieve the latter, we include formulations of evapotranspiration and drainage losses to account for vertical fluxes, which may significantly influence sub-daily soil Citation: Zappa, L.; Schlaffer, S.; moisture variations. The proposed approach was evaluated against field-scale irrigation data reported Bauer-Marschallinger, B.; Nendel, C.; by farmers at three sites in Germany with heterogeneous field sizes, crop patterns, irrigation systems Zimmerman, B.; Dorigo, W.