Tracking Centimeter‐Scale Water Level Changes in Swedish Lakes Using D‐InSAR

Lakes are valuable water resources that support aquatic and terrestrial ecosystems and supply fresh water for the agricultural, industrial, and urban sectors worldwide. Although water levels should be tracked to monitor these services, conventional gauging is unfeasible in most lakes. This study applies Differential Interferometric Synthetic Aperture Radar (D‐InSAR) to estimate small water level changes, less than 2 cm, in Swedish lakes over 6‐day intervals. We validated the method across the shores of 30 Swedish lakes with gauged observations in 2019. We used Sentinel‐1A/B images with a 6‐day temporal separation to construct consecutive interferograms and accumulated the phase changes in pixels of high coherence to build a time series of water levels. We find that the accumulated phase change obtained by D‐InSAR replicates the magnitude of water levels in seven lakes in Southern Sweden, where water levels change slowly, less than 2 cm per 6‐day period, as validated by in‐situ gauges. In addition, this study demonstrates the application of D‐InSAR to estimate the long‐term direction of water level change (i.e., increase or decrease) in all 30 lakes. This work reveals the utility of high temporal resolution water level observations in support of other satellite water level instruments such as conventional altimeters and the recently launched Surface Water and Ocean Topography Mission.