Integrated study of water levels and water storage variations using GNSS-MR and remote Sensing: A case study of Sarez Lake, the world's Highest-Altitude dammed lake

Sarez Lake, recognized as the world's highest-altitude dammed lake, necessitates meticulous monitoring of dam deformation, lake water levels, and water storage fluctuations to ensure its safety. In pursuit of this critical objective, a Global Navigation Satellite System (GNSS) monitoring network has been established around the lake to compute real-time station coordinates for deformation monitoring. GNSS Multipath Reflectometry (GNSS-MR) technology has been introduced as an innovative approach, enabling water level retrieval through conventional GNSS geodetic receivers. However, the complex and rugged terrain surrounding Sarez Lake poses challenges to the application of GNSS-MR in this region. This research is dedicated to addressing the challenges posed by the limited available elevation range selection and the retrieval of inter-site water level combinations in such demanding terrain. It proposes a novel method for effectively discerning valid Signal-to-Noise Ratio (SNR) arcs and an inter-site inter-signal water level combination retrieval approach, resulting in a continuous sequence of water level retrievals for this region. The incorporation of remote sensing techniques further facilitates the estimation of water storage fluctuations in the area. The outcomes of this study demonstrate the efficacy of GNSS-MR in capturing the lake's seasonal water-level variations, with retrieval uncertainties ranging from centimeters to low decimeters. The fusion of GNSS-MR with remote sensing data offers a comprehensive approach for monitoring the water levels and water storage fluctuations of Sarez Lake within its challenging environmental conditions. This research provides a valuable methodology applicable to the study and monitoring of other dammed lakes.