Feasibility Study on Qinghai Lake Boundary Detection Using CYGNSS Raw IF Data

Qinghai Lake, the largest inland saltwater lake in China, is an important water body that maintains the ecological security of the northeastern Tibetan Plateau. Global navigation satellite system reflectometry technology (GNSS-R) is rarely used in lake detection, especially in lake boundary detection under the circumstances of spaceborne. This article attempts to implement lake boundary detection using cyclone global navigation satellite system (CYGNSS) raw intermediate frequency (IF) data for the first time. First, the second-order frequency-locked loop is used to assist the third-order phase-locked loop closed-loop tracking to successfully generate higher delay resolution and Doppler resolution (67 x 51) delay Doppler maps (DDM) than CYGNSS compressed DDM (11 x 17); second, based on the principle of scattering characteristics of different reflectors of GNSS-R, and the fusion method of signal power ratio and effective area delay distance (D-LR), the 2018 Qinghai Lake boundary detection inversion was carried out in the lake area to explore the feasibility of achieving higher spatial resolution (0.7 km) and high-precision lake boundary detection with the raw IF data of CYGNSS. The inversion detection results are compared with the topographic distribution results of Google Earth and global land analysis and discovery, and the inversion result error is about 0.5 km, which is consistent with the theoretical spatial resolution. It proves that spaceborne GNSS-R technology and CYGNSS raw IF data have great potential in the field of lake boundary detection.