Influence of flooding on GPS carrier-to-noise ratio and water content variation analysis: a case study in Zhengzhou, China

Based on the Global Positioning System interferometric reflectometry (GPS-IR), the influence of flood on GPS carrier-to-noise ratio (CNR) and water content variation is analyzed by using data sets collected during (day-of-year) DOY 197–206, 2021. The observation station ZHNZ is located in Zhengzhou, China, and is operated by the Crustal Movement Observation Network of China. The flood occurred on DOY 201, 2021, which was caused by heavy rain that lasted for three days. Experimental results showed that the CNR on L1 and L2 frequencies decreased during the flood, especially for elevations larger than 50 deg. In addition, affected by the surrounding of the observation station and the tracks of the satellites, the extent and duration of the impact of the flood on each satellite slightly differ. Before analyzing the water content variation by using CNR, the influence of the station environment, satellite trajectory, signal frequency, and satellite type is investigated. Moreover, real data sets were used to validate the importance of the independent calculation of the effective reflector height. The results showed that the effective reflector height performs independently of the satellite and slightly varies over time. The CNR was used to analyze the water content variation; experimental results demonstrated that the water content variation retrieved by CNR correlates consistently with the real observed rainfall overall. Although the correlation between the calculated volumetric water content and precipitation was only approximately 0.57, it was mainly induced by the influence of soil saturation caused by continuous and heavy rain.