Effects of Parameter Selections on Soil Moisture Retrieval Using GNSS-IR

Soil moisture is an important geophysical quantity for evaluating soil conditions. Traditional measurement methods such as remote sensing and field measurements cannot meet the requirements with high spatial and temporal resolution. Soil moisture retrieval based on Global Navigation Satellite System- Interferometry and Reflectometry (GNSS-IR) can be applied on the existing GNSS networks to solve these problems and has the great potential to complement existing soil moisture monitoring networks. Parameters (satellite elevation ranges, priori reflector height, and signal frequency) play a very important role in soil moisture retrieval using GNSS-IR and different selections could have great influence on the results. Previous research often relied on experience in the parameter selections, which was not conducive to the application and promotion of the technology. This study aims to investigate the effects of soil moisture retrieval using GNSS-IR based on different parameter selections. After describing the basic theory of soil moisture retrieval, the influence of the satellite elevation ranges, the priori reflector height, and the chosen signal frequency are investigated with National Science Foundation's (NSF) Plate Boundary Observatory (PBO) data and experimental data obtained in Nanjing, China. The results show that using data within an elevation range of [5°, 30°] and arc lengths greater than 20° can reduce the mean RMSE and MAE by 1%-31.5% and 2%-31%. The selection of the priori reflector height does not have a significant influence. L2 signals (compared to L1 signals) can improve the accuracy of soil moisture retrieval and can reduce the mean RMSE and MAE by 20.9% and 20.4%.