Incoherent GNSS-IR Model and Its Application in Wind Speed Retrieval

With the development of Global Navigation Satellite Systems (GNSSs), it has been demonstrated that signal-to-noise ratio (SNR) observations from geodetic GNSS receivers can be used to estimate the parameters of reflecting surfaces, through a technique called GNSS-interferometry reflectometry (GNSS-IR). Recent studies have revealed that SNR-derived cutoff elevation and damping coefficient have the potential to estimate wind speed. However, the specific mathematical relationship between them and the wind speed remains undetermined. Consequently, this study, based on the existing approximate models for coherent and incoherent components of specular scattering, upgraded an existing SNR simulator to account for incoherent power of scattering signals. This upgraded simulator was used to conduct SNR simulations under varying wind speeds, allowing for the derivation of the relationship between damping coefficient and wind speed, as well as the relationship between cutoff elevation and wind speed. Moreover, an optimal design approach was introduced to estimate the damping coefficient of an SNR arc, preventing divergence in cases of insufficient matrix rank using the least-squares method. Data from GPS L5 signals recorded at the HKQT station during Super Typhoon “Mangkhut” were used. The results indicate that the simulated cutoff elevations and damping coefficients can reflect the trend of actual parameters varying with wind speed. However, there are still some differences between the simulated data and the actual data. At high wind speeds, the simulated cutoff elevation angles are lower than the actual extracted values, while the simulated damping coefficients are higher than the extracted coefficients.