Research On The Method Of SEA Surface Wind Field Inversion Based On GNSS-R Reflected Signals

With the unique advantage, GNSS-R remote sensing detection technology gets rapid development in the field of sea surface wind, sea ice, air target and soil moisture detection. The continuous improvements of BeiDou system make this technology application gradually popularized in our country. Under the condition of shore-based signals receiver and BeiDou GEO satellites, it can provide stable scattering geometry relationship for the related sea surface parameters detection. But as a result of shore-based conditions, lower receiver height makes the smaller coverage area of antenna and smaller effective delay range, so the quantity of effective data in the power spectrum is limited which bring certain difficulty for the inversion of sea surface wind speed. In this paper, the method of sea surface wind speed detection based on coastal BeiDou satellite reflected signals is researched, and mainly includes the following research points:1. Analyzed the BeiDou satellite signal structure, composition, modulation mode, the generation of ordinary ranging code in B1 band I branch and its good correlation features, the form of direct and reflected signals correlation function. Then, using numerical simulation method analyzes the size of equal delay area and the influence of the receiver height on the first delay area.2. Analyzed the geometric relations of wind speed inversion using shore-based BeiDou reflected signal, the scattering area, the change of antenna coverage area size with different satellite altitude angle and receiver height. Pointed out that the effective delay range of power spectrum is small and valid data is less due to the limited receiver height. Analyzed the influence of water dielectric constant, satellite altitude angle on the Fresnel reflection coefficient using MATLAB simulation, and studied the relevant mathematical model of wind field retrieval which included the wave spectrum model, the electromagnetic scattering model and the power model of scattering signal.3. In order to make full use of effective data in limited delay range, the paper used the power spectrum area exceed the threshold as the reflected signal characteristic parameters. According to the data characteristics, this paper utilized power spectrum peak as the benchmark for the setting of threshold, and determined the threshold based on the change of correlation coefficient under different thresholds. By analyzing the relationship of the power spectrum area, wind speed and significant wave height, the indirect wind speed inversion method using power spectrum area was put forward in which the significant wave height as transitional inversion parameters. And the feasibility of indirect method is verified using the actual data.4. Considering the period of wind speed detection is one hour, so it can assume that wind speed is constant in a short time. Under this assumption, the paper explores the change of power spectrum peak in a short time. And after the detailed analysis of randomness and statistical properties for the power spectrum peak, the direct method of wind speed detection using the statistical features of power spectrum peak is put forward. At last, the feasibility of direct method is verified using the actual data.