地基GNSS-IR风速反演原理及方法初探

Preliminary study on theory and method of ground-based GNSS-IR wind speed

随着全球导航卫星系统(Global Navigation Satellite Systems,GNSS)的发展,曾经被认为是误差源的多路径效应,已经被证实可以用来监测水位、雪深、植被指数、土壤湿度等反射面参数,其中的地基分支逐步发展为GNSS干涉遥感(GNSS-interferometry reflectometry,GNSS-IR)技术。为了扩展GNSS-IR技术的监测对象和应用范围,本文提出了一套地基GNSS-IR风速反演的原理及方法。首先,本文基于信噪比(signal-to-noise ratio,SNR)振荡原理、散射模型原理、波浪谱原理,从理论上证明了SNR截止高度角参数与风速之间存在一一对应的数学关系,并仿真得到了具体的数学关系。然后,本文使用小波分析方法从实测SNR序列中获取SNR截止高度角,并将同一GPS卫星、每天同一时间内SNR序列的截止高度角进行基准统一,获得截止高度角变化量;根据该变化量反演风速。算例选取香港HKQT站在“山竹”和“天鸽”台风前后时间的数据进行分析,结果发现:GPS L5信号的截止高度角变化量与实测风速数据对应关系良好,相关性达到70%~85%;截止高度角变化量可以刻画风速从低风速逐步抬升至高风速的变化情况;同一站点截止高度角变化量与风速之间存在特定的数学关系;相关结论证实了利用SNR可以估计风速变化。最后,本文讨论了GNSS-IR风速反演技术中下一步的研究方向,以期推进该技术的实际应用进程。

With the development of Global Navigation Satellite Systems(GNSS),the multipath effect that was once regarded as one error source has been proven can be used to monitor reflecting surface parameters such as water level,snow depth,vegetation water content,and soil moisture using a technology named GNSS-interferometry reflectomety(GNSS-IR).In order to expand monitoring objects and applications of GNSS-IR,this paper proposed the theory and method to retrieve wind speed using ground-based GNSS-IR.The theory includes the signal-to-noise ratio(SNR)multipath oscillation theory,the scattering model theory,and wave spectrum theory.This paper simulated the mathematical model between the SNR cutoff elevation angle and the wind speed,and used the wavelet analysis to extract SNR cutoff elevation angle and a unified method to unify reference of cutoff elevation angle.Data of HKQT station,located in Hong Kong,during the period of“Mangkhut”and“Hato”were used.The results showed that the variations of GPS L5 SNR cutoff elevation angles had a good corresponding relationship with the measured wind speeds,and the correlation coefficient reached 70%~85%.Also,the variations of cutoff elevation angles can describe the change of wind speed from low wind speed to high wind speed and there was a specific mathematical relationship between them.Finally,this paper discussed two difficulties to overcome in the GNSS-IR wind speed retrieval technology.