北斗信号沙漠回波特性及陕北沙地参数反演算法研究

Desert exploration plays an important role in our national desert-control strategic plan, and will support the state to understand and monitor the desert situations. It is a new focus of geophysical exploration to take the signal of Compass navigation satellite as the survey wave source to explore the desert of Northwest of Shaanxi province (Shan-bei). Based on the theory of GNSS Remote Sensing and Multipath echo analysis and processing, and by using Compass navigation L-band signals, an inversion analysis is conducted to explore the Shan-bei desert texture and dunes status. The project is also trying to build up the mathematical model to extract the weak echo signals based on the reaction of the desert to the signal of Compass navigation satellite. Following steps are found out the dielectric coefficient and reflectance as the bridge to set up the internal relationship between the parameters of the reflected signals (Polar characteristics, Amplitude, phase and frequency etc) and the desert moisture change rate and surface temperature. Combine the principle experiment with the theory to carry out an experimental study of applying methods on to multi locations, multi object points and double frequencies tests, simulate the key factors such as sand-dust, wind, and light conditions, and analyze the effects of these factors on the echo of Compass navigation system, to expound the mechanism that how the macro geometry will influence the micro geometry with different test methods, and set up the exploration model of desert texture and dunes status to study the approach to defining and mapping the desert distribution area per different desert texture. This study will sets up the theoretical base for expanding the application of Compass navigation satellite to the identification of ground features, and it is significant to reveal the scattering law of microwave signal in desert.

沙漠探测关系到国家对沙漠治理情况的掌握和防沙治沙的安排部署，将北斗导航卫星信号作为波源探测陕北沙漠属于地物探测新的着眼点。项目基于GNSS-R探测理论和多径回波分析及处理方法，研究利用北斗导航L波段信号进行陕北沙漠构性和沙丘状态探测的反演识别问题。根据沙漠对北斗信号作用，探索弱回波信号提取算法，以介电系数和反射率为桥梁，建立反射信号参数（极化特性、振幅、相位和频率等）与沙漠湿度变化率、沙表温度的关系；理论结合原理性实验，开展多基、多点、双频测试的实验研究，仿真分析沙尘、风场和光照条件等因素对北斗回波的影响，阐明测试手段上的宏观几何关系对微观几何关系的影响机制；建立沙漠物理构性与沙丘状态的探测模型，研究不同特质沙漠分布区域的界定和描绘方法。该研究为北斗系统地物识别的拓展应用奠定理论基础，对揭示微波信号的沙漠散射规律有重要意义。

随着北斗全球卫星导航系统的发展，北斗系统在土地确权、精准农业、数字施工、智慧港口等方面得到成功应用。用北斗导航卫星信号作为波源探测沙漠属于地物探测新的着眼点，对拓展北斗系统应用领域具有实际意义。.沙漠探测事关国家对沙漠治理情况的掌握和防沙治沙的安排部署。项目基于GNSS-R探测理论和多径回波分析及处理方法，研究了利用北斗导航信号进行沙漠构成特性和沙丘状态探测的反演识别问题。取得了如下成果：①寻找沙漠反射回波参数与沙地湿度、沙表粗糙度之间的关系，并建立了沙漠探测与沙地参数反演模型，包括沙表湿度感测与反演模型、沙土表面粗糙度的感测与反演技术，以及对流层对信号衰减模型；②提出确定沙丘表面反射点位置的“天线方向矢指定椭圆一点”方法。根据沙丘表面多点位置坐标，用曲面拟合的方法可以获得固定沙丘的位置与形状，沙丘位置与形状前后改变情况判定沙丘类型；③采用地基、多点、双多频、“类GNSS-R法”的方法对与沙漠性质和状态相关的目标参数进行实地测量，总结BD测试沙漠的方法和BD信号对沙漠性质和状态参数的敏感程度。④探索了弱信号的接收、放大、采集与处理的方法，取得了“多普勒频移提取方法”、“卫星信号的捕获算法”和适用于GPS/BD射频接收机的镜像抑制混频器、射频放大器等多项软件算法和硬件电路成果。.研究结果发现：北斗反射信号对沙漠湿度感测敏感、在宏观几何关系感测沙丘可行，对微观几何关系（粒径粒度）的影响到反射率；对不同特质沙漠几乎无分辨能力。.研究取得的系列成果丰富了GNSS-R技术内容，对沙土湿度、粒度遥感结果，可作为对沙漠利用的参考依据；确定沙丘表面反射点以及多点曲面拟合沙丘形态的方法不仅可以用来描绘沙丘形状，也可以推广用于相对光滑裸土图形的描绘。