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摘要:
针对如何利用全球导航卫星系统反射计(GNSS-R)测量河流水文参数的问题,利用GNSS反射信号相关时间为相干性判决算子研究河流反射的GNSS的相干性,研究GNSS反射信号相对于直射信号的多普勒频率现象,验证GNSS-R测量河流边界、河流水位和河流流速的测量方法,并开展相应的外场试验验证。在河流水位测量方面,提出多样本观测和两步拟合法分别解决码相位高度计存在通道偏差和载波相位存在野点的问题。研究结果表明:前向构型无明显的多普勒频移,而后向构型的GNSS反射信号存在多普勒现象,前向和后向构型分别以强相干和弱相干信号为主,前向构型的强相干信号可被用于河流边界和水位测量,而后向构型被用于测量流速,利用后向构型的多普勒频率测量河流流速。试验结果表明:河流表面较河岸表面有更强的反-直功率比,通过检测镜面反射点轨迹上反-直功率比的突变点可获得河流边界;采集的北斗B1I和B3I信号测量的河流流速分别为0.34 m/s和0.51 m/s。
Abstract:To measure river parameters using global navigation satellite system-reflectometry (GNSS-R), this paper studies the coherence of the GNSS signal reflected offthe river surface, and the Doppler frequency shift of the GNSS signal relative to the direct signal, explores the methods of using GNSS-R to measure river boundary, water level, and water velocity, and conducted an experimental demonstration. To measure water level, a multi sample observation and two step fitting method are proposed to overcome the channel bias in the code phase altimeter and the outlier in the carrier phase.The research results show that there is no obvious Doppler freuqncy shift in the forward scattered signal, but there is a Doppler frequency shift phenomenon in the backward scattered GNSS signal, and the strong and weak coherent signals respectively dominate the forward scattered and backward scattered signals, so that the strong coherent signal in the forward scattered signal can be used to measure the river boundary and water level, while the backward scattered signal can be used to measure water velocity. The experimental results show that the reflected to direct power ratio from the river surface is larger than that from the river bank so that it is possible to measure river boundaries through detected mutation points of the reflected to direct power ratio in the specular point trajectories, and the measured water velocities of the B11 and B3I signals are 0.34 m/s and 0.51 m/s, respectively.
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