GNSS信号土壤衰减模型的试验验证方法

An experimental validation method on GNSS signal attenuation model in soil

GNSS(global navigation satellite system)信号在土壤中的衰减情况对于研究GNSS反射信号的有效遥感深度具有重要意义。本文通过试验研究了北斗信号与GPS(global positioning system)信号在土壤中的衰减情况。在试验设计上将GNSS天线置入土壤中并不断改变天线上方的土壤厚度与湿度以采集GNSS信号的功率衰减数据,最后利用这些数据反演土壤湿度以对GNSS信号土壤衰减模型进行验证。试验结果表明,土壤能够使GNSS信号发生明显的衰减。土壤的湿度值与厚度值越大,GNSS信号功率衰减越严重。在黏土土质,土壤湿度为0.15~0.30 cm^3/cm^3的情况下,当土壤厚度达到21 cm时,GNSS信号功率已衰减至无法被GNSS接收机测出。进一步根据GNSS信号衰减模型反演土壤湿度,结果显示,模型在土壤厚度大于等于10 cm、卫星仰角高于50°的情况下较为精确,此时利用北斗B1信号与GPS L1信号反演土壤湿度的均方根误差分别小于0.04 cm^3/cm^3与0.09 cm^3/cm^3。

The attenuation of GNSS signals in soil is of great significance for the related research of using GNSS signals to measure soil moisture.In this paper,for the first time,the attenuation of BDS(BeiDou navigation satellite system)and GPS(global positioning system)signals in the soil was studied through experiments.In the experimental design,the GNSS antenna was placed into the soil,then the soil thickness and moisture above the antenna were continuously changed to collect the power attenuation data of the GNSS signal.Finally,these data were used to retrieve soil moisture in order to validate the GNSS signal attenuation model.Experimental results show that soil can significantly attenuate GNSS signals.The greater the soil moisture value and thickness value is,the more severe the attenuation is.In the case of clay type soil and soil moisture of 0.15~0.30 cm^3/cm^3,the GNSS signal power has been attenuated to be undetectable by the GNSS receiver when the soil thickness reaches 21 cm.Further retrieval of soil moisture based on the GNSS signal attenuation model was carried out,the results show that the attenuation model is more accurate when the soil thickness is larger than or equal to 10 cm and when the satellite elevation angle is larger than 50°.And under this situation,the root mean square error of soil moisture retrieval using BeiDou B1 signal and GPS L1 signal is less than 0.04 cm^3/cm^3 and 0.09 cm^3/cm^3,respectively.