基于SNR的GPS-IR技术机理分析

Mechanism Analysis of GPS-IR Technology Based on SNR

鉴于现有研究对GPS-IR技术的反射波接收、低高度角信噪比观测值的使用、信噪比残差的形态等机理还未阐释清楚,且几乎是通过实验进行解释,因此,从理论和实验2个方面对GPS-IR技术机理进行分析。理论和实验证明:GPS卫星发射的右旋圆极化波经一次反射后部分转换为左旋圆极化波,转换比例随着高度角和介电常数增大而变大,当右旋圆极化波垂直入射到理想导体表面时,经一次反射才能全部转换为左旋圆极化波;同时在测量型GPS接收机安装有抑径板的情况下,因衍射现象的存在,测量型GPS接收机天线仍能接收反射波中的右旋圆极化波。当高度角越小或介电常数越大时,GPS入射波中的垂直极化波和平行极化波的能量透射到反射物中就越少,其反射波的强度就越大,信噪比受反射波影响就越严重,且能够接收的右旋圆极化波较多,因此GPS-IR使用的是低高度角(如30°以下)的信噪比观测值。当高度角变化范围较小时,信噪比残差序列呈近似"余弦曲线"形态,从而建立了基于信噪比残差的反演模型。

The available research on technology mechanism of reflected wave reception,the use of the SNR observations of low elevating angle and the form of SNR residuals for GPS-IR is not clear enough,and they are almost interpreted by experiments. This paper analyzed the GPS-IR technology mechanism from the aspects of theories and experiments. The right hand circular polarized wave transmitted by GPS satellite is partly converted into left hand circular polarized wave after one reflection,and the conversion ratio increases with the increase of satellite elevating angle and dielectric constant. When the right hand circular polarized wave is perpendicular to the surface of the perfect conductor,it can be all converted into left hand circular polarized wave after a reflection;At the same time,in the case of the measuring GPS receiver equipped with the baffle plate,because of the diffraction phenomenon,the antenna of the measuring GPS receiver can still receive the right hand circular polarized wave in the reflected signal. When the elevating angle is smaller or the dielectric constant of the reflector is larger,the less GPS incident wave energy of vertically polarized wave and parallel polarized wave is transmitted to the reflector. The more intense the reflected wave is,the worse the SNR is affected by the reflected wave,and there are more right hand circular polarized waves that can be received. Therefore,the GPS-IR uses the SNR observations of low elevating angle(such as under 30°). When the elevating angle changes and the range is smaller,the SNR residuals sequence is approximately "cosine curve",and thus,an inversion model based on SNR residuals is established.