组合定位系统

Combined positioning system

组合定位系统由GPS(Global Position System)、航向姿态传感器以及超短基线定位系统所组成.常规的超短基线阵采用相位法进行定位.为了避免相位模糊,阵元间距必须小于半个波长,因此定位精度不会很高.组合定位系统中的超短基线阵采用时延法进行定位,阵元间距可以取得远比半波长大.定位时,组合定位系统在海面飘浮,一个向上发射的声波发射器与海水中的被定位目标安装在一起.声波发射器发射宽带信号且被阵元所接收.采用最大似然估计,以得到发射信号与阵元接收信号之间的时延.大的阵元间距、宽的信号带宽以及精确的时延估计,能使定位精度有很大的提高.超短基线阵具有4个阵元.由4个时延可以得到4个斜距.再利用最小二乘法和坐标变换就可求得目标的经度、纬度以及深度.本文还给出了定位误差仿真、时延估计仿真以及湖试的结果.

Combined positioning system consists of GPS,attitude sensor and USBL(Ultra-short Base Line) system.For ordinary USBL,target position is determined by the phase method.In order to avoid phase ambiguity,the distance between two elements should be less than 0.5 wave length,and thus the accuracy will not be very high.For the USBL in the combined system,position is determined by the time method,the distance between two elements is larger than that of the ordinary USBL.During positioning,the combined positioning system floats at the sea surface.A sound projector is mounted on the target beneath the sea surface.Wideband signal is transmitted by the projector and received by the array elements.By maximum likelihood estimation,the time delay between transmitted and received signal can be obtained.Thanks to the large element-distance,wide signal bandwidth and accurate time delay estimation,the accuracy of the positioning is much higher than that of the ordinary USBL.There are four elements in the USBL array.From four time delays,four ranges can quickly be got.The latitude,longitude and depth of the target can be calculated by the method of least squares and the conversion of coordinate system.The position error simulation,time delay estimation simulation and results of the lake testing are present in the paper.