深海分层介质中的无源声定位时差交会特性

Time difference intersection characteristics of passive underwater acoustic localization in the stratified deep sea

利用无源声信号的到达时差对目标入水点进行定位在浅海中已有成功应用,但在深海条件下因测量区域变大、声传播路径弯曲、测量条件受限等因素,定位性能不确定度增加.针对这一问题,建立基于水平分层介质假设的多基站时差定位模型,对比了等声速介质信道与水平分层介质信道定位求解的性能差异,并结合西北太平洋夏季环境条件下的仿真算例对模型进行了验证.研究揭示了有明显等效声速差异条件下的深海时差交会变异性特征,当两基站的等效声速相接近时,等时差线趋于标准双曲线样式;当两基站的等效声速相差较大时,等时差线呈现不规则分布,一侧趋于闭合,另一侧趋于平行,且多个基站等时差线均位于闭合一侧时,定位性能明显下降.在测量系统论证和设计时应充分考虑时差交会特性,结合具体海区环境条件合理选取基阵构型和布设深度.

Passive underwater acoustic localization by time difference of arrival(TDOA) has been successfully applied in determining the entering target position in shallow sea, but when it comes to deep sea, the large test sea area, curved ray paths and limited measuring conditions increase the uncertainty on localization performance. According to this problem, a TDOA localization model using multiple base stations was presented based on the assumption that the medium in deep sea was stratified, by which differences between the constant velocity medium and stratified medium in solving the target position was compared, and effects of the key variable, equivalent sound velocity(ESV), on time difference intersection were discussed by theoretical and numerical method. The variability of TDOA intersection under inhomogeneous ESV conditions in deep sea was revealed. The TDOA contour tended to be standard hyperbolic curves when the ESVs from two different stations were close, and it showed an irregular distribution when the ESVs from two base stations had an obvious bias, which tended to be close on the one side and parallel to the another one. Aworse localization performance appeared as all TDOA contours were on the same side with close curves. The method was examined by the simulation case in a summer environment of Northwest Pacific, in which the test sea area was set to 8 km×8 km in coverage and 5500 m in depth. A 4-receivers array in the squared configuration was used, and the target located at x=1 km, z=3 km. According to the simulated results, the localization performance related to receiver depth:(1) When the receiver depth was 1000 m, the favorable intersection situation was formed by the mixed acoustic ray paths composed of the direct wave and the seabed firstreflected wave, such that the relative high accuracy was achieved, the root mean square error(RMSE) was 30.4 m with typical errors randomly added;(2) when the receiver depth was 100 m, the terrible intersection situation was formed by nearly tangent and close quadratic curves which was formed by a single kind of seabed first-reflected ray paths, and the RMSE was nearly double compared with the one under 1000 m receiver depth condition;(3) when the receiver depth was5450 m, a better intersection situation was achieved due to full coverage of direct wave, and the relative accuracy without random errors was superior to that under 1000 m receiver depth condition. This work indicates that intersecting localization by TDOA is evidently limited by sound channel in the stratified deep sea, and multipaths make the ESV different as arriving at each base station, such that intersection characteristics of the TDOA contour are changed. So the intersection condition of TDOA should be carefully considered in designing the measurement system and the array configuration and deployed receiver depth should be reasonably arranged to adapt the specific oceanographic environment.