多波束测深表层声速误差的动态影响及改正方法

Dynamic influence and correction of inaccurate surface sound speed on multibeam bathymetry data

表层声速不准确会对多波束测深波束的归位产生影响,对于平面换能器阵,使波束角产生偏差,从而影响波束最终位置,但Snell常数保持不变;对于曲面换能器阵,虽然波束未束控不产生波束角偏差,但Snell常数发生改变,会使波束在传播过程中出现折射误差,对深水环境测量不利。对于表层声速误差带来的水深误差,外部波束比内部波束受到的影响更严重。当表层声速无法实时准确获取时,根据内外部波束对水深的影响大小识别表层声速误差的存在,通过逐步调整表层声速值,计算波束指向角差值,再重新进行声线跟踪,计算改正后的波束位置,消除其带来的水深的影响,完成表层声速误差的改正。文中用实测数据进行了验证,对多波束测深数据质量的改善有一定的参考意义。

Multibeam bathymetry data are contaminated by inaccurate surface sound speed.For the level transmit or receive arrays,the erroneous beam steering angle will be produced.The positions of beams will not be true,but the Snell＇s constant is preserved.For the barrel arrays,the beam steering angles are not influenced because of no beam steering,but refract artifacts will exist because the Snell＇s constant is not preserved.The depth bias will be larger in dee Pwater in this situation.The influences of inaccurate surface sound speed are more serious on outer beams than on inner beams.The paper studied if the instantaneous surface sound speed can not be surveyed accurately,especially in estuaries,a post-processing method could be used to remove the influences.According to the obvious differences of depth biases between the inner and outer beams,we could judge whether surface sound speed error exists or not.We could obtain the correct beam angles through adjusting the surface sound speed until the depth biases are disappeared.Finally,all beams could be re-calculated according to the correct beam angles.The method was verified by the real data.