GNSS‑声学海底定位的声速误差处理方法综述

Review on the Processing Methods of Sound Speed Errors in GNSS‑Acoustic Seafloor Positioning

全球导航卫星系统(global navigation satellite system,GNSS)⁃声学海底定位是面向海底俯冲带板块形变监测需求提出的一种定位技术,也是建设海洋时空基准网的一种重要技术,有着广阔的应用前景。虽然目前GNSS⁃声学海底定位技术的研究成果还不能满足海洋时空基准网的建设需求,但其数据处理方法尤其是声速误差精细处理方法,对海洋时空基准网海底部分(海底大地基准)的建设具有重要借鉴意义。介绍了GNSS⁃声学海底定位技术的起源,并将其分为静态测量和动态测量两类,同时将声速误差处理方法作为该技术的发展脉络进行梳理,提炼了该技术的3个发展阶段:仅假设海洋声速垂向分层、考虑声速的时域变化、考虑声速的水平梯度。对于仅假设海洋声速垂向分层的阶段,国外学者采用几何结构对称的方式来削弱声速误差的影响;国内学者则主要对声速以外误差源(杆臂矢量误差、时标偏差、姿态角误差等)进行了研究,并用优化随机模型的方式削弱系统误差对定位的影响。对于考虑声速时域变化的阶段,国外学者利用拟合方法(多项式拟合或三次样条拟合)结合参数平滑约束来解算声速的时域变化量,提高定位的稳定性;国内学者基于此细化了参数拟合的方法(考虑参数长周期项的变化特征),并创新性地提出了水下差分定位算法。对于考虑声速水平梯度的阶段,国内外学者在GNSS⁃声学海底定位中解算了声速水平梯度参数,提高了水平方向定位的稳定性,并利用海洋数值模型验证了结果的可靠性。展望了将GNSS⁃声学海底定位高精度数据处理方法应用于海底大地基准建设的前景,并引入了小时空尺度声速层析的概念(基于海洋时空基准网的声速误差处理方法),以期解决数值预报模型不能提供小时空尺度产品的问题,进而为水下潜器提供更高精度的声速误差改正服务。

Global navigation satellite system(GNSS)⁃acoustic seafloor positioning is a technology proposed and developed for deformation monitoring of plates in the submarine subduction zone.As an important technolo⁃gy for the construction of marine spacetime reference network,it has broad application prospects.Although the current research results of GNSS⁃acoustic seafloor positioning cannot meet the construction requirement of marine space⁃time reference network,its data processing method,especially the fine pro⁃cessing method of sound speed error,has important reference significance for the construction of seafloor part(seafloor geodetic reference station)of marine space⁃time reference network.This paper firstly intro⁃duces the origin of GNSS⁃acoustic seafloor positioning and summarizes it into two categories:Static mea⁃surements and dynamic measurements.At the same time,the sound speed error processing method is used as the development line to refine three development stages of the technology:Only assuming the vertical stratification of ocean sound speed,considering the temporal variation of sound speed,and considering the horizontal gradient of sound speed.For the stage of only assuming vertical stratification of ocean sound speed,foreign scholars used geometric structure symmetry to weaken the influence of sound speed error;domestic scholars mainly studied the error sources besides the sound speed(lever arm offset,time tag deviation,attitude angle error,etc.)and used the stochastic model to weaken the influence of system error on the positioning results.For the stage of considering the time⁃domain variation of sound speed,foreign scholars used fitting method(polynomial fitting or cubic spline fitting)combined with parameter smoothing con⁃straint to solve the time⁃domain variation of sound speed,and improve the stability of positioning results.Based on this,domestic scholars have refined the parameter fitting method(considering the variation charac⁃teristics of the long period term of parameters).In addition,domestic scholars have proposed the underwa⁃ter differential positioning algorithm to innovate the seafloor positioning technology.For the stage of con⁃sidering the sound speed horizontal gradient,scholars have solved the sound speed horizontal gradient pa⁃rameters in the GNSS⁃acoustic seafloor positioning processing,which improves the stability of the horizon⁃tal positioning results,and verified the reliability of the results by using the marine numerical model.This paper presents the prospect of high⁃precision data processing methods of GNSS⁃acoustic seafloor posi⁃tioning for the seafloor reference station construction,and introduces the concept of small spatialtemporal scale sound speed tomography(sound speed error processing method based on ocean positioning reference network)in order to solve the problem that numerical prediction model cannot provide small spatialtempo⁃ral scale products,so as to provide high⁃precision sound speed error correction services for underwater vehicles.