自适应空间密度滤波的ICESat‑2激光雷达测深

谌一夫, 李帅, 张东方, 乐源, 王力哲

谌一夫, 李帅, 张东方, 乐源, 王力哲. 自适应空间密度滤波的ICESat‑2激光雷达测深[J]. 武汉大学学报 ( 信息科学版), 2025, 50(1): 83-96. DOI: 10.13203/j.whugis20220453
引用本文: 谌一夫, 李帅, 张东方, 乐源, 王力哲. 自适应空间密度滤波的ICESat‑2激光雷达测深[J]. 武汉大学学报 ( 信息科学版), 2025, 50(1): 83-96. DOI: 10.13203/j.whugis20220453
CHEN Yifu, LI Shuai, ZHANG Dongfang, LE Yuan, WANG Lizhe. ICESat‑2 LiDAR Bathymetry Based on Adaptive Spatial Density Filtering[J]. Geomatics and Information Science of Wuhan University, 2025, 50(1): 83-96. DOI: 10.13203/j.whugis20220453
Citation: CHEN Yifu, LI Shuai, ZHANG Dongfang, LE Yuan, WANG Lizhe. ICESat‑2 LiDAR Bathymetry Based on Adaptive Spatial Density Filtering[J]. Geomatics and Information Science of Wuhan University, 2025, 50(1): 83-96. DOI: 10.13203/j.whugis20220453

自适应空间密度滤波的ICESat‑2激光雷达测深

基金项目: 

湖北珞珈实验室专项基金 220100035

国家自然科学基金 42171373

东海实验室开放基金 DH-2022KF01003

智能地学信息处理湖北省重点实验室开放基金 KLIGIP-2022-C01

智能地学信息处理湖北省重点实验室开放基金 KLIGIP-2022-B04

详细信息
    作者简介:

    谌一夫,博士,副教授,研究方向为卫星遥感对地观测、激光海洋测量、遥感信息工程。stein_syf@foxmail.com

    通讯作者:

    张东方,博士。zhangdongfang@cug.edu.cn

ICESat‑2 LiDAR Bathymetry Based on Adaptive Spatial Density Filtering

  • 摘要:

    冰、云和陆地高程卫星2号(ice, cloud and land elevation satellite-2, ICESat-2)搭载了先进地形激光测高系统(advanced topographic laser altimeter system,ATLAS),该系统采用光子计数探测模式,可获取高精度的地表高程信息。ATLAS使用532 nm波段激光器,具备一定的水深探测能力,为星载数据近岸水深探测提供了新手段。利用ICESat-2 ATLAS数据进行测深,关键问题是如何实现不同区域、不同环境、不同密度分布条件下信号光子的自动探测与提取。为解决此问题,提出了一种基于自适应空间滤波的ICESat-2数据测深方法,该方法首先将水面以上、水面和水下区域的原始光子进行分离,随后基于可变椭圆密度滤波核精确提取水面与水底光子,椭圆密度滤波核参数根据不同水深下光子密度的分布特点自适应确定,最终实现浅海水深测量。实验结果表明,所提方法获取的ICESat-2测深结果与机载激光雷达测深结果的相关系数达到0.93,均方根误差为0.51 m,具有较高的测深精度。

    Abstract:
    Objectives 

    The ice, cloud, and land elevation satellite-2 (ICESat-2), equipped with the advanced topographic laser altimeter system (ATLAS), is a new measurement strategy with a photon-counting technique to obtain the high-accuracy elevation information in the surface of the Earth. ATLAS uses a 532 nm band laser to emit three pairs of scanning laser beams, each pair containing one strong and one weak sub-beam. The receiver collects millions of return photons from the echo, and each received photon is recorded. In the field of bathymetry, photon counting LiDAR has great advantages. For traditional LiDAR with linear detection regime, the only way to achieve high signal-to-noise ratio requirement is to increase the emitted laser energy, which results in a very bulky and huge system and high design power consumption. Photon counting LiDAR is no longer confined to the detection of clear high signal-to-noise ratio echo waveform. It uses statistical optics theory to achieve effective ranging, and maximizes the use of each photon energy in the laser echo, which can greatly improve the detection efficiency of bathymetry detection while reducing the system complexity, providing new opportunities for near-shore bathymetry detection. Based on ICESat-2 ATLAS data for bathymetry, the main problem is how to achieve automatic detection and extraction of signal photons for raw photons in different regions, different environments and different density distributions.

    Methods 

    To overcome these existing problems, an adaptive spatial filtering bathymetric method based on photon density distribution is proposed. The method first separate the photons into above the water, water-surface, and underwater photons. The filter parameters can be automatically determined by the photon density distribution generated based on the optical characteristics of different water bodies and water depth distribution, so that the signal photons of the water surface and bottom can be precisely extracted to achieve bathymetry. In order to verify the bathymetric accuracy of the method, experiments were conducted using ATLAS datasets obtained in different areas of the South China Sea, and finally the experimental results were verified by using high-precision bathymetric data acquired by airborne LiDAR.

    Results 

    The validation results show that the coefficient of determination between the ICESat-2 bathymetric results and the airborne LiDAR bathymetric results reaches 0.93, and the correspond root mean square error is 0.51 m, which illustrate the bathymetric potential of the method proposed in this research. In addition, when using photonic data for bathymetry, it is influenced by the refraction of the water body, which mainly exists in the vertical direction and increases with the increase of depth.

    Conclusions 

    Due to the complex diversity of water body environment, the photon bathymetry accuracy will show a certain decreasing trend with the increase of water depth. In future research, bathymetric experiments will be conducted using the method of this paper and the ATLAS dataset to investigate a more accurate refraction correction model in order to explore the bathymetric potential of the satellite-based photon counting LiDAR in different water environments.

  • 经典平差模型和最小二乘估计理论[1]在大地测量等众多科学研究和工程领域中应用广泛,其中,高斯-马尔科夫模型(Gauss-Markov model, GMM)最为常用,而高斯-赫尔默特模型(GaussHelmert model, GHM)可视为经典平差模型的一般通用形式。在实际应用中,坐标转换、回归模型、数字地面模型和大地测量反演等平差模型的系数矩阵包含随机的观测误差,从而使得GMM扩展为随机系数矩阵的变量含误差(errors-invariables, EIV)模型[2]。文献[3]提出同时顾及观测向量和系数矩阵中随机误差的整体最小二乘(total least squares, TLS)估计算法。TLS的非线性特征导致其受制于计算机技术的发展,直至20世纪80年代,文献[4]将TLS引入数值分析领域并提出奇异值分解算法,TLS才开始广泛应用于各专业领域并取得丰富的研究成果。文献[2]中对TLS进行了改进和扩展;文献[5]从TLS的算法、统计特性和可靠性研究等方面综述了TLS方法的研究进展。当误差相关且精度不等时,采用加权整体最小二乘估计(weighted total least squares, WTLS)方法进行求解。文献[6]研究了基于高斯-牛顿迭代法的WTLS算法,该算法假设权矩阵为特殊情况,得到的解在形式上与最小二乘(least squares, LS)解相同;文献[7]研究了在任意权矩阵的一般情况下的WTLS算法;文献[8]研究了特殊结构下WTLS算法的迭代方法并将其应用于实际场景;文献[9-12]研究了附有等式和不等式约束情况下的WTLS算法;文献[13]研究了稳健WTLS算法。

    通过对EIV模型的形式进行变换,文献[14]提出部分EIV(partial EIV, PEIV)模型,提高了系数矩阵仅含部分随机量情况下的计算效率。文献[15]对PEIV模型进行线性化,推导了PEIV模型的LS算法。文献[16-17]从模型的一般性出发,将EIV模型扩展至通用EIV模型,将经典平差的GHM中观测向量的系数矩阵和参数向量的系数矩阵由固定矩阵推广为随机矩阵,涵括随机系数矩阵的各类情况,同时推导了通用EIV模型在任意权矩阵情况下的一般性WTLS算法。

    通用EIV模型的非线性使得该算法在估计量较多时计算量大。本文利用非线性平差原理,将通用EIV模型展开后的二阶项纳入平差方程的常数项,从而将其转化为GHM形式,推导出通用EIV模型的线性化整体最小二乘(linearized total least squares, LTLS)算法。相较于WTLS算法,LTLS算法提高了通用EIV模型的计算效率,当参数向量初始值与最优值相差较大时,提升了迭代收敛速度。

    GHM的形式为:

    $$ \mathit{\boldsymbol{A}}\left( {\mathit{\boldsymbol{y}} + {\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \right) + \mathit{\boldsymbol{BX}} + \mathit{\boldsymbol{w}} = \mathit{\boldsymbol{0}} $$ (1)

    式中,yvy分别为n×1维观测值向量和观测值改正数向量;Xu×1维参数向量;A为观测值向量对应的f×n维系数矩阵;B为参数向量对应的f×u维系数矩阵;wf×1维常数向量;在经典平差函数模型的定义中,AB均不含随机误差,为固定矩阵。

    当参数向量的系数矩阵B含随机误差时,GHM(式(1))扩展为经典EIV模型。当观测值向量的系数矩阵A和参数向量的系数矩阵B均含随机误差时,GHM(式(1))扩展为通用EIV平差模型[16]:

    $$ \left( {\mathit{\boldsymbol{A}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}} \right)\left( {\mathit{\boldsymbol{y}} + {\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \right) + \left( {\mathit{\boldsymbol{B}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}} \right)\mathit{\boldsymbol{X}} + \mathit{\boldsymbol{w}} = \mathit{\boldsymbol{0}} $$ (2)

    式中,AVA分别为观测值向量对应的f×n维系数矩阵及其改正数矩阵;BVB分别为参数向量对应的f×u维系数矩阵及其改正数矩阵。由于ABy均为随机矩阵,则通用EIV的随机模型为:

    $$ \mathit{\boldsymbol{L}} = \left[ {\begin{array}{*{20}{c}} {{\mathop{\rm vec}\nolimits} (\mathit{\boldsymbol{A}})}\\ {{\mathop{\rm vec}\nolimits} (\mathit{\boldsymbol{B}})}\\ \mathit{\boldsymbol{y}} \end{array}} \right],\mathit{\boldsymbol{v}} = \left[ {\begin{array}{*{20}{c}} {{\mathop{\rm vec}\nolimits} \left( {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}} \right)}\\ {{\mathop{\rm vec}\nolimits} \left( {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}} \right)}\\ {{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \end{array}} \right] = \left[ {\begin{array}{*{20}{l}} {{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{A}}}}\\ {{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{B}}}}\\ {{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \end{array}} \right] $$ (3)
    $$ \mathit{\boldsymbol{D}}(\mathit{\boldsymbol{L}}) = \delta _0^2{\mathit{\boldsymbol{P}}^{ - 1}} = \delta _0^2\mathit{\boldsymbol{Q}} = \delta _0^2\left[ {\begin{array}{*{20}{c}} {{\mathit{\boldsymbol{Q}}_\mathit{\boldsymbol{A}}}}&{{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{AB}}}}}&{{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{Ay}}}}}\\ {{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{BA}}}}}&{{\mathit{\boldsymbol{Q}}_\mathit{\boldsymbol{B}}}}&{{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{By}}}}}\\ {{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{yA}}}}}&{{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{yB}}}}}&{{\mathit{\boldsymbol{Q}}_\mathit{\boldsymbol{y}}}} \end{array}} \right] $$ (4)

    式中,vec(.)表示将矩阵按列向量化;Lv分别为观测数据的k×1维观测值向量及其改正数向量,包括ABy中所有观测值及其改正数,其中k=fn+fu+n; PQD(L)分别为L的权矩阵、协因数矩阵和方差协方差矩阵;δ02为单位权方差。

    根据TLS准则,通用EIV平差模型的求解可转化为最优化估计问题[16]:

    $$ \left\{ {\begin{array}{*{20}{l}} {\min {\mathit{\boldsymbol{v}}^{\rm{T}}}\mathit{\boldsymbol{Pv}}}\\ {s.t.{\rm{ }}\left( {\mathit{\boldsymbol{A}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}} \right)\left( {\mathit{\boldsymbol{y}} + {\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \right) + \left( {\mathit{\boldsymbol{B}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}} \right)\mathit{\boldsymbol{X}} + \mathit{\boldsymbol{w}} = \mathit{\boldsymbol{0}}} \end{array}} \right. $$ (5)

    相应目标函数为:

    $$ \begin{array}{*{20}{c}} {\mathit{\Phi }(\mathit{\boldsymbol{r}},\mathit{\boldsymbol{\lambda }},\mathit{\boldsymbol{X}}) = {\mathit{\boldsymbol{v}}^{\rm{T}}}\mathit{\boldsymbol{Pv}} + 2{\mathit{\boldsymbol{\lambda }}^{\rm{T}}}\left( {\mathit{\boldsymbol{Ay}} + \mathit{\boldsymbol{A}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}} + } \right.}\\ {\left. {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}\mathit{\boldsymbol{y}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}} + \mathit{\boldsymbol{BX}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}\mathit{\boldsymbol{X}} + \mathit{\boldsymbol{w}}} \right)} \end{array} $$ (6)

    将目标函数对估计量分别求偏导并令其等于0,得到非线性方程组:

    $$ \frac{{\partial \mathit{\Phi }}}{{\partial \mathit{\boldsymbol{\hat X}}}} = 2\left( {{\mathit{\boldsymbol{B}}^{\rm{T}}}\mathit{\boldsymbol{\hat \lambda }} + \mathit{\boldsymbol{\hat V}}_\mathit{\boldsymbol{B}}^{\rm{T}}\mathit{\boldsymbol{\hat \lambda }}} \right) = \mathit{\boldsymbol{0}} $$ (7)
    $$ \frac{{\partial \mathit{\Phi }}}{{\partial \mathit{\boldsymbol{\hat v}}}} = 2\left( {\mathit{\boldsymbol{P\hat v}} + {{\mathit{\boldsymbol{\hat C}}}^{\rm{T}}}\mathit{\boldsymbol{\hat \lambda }}} \right) = \mathit{\boldsymbol{0}} $$ (8)
    $$ \frac{{\partial \mathit{\Phi }}}{{\partial \mathit{\boldsymbol{\hat \lambda }}}} = 2(\mathit{\boldsymbol{Ay}} + \mathit{\boldsymbol{B\hat X}} + \mathit{\boldsymbol{\hat C\hat v}} + \mathit{\boldsymbol{w}}) = \mathit{\boldsymbol{0}} $$ (9)

    式中,$ {\boldsymbol{C}}=\left[{\boldsymbol{y}}^{\mathrm{T}} \otimes {\boldsymbol{I}}_{f} \boldsymbol{X}^{\mathrm{T}} \otimes {\boldsymbol{I}}_{f} A+\boldsymbol{V}_{{\boldsymbol{A}}}\right] ; \hat{{\boldsymbol{v}}}, \hat{\boldsymbol{X}} $分别为观测值向量和参数向量的估计值。

    根据式(7)~式(9)可导出:

    $$ \mathit{\boldsymbol{\hat v}} = - \mathit{\boldsymbol{Q}}{\mathit{\boldsymbol{\hat C}}^{\rm{T}}}\mathit{\boldsymbol{\hat Q}}_\mathit{\boldsymbol{C}}^{ - 1}(\mathit{\boldsymbol{Ay}} + \mathit{\boldsymbol{B\hat X}} + \mathit{\boldsymbol{w}}) $$ (10)
    $$ \begin{array}{*{20}{c}} {\mathit{\boldsymbol{\hat X}} = - {{\left[ {\left( {{\mathit{\boldsymbol{B}}^{\rm{T}}} + \mathit{\boldsymbol{\hat V}}_\mathit{\boldsymbol{B}}^{\rm{T}}} \right)\mathit{\boldsymbol{\hat Q}}_\mathit{\boldsymbol{C}}^{ - 1}\mathit{\boldsymbol{B}}} \right]}^{ - 1}}\left( {{\mathit{\boldsymbol{B}}^{\rm{T}}} + } \right.}\\ {\left. {\mathit{\boldsymbol{\hat V}}_\mathit{\boldsymbol{B}}^{\rm{T}}} \right)\mathit{\boldsymbol{\hat Q}}_\mathit{\boldsymbol{C}}^{ - 1}(\mathit{\boldsymbol{Ay}} + \mathit{\boldsymbol{w}})} \end{array} $$ (11)

    式中,$ \hat{\boldsymbol{Q}}_{C}=\hat{\boldsymbol{C}} \boldsymbol{Q} \hat{\boldsymbol{C}}^{\mathrm{T}} $。

    以式(2)的LS解作为初始值,根据式(10)和式(11)进行迭代计算可得通用EIV模型的WTLS最优解。

    通用EIV模型是非线性模型,观测值矩阵和系数矩阵均为随机量,WTLS算法的计算量随着待估量个数增多将迅速增加。将式(2)展开,利用非线性函数平差原理[18]将二阶项作为模型误差纳入方程的常数项,从而将通用EIV模型转化为线性的GHM,推导出通用EIV模型的LTLS算法。

    X=X0+x,将式(2)展开得:

    $$ \begin{array}{c} \left( {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}\mathit{\boldsymbol{y}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}{\mathit{\boldsymbol{X}}_0} + \mathit{\boldsymbol{A}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \right) + \mathit{\boldsymbol{Bx}} + (\mathit{\boldsymbol{w}} + \mathit{\boldsymbol{Ay}} + \\ \left. {\mathit{\boldsymbol{B}}{\mathit{\boldsymbol{X}}_0} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}\mathit{\boldsymbol{x}}} \right) = \mathit{\boldsymbol{0}} \end{array} $$ (12)

    式(12)可表示为:

    $$ \begin{array}{*{20}{c}} {\left[ {\left( {{\mathit{\boldsymbol{y}}^{\rm{T}}} \otimes {\mathit{\boldsymbol{I}}_\mathit{\boldsymbol{f}}}} \right){\mathop{\rm vec}\nolimits} \left( {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}} \right) + \left( {\mathit{\boldsymbol{X}}_0^{\rm{T}} \otimes {\mathit{\boldsymbol{I}}_\mathit{\boldsymbol{f}}}} \right){\mathop{\rm vec}\nolimits} \left( {{\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}} \right) + \mathit{\boldsymbol{A}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}}} \right] + }\\ {\mathit{\boldsymbol{Bx}} + \left( {\mathit{\boldsymbol{w}} + \mathit{\boldsymbol{Ay}} + \mathit{\boldsymbol{B}}{\mathit{\boldsymbol{X}}_0} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{A}}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{y}}} + {\mathit{\boldsymbol{V}}_\mathit{\boldsymbol{B}}}\mathit{\boldsymbol{x}}} \right) = \mathit{\boldsymbol{0}}} \end{array} $$ (13)

    则通用EIV模型的线性化形式为:

    $$ {\mathit{\boldsymbol{A}}_\mathit{\boldsymbol{l}}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{l}}} + \mathit{\boldsymbol{Bx}} + {\mathit{\boldsymbol{w}}_\mathit{\boldsymbol{l}}} = \mathit{\boldsymbol{0}} $$ (14)

    式中,$ {\boldsymbol{A}}_{{\boldsymbol{l}}}=\left[\begin{array}{llll} {\boldsymbol{y}}^{\mathrm{T}} \otimes {\boldsymbol{I_{f}}} & \boldsymbol{X}_{0}^{\mathrm{T}} & \otimes {\boldsymbol{I_{f}}} & {\boldsymbol{A}} \end{array}\right] ; \ {\boldsymbol{v_{l}}}= \left[\begin{array}{c} \operatorname{vec}\left(\boldsymbol{V}_{{\boldsymbol{A}}}\right) \\ \operatorname{vec}\left(\boldsymbol{V}_{{\boldsymbol{B}}}\right) \\ \boldsymbol{v}_{{\boldsymbol{y}}} \end{array}\right] ; \boldsymbol{w}_{{\boldsymbol{l}}}=\boldsymbol{w}+\boldsymbol{Ay} + {\boldsymbol{B}} \boldsymbol{X}_{0}+\boldsymbol{V}_{{\boldsymbol{A}}} \boldsymbol{v}_{{\boldsymbol{y}}}+\boldsymbol{V}_{{\boldsymbol{B}}} {\boldsymbol{x}}$为常数项,即将式(2)按泰勒展开略去的二阶项VAvy+VBx作为模型误差纳入常数项。

    由式(14)可知,线性化后的通用EIV模型与GHM形式一致,可使用最小二乘法得到观测值向量和参数向量:

    $$ \mathit{\boldsymbol{\hat x}} = - \mathit{\boldsymbol{\hat N}}_{\mathit{\boldsymbol{bb}}}^{ - 1}{\mathit{\boldsymbol{B}}^{\rm{T}}}\mathit{\boldsymbol{\hat N}}_{\mathit{\boldsymbol{aa}}}^{ - 1}{\mathit{\boldsymbol{w}}_\mathit{\boldsymbol{l}}} $$ (15)
    $$ {{\mathit{\boldsymbol{\hat v}}}_\mathit{\boldsymbol{l}}} = - \mathit{\boldsymbol{Q}}{{\mathit{\boldsymbol{\hat A}}}_\mathit{\boldsymbol{l}}}\mathit{\boldsymbol{\hat N}}_{\mathit{\boldsymbol{aa}}}^{ - 1}\left( {\mathit{\boldsymbol{B\hat x}} + {\mathit{\boldsymbol{w}}_\mathit{\boldsymbol{l}}}} \right) $$ (16)

    式中,$ \boldsymbol{N}_{{\boldsymbol{a a}}}=\boldsymbol{A}_{{\boldsymbol{l}}} \boldsymbol{Q} \boldsymbol{A}_{{\boldsymbol{l}}}^{\mathrm{T}} ; \boldsymbol{N}_{{\boldsymbol{b b}}}= {\boldsymbol{B}}^{\mathrm{T}} \boldsymbol{N}_{{\boldsymbol{a a}}}^{-1} {\boldsymbol{B}} $; Q为观测值向量的协因数矩阵。

    通用EIV模型的LTLS算法步骤如下:

    1)将实际模型表示为式(2),将观测数据代入得到ABy矩阵,并给出观测值数据的协因数阵Q,包括观测值向量Qy、观测值向量系数矩阵QA、参数向量系数矩阵QB

    2)计算通用EIV模型的LS解作为初始参数解:$ \hat{\boldsymbol{X}}^{0}=-\left({\boldsymbol{B}}^{\mathrm{T}}\left({\boldsymbol{A }}\boldsymbol{Q}_{{\boldsymbol{y}}} {\boldsymbol{A}}^{\mathrm{T}}\right)^{-1} {\boldsymbol{B}}\right)^{-1} {\boldsymbol{B}}^{\mathrm{T}}\left({\boldsymbol{A}} \boldsymbol{Q}_{{\boldsymbol{y}}} {\boldsymbol{A}}^{\mathrm{T}}\right)^{-1} · ({\boldsymbol{A y}}+{\boldsymbol{w}})$, 观测值向量改正数初始值取0。

    3)根据式(15)和式(16)进行迭代计算,每次迭代将上一次估计值作为初始值代入新的迭代过程,直至前后两次估计值之差小于设定阈值。

    GHM按泰勒级数展开仅包含常数项、一阶项(二阶及以上项全部为零),将二阶项纳入线性化后的常数项,该方法极大地减弱了线性化引起的模型误差。因此,在同样以LS解作为初值的情况下,GHM线性化的LTLS解与WTLS解的收敛性一致。此外,根据文献[19]中EIV模型LS解偏差的研究结果,在当前测量技术手段和观测精度条件下,以有偏的LS解作为初值,能够保证TLS迭代计算收敛,除非出现极特殊情况导致LS初始解严重偏离最优值。

    参考GHM,式(2)的LTLS算法估计结果的精度计算式为:

    $$ \left\{ {\begin{array}{*{20}{l}} {\hat \delta _0^2 = \mathit{\boldsymbol{v}}_\mathit{\boldsymbol{l}}^{\rm{T}}\mathit{\boldsymbol{P}}{\mathit{\boldsymbol{v}}_\mathit{\boldsymbol{l}}}/\mathit{r}}\\ {\mathit{\boldsymbol{Q}}(\mathit{\boldsymbol{\hat x}}) = {{\left( {{\mathit{\boldsymbol{B}}^{\rm{T}}}{{\left( {{\mathit{\boldsymbol{A}}_\mathit{\boldsymbol{l}}}\mathit{\boldsymbol{QA}}_\mathit{\boldsymbol{l}}^{\rm{T}}} \right)}^{ - 1}}\mathit{\boldsymbol{B}}} \right)}^{ - 1}}}\\ {\mathit{\boldsymbol{Q}}(\mathit{\boldsymbol{\hat L}}) = \mathit{\boldsymbol{Q}} - \mathit{\boldsymbol{QA}}_\mathit{\boldsymbol{l}}^{\rm{T}}\left( {\mathit{\boldsymbol{N}}_\mathit{\boldsymbol{A}}^{ - 1}\left( {\mathit{\boldsymbol{I}} - \mathit{\boldsymbol{B}}{\mathit{\boldsymbol{Q}}_{\mathit{\boldsymbol{\hat x}}}}{\mathit{\boldsymbol{B}}^{\rm{T}}}\mathit{\boldsymbol{N}}_\mathit{\boldsymbol{A}}^{ - 1}} \right){\mathit{\boldsymbol{A}}_\mathit{\boldsymbol{l}}}\mathit{\boldsymbol{Q}}} \right)}\\ {\mathit{\boldsymbol{D}}(\mathit{\boldsymbol{\hat x}}) = \hat \delta _0^2\mathit{\boldsymbol{Q}}(\mathit{\boldsymbol{\hat x}})}\\ {\mathit{\boldsymbol{D}}(\mathit{\boldsymbol{\hat L}}) = \hat \delta _0^2\mathit{\boldsymbol{Q}}(\mathit{\boldsymbol{\hat L}})} \end{array}} \right. $$ (17)

    式中,多余观测数r=n-t; n为观测值个数;t为必要观测值个数;r与GHM的多余观测数相同;$ \boldsymbol{N}_{{\boldsymbol{A}}}=\boldsymbol{A}_{{\boldsymbol{l}}} \boldsymbol{P}^{-1} \boldsymbol{A}_{{\boldsymbol{l}}}^{\mathrm{T}} $。

    按照LTLS算法步骤设计实验,比较LTLS算法与WTLS算法的计算结果,验证LTLS算法的正确性、高效性和可行性。实验1设计模拟数据,比较分析单组实验结果和1 000组实验统计结果,验证LTLS算法的正确性;实验2在待估计量数目取不同量级时,比较两种算法的计算时间,验证LTLS算法的高效性;实验3通过实例验证LTLS算法的可行性。

    在通用EIV模型(式(2))中,设置参数真值X=[5 10]T,系数矩阵AB中随机量的中误差分别设为0.01和0.02,观测向量y的中误差设为0.03。ABy和常数向量w的模拟数据如下:

    $$ \mathit{\boldsymbol{A}} = \left[ {\begin{array}{*{20}{c}} {12.469}&{11.096}&{15.872}&{11.725}\\ {8.883}&{10.291}&{2.929}&{3.666}\\ {12.321}&{1.109}&{6.392}&{15.809}\\ {3.551}&{12.104}&{3.867}&{1.257} \end{array}} \right], $$
    $$ \mathit{\boldsymbol{B}} = \left[ {\begin{array}{*{20}{l}} {10.410}&{17.544}\\ {18.033}&{15.171}\\ {18.631}&{15.855}\\ {15.671}&{11.878} \end{array}} \right], $$
    $$ \mathit{\boldsymbol{y}} = \left[ {\begin{array}{*{20}{l}} {27.543}\\ {20.727}\\ {20.839}\\ {25.033} \end{array}} \right],\mathit{\boldsymbol{w}} = \left[ {\begin{array}{*{20}{c}} { - 1425.323}\\ { - 852.619}\\ { - 1142.913}\\ { - 658.407} \end{array}} \right]。 $$

    采用LTLS算法和WTLS算法的估计结果如表 1所示,LTLS参数解与WTLS参数解完全相等,验证了LTLS算法的正确性。

    表  1  参数解及其方差估计值
    Table  1.  Parameter Values and Mean Square Deviations
    算法 参数解 中误差
    $ \hat {\boldsymbol{X}} _1 $ $ \hat {\boldsymbol{X}} _2 $ $ σ _{\hat{\boldsymbol{X}}_1} $ $ σ_ {\hat{\boldsymbol{X}}_2} $
    LTLS算法 5.012 551 9.994 964 0.039 9 0.051 9
    WTLS算法 5.012 551 9.994 964 0.039 9 0.051 9
    下载: 导出CSV 
    | 显示表格

    为了进一步验证LTLS算法的正确性,首先采用模拟的1 000组数据计算LTLS和WTLS参数解的均值$ {\rm{avg}} (\hat {\boldsymbol{X}} _1) 和 {\rm{avg}} (\hat {\boldsymbol{X}} _2) $,并将参数解均值代入式(17),求得LTLS参数解的协因数阵估值$ {\boldsymbol{Q}}(\hat {\boldsymbol{X}} )$,然后利用参数真值求得精确的参数协因数阵$ \overline{\boldsymbol{Q}}(\hat{\boldsymbol{X}})={\boldsymbol{E}}_{{\boldsymbol{X}}}^{\mathrm{T}} \boldsymbol{E}_{{\boldsymbol{X}}} /(m-n) , {\boldsymbol{E}}_{{\boldsymbol{X}}}=\left[\begin{array}{ll} \hat{{\boldsymbol{X}}}_{1}^{(j)}-5 & \hat{{\boldsymbol{X}}}_{2}^{(j)}-10 \end{array}\right] $,计算结果见表 2。1 000组数据的LTLS参数解和WTLS参数解与参数真值偏差的统计分析见图 1图 2

    表  2  1000组实验的参数解均值和协因数阵
    Table  2.  Average Parameter Values and Co⁃variance Matrix in 1 000 Experiments
    算法 参数解均值 协因数阵
    $ {\rm{avg}} ( \hat{\boldsymbol{X}}_1) $ $ {\rm{avg}} ( \hat{\boldsymbol{X}}_2) $ $ {\boldsymbol{Q }}( \hat{\boldsymbol{X}} ) $ $ \bar{ \boldsymbol{Q }}( \hat{\boldsymbol{X}} ) $
    LTLS算法 5.009 427 9.998 257 0.004 3 −0.005 1 0.004 2 −0.004 9
    −0.005 1 0.007 3 −0.004 9 0.007 2
    WTLS算法 5.009 427 9.998 257 0.004 3 −0.005 1 0.004 2 −0.004 9
    −0.005 1 0.007 3 −0.004 9 0.007 2
    下载: 导出CSV 
    | 显示表格
    图  1  1 000组实验数据的LTLS参数解与参数真值偏差统计图
    Figure  1.  Statistical Graph of Deviations Between Truth Values and Parameter Values Soluted by LTLS in 1 000 Experiments
    图  2  1 000组实验数据的WTLS参数解与参数真值偏差统计图
    Figure  2.  Statistical Graph of Deviations Between Truth Values and Parameter Values Soluted by WTLS in 1 000 Experiments

    表 2图 1图 2可以看出,LTLS算法与WTLS算法的统计结果完全一致,说明在每次实验中两种算法所求参数解均一致,验证了LTLS算法的正确性。同时两种计算协因数阵的方法结果非常相近,验证了参数协因数阵一阶近似估计公式(17)的有效性[17]

    为分析LTLS算法的计算效率,设计通用EIV模型中待估计量个数在不同的数量级情况,采用LTLS算法和WTLS算法计算100组模拟数据的平均迭代次数N、平均解算时间t和减少比例(LTLS算法较WTLS算法减少的平均解算时间与WTLS算法平均解算时间之比),结果见表 3

    表  3  LTLS算法和WTLS算法计算效率的比较
    Table  3.  Comparison of Computational Efficiency Between LTLS Algorithm and WTLS Algorithm
    待估量数量 NLTLS NWTLS tLTLS tWTLS 减少比例/%
    10 5.18 4.5 0.224 ms 0.191 ms
    100 5.04 6.36 0.681 ms 0.724 ms 5.9
    1 000 5 6.75 0.033 s 0.044 s 25.0
    10 000 5 7.5 2.681 s 3.909 s 31.4
    下载: 导出CSV 
    | 显示表格

    表 3可以看出,两种算法每次迭代的平均时间基本一致;当模型估计量数量较少时,两种算法的效率基本相当,随着估计量的数量级逐渐增大,LTLS算法的效率高于WTLS算法。原因在于GHM按泰勒级数展开后,仅包含常数项、一阶项(二阶及以上项全部为零),LTLS算法将二阶项纳入常数项,减小了线性化引起的模型误差,迭代计算收敛更快,迭代次数减少,使得计算效率提高。

    本文采用的摄影测量实例示意图如图 3所示,由3个地面摄像机S1S2S3拍摄两个目标点P1P2组成,相机主距f=100 mm,距离l1l2l3l4l5l6y1y2的观测值和中误差见表 4

    图  3  摄影测量实例图
    Figure  3.  Diagram of the Photogrammetry Example in This Paper
    表  4  距离观测值及其中误差
    Table  4.  Distance Observations and Standard Deviations
    统计项 l1/mm l2/mm l3/mm l4/mm l5/mm l6/mm y1/m y2/m
    观测值 14.1 16.6 6.1 7.1 22.1 26.3 10.0 8.0
    中误差 0.10 0.10 0.10 0.10 0.10 0.10 0.05 0.05
    下载: 导出CSV 
    | 显示表格

    根据图 3可得到误差方程:

    $$ \left\{\begin{array}{l} l_{1} x_{2}-f x_{1}=0 \\ l_{2} x_{4}-f x_{3}=0 \\ l_{3} x_{2}+f y_{1}+f x_{1}=0 \\ l_{4} x_{4}+f y_{1}+f x_{3}=0 \\ l_{5} x_{2}-f y_{1}-f y_{2}+f x_{1}=0 \\ l_{6} x_{4}-f y_{1}-f y_{2}+f x_{3}=0 \end{array}\right. $$ (18)

    构建通用EIV模型来估计点P1和点P2的坐标,由误差方程可得:

    $$ \begin{array}{l} \mathit{\boldsymbol{A}} = \left[ {\begin{array}{*{20}{c}} 0&0\\ 0&0\\ { - f}&0\\ { - f}&0\\ { - f}&{ - f}\\ { - f}&{ - f} \end{array}} \right],\mathit{\boldsymbol{B}} = \left[ {\begin{array}{*{20}{c}} { - f}&{{l_1}}&0&0\\ 0&0&{ - f}&{{l_2}}\\ f&{{l_3}}&0&0\\ 0&0&f&{{l_4}}\\ f&{{l_5}}&0&0\\ 0&0&f&{{l_6}} \end{array}} \right],\\ \mathit{\boldsymbol{y}} = \left[ {\begin{array}{*{20}{l}} {{y_1}}\\ {{y_2}} \end{array}} \right],\mathit{\boldsymbol{x}} = \left[ {\begin{array}{*{20}{l}} {{x_1}}\\ {{x_2}}\\ {{x_3}}\\ {{x_4}} \end{array}} \right],\mathit{\boldsymbol{w}} = \left[ {\begin{array}{*{20}{l}} 0\\ 0\\ 0\\ 0\\ 0\\ 0 \end{array}} \right] \end{array} $$ (19)

    由式(19)可知矩阵A不含有随机误差,则该矩阵的改正数矩阵为零矩阵。采用LTLS算法和WTLS算法解算,设置阈值为1×10-8,结果见表 5表 6。两种方法所得坐标估值和距离观测值估值完全一致,该实例表示为通用EIV模型时系数矩阵中待估计量较少,所以两个算法收敛速度相差不大。

    表  5  P1和点P2的坐标估值/m
    Table  5.  Coordinate Estimates of P1 and P2 /m
    算法 坐标估值
    $ \hat x_1 $ $ \hat x_2 $ $ \hat x_3 $ $ \hat x_4 $
    LTLS算法 6.995 056 5 49.715 632 6.981 465 5 41.968 315 9
    WTLS算法 6.995 056 5 49.715 632 6.981 465 5 41.968 315 9
    下载: 导出CSV 
    | 显示表格
    表  6  距离观测值估值
    Table  6.  Estimation of Distance Observations
    算法 $ \hat l_1 $/mm $ \hat l_2 $/mm $ \hat l_3 $/mm $ \hat l_4 $/mm $ \hat l_5 $5/mm $ \hat l_6 $/mm $ \hat y_1 $/m $ \hat y_2 $/m
    LTLS算法 14.070 1 16.635 1 6.032 4 7.178 4 22.137 7 26.256 7 9.994 1 8.006 8
    WTLS算法 14.070 1 16.635 1 6.032 4 7.178 4 22.137 7 26.256 7 9.994 1 8.006 8
    下载: 导出CSV 
    | 显示表格

    本文将通用EIV函数模型展开后的二阶项纳入模型的常数项,将通用EIV模型表示为线性形式的GHM,推导出通用EIV模型的线性化整体最小二乘算法和近似精度估计公式。实验结果表明,通用EIV模型的LTLS算法与WTLS算法结果一致,验证了该算法的正确性。此外,LTLS算法估计精度公式和WTLS估计精度公式均为一阶近似精度,因此两种算法参数的估计精度相同。当通用EIV模型的待估量数量较多时,LTLS算法比WTLS计算效率更高,在处理海量数据时更具有优势。

    http://ch.whu.edu.cn/cn/article/doi/10.13203/j.whugis20220453
  • 图  1   水面光子局部放大示意图

    Figure  1.   Diagram of Local Amplification of Water Surface Photons

    图  2   光子计数测深数据提取流程

    Figure  2.   Flowchart of Photon-Counting Bathymetry Data Extraction

    图  3   椭圆滤波器示意图

    Figure  3.   Diagram of Elliptic Filter

    图  4   初始光子数据在高程方向上的分段示意图

    Figure  4.   Segment Diagram of Raw Photon Data Along Elevation Direction

    图  5   基于高斯曲线的水面光子自动识别与提取

    Figure  5.   Automatic Identification and Extraction of Water Surface Photons Based on Gaussian Curve

    图  6   随水深变化的椭圆滤波器

    Figure  6.   Elliptical Filters that Vary with Water Depth

    图  7   光子在水中发生折射后的偏移量计算模型

    Figure  7.   Model for Calculating the Deflection of Photons After Refraction in Water

    图  8   研究区域内的ATL03数据集和验证数据

    Figure  8.   ATL03 Datasets Obtained for the Study Areas and Corresponding In-Situ Data

    图  9   位于南沙区域的光子轨迹数据

    Figure  9.   Photon Tracks Data in Nansha Area

    图  10   本文光子滤波方法与传统方法(AVEBM、改进的DBSCAN)比较

    Figure  10.   Comparison of Filtering Results Among AVEBM, Improved DBSCAN and the Proposed Method

    图  11   光子数据集的陆地、水面和水底信号光子自动分离与提取结果

    Figure  11.   Results of Automatic Separation and Extraction of Signal Photons from Land, Water Surface and Water Bottom for Different Photon Datasets

    图  12   折射校正前后的水底信号光子及陆地、水面和水底的拟合曲线

    Figure  12.   Underwater Signal Photons Before and After Refraction Correction and Fitted Curves of Land, Water Surface and Underwater

    图  13   ATLAS测深结果和验证数据对比

    Figure  13.   Comparison of ATLAS Bathymetry Results and Validation Data

    表  1   ATLAS数据集分布信息

    Table  1   Distribution Information of ATLAS Datasets

    经过岛屿ATLAS数据集世界标准时间地面轨迹大地坐标范围
    东岛2020022908:08:00GT1L(109.412°E,18.214°N)—(109.411°E,18.218°N)
    GT1R(109.412°E,18.217°N)—(109.411°E,18.220°N)
    羚羊礁2020022020:31:00GT3R(111.577°E,16.490°N)—(111.574°E,16.459°N)
    2020082011:50:00GT3L(111.578°E,16.491°N)—(111.574°E,16.450°N)
    西沙洲2020011822:03:00GT1R(112.208°E,16.989°N)—(112.205°E,16.962°N)
    2020041817:43:00GT3L(112.213°E,16.991°N)—(112.211°E,16.962°N)
    贡士礁2020040706:02:00GT1R(114.388°E,11.456°N)—(114.386°E,11.471°N)
    2022070315:01:00GT1R(114.391°E,11.427°N)—(114.386°E,11.469°N)
    鸿庥岛2021083117:39:00GT1R(114.367°E,10.184°N)—(114.366°E,10.174°N)
    2020060315:20:00GT3L(114.374°E, 10.182°N)—(114.374°E,10.177°N)
    下载: 导出CSV

    表  2   使用本文方法滤波后不同类型的光子(陆地、水面和水底)在每轨数据集的总光子数中的占比

    Table  2   Percentage of Different Types of Photons (Land, Surface and Bottom) in Total Number of Photons for Each Dataset After Using the Proposed Method

    ATLAS数据总光子数/个水面光子数/个水面光子数占比/%水底光子数/个水底光子数占比/%陆地光子数/个陆地光子数占比/%噪声光子数/个噪声光子数占比/%
    20200229GT1L2 67643916298111 93973
    20200229GT1R2 7241 16443365131 19544
    20200220GT3R12 8668 873693 403265905
    20200820GT3L13 4306 300476 404487265
    20200118GT1R12 7975 514436 281491 0028
    20200418GT3L5 1662 122412 2954445192986
    下载: 导出CSV

    表  3   折射校正前后6轨数据的最小和最大测深结果以及相应的高程和沿轨方向的折射偏移量/m

    Table  3   Minimum and Maximum Bathymetric Results for Six-Track Data Before and After Refraction Correction, and Corresponding Refraction Displacements in the Elevation and Along-Track Directions/m

    ATLAS数据校正前深度校正后深度高程偏移沿轨方向偏移
    最小最大最小最大最小最大最小最大
    20200229GT1L0.031.360.031.020.020.660.003 10.033 5
    20200229GT1R0.401.640.301.240.140.730.002 00.035 0
    20200220GT3R0.2711.750.208.760.072.990.001 20.027 0
    20200820GT3L0.2410.040.207.600.112.760.000 10.038 0
    20200118GT1R0.1217.570.1013.180.094.750.000 20.064 0
    20200418GT3L0.079.610.067.280.063.490.021 00.065 0
    下载: 导出CSV

    表  4   折射校正前后光子计数测深精度验证

    Table  4   Validation of Photon-Counting Bathymetry Accuracy After Refraction Correction

    ATLAS数据折射校正前折射校正后
    KSlopeR2SRMSE/mKSlopeR2SRMSE/m
    20200229GT1L1.310.900.961.030.890.34
    20200229GT1R1.330.881.021.020.880.39
    20200220GT3R1.400.961.241.100.960.57
    20200820GT3L1.340.951.201.060.950.52
    20200118GT1R1.220.941.050.980.930.48
    20200418GT3L1.200.951.310.970.950.59
    总体1.330.931.141.050.930.51
    下载: 导出CSV

    表  5   3种方法的测深精度对比

    Table  5   Comparison of Bathymetry Accuracy of 3 Methods

    ATLAS数据改进的DBSCANAVEBM本文方法
    KSlopeR2SRMSE/mKSlopeR2SRMSE/mKSlopeR2SRMSE/m
    20200229GT1L1.120.850.451.110.870.391.030.890.34
    20200229GT1R1.110.840.421.050.840.401.020.880.39
    20200220GT3R1.150.930.591.180.940.591.100.960.57
    20200820GT3L1.170.910.551.140.930.531.060.950.52
    20200118GT1R0.950.900.540.970.910.490.980.930.48
    20200418GT3L0.920.920.610.950.930.620.970.950.59
    总体1.130.880.561.100.900.531.050.930.51
    下载: 导出CSV

    表  6   不同水深分区下ICESat-2的测深精度/m

    Table  6   Bathymetry Accuracy for Different Intervals of Water Depth/m

    ATLAS数据水深分区
    [0,2)[2,4)[4,6)[6,8)≥8
    20200229GT1L0.34
    20200229GT1R0.39
    20200220GT3R0.320.510.590.620.74
    20200820GT3L0.300.670.660.71
    20200118GT1R0.280.840.620.881.25
    20200418GT3L0.250.610.580.661.04
    总体0.290.640.630.750.97
    下载: 导出CSV
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  • 收稿日期:  2023-03-08
  • 网络出版日期:  2023-06-07
  • 刊出日期:  2025-01-04

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