Abstract

The log-ratio model (LRM) with three model parameters ( ${\boldsymbol{n}}$ , ${{\boldsymbol{m}}_1},$ and ${{\boldsymbol{m}}_0}$ ) has been widely used in shallow water bathymetry of multispectral images. At present, obtaining LRM model parameters by optimization algorithms depends on the setting of initial values [ ${\boldsymbol{n}}(0)$ , ${{\boldsymbol{m}}_1}(0),$ and ${{\boldsymbol{m}}_0}(0)$ ] or initial value ranges. However, how to set the initial value can obtain model parameters more effectively and credibly, and the significance of each initial value in the optimization process is very important for LRM bathymetric retrieval method. In this article, remote sensing images and bathymetric data were used to determine the initial value ranges of credible model parameters, and then the sensitivity of each parameter was analyzed in the algorithm optimization process from the partial differential perspective, and the bathymetry was retrieved in the sea area near Ganquan Island. The results show that according to the partial differential analysis of model parameters, ${\boldsymbol{n}}$ , with the smallest change rate in three LRM parameters and the rate of ${{\boldsymbol{m}}_1}$ and ${{\boldsymbol{m}}_0}$ is at least five times of it. So ${\boldsymbol{n}}(0)$ needs more iterations to achieve the optimal. Therefore, the initial value ${\boldsymbol{n}}(0)$ determines whether the optimization method can obtain credible LRM model parameters and the algorithm convergence speed. And when ${\boldsymbol{n}}(0) \in ({1/{{\boldsymbol{R}}_{{{\bf min}}}}, 1000} ]$ ( ${{\boldsymbol{R}}_{{{\bf min}}}}$ is the minimum reflectance in blue and green bands), there must be a credible model parameter solution. The bathymetric retrieval results of the sea area with coral and sand substrates show the applicability of our initial value ranges in different substrate area.

Highlights

  • As one of the basic elements of hydrographic and marine environment surveys, bathymetry can be used for environmental management and monitoring, coast construction projects, ship navigation and island exploitation [1]

  • Remote sensing images and in situ bathymetric data were used to determine the initial value ranges of credible model parameters, and the sensitivity of each parameter was analysed in the algorithm optimization process from the partial differential perspective, and the bathymetric retrieval and verification analysis were performed in the sea area near Ganquan Island

  • The initial value ranges of Log-ratio model (LRM) based on LM optimization algorithm were determined, and reasonable and credible model parameters can be obtained according to these ranges

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Summary

Introduction

As one of the basic elements of hydrographic and marine environment surveys, bathymetry can be used for environmental management and monitoring, coast construction projects, ship navigation and island exploitation [1]. Traditional methods are difficult to implement in shallow water areas due to the effects of tides and reefs. Multispectral optical remote sensing imagery provides another way to quantitatively invert shallow water. Compared with conventional acoustic and laser sounding, optical remote sensing has the advantages of a large coverage area, high efficiency and low cost and is an effective supplement to traditional sounding methods in areas that have complex underwater topography or are affected by maritime disputes [4]-[6]

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