Analysis and quantification of seabed adjacency effects in the subsurface upward radiance in shallow waters

Abstract

The estimation of the bathymetry and the detection of targets located on the seabed of shallow waters using remote sensing techniques is of great interest for many environmental applications in coastal areas such as benthic habitat mapping, monitoring of seabed aquatic plants and the subsequent management of littoral zones. For that purpose, knowledge of the optical effects induced by the neighborhood of a given seabed target and by the water column itself is required to better interpret the subsurface upward radiance measured by satellite or shipborne radiometers. In this paper, the various sources of photons that contribute to the subsurface upward radiance are analyzed. In particular, the adjacency effects caused by the neighborhood of a given seabed target are quantified for three water turbidity conditions, namely clear, moderately turbid and turbid waters. Firstly, an analytical expression of the subsurface radiance is proposed in order to make explicit the radiance terms corresponding to these effects. Secondly, a sensitivity study is performed using radiative transfer modeling to determine the influence of the seabed adjacency effects on the upward signal with respect to various parameters such as the bathymetry or the bottom brightness. The results show that the highest contributions of the adjacency effects induced by the neighborhood of a seabed target to the subsurface radiance could reach 26%, 18% and 9% for clear, moderately turbid and turbid water conditions respectively. Therefore, the detection of a seabed target could be significantly biased if the seabed adjacency effects are ignored in the analysis of remote sensing measurements. Our results could be further used to improve the performance of inverse algorithms dedicated to the retrieval of bottom composition, water optical properties and/or bathymetry.

Mapping Benthic Habitats by Extending Non-Negative Matrix Factorization to Address the Water Column and Seabed Adjacency Effects

“…In this section, the underwater radiative transfer equation that was recently developed in [45] is briefly described. Such an analytic formulation has been established from the complete equation of the radiative transfer into the water column.…”

“…The notations used in the paper are given in Table 1. This work follows an in-depth analysis of various sources of photons that contribute to the sub-surface upward radiance radiative transfer phenomena within the water column, presented in [45]. From this paper, a schematic representation of the upward radiances corresponding to direct, diffuse, and water-leaving radiance is shown in Figure 1a.…”

“…Authors [44] have investigated the detection of adjacency effects in the ground implying water areas, as being a general unmixing problem, using several N MF-based methods. In [45], the focus is made for the first time on the analysis of the influence of the seabed adjacency effects; an analytical formulation of the radiative transfer equation is developed that includes the adjacency effects. The radiative transfer model developed in [45] has been used in a previous work [46], to introduce the new specific N MF-based unmixing method that is developed here.…”

“…To reach these objectives, the analytical formulation of the radiative transfer into the water column, recently proposed in [45], is taken into account as the original complete model, which is then adapted to the unmixing purpose. The adapted radiative transfer model and the mixed pixel decomposition are accounted for to derive a specific sub-surface mixing model.…”

A Dark Target Detection Method Based on the Adjacency Effect: A Case Study on Crack Detection

“…There are two main methods for obtaining the PSF. The first is the implementation of the radiation transfer equation by parameterizing various atmospheric and observational conditions [39,40,41,42,43]. The second is the Monte Carlo simulation [44,45,46,47].…”