Chami Malik, Lenot Xavier, Guillaume Mireille, Lafrance Bruno, Briottet Xavier, Minghelli Audrey, Jay Sylvain, Deville Yannick, Serfaty Véronique
Opt Express. 2019 Apr 15;27(8):A319-A338. doi: 10.1364/OE.27.00A319.
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.
利用遥感技术估算浅海海底地形并探测位于海底的目标，对于沿海地区的许多环境应用具有重要意义，如底栖生境测绘、海底水生植物监测以及随后的海岸带管理。为此，需要了解给定海底目标附近以及水柱本身所引起的光学效应，以便更好地解释卫星或船载辐射计测量的水下向上辐射。本文分析了对水下向上辐射有贡献的各种光子源。特别是，针对三种水体浑浊度条件，即清澈、中度浑浊和浑浊水体，对给定海底目标附近引起的邻接效应进行了量化。首先，提出了水下辐射率的解析表达式，以明确与这些效应相对应的辐射率项。其次，使用辐射传输模型进行了敏感性研究，以确定海底邻接效应相对于各种参数（如海底地形或海底亮度）对向上信号的影响。结果表明，在清澈、中度浑浊和浑浊水体条件下，海底目标附近引起的邻接效应分别对水下辐射率的最大贡献可达26%、18%和9%。因此，如果在遥感测量分析中忽略海底邻接效应，则对海底目标的探测可能会产生显著偏差。我们的结果可进一步用于提高致力于反演海底成分、水体光学特性和/或海底地形的反演算法的性能。
