Advances in Earth Science ›› 2011, Vol. 26 ›› Issue (6): 608-614. doi: 10.11867/j.issn.1001-8166.2011.06.0608

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Review of Correction of Bottom Effects of Optical Shallow Water Remote Sensing

Zhou Guanhua   

  1. School of Instrumentation Science and Opto-electronics Engineering, Beijing University of Aeronautics & Astronautics, Beijing100191,China
  • Received:2010-03-31 Revised:2010-11-16 Online:2011-06-10 Published:2011-06-10

Zhou Guanhua. Review of Correction of Bottom Effects of Optical Shallow Water Remote Sensing[J]. Advances in Earth Science, 2011, 26(6): 608-614.

Until recently, optical processes in shallow water, where the sea bottom is shallow enough to be optically detected, has received little attention outside of a relatively small number of modeling and remote sensing investigations. The contribution from the bottom of optical shallow water changes the intensity and spectral distribution of remotely sensed signal above water surface, which became one of the key problems for water quality remote sensing inversion accuracy. In shallow water, where the depth is much less than the potential for light to penetrate, a large fraction of the subsurface light reaches the ocean floor, where portions of the light energy are absorbed, reflected back into the overlying water column, or re-emitted as fluorescence. So variability in the subsurface light field is not only determined by the distribution of optically important matter dissolved and suspended in the water column, but also of the function of the depth and properties of the ocean floor. It is important to understand how light interacts with the sea floor. Though many of the techniques and approaches to investigate light in the deep water are relevant in the shallow water, they are insufficient to address the entire problem, and the treatment of remote sensing reflectance is more complex than for optically deep waters, when water bottom effects are considered. In order to completely understand the details of how light is distributed within the shallow water and to determine the interrelationships and variability of optical properties of water bottom and waterleaving radiance, the measurements of spectral bidirectional reflectance distribution function (BRDF) along with concurrent measurements of the sediment properties (composition, grain size, etc.) should be taken. The foundation of spectral database of typical sediment types in the typical coastal areas by experiment is necessary work to do, which can provide the basic data for modeling and application in optically shallow water remote sensing. New in-situ sensors and approaches designed specifically to take into account the complex distribution, structure, and optical properties of benthic features should be developed. Sophisticated models and methods are required to adequately separate the signal from the water column and that from the water bottom to derive the water-leaving radiance, bottom depth or bottom features. The magnitude and angular distribution of the bottom-reflected radiance are determined by the BRDF of the bottom. If the bottom is inhomogeneous, or patchy, or not horizontal, the upwelling radiance is a spatial function of horizontal location as well as depth, and therefore three-dimensional (3D) radiative Transfer (RT) calculations are necessary to predict the in-water and water-leaving radiances. 

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