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Proceedings Paper

Study on extracting reflectance just beneath water surface from remote sensing reflectance
Author(s): Tangyou Liu; Aihua Dong; Wujun Xu; Demin Li
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Paper Abstract

One of the bases of remote-sensing on water quality is to analyze reflectance just beneath water surface (0- deepness). Because reflectance just beneath water surface can not be obtained directly, and remote sensing reflectance which is ratio between water-leaving radiance and total radiance on water surface from sky can be obtained by spectroradiometer, remote sensing reflectance is used commonly for building remote sensing model instead of reflectance just beneath water surface. However, the water-leaving radiance obtained from the water surface includes some mirror reflections of the water surface which reflect little information of the waterbodies. What's more, since the mirror reflections of the same water surface are fluctuating when repeating the measurements in the same area of the water surface, the water-leaving radiances obtained from this water surface are not identical in these measurements. Obviously, there is significant difference between remote sensing reflectance and reflectance just beneath water surface. The remote-sensing model of the waterbodies based on remote sensing reflectance exists some errors in retrieving the water quality. Therefore, it is necessary to extracting reflectance just beneath water surface from measured remote sensing reflectance when building the remote-sensing model of the waterbodies and retrieving the parameters of the water quality. This paper builds a novel remote-sensing model and proposes an approach to extracting reflectance just beneath water surface from measured remote sensing reflectance based on the model. In the proposed model, there are two assumptions: the radiance from the underwater is steady and identical in all directions after the radiance entering into the under water is scattered entirely by the water molecule and the particle of other material in the waterbodies, and the measurements of the radiance are completed in a short period of time. Based on the above assumption, the differences among several remote sensing reflectance which were measured repeatedly in same area of the waterbodies in a short time are related to fluctuation of the water surface. In this model, the mirror reflectance model of water surface about wavelength is firstly obtained from a group of remote sensing reflectance spectra measured repeatedly over same area of waterbodies, and then reflectance just beneath water surface is extracted from the remote sensing reflectance using the least squared method and the Levenberg -Marquardt algorithm. After the proposed model being built, three groups of experiments for remote sensing reflectance measured above clean waterbodies, waterbodies with suspended sand and alga in Lake Taihu are conducted and reflectance just beneath water surface of these three waterbodies are extracted successfully. Both the theoretical deduction and the experimental result demonstrate that the proposed model is effective and efficient.

Paper Details

Date Published: 26 July 2007
PDF: 12 pages
Proc. SPIE 6752, Geoinformatics 2007: Remotely Sensed Data and Information, 67521D (26 July 2007); doi: 10.1117/12.760694
Show Author Affiliations
Tangyou Liu, Donghua Univ. (China)
Aihua Dong, Donghua Univ. (China)
Wujun Xu, Donghua Univ. (China)
Demin Li, Donghua Univ. (China)


Published in SPIE Proceedings Vol. 6752:
Geoinformatics 2007: Remotely Sensed Data and Information

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