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Oceanography
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The Remote Sensing Grey Model for Extracting the Informations on Marine Silts Suspended
Chen Xiao – xiang, Yi Jian-chun and Li Tie-fang
Centre for Remote Sensing, Zhongshan Univ.
Guangzhou 510275, P,R. China
Abstract
The grey feature of marine remote sensing information determines that extracting information’s on the suspended silts from it should use the method of grey mathematics and relative degree analysis.
Through the remote sensing test on marine silts suspended in Huangmao Sea, Yamen, Pearl River Mouth, the authors compared 3 kinds of suspended silts estimating models with relevant grey models, pointed out that grey model can obviously improve the estimating precision and, therefore, proved the marine grey theory introduled by prof. Li Tie-fang, i.e. the transmitting process of marine remote sensing information is a grey system with multi-variable.
The causes of using grey model being able to improve the precision of estimation of silt are as follows:
- The way of relative degree analysis is less affected by small sample.
- The processing of data adding up improved the linear future of data, so that it can match with actual changes of silt content.
- The values of different brightness are separately transformed by different ranges, so the total error will be decreased.
- The processing of data adding up may fully used known data, to some extent, the processing is equal to the processing of signal overlay, so as to enhance the signal/ noice rate.
1. The common models if estimating suspended silt with remote sensing and their problems to be solved
Up to now, the remote sensing models in actual use on suspended silts are mostly the semi-experienced model combined physical model with statistics. According to water bodies in different marine areas, some models were introduced by some experts. the common models in use are as follows:
- To regard the spectral reflection of suspended silts as a linear function.
S- A + B * R (l) -------------------------(1)
- To suppose that the vertical distribution of suspended silts is equal in research area, and absorption coefficient, forward and backward scattering coefficients are constant in given hours.
- To suppose that spectral scattering of silts in water is mainly Mie scattering.
R = A + B ( 1 - eDS) ------------------- ( 3)
- To regard the transference of scattering signal of suspended silts in air and in water as an exponential attenuation function, so logarithm retrieval function is adopted.
Ln (S) = A + B * R ------------------------ (4)
- Proportional value model
S = A + B (Ri (l) / Rj(l) } ------------------------(5)
Note Here, S: Silts Content
R: Remote Sensing Data
i, j,: Different Bands i, j.
A,B,C,D: the coefficients to be determined.
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