Satellite Estimates of WideRange Suspended Sedime

Authors: Fang Shen Wouter Verhoef Yunxuan Zhou Mhd Suhyb Salama Xiaoli Liu

Publish Date: 2010/06/22

Volume: 33, Issue: 6, Pages: 1420-1429

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Abstract

The Changjiang Yangtze estuarine and coastal waters are characterized by suspended sediments over a wide range of concentrations from 20 to 2500 mg l−1 Suspended sediment plays important roles in the estuarine and coastal system and environment Previous algorithms for satellite estimates of suspended sediment concentration SSC showed a great limitation in that only low to moderate concentrations up to 50 mg l−1 could be reliably estimated In this study we developed a semiempirical radiative transfer SERT model with physically based empirical coefficients to estimate SSC from MERIS data over turbid waters with a much wider range of SSC The model was based on the Kubelka–Munk twostream approximation of radiative transfer theory and calibrated using datasets from in situ measurements and outdoor controlled tank experiments The results show that the sensitivity and saturation level of remotesensing reflectance to SSC are dependent on wavelengths and SSC levels Therefore the SERT model coupled with a multiconditional algorithm scheme adapted to satellite retrieval of widerange SSC was proposed Results suggest that this method is more effective and accurate in the estimation of SSC over turbid watersThis research was funded by National Natural Science Foundation of China no 40871165 and the “111 Project” B08022 Field data were supported by the Creative Research Groups of China from the NSFC no 40721004 and the “973 National Basic Research Program” The authors are grateful to scientists and graduate students from our laboratory for their assistance in in situ measurements and samplings Thanks to the European Space Agency ESA for providing MERIS data via the support of ESA approved Cat1 project id 4359 We are grateful to three anonymous reviewers and editors for their helpful comments and suggestionsThe parameters L 0 S and G are spectral variables and dependent on atmospheric conditions such as visibility and aerosol types In the absence of in situ measured atmospheric composition data and meteorological data over the study area at the moment of the satellite overpass these parameters can be simulated for various atmospheric conditions and viewing geometries so as to form LUTsThe generated LUTs included atmospheric visibilities of 5 10 20 and 40 km The atmospheric model used for the simulations was midlatitude summer and the candidate aerosol types were maritime rural desert urban tropical and Navy maritime with air mass character of 3 default value The zenith angles of sun and viewing were respectively varied from 0° to 70° 5° interval and the relative viewing azimuth varied over the angles of 0° 45° 90° 135° and 180° Atmospheric components such as CO2 water vapor and ozone gas were set to 380 ppmv 40 g/cm2 and 027 atmcm respectivelyFor a Lambertian surface the relationship between the directional surface radiance L and the total incident irradiance E i is given by L = rE i/pi while the remotesensing reflectance is defined by R rs = L/E i which thus implies that R rs = r/pi

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