Retrieval Of Suspended Sediment Concentration And Particle Size Distribution In Hangzhou Bay Based On HJ CCD Images

Case Ⅱ Water are usually located at estuary and coastal areas where water is most closely related to human and strongly affected by human activities. Suspended sediment is one of the most important affect factor for the optical properties of case Ⅱ water, and is also significant greatly to the changes of aquatic ecological environment and silting process of coastal area. Traditional methods about suspended sediment research in large-scale and high dynamic estuaries are limited by time-consuming and labourious. With its advantage of large synchronous data, remote sensing gradually occupied the main position in the field of water research. Based on the measured data and the domestic HJ CCD image data, choosing the appropriate atmospheric correction methods for image processing, the high-accuracy quantitative inversion models of suspended sediment concentration and the related fitting parameters of particle size in Hangzhou Bay is established, respectively. The results will probide a solid theoretical basis and data for later research on the inherent optical properties of suspended sediment. The main research contents and results in this paper are as follows:(1) HJ CCD image atmospheric correction aided by MODIS aerosol dataThe inversion aerosol optical depth (AOD) data of HJ CCD images are obtained by using NIR-SWIR atmospheric correction expansion algorithm to process the MODIS images which quasi-synchronously with the HJ CCD images. The atmospheric correction of HJ CCD is carried out by FLAASH atmospheric correction module, and the visibility data, retrodicted from the AOD data, are inputted as parameters. The results show that the atmospheric correction result at the the first, third and fourth band are all higher than the measured data, while the second band below the measured data; the results accuracy at the third and fourth bands are18.99%and12.60%, respectively, while the first and second band atmospheric correction results accuracy are poor. As a result, the third and fourth bands of atmospheric correction results can be used for the inversion of the suspended sediment concentration. (2) Quantitative retrieval of suspended sediment concentration using HJ CCD image in Hangzhou BayUsing the measured data of SSC and HJ CCD band equivalent measured remote sensing reflectance, the index inversion model was built based on the HJ CCD4,3bands reflectance ratio with the average error of13.60%. Then the SSC in Hangzhou Bay and adjacent waters are inverted from the HJ CCD image after atmospheric correction, the absolute error of result is70.76mg/L, and the relative error is7.12%. The inversion results show that the SSC in the overall Hangzhou Bay is higher and internal difference. The central region has the highest SSC, then gradually descending to the inside and offshore of the bay. Combined with the tide data, the flow rate change and water exchange caused by the trend will affect the SSC distribution of Hangzhou Bay.(3) Suspended sediment particle size parameter fitting and remote sensing inversion inquiryThe amount percentage and the quality percentage of each particle size obtained by laboratory analysis are used to get the number of particles within the instrument range to fit the measured particle number distribution by Junge and2C model, respectively. Fitting result shows that in the radius range of0.55-0.63μm, the fitted values of Junge model significantly higher than the actual value, relative error reaches50.00to178.96%, and2C model relative error is4.22～9.59%. So the number of particles in small particle size can inversed by2C model, and can be used for the MIE scattering study of the inherent optical properties of water body. Then the correlation analysis between fitting parameters and measured HJ CCD-band carried out, results show that the parameter "j" of Junge model and the parameter "a" of2C model have good correlation with reflectance ratio of the4,3-band. Combined with the flow rate data and bottom substances, analysis shows that both of them have significant effect on the value of the parameter of the sediment particle size.