Remote Sensing Detection Model Of Particulate Organic Carbon In Hangzhou Bay Turbid Water

Particulate organic carbon?POC?is the organic particulate matter produced by marine organism metabolism,sediment resuspension and the input of land source.It is the main form of carbonation and migration in seawater.POC plays an important role in the overall ocean carbon cycle and global climate system.Conventional methods are always not qualified for large-scale marine research of POC,with the development of remote sensing technology,remote sensing monitoring has become an important way to monitor POC concentration.The remote sensing inversion of POC also has significant regional characteristics in Hangzhou Bay becase of the high sediment concentration.Sediment resuspension leads to the change of TSM concentration and PSD,which is not only the main factor affecting the adsorption capacity of POC,but also the main factor affecting the change of remote sensing signal.Only using TSM concentration to establish the remote sensing inversion model of POC concentration is overestimated.considering the PSD of suspended matter can improve the accuracy of remote sensing inversion of POC.Four sampling points of Zhapu,Andong,Jinshan and Luchaogang were set up in Hangzhou Bay,continuous spectral observation and water sampling were carried out.Based on TSM and the composition of PSD,the remote sensing inversion algorithm between remote sensing reflectance and POC concentration was established,and the short-period spatiotemporal variation of POC concentration in Hangzhou Bay was revealed by MODIS remote sensing image.The main contents and results are following:?1?Field data acquisition and processing.Collecting surface and vertical water covering large,medium and small tides by the fixed-point observation,TSM concentration,POC concentration,PSD of suspended particles and other data were obtained in the laboratory,spectral data obtained by spectral measurements above the water surface.The spectral data show that the reflectivity of surface water in Hangzhou Bay has typical spectral characteristics of high sediment concentration with obvious double reflection peak characteristic,the second reflection peak is obviously higher than the first one.Through the consideration of the spectral range of the peak and the remote sensing sensitive band to the change of TSM and POC concentration,the first two channels 645nm and 858nm of MODIS were selected to participate in the establishment of the POC model.?2?Study on remote sensing inversion empirical model of POC concentration in surface water.The remote sensing inversion model of TSM concentration and PSD were established respectively by analyzing the two factors that influence POC concentration?TSM concentration and PSD?.Finally a POC concentration remote sensing model only based on remote sensing reflectivity,a POC concentration remote sensing model based on TSM,a POC concentration remote sensing model based on TSM and particle size distribution D50,a POC concentration remote sensing model based on TSM and particle size distribution D₁₀,D₅₀,D₉₀ were established combined with the empirical relationship between POC,TSM and PSD.Through the comparison and analysis of these four POC concentration remote sensing models,it is found that TSM and particle size D₁₀,D₅₀,D₉₀ are involved in the POC concentration remote sensing model have the highest accuracy,indicating that the POC remote sensing model based on TSM concentration and PSD has clear physical meaning,and fully consider the influence of TSM and PSD on the mass concentration and volume concentration of POC,which can estimate the POC concentration more accurately.In addition,only D₅₀ can not fully express the particle size composition of suspended particles,D₁₀,D₅₀,D₉₀ are involved in the model can be relatively complete expression of particle size distribution,a more comprehensive grasp of underwater information.?3?Application of MODIS remote sensing image of POC concentration in surface water.The MRT software is used to pre-process the MODIS remote sensing image,such as spatial stitching,projection conversion and resampling.After the ENVI image cutting,water extraction,masking and calculation,the POC concentration map of Hangzhou Bay is obtained,and finally through ArcGIS for image finishing output.The temporal and spatial variation characteristics of the Hangzhou bay can be seen from the POC map:the POC concentration during the spring tide was significantly higher than that during the neap tide and high concentration in the north and low in the southwest,the concentration of POC in the nearshore is higher than that in the far offshore.?4?A preliminary study on the empirical mode of POC concentration in vertical water.the vertical water POC remote sensing model was established by the relationship between the surface TSM and the POC concentration of each water layers and combined with the TSM concentration remote sensing model.The vertical water POC concentration can be demonstrated by remote sensing images.The results showed that the change of POC concentration in the Hangzhou Bay area was not obvious and the POC concentration was basically in the mixed state due to the effects of sand carrying and resuscitation caused by tide,runoff,wind and waves.