| In inshore areas,there are abundant natural resources which is closely connected with human's economic production and living.With human's coastal activities increasing,the quality of inshore oceans water is severely affected.Therefore,it seems to be especially important to promptly and precisely monitor the quality elements of inshore ocean water.Compared with the traditional underway-pumping sampling measurement which consumes a large number of labor and financial resources,remote sensing measurement has apparent advantages in monitoring quality elements of ocean water,such as celerity,continuousness and large-area monitoring.With the remote sensing data from LANDSAT 8 satellite,this paper carried out inverse studies on the densities of chlorophyll a and suspended sediment in the surface layer of Zhanjiang inshore ocean.Meanwhile,taking some elements like ocean terrain and meteorology into account,the reasons for the concentration distribution of chlorophyll a and suspended sediment were explored,which provided theoretical and data basis for researching the water quality in study area.The main findings of this paper are described as below:1.The inshore ocean in Zhanjiang has the spectral features of case II waters.Because of the influence of suspended sediment,the remote sensing reflectance in the near-infrared area is not equal to zero.Meanwhile,the surface spectrum curves inside and outside Zhanjiang Bay have apparent individual spectral features respectively.The spectrum value inside Zhanjiang Bay start its sharp declination from the spectrum peak of 550 nm along the direction of red light.And the fluorescence peak of chlorophyll appears at the position of about 685 nm.The spectrum data outside Zhanjiang Bay has its minimum at the position of about 440 nm which is connected with the chlorophyll absorption within this waveband.Similarly,the spectrum value has its fluorescence peak of chlorophyll at the position of about 685 nm after its sharp declination from the spectrum peak at 500 nm.Compared with other areas,the absorption near 760 nm is stable,and the region can be used to identify the spectral of Zhanjiang bay as the characteristic.2.After analyzing the correlation of the spectra inside and outside Zhanjiang Bay respectively with the corresponding measured data,the result shows that there is a low correlation.For different waters,the different concentration distribution of water color components will lead to the different optical features of water surfaces.Based on the differences in spectral features,water body can be divided into different subareas.The modeling for each subarea plays an important role in increasing inversion accuracy.After Zhanjiang Bay was divided into inner bay and outer bay according to their different spectral features,correlation analysis was carried out for them respectively.The result shows that there is a greatly increased overall correlation with a peak value of 0.8.The relative errors of models are all about 30%,which means favorable inversion accuracy.3.In general,the inshore ocean of Zhanjiang has a relative high density of chlorophyll a.The density of chlorophyll a inside Zhanjiang Bay is lower than that in the relevant area outside Zhanjiang Bay.The suspended sediment content inside Zhanjiang Bay is higher than that outside Zhanjiang Bay which decreases with the increasing distance from the seacoast.In the study area,the average density of chlorophyll a in May is higher than that in September,while the average content of suspended sediment in May is lower than that in September.In the relatively shallow water area inside Zhanjiang Bay,both chlorophyll a and suspended sediment have a high density for the two voyages.The water where the depth is shallow is easily agitated.This is the result of the phenomenon of the higher concentration of suspended sediment.At the same time,the agitation is promote the nutrient mixing of the whole water,which has a positive effect on the growth of phytoplankton. |
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