Spatio-temporal distribution of Chlorophyll-α concentration derived from MODIS satellite remote-sensing and in situ observations in Sanya Bay, China

摘要

This study examined satellite Chlorophyll-A (chl-α) concentration and in situ observations in Sanya Bay (SYB). In situ observation of chl-α was conducted four times per year at 12 sampling stations in SYB from January 2004 to October 2008. Monthly satellite chl-α was derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) during 2000-2012. This study compared satellite chl-α values to in situ measurements in SYB. The two data sets match well in the whole region except for two estuaries. Results show that the average in situ chl-α was 1.49 mg m~(-3) in SYB. Chl-α was relatively higher (＞2 mg m~(-3)) and more variable in coastal areas, with a tendency to decrease offshore (＜0.4 mg m~(-3)). The chl-α level in summer displayed obviously vertical stratification, with higher values at the bottom and lower values at the surface. Analysis of monthly mean chl-α showed that the highest level (＞2 mg m~(-3)) appeared in December, with the lowest in March (＜1 mg m~(-3)). The gradients are ranked winter, autumn, summer and spring. There was higher chl-α in autumn and winter, which may be associated with the stronger wind monsoon then. Annual mean chl-α from 2000 to 2012 varied from 1.17 to 2.05 mg m~(-3), with the minimum in 2001 and the maximum in 2005. The chl-α level presented a roughly increasing tendency from 2000 to 2012, which may be related to the increasing nutrients associated with the development of tourism and fishery.