Vegetation includes all plant communities that cover the earth surface. And vegetation cover is the most important
index to scale the status of the vegetation of the region, so the vegetation is the composition and the function body of
ecological system. Vegetation cover in different districts of Wuhan were calculated based on remote sensing images (TM
images and ETM+ images) in 1988, 1991, 1996 and 2002 by employing NDVI method for dimidiate pixel model, and
the vegetation cover maps of different periods were generated to analysis the temporal change of vegetation cover of
Wuhan area. The results showed that, the vegetation cover changed much from 1988-2002; the average vegetation cover
of the whole area was decreased from 58.41% to 50.45%, especially in Jiangxia district and the central district. From
1996 to 2002 is the period which vegetation cover decreased the most sharply in this period. From 1991 to 1996 the
vegetation cover was lightly increased in the whole study area. Analyzing spatial changing characteristics in the whole
study area we can see that, the whole area was in the decreasing moment, especially in Jiangxia district and the central
district, this was the result of urban development, and led to the huge development of the environment, worthy of all
aspects of attention.
The occurrence of algal bloom has threatened the water quality of Taihu Lake that provides drinking water for millions
of people in the eastern Chinese city of Wuxi, Jiangsu Province. Chlorophyll a presented in living phytoplankton is a
very important ecological and environmental parameter of waters and it is usually used as indicator of the algal bloom.
To assess changes in chlorophyll a concentration distributions before an algal bloom in Taihu Lake on May 29,2007, a
linear model was established between the radio of band 1 (620-670nm) to band 2 (841-876nm) of the MODIS mediumresolution
bands and the in situ measurements of chlorophyll a concentration. The distributions of chlorophyll a
concentration are mapped. The phytoplankton patches are evenly distributed over the Taihu Lake during March 2007,
while the patches are confined to north part of the lake along the bank during May 2007, including Meiliang Bay where
the water supply of Wuxi city is. This study demonstrates that the moderately high resolution of MODIS/Terra 250-m
data is useful for monitoring the chlorophyll a distribution in small inland water body such as Taihu Lake.
The Pearl River system is mainly located in the Guangdong Province in southern China, with the length of 2214 km and total area of 453,690 km2. The Pearl River estuary is the largest estuary in the South China Sea (SCS), with a mean annual discharge of 326 billion m3, of which are about 30 million tons of dissolved matters annually discharged into the estuary. The high concentration of suspended sediments and dissolved matters makes the optical properties of the coastal waters very complex.
The spectral absorption coefficient of yellow substance [Ay(λ)] is one of the inherent optical properties that influence the reflectance (or water-leaving radiance) of the water body. It is essential to measure Ay(λ) and to quantify its contributions to the total absorption of the water body. In this study, the Gelbstoff Optical Analyse Laboratory System (GOALS), with spectral range from 200 to 850 nm and with spectral resolution of 0.37 nm per pixel, was used to measure Ay(λ) in the Pearl River estuary and in the adjacent coastal waters in July 2002. Ay(400) was around 1.5 m-1 near the river mouth (zero salinity). It decreases with increasing salinity following an apparent non-linear mixing line. There is no apparent relationship between Ay(400) and dissolved organic carbon (DOC) concentration, indicating that the estuary is a complex, non-point source environment. This presents a great challenge to remote sensing study in this area.
The atmospheric-correction of satellite ocean color data is fundamental for applications of the satellite data. The atmospheric-correction of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data is successful for open ocean waters, but fails for turbid coastal waters, when using the default algorithm of SeaWiFS Data Analyze System (SeaDAS), resulting in an over-correction of atmospheric effects. Based on the basic principle of atmospheric correction, a practical approach was developed for atmospheric correction of SeaWiFS imagery for turbid coastal waters. We took the assumption of spatial homogeneity of band7-band8 ratio of aerosol radiance and of water-leaving radiance over relatively small spatial scales (100-200 km), the two ratios were calculated from the processed results of SeaDAS standard atmospheric correction algorithm. The correction approach could reduce the errors of water-leaving radiance. In addition the water-leaving radiance in turbid water areas where the default SeaDAS algorithms added a mask for atmospheric correction failure could be retrieved. Then the results were compared with that of other atmospheric-correction method for turbid coastal waters.
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