The area of seagrass distribution in Sanya bay reduced greatly in recent years. In order to make clear the reason of
seagrass decline, the relationship between seagrass distribution and land use change in Sanya Bay was retrieved in the
paper, Landsat TM and ETM+ data of 1991, 1999, in situ observation of seagrass distribution and water chemical indexes
were used to retrieve the information of land use change, seagrass distribution and water quality status in Sanya bay.
From the satellite images, area of eastern and western Sanya Rivers reduced in 1999 compared with that in 1991.
Seashore land use change detection showed that the shape of costal line at the northeast of Lu Huitou peninsular changed
greatly. Corresponding to land use change, the area of seagrass distribution in Sanya bay decreased, from distributed in
the great part of south coast in 1991 to less than 1 hectare in southwest coast of Sanya bay in 1999. The effect of land use
change on seagrass distribution can be concluded as following: seagrass distribution in Sanya area conversely correlated
with land use change, the more area of land use change the less coverage of seagrass distribution. Mainly because of land
use change changed the water quality and sediment type.
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 <i>in situ</i> 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.
Knowledge of shallow water substrate is very important for protection and management of coastal ecosystem.
Traditional methods for observing shallow water substrate was by sending diver to photography and recorded with eye,
which was laborious and money taking. In order to obtain the easier way to study the shallow water substrate, an
underwater video system was designed. Underwater video sensor, optical sensor, sonar sensor, tiltometer, GPS system,
and ascending and descending system were all attached to the buoy system, and data was gathered and processed by the
computer on the ship. The obtained data could be used for analyzing substrate type, activity of benthos and ground truth
data for satellite remote sensing.
In this paper, the light attenuation, fluorescence and absorbance of DOM in Lake TaiHu was mainly studied from July 2001 to December 2002. Results showed that DOM mainly contributed to the attenuation at the ultraviolet, and the best correlation coefficient was at 355 nm. The absorption of DOM could be well described by the exponential decay model. The slope value S, retrieved from absorbance of 350 nm and 440 nm, was 0.0046 nm^-1(SD=0.0015,n=284), far less than the published 0.014 nm^-1. The absorbance at 350 nm (a(350)) well correlated with DOM concentration (R^2=0.673, n=284), and also linearly correlated with fluorescence at 430 nm (R^2=0.497, n=214). The relationship between DOM concentration and fluorescence intensity was also regressed, and showed that it was polynomial.
Light absorption, chlorophyll-specific absorption and package effect of phytoplankton in Zhujiang River mouth was studied on the two cruises of "Shiyan 2". The vertical distribution of phytoplankton in waters can be simulated by Gaussian equation; light absorption of phytoplankton was made on 25 mm GF/F filter, maximum light absorption of phytoplankton was at the depth 5-10m underwater. The value of chlorophyll-specific absorption was negatively correlated with chlorophyll a concentration. Package effect index also had a negative relationship with chlorophyll concentration. These results indicated that the characteristics of light absorption by phytoplankton varied in different waters were properly related to the phytoplankton concentration.
In recent years, great amount of polluted water discharged into the north part of Lake TaiHu, results in water eutrophication and frequent occurrences of blue-green algal bloom in the area. In order to obtain the information about blue-green algal bloom distribution for monitoring water quality, four navigation of in situ hyperspectral measurement and MODIS data of 250 m resolution were used to study the radiance reflectance character and distribution of blue-green algal bloom in the lake. Hyperspectral measurement showed that the peak of water leaving radiance near 700 nm transferred to 750-780 nm as the water covered with blue-green algal bloom and increased with the increasing density of water bloom. Band ratio of channel I to channel II and band synthesize of MODIS image of 250 m resolution were used for detection of algal bloom, and proved that band ratio of channel I to channel II was more suitable for detection of algal bloom. The methods for differentiating submerged vegetation and algal bloom from MODIS image were also tested: The area covered with submerged vegetation usually had high secchi depth, with algal bloom usually low secchi depth, and the phenomena can be used efficiently for differentiating submerged vegetation and algal bloom on MODIS image.
EOS\MODIS data have been proved a suitable and relative low-cost complementary tool to monitor large inland lake water quality for its re-visit frequency, moderate spatial and spectral resolution and appropriate channels designed for inversing water quality parameters. In this study, by the support of hi-tech research and development program of China, Lake water quality remote monitoring pre-operational system (LWQRMPS) was constructed aimed for practical monitoring of Taihu Lake water quality. The main water quality parameters including Chl-a and SPM, TN and TP inversion algorithm were developed. These parameters were obtained every month from time series fusion satellite data. With the routine trophic state evaluation system, the water quality was assessed every month based on the above retrieved MODIS water quality parameters, varied level of eutrophic area was computed. The obvious high reflectance in near-infrared spectrum caused by blue-green algal bloom support the application of 250m MODIS data in the algal bloom emergency monitor. Therefore, MODIS data were utilized successfully for inversing water quality parameters, evaluating eutrophication status, and detecting algal bloom in near real time. Standard thematic maps were produced and distributed to corresponding management departments. The accuracy of products and retrieve algorithm for operational use were tested with separate data sets. The result suggested that system is good enough for practical monitoring water quality of large size lakes and acquired identification.
Monitoring and restoration the water quality of lake need proper water quality parameters. Traditional measurement of water quality requiring laborious laboratory work is expensive and time consuming. Hyperspectral measurement can offer fast and easy way for estimating trophic status. Hyperspectral data on 7-8 March 2004 and water chemical data from 1997 to 2003 was used for retrieval of water quality parameters. The quantification of spectra with water quality parameters: chlorophyll a suspended solids total nitrogen(TN) total phosphorus(TP) chemical oxygen demand(COD) secchi depth(SD) were regressed. Results showed that the reflectance ratio of R702/R685 R6201R53 1 and R554/R675 had high correlations with the concentration of chlorophyll a suspended solids and total phosphorus respectively TN COD can be calculated from TP or Chi a for good relations between them SD is negatively correlated with suspended solids concentration total phosphorus (TP) (less than 0. 25 mg/L) linearly correlated with logarithm chlorophyll a concentration trophic status index (TSI) exponentially correlated with COD concentration.