Poyang Lake is the largest freshwater lake in China, and
it plays an important role in flood control regulation and
storage and biodiversity protection. Chlorophyll-a concentration
levels in the water can reflect the primary productivity
status, and it is also an important indicator to evaluate
the degree of eutrophication. Remote sensing technology is
conducive to the chlorophyll-a concentration monitoring of
Poyang Lake, and has the advantages of covering a wide range,
low cost, and ease of long-term dynamic monitoring.
The water quality experimental data was collected and
analyzed by the staff of the Poyang Lake Wetland Observation
and Research Station of the Nanjing Institute of Geography &
Limnology, Chinese Academy of Sciences. The water samples
were collected on the spot and pretreated on the ship. After
the lake test, the samples were taken back to the laboratory
for analysis and determination, and the chlorophyll a
concentration was measured. There were three instances when
water quality sampling and synchronized water spectra measurements
were conducted: in October 2011, July 2012, and October 2012.
The geographic location and altitude information of the
corresponding sampling sites was recorded.
Inversion models of each of the seasonal chlorophyll-a concentration
data from 2009 to 2012 in Poyang Lake were built by a
semi-empirical method. A chlorophyll-a sensitive band range
was determined based on analysis of spectral characteristics
of the water body. According to the regression analysis between
the reflectivity of Moderate Resolution Imaging Spectroradiometer
(MODIS) channels in the sensitive zone and the measured
chlorophyll-a concentration, a relationship between
chlorophyll-a concentration and spectral indices consisting
of various combinations of MODIS data bands can be built by
seasonal quarters (January represents winter, April represents
spring, July represents summer, and October represents autumn).
The models that have a maximum coefficient of determination
and minimum root-mean-square error were chosen as the inversion
models of chlorophyll-a concentration.
The MODIS remote sensing data and the independent measured
data were used to verify the accuracy of inversion models.
The relative error was used to measure the effectiveness of
The verification results showed that the dataset was reliable,
and the analysis revealed that the chlorophyll-a concentration
in Poyang Lake increased slowly from 2009 to 2012 . The
lowest annual chlorophyll-a concentration occurred from
December to February, then rapidly rose to peak from March
to July, and declined from August to November. In terms of
spatial distribution, the highest areas of chlorophyll-a
concentrations were located in the coastal waters and five
river estuary areas. The higher the concentration that was
observed, the more significantly the spatial characteristics
The varied temporal and spatial characteristics of chlorophyll-a
concentrations in Poyang Lake were the result of the combined
effects of lake nutritional conditions, water temperature, water
level changes, storms, and human activities. The temporal variation
was mainly affected by natural factors such as changes in water area,
while the differences in spatial distribution were predominantly
influenced by ship traffic, sand mining, and agricultural activities
in the surrounding areas.