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DETERMINATION OF CHLOROPHYLL CONCENTRATION
IN THREE GORGES DAM USING CHRIS/PROBA IMAGE DATA
GAI Li-ya 3 ’ b , LIU Zheng-jun a ,ZHANG Ji-xian a
a Chinese Academy of Surveying and Mapping, Beijing 100039,China-(zjliu,zhangjx)@casm.ac.cn
b ShanDong University of Science and Technolgy,Qingdao,266510,China-gailiyal982@163.com
KEY WORDS: CHRIS/PROBA; Chlorophyll; Retrieval; Three Gorges Dam
ABSTRACT:
Quantitative remote sensing inversion methods of chlorophyll concentration in Three Gorges Dam based on CHRIS/PROBA data are
mainly discussed in this paper. Destriping, geometric correction, radiation correction, atmospheric correction of CHRIS/PROBA is
processed firstly, and the remote sensing reflectance is acquired. According to the water characteristics of Three Gorges Dam area,
we analyze the influences of suspended substance on the retrieval of chlorophyll contribution and obtain that the ratio of band red
and blue (.R652/R566)' 1 can reduce the influences of suspended substance than the ratio of blue and green band
(i?461//?566) effectively. Based on this rule, we choose the ratio of the absorption peak and the reflection peak R6M/R566 of
chlorophyll spectrum characteristic, and establish the retrieval algorithm of chlorophyll concentration with the semi-empirical linear
regression method. With the remnant samples the precision of the model is tested and reliable. At last, we apply the model on the
images that we obtained, the distribution of chlorophyll concentration retrieved is consistent with the results measured. Analyses
show that CHRIS/PROBA images have the potential to be applied in water quality remote sensing monitor of Three Gorge Dam area.
Chlorophyll is an important parameter for water quality
estimation of inland water. It determines the spectrum
characteristic of water on a certain extent (Zhu Ling-ya, 2006)
Many research efforts have been done on it to establish remote
sensing estimation models. For example, Thiemann S (2000)
detected the concentration of chlorophyll in Mecklenburg Lake
using spectrum ,which are measured in situ, and IRS-1 C
satellite data; P.A Brivio (2001) evaluated the concentration
diversification of chlorophyll in Garda Lake using TM data;
Shu Xiao Zhou (2000) estimated the concentration distribution
of chlorophyll in Taihu Lake using OMIS- II aviation imagery
spectrum. However, as the otherness of research areas, the
precision and the adaptability of models is regional (Zhou Yi,
2004).
New satellite remote sensing data such as CHRIS/PROBA
provides opportunity for water quality remote sensing monitor
of inland water. The Compact High Resolution Imaging
Spectrometer (CHRIS) on board the Project for On-Board
Autonomy (PROBA) platform system provides the first high
spatial resolution hyperspectral/multiangular remote sensing
data from a satellite system, which represents a new source of
information for Earth Observation purpose.
On one hand, the PROBA platform provides pointing in both
across-track and along-track directions. In this way, the
CHRIS/PROBA system has multiangular capabilities,
acquiring up to 5 consecutive images from 5 different view
zenith angles (VZA).Each imaged target has an associated
“fly-by” position, that is the position on the ground track when
the platform zenith angle, as seen from the target ,is a minimum.
The platform acquires the images at times when position is
equal to a set of fly-by Zenith angle (FZA): 0° ,±36° or ±
55° . Negative FZAs acquire geometries when the satellite has
already flown over the target position.
On the other hand, CHRIS measures over the
visible/near-infrared (NIR) bands from 400 nm to 1050
nm,with a minimum spectral sampling interval ranging
between 1.25 (@400 nm) and 11 nm (@1000 nm).It can
operate in different modes, compromising because of storage
reasons. The data we are presenting in this work were acquired
using operation Mode-2, with 18 spectral bands at a spatial
resolution of 18 m. CHRIS/PROBA images will be another
potential data for water quality remote sensing monitor of
inland water.
1. INTRODUCTION
The Three Gorges Dam is the biggest water power generation
in the world. It’s located at 30.73N, 108.13E, in HuBei
province, China (See fig 1).
Figl. Location of the Three Gorges Dam in China
There are three pollution sources along the Yangtze River
between the Sandouping and Chongqing city, such as
Chongqing urban area, Wanzhou district and Fuling district,
which let a thousand million tons industry and life sewerages
into the Yangtze River every year. In addition, the primary
branch of the Yangtze River and the area along the line are also
the important pollution sources, letting2, 700,000,000 tons of
industry and life sewerages in it every year (See
http://www.people.com.cn/GB/jinji/222/10814/10824/10836/20
030528/1002716.html ).From June, 2003, the Three Gorges
Dam begins its water storage. Now, its construction has almost
