Full text: Mapping without the sun

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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
	        
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