ANALYSIS ON OPTIMAL BANDS FOR RETRIEVAL OF MIXED CANOPY 
CHLOROPHYLL CONTENT BASED ON REMOTE SENSING 
GAO Yan-hua*' b 'CHEN Liang-fti w , ZHOU Xu d , LI Li’, LIU Qin-huo 1 , TIAN Guo-liang’ 
State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing Applications, Chinese 
Academy of Sciences, Beijing 100101, China 
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 
Beijing 100101, China 
c The Center for National Spacebome Demonstration, Beijing 100101, China 
d National Geomatics Center of China, Beijing 100044, China 
KEY WORDS: Spectral indices, Chlorophyll content, Spectral derivative, Optimal bands, Mixed canopy 
ABSTRACT: 
A large number of spectral indices have been developed for estimation of leaf chlorophyll content. However, in most cases these 
indices have been tested for only one or at most a few related species and thus it is not clear whether they can be applied across 
species with varying leaf structure characteristics. The main objective of the study was to find spectral bands that are sensitive to 
variation in chlorophyll content and are relatively insensitive to species and leaf structure variation, and determine optimal wide 
bands range for retrieving chlorophyll content of mixed canopies that consist of diverse species, then develop wide bands based 
approach to retrieve chlorophyll content of mixed canopies. We analyzed the correlation between chlorophyll content and reflectance, 
the first derivative of reflectance using LOPEX93 database respectively. The results showed: (1) red edge spectral indices provided 
relatively good correlation with chlorophyll content when applied across a wide range of species; (2) the optimal band for estimation 
of chlorophyll content was found at 698-715nm range; (3) for the first derivative of reflectance, the optimal bands for estimation of 
chlorophyll content were at 720-735nm range and 535-550nm range. 
1. INTRODUCTION 
The content of chlorophyll is an important biomarker of the 
actual plant status. Natural or anthropogenic stressors have a 
direct effect on chlorophyll content, which suggests that a 
chlorophyll measurement may provide information on the plant 
physiological state. Chlorophyll content is also linked to 
nitrogen content and, hence, to photosynthesis. Nondestructive 
remote determination of leaf chlorophyll content permits the 
measurements of changes in pigments over time for leaves and 
avoids time-consuming and expensive traditional chlorophyll 
concentration measurements. A number of studies have been 
carried out to design an appropriate algorithm to estimate the 
chlorophyll content of structurally homogeneous agriculture 
crops (Daughtry et al., 2000; Haboudane et al., 2002), but also 
for structurally complex coniferous forest canopies 
(Zarco-Tejada et al., 2004), using optical remote sensing data. 
Many spectral indices have been developed for estimation of 
leaf chlorophyll content. However, in most cases these indices 
have been tested for only one or at most a few related species 
and thus it is not clear whether they can be applied across 
species with varying leaf structure characteristics. 
The main objective of the study was to find spectral bands that 
are sensitive to variation in chlorophyll content and are 
relatively insensitive to species and leaf structure variation, and 
determine optimal bands range for retrieving chlorophyll 
content of mixed canopies that consist of diverse species, then 
develop wide bands based approach to retrieve chlorophyll 
content of mixed canopies. 
2. METHODS 
2.1 database used in this study 
In order to have a wide range of variation of leaf internal 
structure, pigmentation, water content and biochemical 
components, plant species with different types of leaves were 
required. The LOPEX93 database was used as a good data 
source. The LOPEX93 experiment was conducted during the 
summer of 1993 in the Joint Research Center at Ispra, Italy. 
About 70 leaf samples representative of more than 50 species 
were collected from trees, crops and plants, and the leaf 
hemispherical reflectance and transmittance were measured 
over the 400nm-2500nm wavelength interval. In parallel with 
the spectral measurements, many physical and biological 
measuiements were performed on the samples (Hosgood et al., 
1994), such as chlorophyll content , water content and 
carotenoids content. In this database, 62 fresh leaf samples with 
measurement of spectral reflectance and chlorophyll content 
were available. 
2.2 Data Analysis 
This study focused on developing an understanding of the 
relationship between the spectral reflectance properties of 
diverse vegetation and the content of chlorophyll within the 
constituent plant tissue. Correlation analysis was performed to 
determine the strength of relationships between total 
chlorophyll content and spectral reflectance, the first derivative 
of reflectance respectively based on LOPEX93 database. 
* GAO Yan-hua*, A 11 Datun Road, Chaoyang District, Beijing, 100101 China (E-mail: gaoyh@igsnrr.ac.cn)