2008 
33 
ACTIVE-PASSIVE OPTICAL REMOTE SENSING FOR WEATHER AND CLIMATE 
RESEARCH 
Jun LI a , Wei GONG 3 , Zhongmin ZHU b , Yingying MA a 
a State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing 
hNational Engineering Research Center for Multimedia Software 
Wuhan University, Wuhan, Hubei, China - larkiner@gmail.com 
KEY WORDS: Lidar, Climate change, Sunphotometer, Aerosol 
ABSTRACT: 
Studying optical properties of atmospheric aerosol is important because aerosol affects people around the world significantly. 
Aerosol can directly affect climate change by scattering and absorption of solar and other radiations, and also indirectly affect the 
radiation by affecting cloud formation. Tropospheric aerosol is associated with air pollution and adverse health effects. These effects 
strongly depend on the physical and optical properties of aerosol particles. In this paper, we present the method combined 
sunphotometer (passive measurement) and Lidar developed by Wuhan University (active remote sensing measurement) to retrieve 
the aerosol optical depth. The primary results show that the proposed method improved the precision of aerosol optical depth 
effectively. Furthermore, long-term atmospheric and aerosol data could be obtained by consecutive Lidar and sunphotometer 
observations. Also these data will be useful for future understanding about their environmental and climate effects. 
1. INTRODUCTION 
Studying climate and a changing climate is important because 
changing environmental conditions will affect people around 
the world. Aerosol is as the most important atmospheric 
composition as a measurement of regional air pollution and for 
the uncertain impact on global climate. According to the U.S. 
Climate Change Science Program, factors such as aerosols, land 
use change, and others may play important roles in climate 
change, although their influence is highly uncertain at the 
present time. However, it is affirmed that their change will alter 
our surrounding condition and impact human health and 
animal-plant ecosystem. 
Aerosols can directly affect climate change by scattering and 
absorption of solar and other radiations, and also indirectly 
affect the radiation by affecting cloud formation. These aerosols 
have residence time of few days, and thus are distributed 
inhomogeneously in the atmosphere, presently, there are still 
many uncertainties concerning the spatial distribution, the shape 
of the atmospheric aerosols (Frejafon et al., 1998). AOD 
(aerosol optical depth) is one of the most important parameter 
of the aerosol optical properties to assess the the variety of the 
atmospheric aerosol. 
For estimating more accurately the abundance and sources of 
aerosols and better understanding how aerosols affect global 
climate, various active and passive measurements have been 
developed to provide aerosol optical properties. Combinatin of 
different observations into an integrated system helps to obtain 
quantitative information from the lidar measurements, for 
which several assumptions concerning the optical properties 
and the composition of the aerosols are necessary (Chih-Wei 
Chiang et al., 2007; D.Balis et al., 2000). Aerosols are now 
widely monitored by using lidars, which can provide vertical 
profiles of backscattering coefficient. There is also a remote 
sensing aerosol monitoring network initiated by NASA under 
the name of AERONET (AErosol RObotic network). Up to now, 
most experiment in china is about dust aerosols for the northern 
region model. Further researches about emending the existing 
atmospheric model and aerosol type and make them more 
compliant for central China area application find lack of data at 
Wuhan. We develop the Lidar-Sunphotometer system (Active- 
Passive Optical Remote Sensing) for obtaining optical attribute 
parameters about aerosols and other atmospheric components. 
The combined use of the active and passive optical remote 
sensing is valuable when attempting to detect atmospheric 
transport phenomena and diffusion properties for climate 
change. 
2. EXPERIMENTAL SETUP 
2.1 Lidar system 
A mobile aerosol lidar named WUML has been developed by 
the State Key Laboratory for Information Engineering in 
Surveying, Mapping and Remote Sensing (LIESMARS) at 
Wuhan University. It is well-known that elastic backscatter 
lidars have been shown to be effective tools for measuring 
aerosol optical properties. The mobile aerosol lidar WUML is 
constructed basis of elastic Mie-scattering theory of particle, 
which can show aerosol distribution in atmosphere in both 
space and time, and provide valuable information in identifying 
boundary layer optical depth, elevated aerosol layers, wave 
activity, and sources of pollution. In this section, the framework 
and theory of WUML system is introduced. 
WUML consists of a laser pulse transmitter, an optical 
receiving telescope and data acquisition and processing 
subsystems. The Nd:YAG laser transmitter works at the 
wavelengths of 1064 nm and 532 nm. It operates at 20 Hz pulse 
repetition frequency. The receiver consists of a 25 cm telescope. 
The detected signals from the PMTs are fed into the amplifier. 
The outputs of the amplifier are connected to a PC-based data 
acquisition system. The system provides backscatter signal