International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
SIGNAL NOISE REDUCTION BASED ON WAVELET TRANSFORM
IN TWO-WAVELENGTH LIDAR SYSTEM
Shuo Shi* *, Wei Gong*, Lilei Lv”, Bo Zhu*, Shalei Song“
? State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University,
Wuhan, Hubei 430079, China
? China Petroleum Engineering Limited liability company in North China branch (CPENC), Jianshe Road, Renqiu,
Hebei 062552, China
* Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China
Commission VII/7
KEY WORDS: LIDAR, Data mining, Proceedings, Algorithms, Estimation
ABSTRACT:
Nowadays lidar has become a leading edge technology for photogrammetry and remote sensing. A new lidar with two detection
wavelengths was presented in this paper. The two-wavelength lidar can obtain spatial information and spectral information, and
intensity of backscatter signals in two-wavelength can be availably used for objects identification and observation. However, the
backscatter signals are weak and strongly influenced by the noise. In order to acquire accurate intensity, the signal noise has to be
removed. As a useful tool for signal processing, wavelet transform was chosen. In this study, the principle of two-wavelength lidar
was introduced and possible noise in the backscatter signal was analysed. Then the signal progressing was executed on the basic of
wavelet de-noising. First, singular values caused by varieties of noise source have to be rejected from the signal based on three
standard deviations. Second, combination of modulus maxima method and threshold method is used to make further improvement
on the signal. Finally, an evaluation of the noise reduction was given to testify the ability of the method. The results show that the
effect of the method based on wavelet transform is better than other classical algorithms, and the method is suitable for signal noise
reduction in two-wavelength lidar system.
1. INTRODUCTION
As an active measurement way of remote sensing, airborne laser
scanning (ALS) has become a well-established technology for
the detection of topography and for mapping the Earth's surface
(A. Wehr and U. Lohr, 1999; K. Kraus and N. Pfeifer, 1998).
However, the detection information of target characteristics by
traditional lidar is poor because of the single-wavelength
measurement (J Grace, et al, 2007). A new lidar with two
detection wavelengths was provided by Wuhan University to
improve the obtained information about properties of surface
objects. Not only spatial information of objects but also spectral
information can be acquired by the two-wavelength lidar, and
intensity of backscatter signals in two-wavelength can be
availably used for objects identification and observation.
Furthermore, the two-wavelength lidar might be widely used for
monitoring in the growth and nutrition status of vegetation.
The two-wavelength lidar has been successfully developed and
was used for features monitoring in the laboratory environment.
As is well known, the backscatter signals of lidar are very weak.
And it is difficult to obtain high-quality signals, especially in the
condition of low-power transmitters and strong absorption on
the objects. Besides, the weak signals received might be strongly
influenced by all kinds of noise from the equipment and the
ambient environment. In fact, the final signals acquired by the
instrument are so poor that further application is hard to
* Corresponding author.
E-mail address: shishuo@whu.edu.cn
continue. As a result, the signal noise has to be removed in order
to get accurate information.
Signal noise reduction based on wavelet transform has become
the hot spot of academia right now. It is an effective method to
reduce the noise in signal by wavelet multiscale decomposition
(Liang Zhang, et al, 2002), and was applied for de-noising of
backscatter signals in two-wavelength lidar system. In this paper,
system description of two-wavelength lidar was given and the
backscatter signals were presented. After the analysis of
characteristic of noise, combination method of modulus maxima
method and threshold method was proposed, and it was testified
to be an effective algorithm to reduce the signal noise.
2. SYSTEM DESCRIPTION AND NOISE ANALYSIS
2.1 System Description
The new breadboard instrument of two-wavelength lidar system
has been developed. The system is mainly composed of three
parts: the transmitting sub-system, the optical receiver sub-
system and data acquisition and processing sub-system. The
block diagram of the two-wavelength lidar system is shown in
Figure 1.
