Stepwise Decomposition of Full‐Waveform Data Based on Levenberg Marquardt

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www.as‐se.org/ssms Studies in Surveying and Mapping Science (SSMS) Volume 2, 2014

Stepwise Decomposition of Full‐Waveform Data Based on Levenberg Marquardt Pengcheng Li*1, Qing Xu1, Pingyuan Cui2, Shuai Xing1, Chaozhen Lan1,2 1

Zhengzhou Institute of Surveying and Mapping, No. 66 Longhai Road, Zhengzhou, China

2

School of Aerospace Engineering, Beijing Institute of Technology, Beijing, China

*

lpclqq@163.com; xq@szdcec.com; cuipy@bit.edu.cn; xing972403@163.com; lan_cz@163.com

Abstract Compared with traditional airborne LiDAR, the advantage of full‐waveform LiDAR is that it digitalizes the full backscattered information. Waveform decomposition is the most important part of waveform data processing. A method of stepwise decomposition of full‐waveform data based on Levenberg Marquardt has been proposed, which employs stepwise decomposition and uses Levenberg Marquardt, which is a Gaussian function with non‐linear least squares fitting algorithm, to obtain precise fitting waveform. Experiment results with 4 different waveform data acquired by RIEGL airborne LiDAR have proved that this method is available and effective. Keywords Full‐waveform LiDAR; Waveform Decomposition; Gaussian function; Levenberg Marquardt

Introduction In the last decade, airborne LiDAR (Light Detection and Ranging) played a very significant role in the fields of terrain surveying and mapping, forest monitoring and city modelling. It was accepted as an important supplement of traditional photogrammetry [1]. The technique of airborne LiDAR integrates Laser Measuring device, Global Positioning System (GPS) and Inertial Measuring Units (IMU) [2]. Laser measuring device determines the distance between emitting source and laser points; GPS gets the exact position of the shooting point and IMU measures the attitude parameters. By synchronized and harmonious cooperation of the above three parts, it can directly obtain the 3 dimensional coordinates of targets. Although airborne LiDAR has positive effects on many fields, there still exist some problems. Nearly all processing algorithms about point clouds are based on the geometry information, inevitably there will be some errors when terrain surface is complex. And now most airborne LiDAR systems just record the peaks of wave using built‐in detection method and lost large number of information. For solving the above problems, a new‐type airborne LiDAR has appeared, which can digitize all backscattered information completely. It is called airborne full‐waveform LiDAR. Technique of full-waveform LiDAR The first full‐waveform systems were designed in the 1980s for bathymetric purposes. And the first truly operational topographic system, LVIS appeared in 1999 and demonstrated the value of recording the entire waveform for vegetation analysis. During that time, some experimental systems were also generated by NASA, and RIEGL developed the first commercial full‐waveform LiDAR system, RIEGL LMS‐Q560 till 2004 [3]. All full‐waveform systems contain a waveform digitizer which can record the entire waveform data by a certain interval. For example, Optech’s IWD‐2 (Intelligent Waveform Digitizer‐2) and Leica’s WDM65 are the important parts to do this. The differences on data recording determine their different post processing methods. In airborne full‐waveform LiDAR data, there is not only geometry information, but also some physical information of targets, such as amplitude, pulse width and backscatter cross‐section etc. The data could be obtained by the most important step: waveform decomposition [4]. Users can get waveform parameters and discrete point clouds after decomposing the waveform, and improve precision of filtering results and DEM combined with such waveform parameters [5]. In addition, a more exact classification with these waveform features has been realized [6]. Finally, the building models could be reconstructed based on the classified building points, so as to realize the city modelling. It can be seen from the above that, the step of waveform decomposition guarantees the generation of high quality LiDAR products. The general processing flow of full‐waveform LiDAR data is shown in Fig. 1.

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