Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [TP-3 OCEAN/COASTAL ZONE MONITORING]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: CHARACTERIZATION AND DECOMPOSITION OF WAVEFORMS FOR LARSEN 500 AIRBORNE SYSTEM. H. Wong and A. Antoniou

Document type:: Multivolume work

Structure type:: Chapter

CHARACTERIZATION AND DECOMPOSITION OF WAVEFORMS FOR LARSEN 500 AIRBORNE SYSTEM H. Wong and A. Antoniou Department of Electrical and Computer Engineering University of Victoria Victoria, B.C., Canada V8W 2Y2 ISPRS Commission VII Abstract The LARSEN 500 airborne laser ranging system devel oped in Canada is an active remote sensor for the mea surement of sea depths in shallow coastal waters. This system transmits a series of laser pulses from an air craft into the ocean and receives the reflections from the ocean for post-mission processing. The nature of the LARSEN waveforms received varies dramatically de pending on the turbidity, depth, and the surface rough ness of the sea, and the shape and texture of the sea bot tom. In many cases, the separation between the surface and bottom reflections, which is essential in estimating the sea depths, is lost and as a result, unreliable depth estimates are obtained. This contribution is concerned with a method that can accurately decompose a LARSEN waveform into two signal components, namely the surface and bottom re flections, independently of the degree of their overlap. First, a mathematical model that can be used to char acterize the LARSEN waveforms received under diverse circumstances is established. This model is then used in conjunction with an optimization technique to facilitate the decomposition of each LARSEN waveform into sur face and bottom reflections. Optimized parameters of the mathematical model are then used to give accurate estimation of the sea depths. The use of optimization techniques in the estimation of sea depths offers several advantages. First, the overlap ping surface and bottom reflections in the waveform are mathematically resolved into two separate components. Therefore, both the detection and resolution problems can be solved simultaneously. Furthermore, the method is insensitive to changes in the degree of overlap and, as a result, accurate sea-depth estimates can be obtained under a diverse range of circumstances. Key Words: laser bathymetry, mathematical modeling of waveforms, nonlinear optimization. 1 INTRODUCTION Airborne laser ranging systems have been used exten sively in shallow-water bathymetry during the last two decades. Both high flexibility of operation and high rate of coverage are their prime advantages of use. The feasibility of using airborne laser techniques in survey ing shallow coastal waters was first demonstrated with a system constructed at the Syracuse University Research Corporation in 1968 (Hickman and Hogg, 1969). Since then, a number of countries such as the United States, Australia, and Canada have been actively involved in the development of their own airborne laser bathymet ric systems. (Bressel et al., 1977; Casey, 19S4; Banic et al., 1984; Penny et al., 19S6). In Canada, the use of airborne laser methods in the field of hydrography was initiated by the development of the MK I low-power neon laser bathymeter. Testing of the MK I over Kingston Harbour in Lake Ontario was carried out by the Canada Centre for Remote Sensing (CCRS) in 1976 (O’Neil et al., 1978). A second genera tion of the system, MIv II, is a nonscanning light detec tion and ranging (LIDAR) system and initially served as a complement to aerial and satellite remote sensing tech niques (O’Neil, 1980). In order to increase speed, extent of coverage and flexibility, a more advanced system, the LARSEN 500, was developed by CCRS and the Cana dian Hydrographic Service (CHS) (Casey, 1984). This is an advanced airborne scanning LIDAR system designed to measure water depths in shallow coastal waters and meets the standards of the Canadian Hydrographic Ser vice. The LARSEN 500 is capable of measuring depths from 1.5 to 40 m to an accuracy of 0.3 m. The concept and operation of this system is briefly described in the next section. 1.1 Concept and Operation The LARSEN 500 laser beam geometry is illustrated in Fig. 1 and the principles of operation are as follows. Blue-green and infrared (IR) laser pulses are transmit ted simultaneously from the aircraft into the ocean in a quasi-circular fashion. The IR pulse is scattered by the water surface and its reflection permits accurate deter mination of the aircraft height. On the other hand, the blue-green pulse is reflected back both from the surface as well as the bottom of the ocean. The surface echo is much stronger than the bottom return since signal attenuation in water is much stronger than in air. The time interval between the surface and bottom reflections serves as a measure of water depth. The reflections from each set of IR and blue-green laser soundings constitute a LARSEN waveform. This wave form is sampled at 2-ns intervals and 256 consecutive samples are digitized to 6-bit accuracy, and are then recorded. The waveform starts with the detection of the reflection of the IR pulse from the sea surface and the waveform is a record of the reflections of the blue- green pulse from the surface, volume, and bot tom of the sea to a depth of approximately 40 meters. Figure 2 il lustrates the received waveform and various parameters of interest. 1.2 Problems Encountered Water quality is an important factor in the depth pene tration of a laser pulse as it affects the range and accu racy of depth measurement. As absorption and scat tering of laser light are very strong in water (Svan- berg, 1981), particle content in water strongly influences the laser-signal attenuation. This problem is partic ularly serious in coastal waters (prime areas for laser bathymetry) since microscopic marine life is abundant in these areas. On the other hand, backscatter from suspended and dis solved particles in water weaken the laser-signal reflec-

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