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Proceedings Paper

Design of an ROV-based lidar for seafloor monitoring
Author(s): Stefan Harsdorf; Manfred Janssen; Rainer Reuter; Bernhard Wachowicz
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Paper Abstract

In recent years, accidents of ships with chemical cargo have led to strong impacts on the marine ecosystem, and to risks for pollution control and clean-up teams. In order to enable a fast, safe, and efficient reaction, a new optical instrument has been designed for the inspection of objects on the seafloor by range-gated scattered light images as well as for the detection of substances by measuring the laser induced emission on the seafloor and within the water column. This new lidar is operated as a payload of a remotely operated vehicle (ROV). A Nd:YAG laser is employed as the light source of the lidar. In the video mode, the submarine lidar system uses the 2nd harmonic laser pulse to illuminate the seafloor. Elastically scattered and reflected light is collected with a gateable intensified CCD camera. The beam divergence of the laser is the same as the camera field-of-view. Synchronization of laser emission and camera gate time allows to suppress backscattered light from the water column and to record only the light backscattered by the object. This results in a contrast enhanced video image which increases the visibility range in turbid water up to four times. Substances seeping out from a container are often invisible in video images because of their low contrast. Therefore, a fluorescence lidar mode is integrated into the submarine lidar. the 3rd harmonic Nd:YAG laser pulse is applied, and the emission response of the water body between ROV and seafloor and of the seafloor itself is recorded at variable wavelengths with a maximum depth resolution is realized by a 2D scanner, which allows to select targets within the range-gated image for a measurement of fluorescence. The analysis of the time- and spectral-resolved signals permits the detection, the exact location, and a classification of fluorescent and/or absorbing substances.

Paper Details

Date Published: 23 May 1997
PDF: 10 pages
Proc. SPIE 3107, Remote Sensing of Vegetation and Water, and Standardization of Remote Sensing Methods, (23 May 1997); doi: 10.1117/12.274728
Show Author Affiliations
Stefan Harsdorf, Carl von Ossietzky Univ. of Oldenburg (Germany)
Manfred Janssen, Carl von Ossietzky Univ. of Oldenburg (Germany)
Rainer Reuter, Carl von Ossietzky Univ. of Oldenburg (Germany)
Bernhard Wachowicz, Carl von Ossietzky Univ. of Oldenburg (Germany)

Published in SPIE Proceedings Vol. 3107:
Remote Sensing of Vegetation and Water, and Standardization of Remote Sensing Methods
Giovanna Cecchi; Torsten Lamp; Rainer Reuter; Konradin Weber, Editor(s)

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