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Microscopy,
An Underwater Digital Photogrammetric System
For Fishery Geomatics
Rongxing Li, Chuang Tao, and Weihong Zou
Department of Geomatics Engineering, The University of Calgary
2500 University Drive, NW, Calgary, Alberta, Canada T2N 1N4
Tel: 403-220-4112, Fax: 403-284-1980
E-mail: rli@acs.ucalgary.ca, WWW: http://loihi.ensu.ucalgary.ca/
R. G. Smith and T. A. Curran
Institute of Ocean Sciences, Canadian Hydrographic Services
P.O. Box 6000, 9860 W Sasnich Road, Sidney, British Columbia, Canada V8L 4B2
KEY WORDS: Underwater photogrammetry, Digital photogrammetry, CCD camera, Calibration
ABSTRACT:
A new Underwater Digital Photogrammetric System (UDPS) has been developed at The University of Calgary and Canadian
Hydrographic Services. An underwater digital CCD imaging system has been mounted on a Remotely Operated Vehicle (ROV).
This system will be used for fisheries and related applications in the marine environment. In this paper, the design and the
implementation of this underwater digital photogrammetric system is described. The mobile photogrammetry and digital imaging
technologies are employed. An efficient system calibration scheme and an underwater photogrammetric model are presented.
Recent test results are given.
1. INTRODUCTION
Exploration of the vast water body of the earth is of increasing
importance for fisheries, development and management of
marine oil and mineral resources, and ocean floor
investigation. Collecting and analyzing underwater data is a
key to the exploration. Requirements for the underwater
imaging technology continue to be diversified in recent years.
Advances in the imaging sensor technology, particularly those
in solid-state devices, led to a trend towards diverless
underwater intervention systems. Intuitively, an efficient and
effective technology is required to meet the demanding needs
of underwater data analysis and interpretation (Turner et al.,
1992).
A research project was initiated at The University of Calgary
and the Canadian Hydrographic Services (CHS) to develop a
mobile underwater digital photogrammetric system for
fisheries and underwater environmental surveys. The current
emphasis is on fish stock assessment which involves the
identification of fish species, calculation of fish size and
volume, visualization and measurement of sea plants.
Traditionally, most of the research on the underwater resource
management depends on the analysis of sonar images.
However, acoustic data are of small scales. On the other hand,
video images provide the capability of direct visual
interpretations. Photogrammetry is recognized as a cost-effect
technology to these applications. Recent advances in
underwater vehicle navigation and digital imaging make
photogrammetry a feasible and practical technology for
applications in underwater surveys and object measurement.
The quantitative rather than qualitative analysis of underwater
images can be achieved by means of digital photogrammetric
processing.
This paper describes an Underwater Digital Photogrammetric
System (UDPS) jointly developed by The University of Calgary
and CHS. Following the introduction, the system design and its
configuration are given. In section 3, a reduced central
319
perspective model and a mathematically rigorous 3D ray
tracing model are described. Section 4 presents an efficient
system calibration. Experimental results and concluding
remarks are given in the last two sections.
2. MOBILE UNDERWATER MAPPING
2.1 Mobility Of The Underwater System
In conventional underwater survey, underwater control is a
complicated work (Leatherdale and Turner, 1991). It is
difficult to select fixed and identifiable points for control.
Serious problems of connections between stereo models may
arise. Artificial magnetic targets and grease paint marks are
used to provide sufficient feature and texture for stereoscopic
measurements. With the navigation capability of the GPS,
underwater mobile mapping becomes a reality in recent years.
Figure 1 gives a brief view of a mobile UDPS. GPS provides
accurate positions of the vessel in a dynamic or semi-dynamic
mode. By means of the integration of multiple local sensors,
such as acoustic systems, pressure sensors and gyrocompasses,
the ROV, which is equipped with a stereo imaging system, can
be positioned with respect to the vessel. After the calibration of
the geometric relationship between the imaging cameras and
the ROV, the stereo image sequences of underwater objects
can be georeferenced in a global coordinate system. Currently,
the gyrocompass and the acoustic system have not been
implemented.
Figure 1. A mobile UDPS framework
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
