New Publication - Range Measuring (fwd)

From: Pita Admininstrator (
Date: Tue Aug 14 2001 - 13:01:54 EDT

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    Dear Colleagues,

    Some subscribers to Marmam may be interested in this paper which describes a
    method for measuring range to animals at sea and accurately tracking their
    movements. It should find applications in survey, behavioural studies and
    mitigation work.

    Jonathan Gordon (


    Jonathan Gordon

    Measuring the range to animals at sea from boats using photographic and
    video images

    Journal of Applied Ecology 38 (4), 879-887

    Estimating range to objects at sea by eye is notoriously difficult yet there
    are many occasions in management and research when accurate measures of
    range are required.
    A new method is described in which range is calculated from the angle
    subtended between the horizon and the waterline of the object measured from
    single video or photographic images taken at a known elevation. Possible
    errors are explored and practical analysis methods outlined. Images can be
    collected and analysis performed using relatively inexpensive standard
    In offshore waters, uncertainty in the height of the camera and target
    object due to the effects of waves and swell are likely to be the most
    significant sources of error. The effects of errors in camera height on
    ranges calculated using this method are approximately proportional to the
    ratio of the height error to camera height. Simulations indicate that wave-
    and swell-induced errors in the height of both object and camera will lead
    to range estimates with a standard deviation (SD) of 0.5 ? (error due to
    wave height)/(camera height).
    Three trials were conducted in which ranges (out to 2000 m) measured using
    this method were compared with those determined using alternative methods
    (laser range-finding binoculars or non-differential global positioning
    system). Mean percentage discrepancies in range measurements between the two
    methods varied from 6.4% to 2.6%, while the SD of discrepancies in trials
    varied between 6.5% and 4.3%. The independent range measuring methods used
    here were not without error, however, and it is suggested that a mean
    absolute error of > 2% is an appropriate figure for the video method.
    Field tests indicated that the necessary photos or video sequences could be
    collected from most types of cetaceans in the field. A variety of
    applications for the method during activities such as line transect surveys,
    mitigation monitoring and behavioural studies are suggested and discussed.
    Key-words : cetacean, line transect, mitigation, photogrammetry,

    Present address and correspondence: Jonathan Gordon, Sea Mammal Research
    Unit, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife
    KY16 8LB, UK (fax 01334 462632;
    Received 4 August 2000; revision received 2 January 2000

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