A system was developed for the delineation of distance intervals in front of an observer during seabird surveys. Delineation is based on a coordinates system (x.y) with the vanishing point on the horizon being the origin (0:0), within a vertical plane in front of the observer. Coordinates of parallel interval limits can be calculated using y = H x/dp (H = height of the observer's eyes; dp = perpendicular distance between transect centerline and interval limit), and coordinates of radial interval limits using (wp = distance between the observer and the vertical plane in direction of interval limit; dc = observer's distance to the interval limit). The use of the delineation system will help reduce observer-induced variation in seabird at-sea surveys.
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1 June 2011
Delineating Distance Intervals for Ship-based Seabird Surveys
François Bolduc,
André Desbiens
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Waterbirds
Vol. 34 • No. 2
June 2011
Vol. 34 • No. 2
June 2011
distance sampling
observer-induced variation
pelagic seabirds
trigonometry