Improving Prairie Pond Counts with Aerial Video
and Global Positioning Systems
Introduction
The U.S. Fish and Wildlife Service and the Canadian Wildlife Service have conducted the BGS annually since 1955 (Pospahala et al. 1974). The BGS provides estimates of the population size and production of duck species and the number of ponds in major North American breeding areas (Reynolds 1987). Surveys also furnish data used to evaluate long-term trends in waterfowl populations and pond numbers (Johnson and Grier 1988, Nichols 1991). The BGS data are ocular counts of ducks and ponds from aircraft 30-45 m aboveground on > 70,800 km of transects that sample 3,367,000 km2. Counts are adjusted for visibility bias by a correction ratio obtained from ground counts of ducks and ponds on a subsample of transects referred to as air-ground segments.
Technological advances include aerial videography, global positioning systems, and video disk recorders. Combined, these advances can improve pond count methods. Aerial videography is a potentially useful method for the BGS because (1) data can be acquired through use of aircraft deployed on short notice, (2) images are instantly available for visual and digital analysis, (3) fine spectral resolution images can be obtained by using narrow-band filters, and (4) cost is low relative to other sources of remotely sensed data (Mausel et al. 1992).
The GPS and video disk recorders are 2 other advances important for developing a rapid video analysis system. The traditional approach to capturing and georeferencing video images is labor intensive and difficult because of the large number of images and the small geographic coverage of an image. A GPS can be used to georeference aerial video images and organize video images by geographic location (Bobbe 1992, Graham 1993). Video disk player technology stores thousands of video images and enables random access recall for analysis (Danziger 1990).
Our objective was to develop an aerial video system to rapidly and accurately estimate the number of ponds on transects used in the BGS. Our use of the terms pond, wetland basin, and wetland follow definitions used by Cowardin (1982:60): wetland- an area that possess homogeneous hydrologic, edaphic, and biological characteristics meeting the definition of Cowardin et al. (1979:3); wetland basin-the wetland portion of a land feature capable of holding water because of topography or soil type; and pond-a body of water occurring within a wetland basin.
D. S. Benning, D. J. Nieman, F. H. Roetker, P. W. Rakoski, J. R. Smith, R. C. Bazin, J. B. Bortner, and J. P. Bladen provided data and aerial photography from the BGS. B. R. Euliss and H. T. Sklebar assisted in acquisition of video imagery and roadside surveys. Pilot B. Pearson was instrumental in collecting video data. We thank B. R. Euliss for assisting with processing and analyzing video imagery. J. A. Beiser and W. E. Newton assisted with statistical analysis. The staff of MicroImages, in particular L. D. Miller and M. J. Unverferth, helped design video analysis software, and B. V. Hollingsworth and D. C. Willis wrote the programs. The paper benefitted from comments by A. B. Sargeant, D. S. Gilmer, D. L. Larson, D. J. Nieman, T. L. Shaffer, and G. W. Smith.
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