Improving Prairie Pond Counts with Aerial Video
and Global Positioning Systems
Methods: Video Survey
We obtained aerial video of 870 km of transects used in the BGS on 12-13 May 1992 from a Cessna 172 aircraft (Table 1). The video system consisted of a Cohu 4810 monochrome camera, a 5.9-mm-wide angle lens, a Panasonic AG-2400 portable video cassette recorder, and a Panasonic CT-500V 14-cm color monitor. (Use of trade names does not constitute an endorsement by the Natl. Biol. Serv.) The camera consisted of an 8.8- x 6.6-mm charge-coupled device detector equipped with a near infrared (0.81-0.89 µm) bandpass interference filter and a Kodak Wratten 96, 0.60 neutral density filter. We acquired video at 460 m above ground level resulting in images with a spatial extent of about 685 m across the transect by 515 m along the transect and a ground resolution element of 1.0 m2. Average aircraft ground speed was 200 km/hr.
Table 1. Dates in May 1992 of aerial and ground Aerial Waterfowl Breeding Ground Population and Habitat Surveys in North America (BGS), aerial video and roadside surveys of ponds conducted for this study, and aerial photography for 12 air-ground segments in southern Saskatchewan.
| Air-ground segment |
BGS | Aerial video |
Roadside |
Aerial photos |
|
| Aerial | Ground | ||||
| Shamrock | 9 | 10 | 13 | 14 | |
| Craik | 10 | 11 | 12 | 11 | |
| Marquis | 10 | 11 | 13 | 14 | |
| Hanley | 14 | 15 | 12 | 10 | |
| Tichfield | 16 | 17 | 12 | 10 | |
| Earl Grey | 19 | 19 | 13 | 11 | |
| Cymric | 19 | 19 | 13 | 11 | |
| Peterson | 23 | 24 | 12 | 26 | |
| St. Gregor | 23 | 24 | 12 | 9 | |
| Hendon | 23 | 25 | 12 | 26 | |
| Nut Mountain | 23 | 25 | 12 | 26 | |
| Pleasantdale | 24 | 25 | 12 | ||
We interfaced a Trimble Pathfinder Professional GPS with the video system using a Horita FP-50/TRG GPS-1 time code generator. The GPS consisted of a receiver, an antenna placed in the front or rear window of the airplane, and a data logger. We used satellites with an elevation angle greater than or equal to 7° to obtain position estimates. We collected most GPS data in the 2-dimensional mode because only 3 satellites were in view. We collected a limited amount of data in the 3-dimensional mode when greater than or equal to 4 satellites were in view. The time code generator recorded GPS time on the audio track of video tape to 0.01 second. We recorded GPS observations (time, latitude, longitude) every second on the data logger.
Within 3 days of the video survey, we conducted a roadside survey of ponds seen from the road defining the center line of each air-ground segment except for Peterson, Hendon, Nut Mountain, and Pleasantdale. We recorded location of each pond observed during the roadside survey on 1:12,000 scale aerial photographs.
We also obtained copies of 1:12,000 scale color infrared photographs for the Hendon, Nut Mountain, and Peterson air-ground segments, acquired on 26 May 1992 as base maps for future ground BGS. We used photographs to examine ponds identified as video interpretation errors when video interpretation was compared with the ground BGS.
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