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Northern Prairie Wildlife Research Center

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Improving Prairie Pond Counts with Aerial Video
and Global Positioning Systems

Methods: Image Processing Software

We processed and analyzed video images using 2 software programs (Prepare Video Disk, MarkWet; MicroImages, Lincoln, Nebr.). The Prepare Video Disk program automated transfer and organization of video images from tape to a Panasonic optical disk recorder TQ-3031F under control of a personal computer. A sample of video images covering the transect with 30% overlap among images was transferred from tape and written as an analog signal on video disk. Inputs to the program included aircraft altitude and speed, focal length of the lens, dimensions of the camera's detector, a file containing GPS time, latitude and longitude, and a file containing the latitude and longitude for the beginning and end of each transect segment. The software estimated latitude and longitude for a video image by linear interpolation between the 2 observations in the GPS data file closest to the GPS time of the video image. The software organized video images on video disk by transect segment from the GPS estimate of the latitude and longitude for each video image.

The MarkWet program enabled selection of a file containing video images for a transect segment, the display of a video image on a monitor, alignment and location of transect boundaries, adjustment of image scale, and use of tools for interpreting and marking ponds. The tools enabled (1) interactive image thresholding (Schowengerdt 1983:68), (2) marking ponds by pointing and clicking with the computer mouse, (3) marking multiple ponds within a single wetland basin, (4) adjusting the calculated overlap between video images so that pond markers occurred in approximately the same location on adjacent images, and (5) selecting colors for marking ponds and highlighting areas meeting image threshold criteria.

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