Northern Prairie Wildlife Research Center
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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