PROCEDURES FOR CORRECTING HIGH-RESOLUTION AIRBORNE VIDEO IMAGERY

Airborne videography is a useful way of producing very high resolution remotely-sensed data. Before video data can be used for digital analysis, individual frames must be corrected for geometric distortion and brightness variation. The most obvious geometric distortion occurs because the odd and even fields in a video frame are collected sequentially and can be displaced relative to each other by aircraft roll and forward motion. We describe a procedure for correcting this distortion based on the cross-correlation between individual fields at different spatial lags. Brightness variation across frames occurs because of differences in viewing geometry, bi-directional reflectance variation and atmospheric scattering. We describe a method for removing much of this variation by calculating scattering angle across the image with an optional adjustment for sensor plane tilt. Relations between scattering angle and scene brightness statistics may then be calculated from sequences of images collected along a given transect. These relations can be used to normalise brightness. Tests of normalisation procedures based on mean, standard deviation, and median brightness show that the median gives the best results. This approach also produces better results than commonly-used band ratioing procedures.