Digital photogrammetry for air-photo-based construction of a digital elevation model over snow-covered areas - Blåmannsisen, Norway
Digital elevation models (DEMs) have been constructed over snow-covered and glaciated areas from 11 air photos optimized during production using a semi-automatic contrast-adjusting method called dodging. Construction of the DEMs from the air photos was accomplished using IMAGINE OrthoMAX software. In general, the results of the DEM construction are promising. Analytical and visual comparisons of GPS field data and published maps with the constructed DEMs indicate a high degree of agreement, with an average difference better than 2.8 m for most of the area. Errors and spurious data cells appear to have been minimized throughout most of the DEMs. One height anomaly, an erroneous peak with a height of between c. 250 m and 1200 m above the actual elevation, persistently appeared in one of the DEMs, despite numerous attempts to address the issue. Enhancements during the air-photo scanning process, such as sharpening and applying a tone curve, have been found to have a beneficial effect in reducing such erroneous results.