Topographic normalization of air photos

Empirical Method for Topographic Correction in Aerial Photographs
Tal Svoray1 and Yohay Carmel
1Department of Geography, Ben Gurion University, Israel.
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We suggest an empirical method to correct topographic effects on vegetation classification of panchromatic aerial photographs. The method is based on the use of spatial interpolation technique that constructs a luminance surface from targets of high brightness values. The luminance surface is then used to correct the topographic effects differentially, by increasing brightness values in shaded areas and decreasing brightness values of lightened areas. For this purpose, the use of a trapezoidal function was found successful in the reduction of standard deviation of brightness values of trees, shrubs and herbaceous plants after empirical correction. This method outperformed a frequently used DEM-based topographic correction in terms of overall classification accuracy of the resulting images.