2009 Volume 29 Issue 3 Pages 471-484
A new topographic correction method was developed, which can be applied to satellite image in the season of low solar elevation. At first, Minnaert method and C method were tested with the ASTER image of the mountainous area for the time when solar elevation was low to clarify problems of these methods. As a result, Minnaert method could not correct the part where the cosine of the solar incidence angle (cos i) was smaller than or equal to zero because of structural problem of the correction formula. In C method, correction effect was insufficient in the part where cos i was positive. Also, overcorrections were found in the part where cos i was negative because distribution characteristics of Digital Number (DN) were different between positive part and negative part of cos i. In addition, in the winter image used in this study, original DN value had elevation dependence caused by colored leaves and fallen leaves.
In order to solve these problems, DPR (Dual Partitioning Regression) method was developed. In this method, sample data were extracted from each land cover and elevation. DPR method uses inclination of the linear regression line of cos i versus original brightness Do as the correction parameter. In this regard, regression was calculated in positive part and negative part of cos i separately. The correction formulas were derived in such a way that corrected brightness Dc became equal to original brightness Do when cos i was 1. Topographic correction by DPR method was performed with the image which Minnaert method and C method were applied to. As a result, the coefficient of correlation for regressions between cos i and Dc showed a very low value, less than 0.03, in all bands.