Minnaert Topographic Normalization of Landsat Tm Imagery in Rugged Forest Areas

Minnaert constants (K) were derived from non atmospherically corrected, high-sun elevation angle Landsat TM data (8 June 1996 and 13 July 1997) and DEMs at 30x30 m spatial resolution using the IDL procedure developed at Dartmouth College. K constants were calculated for two contiguous areas in northern Apennines, the former (366 ha) covered by beech (Fagus Sylvatica) forest and the latter (343 ha) by mixed deciduous forest (Quercetalia pubescentis). Calculated Minnaert K ranges for the two forest types and dates were 0.21-0.26, 0.49-0.55 and 0.58-0.63 for bands 3, 4 and 5 respectively, with an r significance level of the K values estimates between 0.77 and 0.91. The correlation factors between uncorrected TM bands 3, 4 and 5 and the cosine of solar illumination angle (i) ranged from 0.70 to 0.91, thus indicating that 49% to 83% of the variance of these bands in this rugged forested area is explained by the topographic effect. K regression significance as well as topographic dependence of TM data tended to increases from band 3 to band 5 for both dates and forest types. Minnaert normalization was effective at removing the topographic effect reducing the correlation coefficients of the three corrected bands with cos (i) within the range -0.07/+0.02.