干旱区生态环境知识资源中心

"Forced invariance" is a processing method that can subdue the expression of vegetation and enhance the expression of the underlying lithology in remotely sensed imagery. Data for each spectral band are altered in an empirically derived manner so as to produce a refined band that largely excludes contrasts attributable to variations in vegetation abundance. This is accomplished by (1) correcting the data for the effects of additive path radiance, (2) statistically characterizing the relationship between the band data and a vegetation index, and (3) multiplying the band data as a function of the index so that the average band value is generally invariant across all index values. Comparison of original and processed color composite displays confirms the method’s utility in unveiling rock patterns consistent with nearby well-exposed bedrock and alluvial patterns downslope, especially in areas of open canopy vegetation such as in mixed and and semi-arid terrains.