Digital processing algorithms that specifically display spectral differences are needed for better use of Landsat images in vegetated areas. A modified principal-component (PC) enhancement was applied to a Landsat scene of eastern Virginia: a second inverse rotation was applied to the uncorrelated axes, so that the image presentation of the PC data resembles the color relationships in a false color composite. Fieldwork showed that several types of coniferous and deciduous oak forests could be readily distinguished on the image.

An E-W elongate zone, 45 km long by 20 km wide along the James River west of Richmond, was defined on the image based on the distribution of a chestnut oak (Quercus prinus) forest. In this area, chestnut oak has a strong affinity for weathered coarse upland gravel deposits. Although such Miocene(?) gravel deposits are scattered throughout the image area, nowhere else are they concentrated into a linear zone. In addition, several other structural features coincide with the linear segments of the James River drainage: (1) a series of offsets in the gravity gradient map, (2) an inland extension of the offshore Norfolk fracture zone, and (3) a zone of seismicity near the James River. Such cross-strike features had an important role in the thin-skinned tectonics of the Valley and Ridge and may have important applications for the extension of the Eastern Overthrust belt postulated beneath the Piedmont.

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