Wilting, chlorosis, and necrosis, which are evidences of plant stress problems, produce tonal differences that color infrared can detect. A true red indicates healthy plants, whereas light red, pink, and bluish-pink indicate plants under stress. Texture is the degree of roughness or smoothness-a visual impression usually related to crop density and plant height variation. Pattern is the repetition of tonal or textural characteristics over a given area. Pattern arrangement is often a clue to its origin.
Shape is the recognition of geometric configurations usually defined by tonal differences.
Shape is seen, for instance, in the contrast between lighter and darker colored soils, more poorly drained vs. better drained soils, etc. A soil survey map of the photographed areas can then be used to identify the different soils present. Interpretation is a skill that improves with training and practice. It also requires confirmation by field evaluation and use of all the information available on that given land area. Aerial photography can be an effective way to evaluate performance of cropland acreage.