Rock outcrops in arid and semiarid regions frequently have abundant lichen cover. We collected lichens and their granite, slate, and hornfels substrates in the Extremadura region of Spain and measured spectral reflectance in the 400–2500 nm region in the laboratory. Lichen cover as low as 30 percent masks the spectral features of spectrally flat rocks such as slate and hornfels. The sharp spectral features of granite are obscured at 60–80 percent lichen cover. The strong reflectance peak at 2220 nm in lichens interferes with recognition of the 2200 nm absorption band in hydroxyl‐bearing minerals that is used to locate hydrothermally altered and potentially mineral‐rich areas. However, lichen spectra are characterized by distinctive absorption features that occur in few minerals and can thus be used to identify lichen presence. From computer modeling of laboratory spectra, we conclude that Landsat Thematic Mapper (TM) band ratios of 3 : 4 and 5 : 2 best minimize lichen effects in TM image analysis.

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Examination of SEASAT SAR images of eastern Maryland and Virginia reveals botanical distinctions between vegetated lowland areas and adjacent upland areas. Radar returns from the lowland areas can be either brighter or darker than returns from the upland forests. Scattering models and scatterometer measurements predict an increase of 6 dB in backscatter from vegetation over standing water. This agrees with the SCWigital number (DN) increase observed in the digital SEASAT data. The brightest areas in the Chickahominy, Virginia, drainage, containing P. virginica about 0.4 m high, contrast with the brightest areas in the Blackwater, Maryland, marshes, which contain mature loblolly pine in standing water. The darkest vegetated area in the Chickahominy drainage contains a forest of Nyssa aquatica (water tupelo) about 18 m high, while the darkest vegetated area in the Blackwater marshes contains the marsh plant Spartina alterniflora, 0.3 m high. The density, morphology, and relative geometry of the lowland vegetation with respect to standing water can all affect the strength of the return L band signal.

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