Effects of variation in look angle and wavelength in radar images of volcanic and aeolian terrains, or Now you see it, now you don't

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Abstract
A variety of geological targets can have similar radar backscatter and be indistinguishable when observed at particular wavelengths and/or look angles. Certain lava flows of various types and forests can appear identical at some wavelengths, but different at others. Conversely, unvegetated sand dunes change appearance dramatically at different look angles but change little with observing wavelength. Unvegetated sand dunes become completely invisible when imaged at radar look angles greater than the angle of repose. Some volcanic features which are easily discriminated from their surroundings when observed at one look angle can be completely indistinguishable at another. Smaller look angles can provide images with superior surface type discrimination for areas of modest relief. In areas of low sand dunes when subsurface radar imaging can occur, it is possible to observe the surface dunes at one look angle and the subsurface at another. At present there is no a priori way to identify surfaces which may be confused under different viewing conditions. Radar images from a single system configuration do not give a complete picture of the observed surface, any more than a single channel visible or near-infrared image. Multi-angle multiple wavelength images would increase the ability to interpret an observed landscape correctly. These observations have implications for the interpretation of radar images of other planets such as Venus.