15. Morphology of the Fan Surface

Vertical incision and lateral shifting of channels across the fan form a characteristic stepped fan morphology. The incised channels are often punctuated by backfillings that become with time entrenched again and finally display inset terraces. The fan surface displays both grain roughness and a microtopography roughness which gradually diminish with time by surface smoothing processes. The roughness can be shown by remote sensing through the different brightness of the fan surface. Estimation of the surface roughness can be accomplished by conducting spectral field measurements, by airborne hyperspectral data analysis, by measurements of the ground-reflected solar radiance, and by using airborne lidar-radar data. The trend of decreasing roughness with age suggests the roughness criteria as a measure of relative-age determination. The average backscatter from a surface can be effectively utilized as a proxy for the surface age.