The effect of sub-pixel slope variations on photoclinometry

Sub-pixel slope variations can have significant effects on the intensity of light scattered from a planetary surface. As a result, determination of the surface slope from the apparent brightness of a given pixel can be confounded by uncertainly in such variations. Under a wide range of conditions, the average slope across the pixel may be different from what is inferred by photoclinometry. Because topography is derived from photoclinometry by integrating the slope across an image composed of many pixels, topographic elevation could in principle be distorted considerably by this effect. As actually applied, photoclinometry generally includes strategies designed to mitigate these effects substantially. Nevertheless, the potential always exists for unknown variations in the character of sub-pixel topography (among other uncertainties such as albedo variations) to introduce errors. The results shown here show the importance of the mitigating strategies and of considering the magnitude of uncertainties in determination of topography.