Volcanic eruption plume top topography and heights as determined from photoclinometric analysis of satellite data

Photoclinometry, a shape-from-shading technique, is applied to satellite data to determine the three-dimensional height and morphology of the upper optical surface of a plume from the eruption of Redoubt Volcano, Alaska. The technique can be applied to visible images of volcanic plumes that have uniform scattering properties and is most effective on images with moderate incident Sun angles and plume transport perpendicular to the azimuth of the Sun. The two most significant sources of error are the finite resolution of the image data and the choice of image data number (DN) value for a flat plume element. Provided the plume spans at least 10 image pixels, useful results can be obtained for the central portion of the plume. The closest approximation to a flat plume element is found to be the visible DN value corresponding to the coldest pixel along a transect. Errors in the element altitude due to uncertainty in the DN value for a flat pixel amount to ;10–20 m per pixel and are cumulative along the plume transect. For Redoubt this results in an uncertainty of approximately 300 m at the highest points. The method indicates that the Redoubt plume rose to an altitude of approximately 3 km while traveling a distance of 150 km from the vent and that the surface topography of the plume exhibits influences of the ambient wind through simple wave structures. This technique will have a tremendous impact on studies of plume spreading dynamics and the timeintegrated evolution of plumes.