Modeling solar radiation in Arizona's Meteor Crater

We have developed a solar radiation model to simulate the patterns of instantaneous insolation and the daytime propagation of shadows across the regular topography of Arizona's Barringer Meteor Crater. The 175-m-deep Meteor Crater has a nearly symmetric 1.2-km-diameter cone with its ridgeline about 50 m above the surrounding flat plain of the Colorado Plateau. The simulation, which uses a theoretical solar radiation model in which there is no atmospheric attenuation, is presented as a time-lapse animation for 15 October. The animation was developed by overlaying shadow masks on gray-scale images of the crater topography representing the instantaneous insolation at 2-minute intervals during the day from sunrise to sunset. The shadowing algorithm was evaluated by comparing aerial photographs of the crater shadows with model simulations.

Realistic calculations of daily total insolation over the crater topography were made by time integration from the theoretical calculations of instantaneous solar radiation at two-minute intervals from astronomical sunrise to astronomical sunset. The calculations account for atmospheric attenuation of the direct solar beam as it passes through the earth's atmosphere, and for diffuse radiation. Estimates of atmospheric attenuation and diffuse radiation were obtained from measurements taken in Colorado's Brush Creek Valley in 1984. Because the interior south wall of the crater is in shadow during much of the day, large spatial differences in daily total radiation are seen across the interior of the crater. Important variations in total daily radiation are also seen around the crater's periphery. We plan to test the model simulations further using radiation data that will be collected in a major meteorological experiment (METCRAX - the Meteor Crater Experiment) to be conducted in the crater in the fall of 2006. The methods used to model solar radiation and shadow propagation at the Meteor Crater can be readily extended to other topographical situations.