Pointing Error Correction for Millimeter Wave Spectroheliograms

Book excerpt: The AFCRL 29-ft millimeter wave antenna at the Prospect Hill Millimeter Wave Observatory, Waltham, Massachusetts, is used to make solar maps (spectroheliograms), at a wavelength of 8.6 mm, for solar forecasting purposes. The half-power beamwidth of the antenna, although only 4 min of arc, is not narrow enough to detect the smaller hot regions that can develop into active centers on the sun. To overcome this limitation, a data-reduction process that can effectively narrow the beamwidth of the antenna, so that finer details on the maps will be visible, is needed. A computer program that can effectively narrow the beamwidth of the scanning antenna system by restoring and enhancing the antenna output has been applied to the Prospect Hill maps. It is believed that the enhanced maps can be further improved if a quiet sun component, or mean map, is subtracted from daily maps before the restoration is attempted. This report describes the technique used on the Prospect Hill IBM 1800 computer system to center the mean and daily maps on a common heliographic reference to effect the subtraction. (Author).