Extension of the 'Two-Colour Method' to Evaluate the Band Intensities in the Night Airglow

Abstract

In the filter photometry of the night airglow two filters are used, one centred on an 'emission line' and the other excluding the line, estimating the 'background'. The extension of this 'two colour method' for reduction of OH molecular band intensities is described. The errors involved due to the approximations are discussed. It is pointed out that one of the most important but uncertain factors in evaluating absolute intensities is the estimation of the ratio of the background intensities in the two wavelength regions transmitted by 'emission' and 'background' filters.