Spectroscopic and imaging studies of nightglow variations
A survey of the literature on the techniques used in and the results obtained from studies of nightglow variability is presented. Three microprocessor controlled instruments (an eight channel tilting filter spectrometer, an earlier six channel version and a CCD based low light level camera) have been constructed with the aim of studying variations in the nightglow, especially of the type associated with the passage of gravity waves through the emitting layers. The final stages of development of the eight channel spectrometer are described, including the design of automatic dark count and reference light systems, a temperature control system for the filters and an interface for transferring the spectrometer data into a computer. Calibration experiments to determine the wavelength, line shape and intensity response of this spectrometer are described. The development of suites of computer programmes for analysing the data from both spectrometers and the camera is then discussed. For the spectrometers, these perform the functions of subtraction of dark count, reduction of the calibration data to a form suitable for use in the analysis of data spectra in terms of a set of line shapes and continuum response functions, and execution of this analysis to produce plots of the emission intensities and OH rotational temperature versus time. For the camera, software was produced to allow separation of stellar images from the airglow emission; stellar image intensities were analysed in an attempt to characterise atmospheric absorption. Software was also written to correct airglow intensities for absorption and the van Rhijn effect and finally to reproject the images in the form of a map of the emitting layer. Observations made with the instruments working separately and in conjunction are described and the results are presented as an example of the performance of the instruments and the software.