A new instrument for the study of mesospheric gravity waves through nightglow observations.

Abstract

The observations of the mesospheric nightglow have been used to study the characteristics of propagating gravity waves for two decades. This study involves the design and construction of an optical instrument with high spatial and temporal resolutions and the development of proper observation mode and data analysis techniques. A new variety of low resolution spectrometer is developed in this dissertation. This device, an Image Plane Detector Spectrophotometer (IPDS), measures the rotational temperature and brightness of molecular band emissions or the brightness of an atomic line. It uses an interference filter as a dispersive element and an Image Plane Detector (IPD) as the photon collecting device. The IPDS can measure a spectrum at twelve wavelength positions simultaneously without mechanical scan. Therefore, it has the advantage of increasing temporal resolution in nightglow observations. The IPDS has high throughput compared to traditional spectroscopic instrument, and it is compact in size and portable. This dissertation describes the principle, design, construction and calibrations of a ground-based IPDS. Although the commercial filter used did not fully meet our specifications, the instrument performed reasonably well. The data reduction technique is described. This technique is used to recover the rotational temperature and brightness of molecular band emissions from observed spectral signals. The errors in recovered parameters are also examined. The ground-based IPDS was set up to measure night-time mesosopheric emissions in Ann Arbor, Michigan. The rotational temperature and brightness of the O$\sb2$(0-1) and OH(6-2) bands were obtained as a function of local time at one position in the sky. Oscillations in the temperature and brightness are clearly revealed, indicating the presence of gravity waves. Some degrees of co-variances showed in the brightness and temperature trends. A four-position observation mode of measuring (OI) green line intensity is described. This measurement is conducted in order to examine the possibility of determining gravity wave parameters. A discussion is given about obtaining wave propagation direction and horizontal wavelength using time delays among the observed intensities at four positions. The result shows that by using only time delays, one cannot uniquely identify the wave. A criterion of eliminating some of possible waves is presented, which is based upon the wave-airglow interaction theory. The effect of background wind is also discussed. As a conclusion, a multi-instrument observation is suggested to completely study the characteristics of gravity waves in the mesosphere.