Observations of thermospheric wind velocities and temperatures by the use of a Fabry-Perot Doppler imaging system at Syowa Station, Antarctica

A new optical instrument, the Fabry-Perot Doppler imaging system (FPDIS), has been developed for observations of two-dimensional distributions of thermospheric wind velocities and temperatures by the measurement of the Doppler shift and width of the aurora or of the airglow emission lines of atomic oxygen OI 557.7 nm and OI 630.0 nm over a wide field of view (165°). A technique for the derivation of Doppler temperatures and wind velocities was developed by use of a truncated Fourier series. Thermospheric wind velocities and temperatures have been obtained with unprecedented high temporal (1 min) and spatial (24 points for an all-sky image) resolutions. Errors in the derived wind velocities and temperatures are estimated to be less than 25 m/s and 100 K, respectively, for inner-fringe positions and 35 m/s and 170 K for outer-fringe positions, respectively. This system was applied to observations of thermospheric wind velocities and temperatures at Syowa Station (69.00° S, 39.58° E), Antarctica for the period of one austral winter in 1990.

Stable and rugged etalon for the Dynamics Explorer Fabry-Perot interferometer. 1: Design and construction

This is one of two papers which describe the development and performance of a very stable and rugged etalon designed for use in the Fabry-Perot interferometer, one of the instruments of the NASA Dynamics Explorer satellite mission, and which will obtain global measurements of the thermospheric and mesospheric wind and temperature with an accuracy of aporoximately 10 m/sec. The etalon consists of two flat plates of fused silica, with spacers constructed of Zerodur (a polycrystalline glass ceramic of extremely low expansion coefficient) which are cemented together using cyanoacrylic adhesives. This provides adequate mechanical integrity and stability for any space flight application and has a thermal expansion coefficient of the etalon cavity of <10(-7)/ degrees C.

High-resolution optical measurements of atmospheric winds from space. 1: Lower atmosphere molecular absorption

The brightness spectrum of light scattered by the earth's atmosphere in the vicinity of molecular rotational lines is investigated. These absorption features are shown to be Doppler shifted by horizontal atmospheric winds. It is demonstrated that a modest aperture multiple etalon Febry-Perot interferometer can be used to monitor the global wind system from space by observing these Doppler shifts.

Design of a multiple-zone aperture and application to a Fabry-Perot interferometer

A design for a multiple-zone aperture (MZA), which is applied to a Fabry-Perot interferometer for gaining greater throughput, is described. It is shown that there exists a definite value for the width of the aperture that gives, the minimum error in Doppler temperature measurements when instrumental parameters and the width of the source profiles are given. The effects caused by the imperfections of the MZA are analyzed. The successful use of an MZA with a 15-cm (6-in.) Fabry-Perot interferometer for measurement of an airglow emission line is described.

Thermospheric dynamics investigations with very high resolution spectrometers

Since 1972 high resolution Fabry-Perot spectrometers have been used at Fritz Peak Observatory (39.9 degrees N, 105.5 degrees W), Colorado to measure the nighttime variation of thermospheric temperatures and winds from the line profiles and Doppler shifts of the OI 15,867 K (630.0-nm) line emission in the nightglow. With the aid of these measurements we have defined the nighttime variation of winds and temperatures at F-layer heights for the various seasons of the year during geomagnetic quiet periods. During geomagnetic storm periods deviation in the nighttime variation of the winds and temperatures from those determined during geomagnetic quiet conditions have been shown to occur. In addition, measurements made during geomagnetic disturbed conditions have shown the existence of large-scale thermospheric waves generated at high latitudes by impulsive auroral heating events that are observed to propagate equatorward. The nighttime winds and temperatures measured from Fritz Peak Observatory have been used in various heoretical models of global thermospheric dynamics to infer the global circulation patterns, temperature structure, and thermospheric response to geomagnetic activity. By requiring agreement between the calculated and measured winds and temperatures over Fritz Peak Observatory, the over-all magnitude of the thermospheric high latitude heat source due to auroral processes has been inferred for both geomagnetic quiet and disturbed conditions. This energy source has been shown to be related to dissipation of the ring current energy in the high latitude ionosphere. The results of various geophysical studies using Fritz Peak Observatory data and theoretical model calculation are summarized.

Feedback stabilized fabry-perot interferometer

A method of stabilizing a Fabry-Perot interferometer with respect to a reference wavelength, while simultaneously stabilizing the parallelism of the flats, is described. The method consists of creating correcting signals proportional to the displacement of the fringe maxima of three auxiliary spectral sources with respect to a fixed reference point and feeding these signals back to the interferometer piezoelectric drive so that the correcting signals become time invariant, and the interferometer is stabilized. The stability of the finished instrument with respect to the reference wavelength and parallelism is near lambda/1000, at 546 nm, for a 6-h period; however, the actual parallelism of the etalon is limited by the surface defects of the flats. The method, as described, allows simultaneous stabilization and data taking, since the instrument is continuously updating itself.