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.

Piezoelectric scanning of Fabry-Perot spectrometers: nonlinearities

Piezoelectric materials used in mechanical scanning of Fabry-Perot spectrometers are found to have measurable nonlinearities. Dynamic scanning has been used in the present investigation in order to decrease the effects of some of the variables, such as creep, of the piezoelectric material in static operation. The results show mainly a decrease in the distance between corresponding maxima, or apparent free spectral range, as the driving voltage increases to higher values. A relationship between this voltage and displacement (in terms of orders) has been derived, and it is given by v(i) = In {1 - (x(i) - x(0))/[a/(1 - b) - x(0)]}/In b, where v(i) is the displacement in orders from an arbitrary starting point, x(i) is a quantity directly proportional to the voltage, while x(0) is also a quantity proportional to the voltage at the arbitrary reference point, a is the distance between the arbitrary reference point and the next order, and b is the nonlinearity constant for a given piezoelectric material. Examples are given for emission and absorption measurements where the usually large effects of the piezoelectric material nonlinearities are derived, as well as schemes to minimize or altogether remove the effects by suitable handling of the data or by changing the experiment such that the scanning is forced to be linear.