Laboratory studies of alkali metal filter deposition, ultraviolet transmission, and visible blocking.

Far-ultraviolet alkali metal or Wood's filters have been produced and tested supporting the production of a flight filter for the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Sodium layers 0.5-1-microm thick transmit up to 40% in the ultraviolet while efficiently blocking visible wavelengths. The prevention of visible pinholes is assisted by a clean, sleek-free surface and a cooled substrate during deposition. The coatings are stabilized efficiently by a bismuth overcoating whose transmission spectrum is presented. We also report for the first time, to our knowledge, the first demonstrated long-wavelength cutoff from a lithium filter, with a shorter cutoff wavelength than sodium and potentially higher stability for astronomical imaging.

Validation of wind profiles measured with incoherent Doppler lidar.

A high-resolution incoherent Doppler lidar has been constructed at the University of Michigan Space Physics Research Laboratory. The primary purpose of this lidar is to measure vertical profiles of the horizontal wind field with high spatial and temporal resolution. In mid-1994 a rawinsonde system was used to assess the performance of the lidar. The resulting comparisons of profiles from the balloons and the lidar are shown. The comparisons show an ~2-m/s rms error between the two systems. The reasons for this error are discussed, and a sensitivity study is shown to illustrate the sensitivity of the lidar wind measurements to various system parameters. Finally, steps that are being taken to improve the systematic errors are discussed.

Analysis techniques for the recovery of winds and backscatter coefficients from a multiple-channel incoherent Doppler lidar.

The University of Michigan has developed an incoherent-detection Doppler lidar system that continuously measures vertical profiles of horizontal winds and aerosol backscatter. An overview of the instrument is given, followed by a description of improvements that have been made to control the system stability. Most notably, an active feedback system has been implemented to improve the laser frequency stability. A detailed forward model of the instrument is developed that includes many subtle effects, such as detector nonlinearity. A nonlinear least-squares inversion method is then described that permits the recovery of Doppler shift and aerosol backscatter without requiring assumptions about the molecular component of the signal. Examples of wind and aerosol backscatter profiles are shown to illustrate the capabilities of the fitting method.

Absorption and emission line shapes in the O(2) atmospheric bands: Theoretical model and limb viewing simulations.

A multiple scattering radiative transfer model has been developed to carry out a line by line calculation of the absorption and emission limb measurements that will be made by the High Resolution Doppler Imager to be flown on the Upper Atmosphere Research Satellite. The multiple scattering model uses the doubling and adding methods to solve the radiative transfer equation, modified to take into account a spherical inhomogeneous atmosphere. Representative absorption and emission line shapes in the O(2)((1)Sigma(+)(g)-(3)Sigma(-)(g)) atmospheric bands (A, B, and gamma) and their variation with altitude are presented. The effects of solar zenith angle, aerosol loading, surface albedo, and cloud height on the line shapes are also discussed.

Inversion of Fabry-Perot CCD images: use in Doppler shift measurements.

We consider how to use a charge-coupled device (CCD) as an imaging device for a Fabry-Perot interferometer. When the CCD is used in a conventional manner (pixel by pixel readout), the read noise limits its usefulness. Instead, we propose using the CCD in an operational mode so that the 2-D circular symmetric Fabry-Perot interference pattern is read as a 1-D array. The recovery of the signal is effected by carrying out an Abel inversion of the 1-D array. We show how by carrying out this operation it is possible to reduce greatly the effect of read noise. Finally, we consider how this image technique reflects on the accuracy of a Doppler shift measurement.

Use of gamma ray radiation to parallel the plates of a Fabry-Perot interferometer.

A technique is described by which radiation is used to shrink Zerodur posts and parallel the plates in anairspaced Fabry-Perot etalon.

Optimization of a triple etalon interferometer.

The High Resolution Doppler Imager (HRDI) is a triple etalon Fabry-Perot interferometer designed to measure Doppler shifts of rotational lines in the O(2) atmospheric system from the Upper Atmosphere Research Satellite. These shifts are used to determine wind vectors in the stratosphere and mesosphere. This paper presents the techniques used to determine the gap thicknesses and reflectivities of the three etalons of the HRDI instrument. The spacings are found to be 1.000, 0.186, and 0.025 cm. These spacings are independent of the reflectivity of the etalons. The reflectivities of the three etalons should be nearly equal to minimize the errors in the wind measurement caused by mistuning of the etalons. The choice of the reflectivity does not strongly influence the statistical error in the wind error when the values are less than ~0.90.