Frederick L. Roesler

High spectral resolution lidar to measure optical scattering properties of atmospheric aerosols. 1: Theory and instrumentation

A high spectral resolution lidar technique to measure optical scattering properties of atmospheric aerosols is described. Light backscattered by the atmosphere from a narrowband optically pumped oscillator-amplifier dye laser is separated into its Doppler broadened molecular and elastically scattered aerosol components by a two-channel Fabry-Perot polyetalon interferometer. Aerosol optical properties, such as the backscatter ratio, optical depth, extinction cross section, scattering cross section, and the backscatter phase function, are derived from the two-channel measurements.

The PEPSIOS Purely Interferometric High-Resolution Scanning Spectrometer. I. The Pilot Model

A description is given of the design principles, structure, and use of the PEPSIOS (trade mark) spectrometer, a versatile, easily portable, purely interferometric, high resolution short-range scanning instrument consisting essentially of an interference filter and several simultaneously pressure-swept Fabry–Perot etalons in series. In the study of a continuum, where it was necessary to isolate a single order, it has exhibited a luminosity 102 as great as that of a comparable modern grating-etalon combination instrument at the same resolution and is considerably lighter, smaller, and mechanically more stable. Although designed primarily for the photoelectric measurement of the total flux through an axial zone, the instrument has the property of producing a two-dimensional spatially resolved image at high spectroscopic resolution.

Emission profiles of neutral oxygen and sulfur in Io's exospheric corona

Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) observations of Io acquired in 1997 [Roesler et al., 1999] provided the first simultaneous spatially resolved measurements of emission from neutral sulfur and oxygen, the dominant atomic species in Ios exospheric corona. Previous measurements of Ios corona relied primarily on sunlight resonantly scattered from sodium, a trace element in Ios atmosphere, and required measurement during mutual satellite eclipses to obtain the necessary spatial resolution. We present here spatial profiles of Ios extended emissions derived from observations spanning the time period from October 1997 to February 2000. The STIS Far Ultraviolet Multi-Anode Microchannel Array (FUV-MAMA) detector permits measurement of the emissions with a spatial resolution of ∼0.05 Io radii out to distances of ∼20 Io radii. Useful measurements are limited to ∼10 Io radii owing to the low signal-to-noise ratio of the extended emission features. The coronal emission profiles vary considerably in slope and intensity and are generally brighter for Io west (duskside) of Jupiter. Emission profiles obtained near western elongation are relatively symmetric about Io; profiles obtained in other orbital positions display varying degrees of asymmetry, with enhanced emissions and generally steeper slopes in the downstream direction relative to the plasma flow. The downstream-upstream profile asymmetry is thought to be caused by higher electron densities in Ios plasma wake. While the coverage of the data is limited in both Jovian System III coordinates and geocentric phase, the intensities of emission from regions both near Io and in the extended corona vary with System III longitude in a near-simultaneous fashion, suggesting local torus electron density as the probable source of this modulation. The observed ratio of oxygen to sulfur emission is relatively constant in time, perhaps reflecting the stoichiometric ratio of the SO 2 source molecules. Eclipse and posteclipse observations on February 25, 2000, show a dramatic increase in profile emission brightness and slope, suggesting a dynamic response by a sublimation-supported component of Ios SO 2 atmosphere and associated atomic species.

Spatial Heterodyne Imager for Mesospheric Radicals on STPSat-1

[1]xa0The Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) was a high-resolution, near ultraviolet spectrometer that imaged the Earths limb for 2.5 years between March 2007 and October 2009. The instrument used the Spatial Heterodyne Spectroscopy technique for the first time on a satellite and successfully demonstrated its capabilities. SHIMMER measured the solar resonance fluorescence of the OH A2Σ+-X2Π (0, 0) band around 309 nm, which allows the retrieval of mesospheric OH density profiles. It also measured the Rayleigh scattered background from the clear atmosphere and solar scattering from polar mesospheric cloud particles. We present details on the SHIMMER mission, the payload design, and the data analysis. A comparison between SHIMMER and concurrent Microwave Limb Sounder OH data shows good agreement between 60 and 90 km altitude for several latitudes and seasons. We also find good agreement of the SHIMMER OH densities and standard photochemical model calculations between 60 and 80 km. We find no evidence of a 25%–35% mesospheric OH deficit, previously reported using Middle Atmosphere High-Resolution Spectrograph Investigation (MAHRSI) OH data. However, independent analysis of Rayleigh scattered background signals observed by SHIMMER and MAHRSI under similar lighting conditions revealed that MAHRSI radiances are systematically smaller than SHIMMER radiances by 24%. Although this difference is well outside of the combined uncertainties for both experiments, the agreement of SHIMMER OH with Microwave Limb Sounder OH and standard photochemistry results, together with our Rayleigh scattering comparison, suggests an unidentified MAHRSI calibration problem that effectively eliminates the mesospheric OH deficit reported using MAHRSI observations.

Design and laboratory tests of a Doppler Asymmetric Spatial Heterodyne (DASH) interferometer for upper atmospheric wind and temperature observations

We describe the design, fabrication and laboratory tests of a Doppler Asymmetric Spatial Heterodyne (DASH) interferometer for upper atmospheric wind and temperature observations of the O[1D] 630 nm emission. The monolithic interferometer has no moving parts, a large étendue, relaxed fabrication and alignment tolerances and can measure multiple emission lines simultaneously. Laboratory measurements indicate that the design resolution and étendue were achieved and that thermal drifts can be determined with sufficient precision for geophysical applications.

Initial ground-based thermospheric wind measurements using Doppler asymmetric spatial heterodyne spectroscopy (DASH)

We present the first thermospheric wind measurements using a Doppler Asymmetric Spatial Heterodyne (DASH) spectrometer and the oxygen red-line nightglow emission. The ground-based observations were made from Washington, DC and include simultaneous calibration measurements to track and correct instrument drifts. Even though the measurements were made under challenging thermal and light pollution conditions, they are of good quality with photon statistics uncertainties between about three and twenty-nine meters per second, depending on the nightglow intensity. The wind data are commensurate with a representative set of Millstone Hill Fabry-Perot wind measurements selected for similar geomagnetic and solar cycle conditions.

Broadband, high-resolution spatial heterodyne spectrometer

Design and performance parameters for a broadband, high-resolution spatial heterodyne spectrometer (SHS) are reported. The Mark 1 SHS achieves more than a factor of 5 in continuous wavenumber coverage with a design resolving power in the hundreds of thousands.

New Fourier Transform All-Reflection Interferometer

This paper describes the design and tests of an all-reflection two-beam interferometer. The interferometer consists of three reflecting diffraction gratings and two collimating mirrors. The use of only reflection optics eliminates the need for a transmitting beam splitter and compensation plate thus permitting the possibility of using the interferometer in the vacuum ultraviolet. This instrument can be used as a Fourier transform spectrometer. Obtaining the spectrum of the incident light from the interferogram is not so straightforward as with a Michelson interferometer. The method of Fourier inversion is described, and examples of interferograms taken with the instrument and the spectra obtained from the interferograms are presented. The interferometer has been tested in the visible and in the near ultraviolet at 2537 A.

High spectral resolution line profiles and images of comet Halley

Abstract High-spectral-resolution line profiles and images of comet Halley were obtained in 1986 at the National Solar Observatory McMath telescope, using a dual-etalon Fabry-Perot spectrometer. The spectrometer was designed to obtain data in four distinct modes: (1) high-resolution (R = 200,000) scanning, (2) high-resolution imaging, (3) moderate resolution (R = 30,000) scanning, and (4) moderate resolution imaging. This paper describes the instrument and some examples of data obtained in the high-resolution scanning mode.

Fabry-perot spectrometer adjustment for the compensation of Doppler shift from rapidly rotating and rapidly flowing sources.

The Doppler shift of light from a rapidly rotating or rapidly flowing source limits the spectroscopic resolution with which it can be studied using Fabry-Perot spectrometers that have the usual axial fringe adjustment. Because of the angular dependence of the wavenumber transmitted by the Fabry-Perot, the entrance aperture can be positioned off-axis at an angle chosen such that the wavenumber shift across the entrance aperture matches the shift presented by the source, thereby compensating for the Doppler effect. The principle can be extended to the Michelson interferometer for Fourier transform spectroscopy when the Michelson is used without field compensation. High resolution spectra obtained with a PEPSIOS spectrometer using the entire disk of Jupiter, a rapidly rotating planet, are presented as an example.