Vincent J. Abreu

The high-resolution Doppler imager on the Upper Atmosphere Research Satellite

The high-resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) is a triple-etalon Fabry-Perot interferometer designed to measure winds in the stratosphere, mesosphere, and lower thermosphere. Winds are determined by measuring the Doppler shifts of rotational lines of the O2 atmospheric band, which are observed in emission in the mesosphere and lower thermosphere and in absorption in the stratosphere. The interferometer has high resolution (0.05 cm−1), good offband rejection and excellent stability. This paper provides details of the design and capabilities of the HRDI instrument.

Tomographic inversion of satellite photometry

An inversion algorithm capable of reconstructing the volume emission rate of thermospheric airglow features from satellite photometry has been developed. The accuracy and resolution of this technique are investigated using simulated data, and the inversions of several sets of observations taken by the Visible Airglow Experiment are presented.

Observations of winds with an incoherent lidar detector

We have developed a Fabry-Perot interferometer and image-plane detector system to be used as a receiver for a Doppler lidar. This system incorporates the latest technology in multichannel detectors, and it is an important step toward the development of operational wind profiler systems for the atmosphere (troposphere, stratosphere, and lower mesosphere). The instrumentation includes a stable highresolution optically contacted plane talon and a multiring anode detector to scan the image plane of the Fabry-Perot interferometer spatially. The high wavelength resolution provided by the interferometer permits the aerosol and molecular components of the backscattered signal to be distinguished, and the Doppler shift of either component can then be used to determine the wind altitude profile. The receiverperformance has been tested by measuring the wind profile in the boundary layer. The Fabry-Perot interferometer and image-plane detector characteristics are described and sample measurements are presented. The potential of the system as a wind profiler in the troposphere, the stratosphere, and the mesosphere is also considered.

The quenching rate of O(1D) by O(3P)

Abstract The rate coefficient for the quenching ofO( 1 D) by O( 3 P) has recently been calculated by Yee et al. (1985). Their results indicate that quenching by atomic oxygen should not be ignored in the analysis of the 6300 A emission airglow. Data obtained by the Visible Airglow Experiment (VAE) on board the AE satellites have been reanalyzed to determine the quenching rate of O( 1 D) by atomic oxygen. The results of this analysis are presented.

Visible wavelength Doppler lidar for measurement of wind and aerosol profiles during day and night

An incoherent (direct detection) Doppler lidar is developed that operates in the middle of the visible spectrum and measures wind and aerosol profiles during the day and night from the planetary boundary layer to the lower stratosphere. The primary challenge of making a lidar measurement in the visible spectrum during daylight hours is the strong presence of background light from the sun. To make a measurement of this type, the laser line must be isolated spectrally to the greatest extent possible. This has been accomplished through the use of a multiple etalon Fabry-Perot interferometer in combination with a narrow-band filter. The incoherent technique and system are a modified version of the Fabry-Perot interlerometer and image-plane detector technology developed for an earlier Doppler lidar developed at the University of Michigan and for the High-Resolution Doppler Imager (HRDI) now flying on the Upper Atmosphere Research Satellite. The incoherent Doppler analysis is discussed and sample measurements are shown. Winds are measured in the boundary layer with 100-m vertical resolution and 5-mm temporal resolution with 1 to 3 m s-1 accuracy.

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.

Wind measurements from an orbital platform using a lidar system with incoherent detection: an analysis.

A lidar system from an orbital platform is used to simulate the measurement of winds in the atmosphere using different scattering regimes. A high-resolution Fabry-Perot interferometer with a multiple-ring anode detector is used in the simulations. The main factors that limit the accuracy and spatial resolution of the measurement, such as laser bandwidth, detector resolution, and pointing accuracy, have been considered. It is shown that winds in the troposphere and stratosphere can be measured with an accuracy of 2 m/sec using the backscattered signal from aerosols and from cloud tops. In the mesosphere a wind accuracy of 5 m/sec can be achieved using the backscattered signal from the resonance fluorescence of sodium.

Further quantification of the sources and sinks of thermospheric O1D) atoms

Abstract In this paper we confirm an earlier finding that the reaction constitutes a major source of OI 6300 A dayglow. The rate coefficient for this reaction is found to be consistent with an auroral result, namely k1 ≈ 6 × 10−12 cm3s−1. We correct an error in an earlier publication and demonstrate that reaction (1) is consistent with the laboratory determined quenching rate for the reaction where k 2 = 2.3 × 10 −11 cm 3 s −1 . Dissociative recombination of O+2 with electrons is found to be a major daytime source in summer above ∼220 km.

ATMOSPHERIC SCATTERING EFFECTS ON GROUND-BASED MEASUREMENTS OF THERMOSPHERIC WINDS

Abstract Inherent in observations of thermospheric winds from the ground with the Fabry-Perot interferometer is the assumption that the measured Doppler shift is a property of the source medium viewed by the instrumental line of sight. However, ground based airglow observations in regions of weak airglow emission near large intensity gradients may be contaminated by scattered light. Light from areas where the emission is strong can be scattered by the lower atmosphere into the field of view of the observations. Thermospheric winds deduced from the observed Doppler shifts will then show apparent convergence or divergence with respect to the site of observation. Examples of this effect are found in observations by the Michigan Airglow Observatory station located near the auroral zone at Calgary, Alberta. Simulation calculations based upon an experimental model for a significant scattering atmosphere also showed results with either convergence or divergence in the apparent neutral wind field observed by the station.

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.