An instrument concept called the Birefringent Imaging Doppler Wind Interferometer (BIDWIN) is being validated in the
Atmospheric and Space Physics Lab at the University of New Brunswick in collaboration with COM DEV Ltd (Ottawa,
Canada) to determine its capabilities for measuring Doppler wind fields in the Earth’s nightglow. The instrument is
adapted from a similar approach used to obtain two dimensional images of high speed (~1000 m/s) flow fields in
plasmas at the Australian National University. For that application the precision of the wind measurements was not
explored in detail. With BIDWIN, the intent is to obtain ~ 5 m/s precision on each bin of a CCD image of the wind
field. An examination of the instrument concept and sensitivity of the wind measurements made using this approach is
undertaken to determine the feasibility of this criterion. The BIDWIN has the advantage over other instruments that can
be used for a similar purpose (such as the field widened Michelson interferometer and Fabry-Perot interferometer) in that
it has no moving parts, has a large throughput, is light weight and is relatively cheap to construct. In this paper, the
instrument concept is presented and the ideal and non-ideal instrument effects are explored. Calibration measurements
conducted using a proto-type of the instrument are used to verify the instrument concept and confirm the feasibility of
the approach for making atmospheric wind measurements.
The SABER radiometer on the TIMED spacecraft scans the earthlimb continuously in ten channels spanning the spectrum from 1.27 to 15 μm. The signature of the diurnal tide in the equatorial region is apparent throughout the mesosphere in TIMED/SABER data, especially in the CO2 15-μm radiance profiles. In addition, layer structures are apparent in a large fraction of the both the radiance profiles and the kinetic temperature profiles derived from them. We present results showing tidal and layer features in the variation with local time and latitude of 15-μm radiance and temperature. Temperature inversion layers (TILs) are regions of extreme perturbations in the retrieved temperature profile where the temperature increases rapidly over 3-10 km range by tens of degrees K, sometimes approaching increases of 100 K, and are not represented in any existing atmospheric climatologies. Theories that have been proposed connect them with the amplitude and phase of atmospheric tides, as well as with the interactions and dissipation of atmospheric gravity waves and planetary waves. The radiance local maxima, or "knees," are more mysterious. Their occurrence is rather unpredictable and not well explained by models, although it is known that they are due to vibrational excitation of CO2 by atomic oxygen and they may have tidal connections. While they may be associated with strong TILs, the most important class occurring at tangent heights in the lower thermosphere between 100 and 115 km appear not to be simply related to local inversion layers. SABER data offers the opportunity to do the first global survey of MLT TILs, determine their spatial extent and persistence time, and develop a global climatology of their occurrence and properties.
To date there have not been any direct measurements of winds in the Martian atmosphere. Measurements such as these are needed in order to understand the nature of the circulation and the transport of constituents in the atmosphere of this planet. In this paper, a conceptual design for a small visible/near-IR imaging interferometer capable of fulfilling this need is described. The design is based on a similar successful instrument, the Wind Imaging Interferometer (WINDII), which flew in Earth orbit. The basic measurement set includes Doppler shifts (from which wind is derived), rotational temperatures, line widths and radiances of isolated lines in the O2(α1Δg) band airglow and O(1S) airglow emission. The design challenges which were met in converting an instrument designed for terrestrial applications to one capable of flying to Mars and operating in conditions there include reducing the mass and power requirements and adapting the instrument to appropriate data rate and S/N requirements. The resulting instrument has a mass of approximately 15 kg, requires on average, 10 Watts of power and has a data rate of 32Mbits/day. In this paper the design of this instrument and how it accommodates the particular requirements of a Mars mission are described.
KEYWORDS: Mirrors, Sensors, Temperature metrology, Oxygen, Michelson interferometers, Interferometers, Thermosphere, Calibration, Space telescopes, Space operations
The Waves Michelson Interferometer (WAMI) is designed to provide simultaneous measurements of dynamical and constituent signatures in the upper stratosphere, mesosphere and lower thermosphere. It is being included as part of the Waves Explorer mission (G. Swenson, P.I. being proposed for NASA's MIDEX program. It is a field-widened Michelson interferometer based on the same design principle as the successful Wind Imaging Interferometer (WINDII). WAMI includes visible and near-IR channels, a segmented interferometer mirror for simultaneous fringe sampling at different optical paths and views the atmosphere in six distinct directions. Use of the segmented mirrors minimizes the aliasing of atmospheric intensity variations into the fringe parameter determinations. This technique also allows two emissions to be viewed simultaneously through the same optical channel. The emissions chosen include lines in the molecular oxygen IR-atmospheric band, a doublet in the hydroxyl Meinel bands and the oxygen green line. The daytime coverage includes winds from 45 to 180 km, and rotational temperature and ozone density from 45 to 95 km. The nighttime coverage is restricted to the airglow layer centered near 90 km where atomic oxygen, horizontal wind and rotational temperature measurements are provided. These measurements provide a rich data set from which dynamics, energetics and constituent budgets can be determined.
Passive radiative cooling is desirable for space borne detectors because it is generally cheaper, less massive and power consumptive than cooling by a mechanical refrigerator or expendable cryogens. Our interest is space borne nadir imaging the OH airglow in Q-branch features of the 9->6 band at approximately 1382.3 nm, and the 2->0 band at approximately 1434.4 nm with sufficient signal to noise to quantitatively retrieve wave structure. Low noise 256 X 256- 40 micrometer pitch HgCdTe detector arrays are available for our application. E.g., the Rockwell Science Center standard 2.5 micrometers PACE product bonded on to the PICNIC read out MUL satisfies our high sensitive and low read noise requirements, but would require a mechanical refrigerator or expendable cryogen to cool sufficiently to satisfy our dark current requirement. To demonstrate an option that would provide our required performance at viable passive radiative cooling temperature, we have procured examples of the more recent RSC double layer planar heterogenous HgCdTe 2D arrays with shorter wavelength cutoff and produced by molecular beam epitaxy on a CdZnTe substrate, and bonded to the PICNIC MUL. Here we describe our test procedures and results that these at relatively warm temperature, the order 160 to 170K, satisfy the requirements for our OH airglow wave imaging application. We describe an instrument model and observational operations to observe the OH airglow wave structure with signal to noise > 100.
KEYWORDS: Sensors, Data modeling, Visibility, Fabry–Perot interferometers, Satellites, Atmospheric modeling, Wind measurement, Interferometers, Optical filters, Signal to noise ratio
The Stratospheric Wind Interferometer for Transport Studies (SWIFT) is a satellite-born limb-viewing instrument which will be capable of globally measuring horizontal winds at altitudes of between 20 and 40 km with a precision of < 5 m/s, a vertical resolution of 2 km and a horizontal resolution on the order of a hundred km. SWIFT will map stratospheric dynamics. The data from the instrument will be important input for models which seek to predict the global distribution of stratospheric ozone. In addition, the SWIFT data will provide observational input to tropospheric weather models, which are currently being extended to the stratosphere. With global stratospheric wind data, these enhanced models have the potential to significantly improve weather forecasting in the troposphere. The instrument will observe a thermal emission line of an abundant atmospheric constituent near 8 micrometers using a field widened Michelson interferometer. A doppler shift of the emission line is detected as a phase shift at the output of the interferometer. A 2D array detector monitors the phase both perpendicular to and along the limb, thus mapping the velocity field. The fundamental feasibility of the instrument will be shown. The basic instrument requirements are described and the instrument parameters are derived from them. The instrument will utilize radiatively cooled optics and Stirling cycle coolers for the detector and filters. This instrument will be suitable for inclusion on a medium to large satellite with multiple instruments. The lack of cryogens is consistent with its intended use on the operational weather satellites of the future.
Among the emissions viewed by the wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) are selected lines in the (0 - 0) transition of the O2 atmospheric band. These lines are viewed simultaneously using a narrow band filter/wide- angle Michelson interferometer combination. The narrow band filter is used to separate the lines on the CCD (spectral-spatial scanning) and the Michelson used to modulate the emissions so that winds and rotational temperatures may be measured from the Doppler shifts and relative intensities of the lines. In this report this technique is outlined and the on-orbit behavior since launch summarized.
The wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) is a CCD imager which views a selection of airglow emissions at the limb through a field-widened Michelson interferometer. Winds are calculated from the Doppler shifts of the spectral lines, detected as changes in the phase of the fringes. WINDII has been operating in space for almost three years and its performance has been monitored over that time. It continues to function well, though subtle changes have been seen. This paper is a discussion of the endurance of the instrument and of the changes that have occurred during the mission.
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