Dr. Tom Hawat Profile

Dr. Tom Hawat

at Univ of Denver

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Publications (2)

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Proceedings Article | 26 October 2004 Paper

Infrared remote sensing of atmospheric composition over the polar region

Tom Hawat, Frank Murcray, Ronald Blatherwick, Pierre Fogal

Proceedings Volume 5542, (2004) https://doi.org/10.1117/12.560159

KEYWORDS: Black bodies, Infrared radiation, Atmospheric sensing, Atmospheric chemistry, Calibration, Data acquisition, Atmospheric modeling, Satellites, Sensors, Spectral resolution

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For monitoring environmental changes, new passive infrared instruments have become available that allow change detection analyses at resolutions and scales that were impossible just a few years ago. Current instruments have been installed in Antarctica will help to better understand the photochemical transport process and accurately predict ozone depletion and climate changes. During the 2003 polar summer one spectrometer was installed at the McMurdo station and another at the South Pole station, for year-around atmospheric chemistry monitoring. These two instruments use the emission technique to deliver high resolution spectra, from which will derive vertical profiles of many atmospheric tracers involved in the ozone destruction process. The first setup uses one channel to acquire the atmospheric data throw two different angles, the second setup uses two simultaneous channels to acquire the data at the same sky angles. Both instruments integrate two black bodies at different temperatures to calibrate the sky data. The data generated will have multipurpose, first is to provide validation for the new generation of the satellite sensors, like the National Polar-orbiting Operation Environmntal Satellite System (NPOESS), second is to allow photochemical transport modelers to compare outputs with actual measurements, and third is to evaluate the trend of some column abundance measurements like HNO₃, CH₄, O₃, CFCs, H₂O... This paper will present description of the instrumentation, the measurement technique and the automated analysis.

Proceedings Article | 4 August 2003 Paper

High-precision heliostat for long-path light tracking

Tom Hawat, Thomas Stephen, Martine DeMaziere, Eddy Neefs

Proceedings Volume 5082, (2003) https://doi.org/10.1117/12.499060

KEYWORDS: Mirrors, Sun, Charge-coupled devices, CCD cameras, Computer programming, Optical tracking, Cameras, Spectroscopy, Stars, Solar radiation

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A heliostat has been designed and built for use in optical remote sensing of the atmosphere. The heliostat uses two flat mirrors to track the sun and direct the sunlight to optical instruments. A stepper motor driven horizontal turntable is used to track the sun in azimuth and support an elevation assembly and a mechanical tower. The stepper motor driven elevation assembly drives an acquisition mirror that tracks the sun in elevation. This mirror directs the solar beam to a secondary mirror fixed on the mechanical tower. The secondary mirror then directs the solar beam along the axis of the tracker for use in measurements. A sensitive, high resolution CCD camera, receives a small part of the solar beam to analyze for fine servo-control. Ground based tests have demonstrated this instrument’s tracking capability for the sun, the moon, stars and for long pathlength sources. Presently, this system is coupled with a high-resolution Brucker 120M spectrometer used to obtain solar absorption spectra. The heliostat directs the solar radiation along the spectrometer optical axis. The pointing precision was measured to be better than 0.5 arcsec. A description of the heliostat is presented, as well as the results of ground tests.

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