Researchers have demonstrated a sub-millimeter-wave spectrometer that combines extremely broad bandwidth with extremely high sensitivity and spectral resolution to enable future spacecraft to measure the composition of the Earth’s troposphere in three dimensions many times per day at spatial resolutions as high as a few kilometers. Microwave limb sounding is a proven remote-sensing technique that measures thermal emission spectra from molecular gases along limb views of the Earth’s atmosphere against a cold space background.

The new receiver will down-convert thermal emission spectra in the 180–300 GHz band using superconductor-insulator-superconductor (SIS) heterodyne mixers. A technique called sideband separation is used to provide 24 GHz of instantaneous bandwidth from a single receiver, enabling many chemical species to be measured simultaneously by a single receiver with accurate calibration. The high sensitivity provided by SIS mixers will enable accurate measurements of chemicals at low concentrations with very short integration times. A novel scanning telescope, also under development at the Jet Propulsion Laboratory, will take advantage of these short integration times to measure three-dimensional maps of the concentration of a large number of key chemical species in the troposphere over nearly the entire planet five to nine times per day. These frequent measurements will enable researchers to both monitor air quality and to understand how pollution is transported by the atmosphere.

This work was done by John S. Ward, Bruce Bumble, Karen A. Lee, Jonathan H. Kawamura, Goutam Chattopadhyay, Paul Stek, and Frank Rice of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-46205


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Sideband-Separating, Millimeter-Wave Heterodyne Receiver

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This article first appeared in the April, 2010 issue of NASA Tech Briefs Magazine.

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