Remote detection of chemicals by millimeter-wave spectroscopy

Nachappa Gopalsami; Apostolos C. Raptis

doi:10.1117/12.331172

13 November 1998 Remote detection of chemicals by millimeter-wave spectroscopy

Nachappa Gopalsami, Apostolos C. Raptis

Proceedings Volume 3465, Millimeter and Submillimeter Waves IV; (1998) https://doi.org/10.1117/12.331172
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

This paper discusses the development and field testing of a remote chemical detection system that is based on millimeter- wave (mm-wave) spectroscopy. The mm-wave system is a monostatic swept-frequency radar that consists of a mm-wave sweeper, a hot-electron-bolometer detector, and a trihedral reflector. The chemical plume to be detected is situated between the transmitter/detector and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening, which hampered open-path spectroscopy in the past, has been mitigated in this work by designing a fast sweeping source over a broad frequency range. The heart of the system is a Russian backward-wave oscillator (BWO) tube that can be tuned over 225 - 315 GHz. A mm-wave sweeper that includes the BWO tube was built to sweep the entire frequency range within 10 ms. The radar system was field-tested at the DOE Nevada Test Site at a standoff distance of 60 m. Methyl chloride was released from a wind tunnel that produced a 2-m diameter plume at is exit point. The mm-wave system detected methyl chloride plumes down to a concentration of 12 ppm. The measurement results agree well with model-fitted data.

Citation Download Citation

Nachappa Gopalsami and Apostolos C. Raptis "Remote detection of chemicals by millimeter-wave spectroscopy", Proc. SPIE 3465, Millimeter and Submillimeter Waves IV, (13 November 1998); https://doi.org/10.1117/12.331172

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