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A new safeguards system under development employs radiometers in the 100-300 GHz spectral band to detect contraband, including shielding materials (used to attenuate the gamma ray emissions from nuclear materials), weapons, or explosives covertly concealed on personnel. Clothing is highly transparent at these frequencies an^ imaging techniques can detect contraband by its emissivity and reflectivity differences relative to human tissues. Experimental data are presented and sample images are uss.i as a basis to discuss system advantages and limitations.

This paper summarizes the findings of an extensive study of the phenomenon of absorption by oxygen of electromagnetic energy in the atmosphere. The purpose of the study was to make sufficient measurements in the oxygen absorption spectrum (50 to 70 GHz) to enable us to confirm or refine the existing theory as necessary. We have calculated new values for the Van Vleck line broadening coefficients, based on 1500 independent attenuation measurements made over a slant range from space to various altitudes in the atmosphere. These measurements were made over a frequency range of 53.4 to 56.4 GHz and an altitude range from zero to 14.75 km. The average relative error between the measured and the calculated attenuation is 8.6%. A similar comparison based on Meeks and Lilley's line broadening coefficients yielded an average relative error of 13%.