Application of Millimeter-Wave Radiometry for Remote Chemical Detection

Passive millimeter-wave systems have been used in the past to remotely map solid targets and to measure low-pressure spectral lines of stratospheric and interstellar gases; however, its application to pressure-broadened spectral line detection of industrial emissions is new. We developed a radiative transfer model to determine feasibility and system requirements for passive millimeter-wave spectral detection of terrestrial gases. We designed and built a Dicke-switched multispectral radiometer in the 146-154-GHz band to detect nitric oxide (NO), a prototypical gas of nuclear fuel processing operations. We first tested the spectral detection capability of the radiometer in the laboratory using a gas cell and then field tested it at the Nevada test site at a distance of 600 m from a stack that released hot plumes of NO and air. With features such as Dicke-switched integration, frequent online calibration, and spectral baseline subtraction, we demonstrated the feasibility of remote detection of terrestrial gases by a ground-based radiometer.

I. Introduction

With recent increased concerns about national security has come the realization that acts of nuclear or chemical terrorism could endanger large numbers of people in a short span of time, as could industrial chemical accidents in densely populated areas. In this regard, detection of chemicals in air, especially remotely, is of paramount importance to national security, counterterrorism, leak detection, and environmental protection. It is important also in nuclear counterterrorism efforts since certain chemical effluents from nuclear fuel reprocessing facilities engaged in the production of fuels for nuclear weapons can be the “tell tale” signatures of these operations.