Combining standoff tomography with point detection: a game changer for the identification of airborne toxic chemicals

Volatile chemicals can form expansive toxic gas clouds after an accidental or deliberate large-scale release. The emerging toxic clouds may be invisible to the optical spectrum of the bare eye, but they are generally detectable using suitable standoff or point detectors. Standoff detectors are particularly suited for monitoring a large area within their line of sight, whereas remotely controlled point detectors may be used to survey specific areas of strategic interest. A favorable spatial and temporal detection resolution is usually achieved using standoff Fourier Transform Infrared (FTIR) spectrometers. To obtain a proper spatial resolution beyond a mere imaging view, at least two imaging systems must operate concurrently with an adequate opening angle concerning the distance of reconnaissance. During a field trial in Umeå, Sweden, we utilized an appropriate setup for standoff tomography to detect and identify comparatively small-scale chemical releases of gaseous substances and evaporating aerosols. We reached high resolutions in space and time at a standoff distance of over a kilometer. Thus, we have shown that a targeted early warning and short response times for emerging threats are possible while operators remain at a safe location. Additionally, the field trial revealed the significant influence of the properties and concentration of the deployed chemicals, wind shear, and turbulence on the detection result. In support of spatially and temporally resolved standoff detection, targeted drones carrying fast and sensitive point detectors, such as ion mobility spectrometers, may be used as an orthogonal technique to independently confirm identification.