Detection of Chemical Warfare Agents Using Spaceborne Spectroradiometers

Abstract

Chemical, Biological, Radiological, and Nuclear (CBRN) threats are becoming more prevalent, as more entities gain access to modern weapons, along with industrial technologies and chemicals. From a review of available literature, it was determined that of the four CBRN hazard types, chemical threats are the most viable candidates for detection by satellite. However, chemical detection from space is primarily limited to large scale, higher altitude measurements of trace gas concentrations and atmospheric content, and these are further limited by their spatial resolutions, which tend to be in the range of a few kilometres. The capability to directly detect releases of a Chemical Warfare Agent (CWA) from satellite data would be invaluable for monitoring purposes. After the review, this thesis begins with a comparison exercise between the existing ‘Infrared Atmospheric Sounding Interferometer’ (IASI) and other existing and upcoming satellite instruments, to select those suitable for use in CWA detection. Two new concepts for a technology demonstration mission are proposed here, which would utilise an IASI-style spectrometer for wide-field identification of an incident and a laser heterodyne radiometer for high-resolution follow-up measurements. One mission concept consists of a single satellite to carry the instruments, and the other consists of two satellites in a tandem with one following behind the other, and each carrying one of the two instruments for initial and follow-up observations of an incident. Next, this thesis uses atmospheric dispersion and radiative transfer modelling to determine whether releases of sarin or sulphur mustard could be detected in an urban environment by the existing IASI instrument. Additionally, an investigation was conducted, using the same approach as for IASI, into the possibility of utilising a linear variable filter to create a novel miniaturised spectrometer suitable for urban CWA release detection. It was found that neither instrument is spectrally capable of detecting the modelled urban releases of either sarin or sulphur mustard, most likely due to the modelled scenarios including a high wind speed and low thermal contrast. This makes these scenarios unfavourable for detection, since the high wind speed resulted in lower concentrations of the agent in the atmosphere, and the low thermal contrast reduced the absorption signature that the instruments would observe. Furthermore, the large cooling systems required by the thermal infrared detectors could negate the benefit of miniaturisation from the linear variable filter. Despite this, the two mission concepts proposed as a result of the instrument comparison exercise were then evaluated with an orbital design study, to determine which concept was better suited to CWA detection. It was found that within the mission constraints, the tandem concept would be feasible if sufficiently sensitive instruments could be developed. Additionally, it was determined that an altitude of 350 km optimises the revisit time for this concept. All of these research outputs were then synthesized to propose a new CWA detection mission concept for future development.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Lucy Berthoud (Supervisor) & Andrei Sarua (Supervisor)