Remote sensing of evaporating gases from chemical spills at sea using multispectral thermal infrared camera

The SIMAGAZ gas monitoring camera was deployed during the IPOMAC and MANIFEST campaigns in 2021 and 2022. These measurement campaigns were carried out several miles off the west coast of France as part of the response to pollution at sea. Various chemicals, legally classified as HNS (Hazardous Noxious Substances), were released on the sea surface and SIMAGAZ measurements were made from the ship and by air. The camera data processing is based on a physical radiometric model, a spectroscopic database containing the compounds of interest and includes a morphological analysis of the images. SIMAGAZ has thus enabled the detection, identification and quantification of several gases evaporating from spilled slicks (acetone, butyl acetate, propyl acetate, MTBE and heptane), sometimes for over half an hour. For other products with absorption lines outside the SIMAGAZ spectral range, no gas was seen as expected. On the basis of this success, the analysis of the concentration fields obtained and their dynamics can be compared with the results of evaporation and atmospheric dispersion modelling tools for HNS.