Measuring pollutant gases using VNIR and TIR imaging spectroscopy

Thermal Imaging Spectrometry (TIS) shows promise dual-use in a wide range of military, governmental, and private industry applications such as identification and quantisation of emissions from hazardous waste sites, industrial processes, emergency response events, locating illicit chemical processing laboratories, indoor/outdoor air quality monitoring, and chemical agent detection. The Antwerp port is the home to the largest petrochemical complex in Europe and worldwide second only to Houston, Texas. The development of the chemical products results in waste plume of different air pollutants to the urban area closed by, and causes increase in respiratory illnesses to its population. The objective of this project is to detect the presence and the concentration of polluted gas compounds in the atmosphere using the AHS-160 airborne spectrometer over the chemical industry situated in the port of Antwerp. In June 2005, AHS-160 flight campaign acquired VIS to LWIR data in two operational periods during the same day (morning and afternoon). The airborne data were calibrated and verified using numerous ground truth measurements that were collected using the field thermal imaging reflectometer (SOC 400T), AHS spectrometer and traditional in-situ measurements collected in AQMSs situated in the port. Due to shut down of most of the refineries operational units in the flight period, the gas plume that has released to the atmosphere was thin, spotted and compounded mainly from SO2. Different spectra match-filters were applied for the detection of the thin plume in the VNIR bands over homogeneous background as water and grass. Orthogonal background technique applied to the LWIR bands was used to separate the thermal radiance contrast of the plume over the heterorganic background. A developed ratio using TIR bands helped in the final detection of the plume over the complete industrial scene. ‘Pasquill-Gifford’ Gaussian plume model has been developed to predict the SO2 concentrations released at a specific source point. This model describes the transport and mixing of the pollutants along the detected plume from the outer of the chimney.

Although we found that the AHS-160 bandwidths are not sufficient for detection of gas compound based on their spectra abundance, combined information based on VNIR and LWIR data are complimentary and can help in the detection and the concentration measurement of pollutant gasses.