Atmospheric modelling using FASCOD to identify CO2 absorption bands and their suitability analysis in variable concentrations for remote sensing applications

Recent climate studies have proven that both temperature and CO2 content of the earth's atmosphere followed a regular 100,000-year cycle of change and that they are closely correlated. Moreover, the observed increase of CO2 in the atmosphere exceeds the predicted values extrapolated from historical data. Other than industrialization and rapid urbanization, geo-natural hazards such as leakage from hydrocarbon reservoirs and spontaneous combustion of coal contribute a considerable amount of CO2 to the atmosphere. Several researchers have studied the possibilities and reliabilities of atmospheric CO2 retrieval by the point-based method (nearly accurate but much localized) and globally (wider observation but many uncertainties). Radiative transfer codes, such as FASCOD (Fast Atmospheric Signature Code) with the HITRAN (High-Resolution Transmission) spectral database can simulate atmospheric transmission and path radiance with customized gas composition (CO2, water vapour, CO, etc.) and concentration in order to understand the phenomena in a specific wavelength region. In the present study, a number of atmospheric models were constructed with different CO2 concentrations (ppmv) with a combination of water vapour and other atmospheric gases such as CO, CH4, N2O, SO2, etc., to find out the interference patterns of these gases over CO2 absorption bands. The transmission features of these gas combinations were analysed by partial least-squares regression models. These models show that the most suitable CO2 absorption bands are located around 2 μm, such as 1.998 and 2.001 μm. The spectral information derived from different concentrations of CO2 can be fitted in multivariate models to predict the CO2 concentration from spectral information in a controlled environment. Furthermore, the present study explores the sensitivity of some available remote sensing sensors in variable CO2 concentrations for use in real world.