Carbon dioxide and water vapour mapping over tropical Indian atmosphere retrieved from AVIRIS-NG hyperspectral images

Abstract

This work estimates the spatial distributions of atmospheric column averages of carbon dioxide (CO2) and water vapour (H2O) at the tropical atmosphere of India using the hyperspectral images of Airborne Visible InfraRed Imaging Spectrometer - Next Generation (AVIRIS-NG) flown over India for the first time in 2015–2016 and 2018. The retrieval algorithm accounts for the effect of altitude variation of the airborne sensor. A significant usefulness of AVIRIS-NG images is established by propounding a methodology for assessing the spatial distribution of atmospheric columnar H2O concentration, an important component of tropical climate, from the comparison of the two consecutive CO2 absorption bands. The spatial disparity of air-mixed CO2 over the places of widely varying natural and man-made features reflects the equilibrium of emission and sequestration in different extents. The gross long term CO2 change over the major portion of Indian atmosphere studied with NASA Giovanni open source data reveals a linear increase of the average CO2 concentration by about 2 ppm/year during years 2003–2016, almost up to the time of AVIRIS-NG first image procurement. The recent CO2 changes in India derived from the database of Orbiting Carbon Observatory-2 (OCO-2) are around 1.5–2.3 ppm/year increase for years 2016–2019 for different Indian sites. The new features of the CO2 trends over India are the extent of temporal increase and the inadequacy of the surrounding marine sequestration. The proportional spatial variations of H2O retrieved by the present method are consistent with the original H2O distributions supplied with the AVIRIS-NG images.