Towards Carbon Dioxide imaging using Fabry-Pérot interferometer correlation spectroscopy

Carbon dioxide (CO2) emissions are the major driver of anthropogenic climate change. While strong point sources contribute significantly to overall emissions, their source strength is not always well quantified by bottom-up estimates or in situ measurements. Passive remote sensing of CO2 emissions could provide a simple tool to substantially refine source strength estimates. However, current approaches from ground-based to space-borne platforms only suit exceptionally strong emitters. We propose a ground-based CO2 imaging technique based on Fabry-Perot interferometer (FPI) correlation spectroscopy. The free spectral range (FSR) of an FPI is matched to the spectral separation of individual rovibrational absorption lines of the CO2 1.57 µm absorption band. This allows to compare the radiance of sky-scattered sunlight between “online” and “offline” wavelengths, i.e., the FPI transmission spectrum correlating and anti-correlating with the CO2 absorption lines, respectively. The advantage of a high FPI light throughput enables imaging measurements of the CO2 column density with a resolving power of 18,000. Instrument simulations based on available optics suggest an integration time of approximately 10 seconds to record a CO2 plume image with 300 by 300 pixels of a medium-sized power plant (7 Mt CO2/yr). This is about two orders of magnitude faster compared to grating-based imaging spectrometers. For recording the emission plume of a passively degassing volcano at the same spatial resolution integration times are on the order of ten minutes. Additionally, we present ongoing work on developing a prototype instrument to validate the feasibility of this CO2 imaging technique.