Potential of point source imaging satellite instruments to infer diffuse methane emissions: a theoretical case study of the Near-Infrared Multispectral Camera (NIMCAM)

Abstract. Satellite measurements have revolutionized methane monitoring, yet persistent clouds and aerosols often limit global-survey instruments like TROPOMI in the tropics. This study evaluates the potential of the Near Infrared Multispectral Camera for Atmospheric Methane (NIMCAM), a high-resolution instrument (60 m pixels) designed for point sources, to quantify large-scale diffuse emissions across tropical Africa. Through closed-loop numerical experiments, we compare an in-orbit demonstrator and small NIMCAM constellations (2–5 satellites) against synthetic data from the TROPOMI (TROPOsphericMonitoring Instrument) instrument. Using Sentinel-2 cloud probabilities and downscaled MODIS aerosol optical depth products, we find that NIMCAM’s finer spatial resolution significantly increases clear-sky data yields. A 5-satellite constellation provides up to six times more clear-sky observations than TROPOMI. As masking criteria for clouds and aerosols become more stringent, the ratio of NIMCAM to TROPOMI random error (σ_NIM/σ_TROP) decreases. This occurs because TROPOMI’s coarser footprint leads to a more rapid loss of data under strict thresholds. Using the GEOS-Chem chemical transport model and an ensemble Kalman Filter, we demonstrate that NIMCAM observations offer substantial added value in resolving tropical emissions. NIMCAM achieves higher uncertainty reduction than TROPOMI, particularly in regions and seasons where cloud and aerosol loading restrict coarser instruments. Our findings support using high-resolution methane technology to complement global surveys in monitoring diffuse tropical emissions.