Towards a Remote Sensing Solution to Quantify Nitrous Oxide Emissions by Integrating Shortwave and Thermal Infrared Bands

Abstract. Nitrous oxide (N₂O) is a potent greenhouse gas whose emissions are dominated by natural and agricultural soils and are highly heterogeneous and episodic, yet existing observational techniques lack the spatial coverage and near-surface sensitivity needed to resolve this variability. In this study, we evaluate a remote sensing framework that integrates shortwave infrared (SWIR) and thermal infrared (TIR) spectral bands to enhance the detectability of column-integrated N₂O mixing ratio (X_N2O). To implement this, we expand the capacity of the SPLAT–VLIDORT radiative transfer model to jointly simulate both spectral regions and apply linear sensitivity analysis to quantify the X_N2O measurement error and vertical sensitivity under realistic environmental conditions and instrumental designs. This framework is applied to both airborne and spaceborne instruments to evaluate the influence of platform characteristics on retrieval performance. The joint SWIR–TIR setting improves near-surface sensitivity relative to the TIR band alone while maintaining the low X_N2O measurement error. It achieves single-sounding measurement error of approximately 3.2 ppb for an airborne instrument with a ground footprint size of 20 m and 1.1 ppb for spaceborne instrument with a footprint size of 0.7 km, while retaining sensitivity to the near-surface layers. Assuming X_N2O variability is observable at twice the precision, natural X_N2O variability inferred from in situ aircraft N₂O observations in the US Midwest becomes observable beyond spatial aggregation scales of ∼ 2.5 km for airborne and ∼ 22 km for spaceborne instruments, subject to significant X_N2O variation between flights. An independent, emission-based detectability analysis indicates that X_N2O variability induced by uniform emissions of 5 nmol m⁻² s⁻¹ becomes observable beyond spatial averaging of about 2.1 km for airborne and 8.4 km for spaceborne instruments. Together, these results constitute a quantitative basis for N₂O detectability using a joint SWIR–TIR setting, with a focus on diffuse soil emissions that are more difficult to detect yet dominate the global N₂O budget, and they provide practical guidance for future N₂O dedicated missions.