Feasibility study of a space-based high pulse energy 2  μm CO₂ IPDA lidar

Sustained high-quality column carbon dioxide (CO₂) atmospheric measurements from space are required to improve estimates of regional and continental-scale sources and sinks of CO₂. Modeling of a space-based 2 μm, high pulse energy, triple-pulse, direct detection integrated path differential absorption (IPDA) lidar was conducted to demonstrate CO₂ measurement capability and to evaluate random and systematic errors. Parameters based on recent technology developments in the 2 μm laser and state-of-the-art HgCdTe (MCT) electron-initiated avalanche photodiode (e-APD) detection system were incorporated in this model. Strong absorption features of CO₂ in the 2 μm region, which allows optimum lower tropospheric and near surface measurements, were used to project simultaneous measurements using two independent altitude-dependent weighting functions with the triple-pulse IPDA. Analysis of measurements over a variety of atmospheric and aerosol models using a variety of Earth's surface target and aerosol loading conditions were conducted. Water vapor (H₂O) influences on CO₂ measurements were assessed, including molecular interference, dry-air estimate, and line broadening. Projected performance shows a <0.35  ppm precision and a <0.3  ppm bias in low-tropospheric weighted measurements related to column CO₂ optical depth for the space-based IPDA using 10 s signal averaging over the Railroad Valley (RRV) reference surface under clear and thin cloud conditions.