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Completed TRL 2 (started at 2, targeting 3)
Water vapor’s (WV) impact on driving the Earth’s near-surface processes is paramount. Otherwise known as the Planetary Boundary Layer (PBL), the region in the lower atmosphere is crucial in the formation of climate models and weather forecasts. Although the PBL is heavily studied, the scientific community has identified a need to acquire global thermodynamic profiles of this region with higher spatial and temporal resolution. To directly measure WV concentrations, the differential absorption lidar (DIAL) technique is an advanced solution that can generate high spatial and temporal WV measurements, with heritage on ground-based and airborne platforms. Additionally, in low signal-to-noise regimes, such as space-based WV retrievals of the PBL, photon counting serves as an effective acquisition method. However, implementing a spaceborne WV DIAL instrument is challenging because of fundamental limitations inherent to single-photon avalanche diode (SPAD) detectors, which are currently used on several NASA lidar instruments. Nonlinearities such as deadtime and afterpulsing induce biases in retrievals that can be uncorrectable in regions of high-density backscatter flux, such as passing clouds. This results in limited signal dynamic range and corrupted WV profile estimates. Motivated by the demand for improved WV PBL measurements through technological advancement, this proposal seeks to investigate advanced photon-counting lidar hardware characterization and advanced signal processing techniques that can mitigate the effects of SPAD detector non-idealities and thus enable high-accuracy WV measurements of the PBL from a DIAL satellite. This will be accomplished by (1) describing SPAD detectors with more complete and practical statistical models, (2) optimizing WV estimates by applying advanced signal processing techniques, and (3) translating this effort to current and future space-based WV DIAL missions.
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