Precision Heterodyne Oxygen-Calibration Spectrometry: Vertical Profiling of Water and Carbon Dioxide in the Troposphere and Lower Stratosphere

We describe the continued development of a new laser heterodyne radiometry (LHR) technique:  Precision Heterodyne Oxygen-Calibration Spectrometry, or PHOCS. The prototype instrument is equipped with two active laser channels for oxygen and water (measured near 1.28 µm) and carbon dioxide (near 1.57 µm) determination. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1.65 µm). Oxygen measurements provide dry gas corrections and – more importantly – determine accurate temperature and pressure profiles that, in turn, improve the precision of the CO₂ and H₂O column retrievals. Vertical profiling is enabled by interrogating the very low-noise, absorption lines shapes collected by the O(10^-3 cm^-1) instrument. The presentation will describe (1) the continued development of column concertation retrieval protocols and (2) the results of initial tests performed at the Smithsonian Environmental Research Center in Edgewater, Maryland during the summer/fall of 2019 and spring of 2020.