We describe the development of a near-infrared laser heterodyne radiometer: the precision heterodyne oxygen-corrected spectrometer (PHOCS). The prototype instrument is equipped with two heterodyne receivers for oxygen and water (measured near 1278 nanometers) and carbon dioxide (near 1572 nanometers) concentration profiles, respectively. The latter may be substituted by a heterodyne receiver module equipped with a laser to monitor atmospheric methane near 1651 nanometers. Oxygen measurements are intended to provide dry gas corrections and—more importantly—determine accurate temperature and pressure profiles that, in turn, improve the precision of theCO2andH2Ocolumn retrievals. Vertical profiling is made feasible by interrogating the very low-noise absorption lines shapes collected at≈0.0067cm−1resolution. PHOCS complements the results from the Orbiting Carbon Observatory (OCO-2), Active Sensing ofCO2Emissions over Nights, Days, and Seasons (ASCENDS), and ground-based Fourier transform spectrometers. In this paper, we describe the development of the instrument by Mesa Photonics and present the results of initial tests in the vicinity of Washington, DC.

The statistical analysis of historic pressure and temperature profiles from radiosonde launches for use in the fitting of molecular oxygen line shapes is presented. As the O₂ mixing ratio is nearly constant throughout the lower atmosphere, only variations in pressure and temperature profiles will affect the fit of observed O₂ features in Laser Heterodyne Radiometry (LHR) spectra. Radiosonde temperature and pressure data are extracted from the Integrated Global Radiosonde Archive (IGRA) for a given station, date, and launch time. Data may be extracted for a single launch, for the same date over several years, and/or within a window centered on a target date. The temperature and pressure profiles are further characterized by the statistical variation in coefficients of polynomial fits in altitude. The properties of the probability distributions for each coefficient are used to constrain fits of O₂ line shapes through Nelder–Mead optimization. The refined temperature and pressure profiles are then used in the retrieval of vertically resolved mixing ratios for greenhouse gases (GHGs) measured in the same instrument. In continuous collections, each vertical profile determination may be treated as a Bayesian prior to inform subsequent measurements and provide an estimate of uncertainties.

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.

A passive remote sensor for full atmospheric columns of O2, CO2 and CH4 has been developed that is based on laser heterodyne radiometry, (LHR), using telecommunications-style diode lasers operating at wavelengths between 1278 and 1650 nm as local oscillators. Spectral resolution is 0.0067 cm^-1 and will soon be improved two-fold. Retrievals require including line narrow effects, particularly for O₂.

A Raman spectrometer for field measurement of isotope ratios of subsurface gases including nitrogen, oxygen and carbon dioxide is presented.

George Washington University and Mesa Photonics are developing and deploying a Laser Heterodyne Radiometer (LHR) that simultaneously measures CO2, CH4, H2O, and O2 mixing ratios throughout the troposphere and lower stratosphere. Spectral fits are constrained by fitting the oxygen spectral line shape – which depends only on pressure and temperature – to improve GHG retrieval precision and provide dry-air corrections. This constraint is achieved by fitting pressure and temperature profiles obtained from the meteorology data measured by radiosondes (vertical resolution ranging from 5-500 m) as part of NOAA’s Integrated Global Radiosonde Archive (IGRA).Atmospheric spectra are simulated for the column using a spectral simulation package (“LahetraSim”) that uses parameters from the HITRAN spectral database to model spectra through the HITRAN Application Programming Interface (HAPI). Integrated path absorption spectra are calculated using the initial sun angle and estimated radiosonde pressure and temperature profiles. Concentration profiles for CO2, CH4, and H2O can then be iterated on their vertical distributions and refining the pressure and temperature profiles to best fit the oxygen spectrum.Here we present a comparison of our spectral simulation software to that of an alternative method that has been presented for LHR data processing which makes use of the Planetary Spectrum Generator (PSG) API. Spectral simulations are generated using several atmospheric databases, templates, and transfer models. This tool allows for the extraction of Modern Era Retrospective Analysis, Version 2 (MERRA-2) vertical profiles of pressure and temperature and species abundances from HITRAN. Two limitations of the MERRA-2 database are the latency of approximately 2 months for the latest data availability and the coarse vertical resolution (~1 km) of the available data. Another benefit of our approach is that approximation of both Planetary Boundary Layer (PBL) and Tropopause Heights can be extracted from the temperature and pressure profiles and these heights can be iterated to refine atmospheric layers; thus increasing their relevance of LHR to GHG modeling.