Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Radiometry Data

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.

A Concept of 2U Spaceborne Multichannel Heterodyne Spectroradiometer for Greenhouse Gases Remote Sensing

We present the project of a 2U CubeSat format spaceborne multichannel laser heterodyne spectroradiometer (MLHS) for studies of the Earth’s atmosphere upper layers in the near-infrared (NIR) spectral range (1258, 1528, and 1640 nm). A spaceborne MLHS operating in the solar occultation mode onboard CubeSat platform, is capable of simultaneous vertical profiling of CO2, H2O, CH4, and O2, as well as Doppler wind measurements, in the tangent heights range of 5–50 km. We considered the low Earth orbit for the MLHS deployment and analyzed the expected surface coverage and spatial resolution during one year of operations. A ground-based prototype of the MLHS for CO2 and CH4 molecular absorption measurements with an ultra-high spectral resolution of 0.0013 cm−1 is presented along with the detailed description of its analytical characteristics and capabilities. Implementation of a multichannel configuration of the heterodyne receiver (four receivers per one spectral channel) provides a significant improvement of the signal-to-noise ratio with the reasonable exposure time typical for observations in the solar occultation mode. Finally, the capability of building up a tomographic picture of sounded gas concentration distributions provided by high spectral resolution is discussed.

Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Data

<div>We present an analysis of historic pressure and temperature profiles from radiosonde</div><div>launches that will be used in retrieval of mixing fractions for greenhouse gases (GHGs, including</div><div>carbon dioxide, methane, and water vapor) in Laser Heterodyne Radiometry (LHR) data. With</div><div>over 2,700 stations worldwide, the global coverage for weather balloon observations is</div><div>extensive. Radiosonde stations included in the Integrated Global Radiosonde Archive (IGRA),</div><div>are launched simultaneously twice daily at 00:00 and 12:00 UTC. Global stations span all time</div><div>zones in both the Northern and Southern Hemisphere.</div><div> </div><div>Mesa Photonics and George Washington University are developing a variant of LHR</div><div>known as Precision Heterodyne, Oxygen-Corrected Spectroscopy (PHOCS) that simultaneously</div><div>collects high-resolution, oxygen spectral line shape data. Because oxygen concentrations in the</div><div>troposphere and lower stratosphere are constant, these line shapes are uniquely sensitive to both</div><div>temperature and pressure profiles and constrained fitting of these line shapes enables more</div><div>precise GHG concentration retrievals.</div><div> </div><div>Our approach is to collect historic data over several years (typically the prior decade) for</div><div>a particular date window surrounding a PHOCS measurement date for stations across the globe,</div><div>and mine this data for observation probability distributions as a function of level altitude, local</div><div>time of day of launch, latitude, etc. These distributions will then be used as Bayesian priors to</div><div>constrain temperature and pressure fits during the oxygen spectral fitting routine. Subsequently,</div><div>these priors will be used to estimate uncertainties in vertically-resolved GHG mixing ratios.</div>

A portable dual-channel laser heterodyne radiometer for simultaneous remote measurements of CH4 and CO2 in the atmospheric column

<p>Laser heterodyne spectroscopic measurement technique<sup>[1]</sup> has been proved to be a powerful and effective remote sensing tool for measurements of greenhouse gases in the atmospheric column<sup>[2-6]</sup>. In the present work, we report the development of a portable all-fiber coupled dual-channel laser heterodyne radiometer (LHR) and its field deployment. Two DFB lasers operating at 1650.9 nm and 1603.6 nm are used for the remote measurements of column CH<sub>4</sub> and CO<sub>2</sub>, respectively. A fiber optic switch is used to modulate and split the collected sunlight into two channels for simultaneous measurements of both target greenhouse gases. Custom-made preamplifiers combined with digital lock-in amplifiers are used to extract the laser heterodyne signals. The spectral resolution of the instrument is about 0.00442 cm<sup>-1</sup>, and the signal-to-noise ratio of the measured spectrum of about 250 is achieved with 0.8 s average time per sampling datum. The developed LHR instrument was successfully deployed to a field atmospheric observation experiment (in Dachaidan district, Qinghai province, China).</p><p>The experimental detail including the LHR instrument integration, dual-channel measurement results of column CH<sub>4</sub> and CO<sub>2</sub> and preliminary data inversion results will be presented and discussed.</p><p><strong>Acknowledgments. </strong>The project was supported by the national key R&D program of China (2017YFC0209705). The authors thank the financial supports from the CPER CLIMIBIO program, the Labex CaPPA project (ANR-10-LABX005).</p><p><strong>References</strong></p><p>[1] D. Weidmann, T. Tsai, N. A. Macleod, G. Wysocki, Opt. Lett. <strong>36 </strong>(2011) 1951-1953.</p><p>[2] E. L. Wilson, A. J. DiGregorio, G. Villanueva, C. E. Grunberg, et al., Appl. Phys. B <strong>125 </strong>(2019) 211-219.</p><p>[3] D. S. Bomse, J. E. Tso, M. M. Flors, J. H. Miller, Appl. Opt. <strong>59 </strong>(2020) B10-B17.</p><p>[4] J. Wang, G. Wang, T. Tan, G. Zhu, C. Sun, Z. Cao, W. Chen, X. Gao, Opt. Express <strong>27</strong> (2019) 9610-9619</p><p>[5] A. Rodin, A. Klimchuk, A. Nadezhdinskiy, D. Churbanov, et al., Opt. Express <strong>22 </strong>(2014) 13825-13834.</p><p>[6] E. L. Wilson, M. L. McLinden, J. H. Miller, H. R. Melroy, et al., Appl. Phys. B <strong>114 </strong>(2014) 385-393.</p>