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>

Water vapor isotopic abundance measurement in Tibetan Plateau based on portable laser heterodyne radiometer

<p>Tibet Plateau is known as the third pole of the world, the environmental changing in this area profoundly impacts on east Asian or even global climate. HDO is the stable isotope of water vapor and is the ideal tracer of water cycle, which has been applied to atmospheric circulation and climatic studies. For monitoring the water vapor isotopic abundance in Tibetan Plateau and providing reliable information for environmental and climatic studies, a portable laser heterodyne radiometer was operated at Golmud (Qinghai Province) in summer 2019. The radiometer adopted a narrow linewidth 3.66 μm DFB laser as the local oscillator and performed high resolution(~0.009 cm<sup>-1</sup>) and high signal-to-noise ratio(~160). Furthermore, the absorption spectra of atmospheric HDO and H<sub>2</sub>O were obtained and the retrieval algorithm of water vapor isotopic abundance was discussed. The optimal estimation method based on LBLRTM was chosen for retrieving, the ratio of HDO/H<sub>2</sub>O at Golmud is 185±7×10<sup>-6</sup> during the observation, the value is less than the Vienna Standard Mean Ocean Water (VSMO, 311.5×10<sup>-6</sup>) but larger than Standard Light Antarctic Precipitation (SLAP, 178.2×10<sup>-6</sup>).</p>

Potential improvements in global carbon flux estimates from a network of laser heterodyne radiometer measurements of column carbon dioxide

We present observing system simulation experiments (OSSEs) to evaluate the impact of a proposed network of ground-based miniaturized laser heterodyne radiometer (mini-LHR) instruments that measure atmospheric column-averaged carbon dioxide (XCO2) with a 1 ppm precision. A particular strength of this passive measurement approach is its insensitivity to clouds and aerosols due to its direct sun pointing and narrow field of view (0.2∘). Developed at the NASA Goddard Space Flight Center (GSFC), these portable, low-cost mini-LHR instruments were designed to operate in tandem with the sun photometers used by the AErosol RObotic NETwork (AERONET). This partnership allows us to leverage the existing framework of AERONET's global ground network of more than 500 sites as well as providing simultaneous measurements of aerosols that are known to be a major source of error in retrievals of XCO2 from passive nadir-viewing satellite observations. We show, using the global 3-D GEOS-Chem chemistry transport model, that a deployment of 50 mini-LHRs at strategic (but not optimized) AERONET sites significantly improves our knowledge of global and regional land-based CO2 fluxes. This improvement varies seasonally and ranges 58 %–81 % over southern lands, 47 %–76 % over tropical lands, 71 %–92 % over northern lands, and 64 %–91 % globally. We also show significant added value from combining mini-LHR instruments with the existing ground-based NOAA flask network. Collectively, these data result in improved a posteriori CO2 flux estimates on spatial scales of ∼10 km2, especially over North America and Europe, where the ground-based networks are densest. Our studies suggest that the mini-LHR network could also play a substantive role in reducing carbon flux uncertainty in Arctic and tropical systems by filling in geographical gaps in measurements left by ground-based networks and space-based observations. A realized network would also provide necessary data for the quinquennial global stocktakes that form part of the Paris Agreement.