A portable miniaturized laser heterodyne radiometer (mini‑LHR) for remote measurements of column CH4 and CO2

E L Wilson; A J DiGregorio; G Villanueva; C E Grunberg; Z Souders; K M Miletti; A Menendez; M H Grunberg; M A M Floyd; J E Bleacher; E S Euskirchen; C Edgar; B J Caldwell; B Shiro; K Binsted

doi:10.1007/s00340-019-7315-8

A portable miniaturized laser heterodyne radiometer (mini‑LHR) for remote measurements of column CH₄ and CO₂

Appl Phys B. 2019 Oct 21;125(211):11. doi: 10.1007/s00340-019-7315-8.

Authors

E L Wilson¹, A J DiGregorio², G Villanueva³, C E Grunberg⁴, Z Souders⁴, K M Miletti⁴, A Menendez⁴, M H Grunberg⁴, M A M Floyd⁵, J E Bleacher⁶, E S Euskirchen⁷, C Edgar⁷, B J Caldwell⁸, B Shiro⁹, K Binsted¹⁰

Affiliations

¹ Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
² Science Systems and Applications, Inc., 10210 Greenbelt Rd, 20, Lanham, MD 20706, USA.
³ Planetary Systems Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
⁴ Center for Research and Exploration in Space Science and Technology (CRESST), University of Maryland, College Park, MD 20740, USA.
⁵ Planetary Environments Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
⁶ Planetary Geology, Geophysics, and Geochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
⁷ Institute of Arctic Biology, University of Alaska Fairbanks, 902 N. Koyukuk Dr, P.O. Box 757000, Fairbanks, AK 99775, USA.
⁸ Exploration Class Management, 414 Bayoo View Drive, El Lago, TX 73472, USA.
⁹ Department of Earth Sciences, University of Hawai'i at Mānoa, POST Building, Suite 701, 1680 East - West Road, Honolulu, HI 96822, USA.
¹⁰ Department of Information and Computer Sciences, University of Hawai'i at Mānoa, POST Building Suite 303D, 1680 East - West Road, Honolulu, HI 96822, USA.

Abstract

We present the design of a portable version of our miniaturized laser heterodyne radiometer (mini-LHR) that simultaneously measures methane (CH₄) and carbon dioxide (CO₂) in the atmospheric column. The mini-LHR fits on a backpack frame, operates autonomously, and requires no infrastructure because it is powered by batteries charged by a folding 30 W solar panel. Similar to our earlier instruments, the mini-LHR is a passive laser heterodyne radiometer that operates by collecting sunlight that has undergone absorption by CH₄ and CO₂. Within the mini-LHR, sunlight is mixed with light from a distributive feedback (DFB) laser centered at approximately 1.64 μm where both gases have absorption features. The laser scans across these absorption features roughly every minute and the resulting beat signal is collected in the radio frequency (RF). Scans are averaged into half hour and hour data products and analyzed using the Planetary Spectrum Generator (PSG) retrieval to extract column mole fractions. Instrument performance is demonstrated through two deployments at significantly different sites in interior Alaska and Hawaii. The resolving power (λ/∆λ) is greater than 500,000 at 1.64 μm with precisions of better than 20 ppb and 1 ppm for CH₄ and CO₂, respectively. Because mini-LHR instruments are portable and can be co-located, they can be used to characterize bias between larger, stationary, column observing instruments. In addition, mini-LHRs can be deployed quickly to respond to transient events such as methane leaks or can be used for field studies targeting geographical regions.

Abstract

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