01 Apr 2022
01 Apr 2022
Status: a revised version of this preprint is currently under review for the journal AMT.

Evaluation of the High Altitude Lidar Observatory Methane Retrievals During the Summer 2019 ACT-America Campaign

Rory A. Barton-Grimley1, Amin R. Nehrir1, Susan A. Kooi2, James E. Collins2, David B. Harper1, Anthony Notari1, Joseph Lee2, Joshua P. DiGangi1, Yonghoon Choi2, and Kenneth J. Davis3 Rory A. Barton-Grimley et al.
  • 1NASA Langley Research Center, Hampton, VA, USA
  • 2Science Systems and Applications, Inc., Hampton, VA, USA
  • 3Department of Meteorology and Atmospheric Science, and Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA, USA

Abstract. The NASA Langley Research Center High Altitude Lidar Observatory (HALO) is a multi-function and modular lidar developed to address the observational needs of NASA’s weather, climate, carbon cycle, and atmospheric composition focus areas. HALO measures atmospheric H2O mixing ratios, CH4 mole fractions, and aerosol/cloud optical properties using the Differential Absorption Lidar (DIAL) and High Spectral Resolution Lidar (HSRL) techniques, respectively. In 2019 HALO participated in the NASA Atmospheric Carbon and Transport – America campaign on board the NASA C-130 to compliment a suite of greenhouse gas in-situ sensors and provide, for the first time, simultaneous measurements of column CH4 and aerosol/cloud profiles. HALO operated in 18 of 19 science flights where the DIAL and Integrated Path Differential Absorption lidar (IPDA) techniques at 1645 nm were used for column and multi-layer measurements of CH4 mole fractions, the HSRL and backscatter techniques at 532 and 1064 nm, respectively, for retrievals of aerosol backscatter, extinction, depolarization, and mixing layer heights. In this paper we present HALO’s measurement theory for the retrievals of column and multi-layer XCH4, retrieval accuracy and precision including methods for bias correction, and a comprehensive total column XCH4 validation comparison to in-situ observations. Comparisons of HALO XCH4 to in-situ derived XCH4, collected during spiral ascents and descents, indicates mean difference of 2.54 ppb and standard deviation of the differences of 16.66 ppb when employing 15 s along track averaging (< 3 km). A high correlation coefficient of R = 0.9058 was observed for the 11 in-situ spiral comparisons. Column XCH4 measured by HALO over regional scales covered by the ACT-America campaign are compared against in-situ CH4 measurements carried out within the planetary boundary layer (PBL) from both the C-130 and B200 aircraft. Favorable correlation between the in-situ point measurements within the PBL and the remote column measurements from HALO elucidates the sensitivity of a column integrating lidar to CH4 variability within the PBL, where surface fluxes dominate the signal. Novel capabilities for CH4 profiling in regions of clear air using the DIAL technique are presented and validated for the first time. Additionally, profiling of CH4 is used to apportion the PBL absorption from the total column and is compared to previously reported IPDA cloud slicing techniques that estimate PBL columns using strong echoes from fair weather cumulus. The analysis presented here points towards HALO’s ability to retrieve accurate and precise CH4 columns with the prospects for future multi-layer profiling in support of future suborbital campaigns.

Rory A. Barton-Grimley et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-106', Anonymous Referee #1, 20 Apr 2022
  • RC2: 'Comment on amt-2022-106', Anonymous Referee #2, 05 May 2022

Rory A. Barton-Grimley et al.

Rory A. Barton-Grimley et al.


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Short summary
HALO is a multi-function lidar that measures CH4 columns and profiles of H2O mixing ratio and aerosol/cloud optical properties. HALO supports carbon cycle, weather/dynamics, and radiation sciences suborbital research and is a technology testbed for future space-based differential absorption lidar missions. In 2019 HALO collected CH4 columns and aerosol/cloud profiles during the ACT-America campaign. Here we assess HALO's CH4 accuracy and precision compared to co-located in-situ observations.