Evaluation of the High Altitude Lidar Observatory (HALO) methane retrievals during the summer 2019 ACT-America campaign

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