The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign

In the fall of 2017, an airborne field campaign was conducted from the NASA Armstrong Flight Research Center in Palmdale, California, to advance the remote sensing of aerosols and clouds with multi-angle polarimeters (MAP) and lidars. The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) campaign was jointly sponsored by NASA and the Netherlands Institute for Space Research (SRON). Six instruments were deployed on the ER-2 high-altitude aircraft. Four were MAPs: the Airborne Hyper Angular Rainbow Polarimeter (AirHARP), the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), the Airborne Spectrometer for Planetary EXploration (SPEX airborne), and the Research Scanning Polarimeter (RSP). The remainder were lidars, including the Cloud Physics Lidar (CPL) and the High Spectral Resolution Lidar 2 (HSRL-2). The southern California base of ACEPOL enabled observation of a wide variety of scene types, including urban, desert, forest, coastal ocean, and agricultural areas, with clear, cloudy, polluted, and pristine atmospheric conditions. Flights were performed in coordination with satellite overpasses and ground-based observations, including the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI), sun photometers, and a surface reflectance spectrometer. ACEPOL is a resource for remote sensing communities as they prepare for the next generation of spaceborne MAP and lidar missions. Data are appropriate for algorithm development and testing, instrument intercomparison, and investigations of active and passive instrument data fusion. They are freely available to the public. The DOI for the primary database is https://doi.org/10.5067/SUBORBITAL/ACEPOL2017/DATA001 (ACEPOL Science Team, 2017), while for AirMSPI it is https://doi.org/10.5067/AIRCRAFT/AIRMSPI/ACEPOL/RADIANCE/ELLIPSOID_V006 and https://doi.org/10.5067/AIRCRAFT/AIRMSPI/ACEPOL/RADIANCE/TERRAIN_V006 (ACEPOL AirMSPI 75 Science Team, 2017a, b). GroundMSPI data are at https://doi.org/10.5067/GROUND/GROUNDMSPI/ACEPOL/RADIANCE_v009 (GroundMSPI Science Team, 2017). Table 3 lists further details of these archives. This paper describes ACEPOL for potential data users and also provides an outline of requirements for future field missions with similar objectives.

The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign

In the fall of 2017, an airborne field campaign was conducted from the NASA Armstrong Flight Research Center in Palmdale, California to advance the remote sensing of aerosols and clouds with Multi-angle Polarimeters (MAP) and Lidars. The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) campaign was jointly sponsored by NASA and the Netherlands Institute for Space Research (SRON). Six instruments were deployed on the ER-2 high altitude aircraft. Four were MAPs: the Airborne Hyper Angular Rainbow Polarimeter (AirHARP), the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), the Airborne Spectrometer for Planetary EXploration (SPEX Airborne) and the Research Scanning Polarimeter (RSP). The remainder were Lidars, including the Cloud Physics Lidar (CPL) and the High Spectral Resolution Lidar 2 (HSRL2). The southern California base of ACEPOL enabled observation of a wide variety of scene types, including urban, desert, forest, coastal ocean and agricultural areas, with clear, cloudy, polluted and pristine atmospheric conditions. Flights were performed in coordination with satellite overpasses and ground based observations, including the Groundbased Multiangle SpectroPolarimetric Imager (GroundMSPI), sun photometers, and a surface reflectance spectrometer. ACEPOL is a resource for remote sensing communities as they prepare for the next generation of spaceborne MAP and lidar missions. Data are appropriate for algorithm development and testing, instrument intercomparison, and investigations of active and passive instrument data fusion. They are freely available to the public, at https://doi.org/10.5067/SUBORBITAL/ACEPOL2017/DATA001 (ACEPOL Science Team, 2017). This paper describes ACEPOL for potential data users, and also provides an outline of requirements for future field missions with similar objectives.

In situ and denuder-based measurements of elemental and reactive gaseous mercury with analysis by laser-induced fluorescence – results from the Reno Atmospheric Mercury Intercomparison Experiment

The University of Miami (UM) deployed a sequential two-photon laser-induced fluorescence (2P-LIF) instrument for the in situ measurement of gaseous elemental mercury, Hg(0), during the Reno Atmospheric Mercury Intercomparison Experiment (RAMIX) campaign. A number of extended sampling experiments, typically lasting 6–8 h but on one occasion extending to ∼ 24 h, were conducted, allowing the 2P-LIF measurements of Hg(0) concentrations to be compared with two independently operated instruments using gold amalgamation sampling coupled with cold vapor atomic fluorescence spectroscopic (CVAFS) analysis. At the highest temporal resolution, ∼ 5 min samples, the three instruments measured concentrations that agreed to within 10–25 %. Measurements of total mercury (TM) were made by using pyrolysis to convert total oxidized mercury (TOM) to Hg(0). TOM was then obtained by difference. Variability in the ambient Hg(0) concentration limited our sensitivity for measurement of ambient TOM using this approach. In addition, manually sampled KCl-coated annular denuders were deployed and analyzed using thermal dissociation coupled with single-photon LIF detection of Hg(0). The TOM measurements obtained were normally consistent with KCl denuder measurements obtained with two Tekran speciation systems and with the manual KCl denuder measurements but with very large uncertainty. They were typically lower than measurements reported by the University of Washington (UW) Detector for Oxidized Hg Species (DOHGS) system. The ability of the 2P-LIF pyrolysis system to measure TM was demonstrated during one of the manifold HgBr2 spikes but the results did not agree well with those reported by the DOHGS system. The limitations of the RAMIX experiment and potential improvements that should be implemented in any future mercury instrument intercomparison are discussed. We suggest that instrumental artifacts make a substantial contribution to the discrepancies in the reported measurements over the course of the RAMIX campaign. This suggests that caution should be used in drawing significant implications for the atmospheric cycling of mercury from the RAMIX results.

EARLINET instrument intercomparison campaigns: overview on strategy and results

This paper introduces the recent European Aerosol Research Lidar Network (EARLINET) quality-assurance efforts at instrument level. Within two dedicated campaigns and five single-site intercomparison activities, 21 EARLINET systems from 18 EARLINET stations were intercompared between 2009 and 2013. A comprehensive strategy for campaign setup and data evaluation has been established. Eleven systems from nine EARLINET stations participated in the EARLINET Lidar Intercomparison 2009 (EARLI09). In this campaign, three reference systems were qualified which served as traveling standards thereafter. EARLINET systems from nine other stations have been compared against these reference systems since 2009. We present and discuss comparisons at signal and at product level from all campaigns for more than 100 individual measurement channels at the wavelengths of 355, 387, 532, and 607 nm. It is shown that in most cases, a very good agreement of the compared systems with the respective reference is obtained. Mean signal deviations in predefined height ranges are typically below ±2 %. Particle backscatter and extinction coefficients agree within ±2 × 10−4 km−1 sr−1 and ± 0.01 km−1, respectively, in most cases. For systems or channels that showed larger discrepancies, an in-depth analysis of deficiencies was performed and technical solutions and upgrades were proposed and realized. The intercomparisons have reinforced confidence in the EARLINET data quality and allowed us to draw conclusions on necessary system improvements for some instruments and to identify major challenges that need to be tackled in the future.

EARLINET instrument intercomparison campaigns: overview on strategy and results

This paper introduces the recent EARLINET quality-assurance efforts at instrument level. Within two dedicated campaigns and five single-site intercomparison activities 21 EARLINET systems from 18 EARLINET stations were intercompared between 2009 and 2013. A comprehensive strategy for campaign setup and data evaluation has been established. Eleven systems from nine EARLINET stations participated in the EARLINET Lidar Intercomparison 2009 (EARLI09). In this campaign, three reference systems were qualified which served as traveling standards thereafter. EARLINET systems from nine other stations have been compared against these reference systems since 2009. We present and discuss comparisons at signal and at product level from all campaigns for more than 100 individual measurement channels at the wavelengths of 355, 387, 532 and 607 nm. It is shown that in most cases a very good agreement of the compared systems with the respective reference is obtained. Mean signal deviations in pre-defined height ranges are typically below ±2 %. Particle backscatter and extinction coefficients agree within ±2 × 10−4 km−1 sr−1 and ± 0.01 km−1, respectively, in most cases. For systems or channels that showed larger discrepancies, an in-depth analysis of deficiences was performed and technical solutions and upgrades were proposed and realized. The intercomparisons have reinforced the confidence in the EARLINET data quality and allowed us to draw conclusions on necessary system improvements for some instruments and to identify major challenges that need to be tackled in the future.