Toronto Water Vapor Lidar Inter-Comparison Campaign

Abstract

This study presents comparisons between vertical water vapor profile measurements from a Raman lidar and a new pre-production broadband differential absorption lidar (DIAL). Vaisala’s novel DIAL system operates autonomously outdoors and measures the vertical profile of water vapor within the boundary layer 24 h a day during all weather conditions. Eight nights of measurements in June and July 2018 were used for the Toronto water vapor lidar inter-comparison field campaign. Both lidars provided reliable atmospheric backscatter and water vapor profile measurements. Comparisons were performed during night-time observations only, when the York Raman lidar could measure the water vapor profile. The purpose was to validate the water vapor profile measurements retrieved by the new DIAL system. The results indicate good agreement between the two lidars, with a mean difference (DIAL–Raman) of 0.17 ± 0.09 g/kg. There were two main causes for differences in their measurements: horizontal displacement between the two lidar sites (3.2 km) and vertical gradients in the water vapor profile. A case study analyzed during the campaign demonstrates the ability for both lidars to measure sudden changes and large gradients in the water vapor’s vertical structure due to a passing frontal system. These results provide an initial validation of the DIAL’s measurements and its ability to be implemented as part of an operational program.

Evaluation of a Prototype Broadband Water-Vapour Profiling Differential Absorption Lidar at Cardington, UK

“…The overall average data availability height is 1300 m for the assessment period. These results are consistent with those published by Newsom et al [16] and Mariani et al [20]. During this experiment, data were missing for occasional short periods due to slow internet connection on the site.…”

“…It was also evaluated in very high humidity subtropical weather conditions in Hong Kong [18]. Another comparison with a Raman Lidar and radiosonde measurements in Canada in an urban area is described in Mariani, 2020 [20]. Recently, Mariani et al 2021 [17] evaluated it over a year in artic condition.…”

Evaluation of Arctic Water Vapor Profile Observations from a Differential Absorption Lidar

“…During its year-long evaluation, the DIAL measured extremely low WVMRs during the Arctic winter (<1 g/kg) and relatively high concentrations (>8 g/kg) during the summer, including frequent large (factor of 2 to 4) and rapid changes over <5 h. In the October 2018 case study, steep gradients and sudden changes in the WVMR structure, similar to the change in the DIAL's WVMR profile during a passing cold front in Toronto [23], was observed by both lidars. Only the DIAL was capable of conducting continuous WVMR observations without large temporal gaps, albeit at altitudes limited to within the PBL.…”

“…With the exception of intermittent power outages at the site, the DIAL experienced no downtime during the study period. The newly developed pre-production DIAL system was installed at the Iqaluit supersite on 6 September 2018 (Figure 2, left) after undergoing a preliminary evaluation in Toronto [23]. A second pre-production model was acquired by Deutscher Wetterdienst (DWD) and deployed to Germany, where it is undergoing its own independent assessment and field campaign.…”

“…In summer 2018, Environment and Climate Change Canada (ECCC) acquired a new broadband DIAL system developed by Vaisala for operational use as a stand-alone system or as part of a larger network. The DIAL demonstrated excellent performance in a summer-time urban environment during the Toronto water vapor lidar inter-comparison campaign [23]. Its earlier prototype version also underwent evaluations in the Southern Great Plains, Germany, Finland, and Hong Kong [24][25][26].…”