On the ability of pseudo-operational ground-based light detection and ranging (LIDAR) sensors to determine boundary-layer structure: intercomparison and comparison with in-situ radiosounding

Abstract. Twenty-one cases of boundary-layer (BL) structure were retrieved by three co-located remote sensors, one lidar (Leosphere ALS300) and two ceilometers (Vaisala CL31, Jenoptik CHM15K). Data were collected during the ICOS field campaign held at the GAW Atmospheric Station of Mace Head, Ireland, from 8 to 28 June 2009. The study is a two-step investigation of the BL structure based (i) on the intercomparison of backscatter profiles from the three laser sensors and (ii) on the comparison of the backscatter profiles with twenty-three radiosoundings performed during the period of 8 to 15 June 2009. The Temporal Height-Tracking (THT) algorithm was applied to the three sensors' backscatter profiles to retrieve the decoupled structure of the BL over Mace Head. The results of the intercomparisons are expressed in terms of the mean correlation coefficients, mean bias (difference between two sensors' detections), mean sigma (the standard deviation of the bias) and the consistency, i.e. the percentage of cases where the detections of the intercompared sensors were closer than 200 m. The ALS300-CHM15K comparison provided the most consistent retrievals amongst the three comparisons with, respectively, the 86.5% and 77.2% of the lower and upper layer detections closer than 200 m and with correlation coefficients equal to 0.88 and 0.83 at the lower and upper layer, respectively.

The lidar and ceilometers-detected BL heights were then compared to the temperature profiles retrieved by radiosoundings. The most consistent retrievals at the lower layer are from the ALS300 with the 75% of detections closer than 200 m to the radiosoundings' first temperature inversion. Despite the lower signal-to-noise ratio and R-value compared to the ASL300 and CHM15K, the CL31 is more consistent with the radiosoundings retrievals at the upper layer with 62.5% of detections closer than 200 m to the radiosoundings' second temperature inversion. The ALS300 has larger pulse-averaged power compared to the two ceilometers and better ability in detecting fine aerosol layers within the BL. The comparison of remote and in-situ data proved both the veracity of the inherent link between temperature and aerosol backscatter profiles, and the existence of possible limitations in using aerosols as a tracer to detect the BL structure.