French airborne lidar measurements for Eyjafjallajökull ash plume survey

Abstract

Abstract. An Ultra-Violet Rayleigh-Mie lidar has been integrated aboard the French research aircraft Falcon20 in order to monitor the ash plume emitted by the Eyjafjallajökul volcano in April-May 2010. Three operational flights were carried out on 21 April, 12 and 16 May 2010 inside French, Spanish and British air spaces, respectively. The original purpose of the flights was to provide the French civil aviation authorities with objective information on the presence and location of the ash plume. The present paper presents the results of detailed analyses elaborated after the volcano crisis. They bear on the structure of the ash clouds and their optical properties such as the extinction coefficient and the lidar ratio. Lidar ratios were measured in the range of 43 to 50 sr, in good agreement with the ratios derived from groundbased lidar near Paris (France) in April 2010 (∼ 48 sr). The ash signature in terms of particulate depolarization was consistent during all flights (between 34 ± 3 % and 38 ± 3 %). Such a value seems to be a good identification parameter for volcanic ash. Using specific cross-sections between 0.19 and 1.1 m 2 g −1 , the minimum (maximal) mass concentrations in the ash plumes derived for the flights on 12 and 16 May were 140 (2300) and 250 (1500) µg m −3 , respectively. It may be rather less than, or of the order of the critical level of damage (2 mg m −3 ) for the aircraft engines, but well above the 200 µg m −3 warning level.

Temporal consistency of lidar observations during aerosol transport events in the framework of the ChArMEx/ADRIMED campaign at Minorca in June 2013

“…The sun-photometer-derived column-integrated BER of the aerosols can be computed at 440 nm from the single scattering albedo and the backscatter phase function derived from the operational algorithm of AERONET (Dubovik and King, 2000). The root mean square error (RMSE in grey area) on the lidar-derived BER, determined as the variabil-ity over 20 min, is close to 0.004 sr −1 on average, which is comparable with the one retrieved by Chazette et al (2012b) with a similar lidar system set-up in Minorca in the 2012 autumn season. We note a good coherence with the BER at 440 nm derived by the AERONET sun photometer.…”

“…PDR is an effective parameter to separate the contribution of the more spherical particles from the ones due to dust-like aerosols (e.g. Chazette et al, 2012b). Between 16 and 19 June the PDR value is between 10 and 27 %, which is representative of non-spherical dust-like aerosols (Müller et al, 2007;Tesche et al, 2011) as identified in Fig.…”

Long-range transport and mixing of aerosol sources during the 2013 North American biomass burning episode: analysis of multiple lidar observations in the western Mediterranean basin

“…The Falcon 20 aircraft was equipped with an airborne lidar LNG (Pelon et al, 2002) All the lidars can record also the depolarization ratio between the signal polarized parallel and perpendicular to the plane of the outgoing beam. For the ground-based lidar, the uncertainty on the aerosol depolarization ratio is of the order of 1-2 % as explained in Chazette et al (2012). For the airborne lidar LNG, the depolarization ratio is measured at 355 nm and it is calibrated on molecular scattering using a value of 1.5 ± 0.3 % for clean air, corresponding also to 1-2 % error on the aerosol depolarization ratio.…”

Lidar profiling of aerosol optical properties from Paris to Lake Baikal (Siberia)

“…Several tests carried on other days earlier during the campaign showed that the gain ratio varied by 5 % at most, so that the value obtained from the Lake Baikal experiment was used during the whole campaign. The PDR is then computed as in Chazette et al (2012). As the PDR is a physical parameter without meaning when there are few aerosols, its calculation is performed only for layers where the aerosol backscatter coefficient is at least 5 % of the molecular backscatter (i.e.…”

“…The volumetric depolarization ratio (VDR) was determined following the procedure described in Chazette et al (2012). It uses the transmission and reflection coefficients of the polarization separation plates as measured in the lab before departure, along with the gain ratio between the total and perpendicular polarization channels.…”