Depolarization–ratio profiling at several wavelengths in pure Saharan dust during SAMUM 2006

Abstract

Vertical profiles of the linear particle depolarization ratio δp of pure dust clouds were measured during the Saharan Mineral Dust Experiment (SAMUM) at Ouarzazate, Morocco (30.9° N, -6.9° E), close to source regions in May-June 2006 with four lidar systems at four wavelengths (355, 532, 710, and 1064 nm). The intercomparison of the lidar systems is accompanied by a discussion of the different calibration methods – including a new, advanced method - and a detailed error analysis. Over the whole SAMUM periode pure dust layers show a mean δp at 532 nm of 0.31 in the range between 0.27 and 0.35 with a mean Ångstrøm exponent AE (440-870 nm) of 0.18 (range 0.04 – 0.34), and still high mean δp between 0.21 and 0.25 during periods with aerosol optical thickness ≤0.1 with a mean AE of 0.76 (range 0.65 – 1.00), which represents a negative correlation of δp with AE. A slight decrease of δp with wavelength was found between 532 nm and 1064 nm from δp = 0.31 ±0.03 to 0.27 ±0.04, respectively.