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Imperfections in a lidar's overlap function lead to artefacts in thebackground, range and overlap-corrected lidar signals. These artefacts canerroneously be interpreted as an aerosol gradient or, in extreme cases, as acloud base leading to false cloud detection. A correct specification of theoverlap function is hence crucial in the use of automatic elastic lidars(ceilometers) for the detection of the planetary boundary layer or of lowcloud.  In this study, an algorithm is presented to correct such artefacts. It isbased on the assumption of a homogeneous boundary layer and a correctspecification of the overlap function down to a minimum range, which must besituated within the boundary layer. The strength of the algorithm lies in asophisticated quality-check scheme which allows the reliable identificationof favourable atmospheric conditions. The algorithm was applied to 2 years ofdata from a CHM15k ceilometer from the company Lufft. Backscatter signalscorrected for background, range and overlap were compared using the overlapfunction provided by the manufacturer and the one corrected with thepresented algorithm. Differences between corrected and uncorrected signalsreached up to 45 % in the first 300 m above ground.  The amplitude of the correction turned out to be temperature dependent andwas larger for higher temperatures. A linear model of the correction as afunction of the instrument's internal temperature was derived from theexperimental data. Case studies and a statistical analysis of the strongestgradient derived from corrected signals reveal that the temperature model iscapable of a high-quality correction of overlap artefacts, in particular thosedue to diurnal variations. The presented correction method has thepotential to significantly improve the detection of the boundary layer withgradient-based methods because it removes false candidates and hencesimplifies the attribution of the detected gradients to the planetaryboundary layer. A particularly significant benefit can be expected for thedetection of shallow stable layers typical of night-time situations.  The algorithm is completely automatic and does not require any on-siteintervention but requires the definition of an adequate instrument-specificconfiguration. It is therefore suited for use in large ceilometernetworks

An empirical method to correct for temperature-dependent variations in the overlap function of CHM15k ceilometers