Aerosol profiling with the Jenoptik ceilometer CHM15kx
Abstract. Since a few years, the number of active remote sensing systems has been rapidly increasing as national weather services started to build up networks of ceilometers. As ceilometers can be considered as "simple" backscatter lidars, it is obvious to investigate to which extent they can provide quantitative aerosol information. In this context, the calibration of the ceilometer is the most crucial point: whereas previous studies primarily have relied on the comparisons with co-incident sun photometer measurements and the Rayleigh calibration, we provide an absolute calibration of the ceilometer. The advantage of this approach is that backscatter profiles can be derived during daytime and nighttime, and even in cases when the signal-to-noise ratio of signals from the free troposphere is very low. Moreover, the retrieval can easily be automated. In this paper, we consider the Jenoptik CHM15kx-ceilometer. We discuss the methodology and the achievable accuracy and present a set of examples to highlight the wide range of applications, and the limitations. The achievable temporal resolution is of the order of a few minutes; the relative error of the particle backscatter coefficient is less than 10%. It is emphasized that the accuracy of extinction coefficients and – as a consequence – of the aerosol optical depth is limited due to the unknown lidar ratio. This is, however, an inherent problem of any backscatter lidar and not a special feature of the ceilometer.