Development and calibration of a star photometer to measure the aerosol optical depth: Smoke observations at a high mountain site

In this paper we present a recently developed star photometer, which allows us to study aerosol optical properties at night, based on a CCD camera. Details about the operation of the system are presented together with the instrument set up. Special attention is paid to instrument calibration and thus details about a high mountain calibration campaign are presented. A combination of a Langley procedure with a calibration transfer supported by a check using the so-called two-star method of star photometry has been used in order to calibrate with an appropriate number of stars. Also, some measurements acquired during an episode of long-range transport of biomass burning aerosol are presented as a case study.