Calibração de um contador fotoéletrico de núcleos de condensação de nuvens

Abstract

A calibration process was performed for the Cloud Condensation Nuclei Counter (CwC). This calibration was based on the comparison between the photodetector output signal and the number of droplets developing in the sample volume of the static thermal-gradient diffusion chamber. To make the calibration process accurate and easy an automatic digital image processing algorithm was developed. This algorithm is based on the modeling of the digital image by Markov' s random fields. The calibrations cover the supersaturation range from 0.3% to 1.0%, and for each supersaturation, CCN concentration was proponional to the photodetector output. It was found that, during the activation and grov,1h of droplers, the time of the peak signal corresponds well to the time at which droplet coums is the maximum within the sample volume. The use of an average output signal oYer a period bracketing the mean position of the peak value is a slightly better measure of àrnplet concentrations than the peak value. The calibràtion equations here derived are specific to the CCN counter used to obtain the data. Also, the calibration constants here reported are not of general validity.