Resumo

MASI, W S et al. Determination of the cloud base height by means of digital stereoscopic vision. An. AFA [online]. 2015, vol.26, n.1, pp.1-11. ISSN 0327-358X.

Among the parameters that characterize a cloud, the height of its base is one of the key factors in the determination of the infrared radiative properties of the clouds, and hence one of the main parameters to measure. Therefore, in this paper we have developed a method for the determination of the Cloud Base Height (CBH). It consists of 3 main stages: 1. The characterization of each camera sensor through a laboratory optical bench calibration; 2. A method to deploy the system outdoors for proper alignment and stabilization; 3.An algorithm for digital image processing in MATLAB programming language, which estimates the cloud base height from two simultaneous images using a triangulation procedure at different points of interest. The resulting measurements of the system, composed of a pair of advanced compact cameras deployed with a known separation (100 m), were checked against a lidar system for validation. Two major cases were studied, one with high clouds (8000~12000 m), and other with multiple layers of low clouds (800~4000 m), resulting for the first case in a maximum uncertainty of less than 38 % of its CBH, and for the second a maximum uncertainty of less than 10 % of its CBH. It was possible to determine the main sources of uncertainty which are associated with the characterization of the digital cameras and the alignment with the zenith in the deployment. The results of this method give an alternative tool for the determination of CBH, making a relative low cost system with respect to commercial ceilometers.

Palavras-chave : Stereo Vision; Digital Image Processing; Artificial Vision; Digital Camera; Clouds; Cloud Cover; Height of Clouds; Atmosphere; CBH.

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