Determination of the cloud coverage using ground-based camera images in the visible and infrared spectral range

Abstract

In this study, ground based image sequences of the sky will be evaluated to analyse the cloud coverage. These images are taken in the visual and infrared spectrum. The main ambition is to determine the cloud coverage without the knowledge of additional measurements (like temperature or precipitable water vapor). The determination of the cloud coverage is is deduced from camera images only. In the visual spectrum, methods from literature are extended according to this application. For example, the ratio of the color channels red and blue is formed. In the infrared spectral range a method is developed that can distinguish the cloud-covered from the cloudless image areas by using the maximum and minimum occurring values in the image. The grey values are parameterised using statistical boundary values in such a way that a temperature relationship is unambiguously possible and consequently a statement about the degree of coverage can be made by the algorithm. The determination of the cloud coverage reaches a higher accuracy and reliability in the infrared spectral range.

Design and implementation of a micrometeorological weather station for ground-based swarm environments

“…This allows us to evaluate cloud coverage by an algorithm reported earlier . 9 The method involves identifying three decision characteristics: the Red/Blue Ratio (RBR), Normalised Red/Blue Ratio (NRBR), and Saturation (SAT) to determine whether a pixel represents a cloud or the cloudless sky. Experimentally determined thresholds are applied to create binary images for each characteristic, and the cloud coverage is calculated by comparing the number of pixels representing clouds to the total number of pixels in the image.…”