Cloud observations in Switzerland using hemispherical sky cameras

Wacker, Stefan; Gröbner, Julian; Zysset, Christoph; Diener, Laurin; Tzoumanikas, Panagiotis; Kazantzidis, Andreas; Vuilleumier, Laurent; Stöckli, Reto; Nyeki, Stephan; Kämpfer, Niklaus (2015). Cloud observations in Switzerland using hemispherical sky cameras. Journal of Geophysical Research: Atmospheres, 120(2), pp. 695-707. American Geophysical Union 10.1002/2014JD022643

[img]
Preview
Text
jgrd51942.pdf - Published Version
Available under License Creative Commons: Attribution-Noncommercial-No Derivative Works (CC-BY-NC-ND).

Download (1MB) | Preview

We present observations of total cloud cover and cloud type classification results from a sky camera network comprising four stations in Switzerland. In a comprehensive intercomparison study, records of total cloud cover from the sky camera, long-wave radiation observations, Meteosat, ceilometer, and visual observations were compared. Total cloud cover from the sky camera was in 65–85% of cases within ±1 okta with respect to the other methods. The sky camera overestimates cloudiness with respect to the other automatic techniques on average by up to 1.1 ± 2.8 oktas but underestimates it by 0.8 ± 1.9 oktas compared to the human observer. However, the bias depends on the cloudiness and therefore needs to be considered when records from various observational techniques are being homogenized. Cloud type classification was conducted using the k-Nearest Neighbor classifier in combination with a set of color and textural features. In addition, a radiative feature was introduced which improved the discrimination by up to 10%. The performance of the algorithm mainly depends on the atmospheric conditions, site-specific characteristics, the randomness of the selected images, and possible visual misclassifications: The mean success rate was 80–90% when the image only contained a single cloud class but dropped to 50–70% if the test images were completely randomly selected and multiple cloud classes occurred in the images.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Applied Physics
08 Faculty of Science > Institute of Applied Physics > Microwaves

UniBE Contributor:

Kämpfer, Niklaus

Subjects:

500 Science
500 Science > 530 Physics
600 Technology > 620 Engineering

ISSN:

2169-897X

Publisher:

American Geophysical Union

Language:

English

Submitter:

Martin Frenz-Lips

Date Deposited:

15 Jan 2016 10:39

Last Modified:

15 Jan 2016 10:39

Publisher DOI:

10.1002/2014JD022643

BORIS DOI:

10.7892/boris.74999

URI:

https://boris.unibe.ch/id/eprint/74999

Actions (login required)

Edit item Edit item
Provide Feedback