okta

kahdeksasosa puhekieltä One eighth of the total area of the celestial dome; used as a measure of cloudiness (one okta means that one eighth of the sky is obscured, two oktas that one quarter is obscured, and so on).
1960, American Meteorological Society, Meteorological and Geoastrophysical Abstracts, American Meteorological Society, Page 480

...64% of the low- and 50% of the high-cloud amount differences were within ± 1 okta, although many of these successes (71% in the low-cloud amount) were for cases of totally clear or totally cloudy skies.

‘Fog is traditional for the season and cloud is anticipated at six to seven oktas, sir.’

Mean cloud amount distributions are transformed to normal distributions. The accuracy of the method is indicated by the retrieval of the original distribution with a typical error of 14% in the frequency of each okta of cloud amount. - Author

For example, it has been estimated that a Landsat satellite, which revisits a particular location once every 16 days, will obtain a cloud-free scene of a particular location in Britain only once per year, and a scene with 1 okta of cloud (an okta is one eighth of the sky obscured by cloud) only twice per year.