Whole sky camera
Whole sky camera - specialized camera used in meteorology and astronomy for photography of the whole sky.
Whole sky camera typically uses a fisheye lens that takes in an extremely wide, hemispherical image. Such lens was originally developed for use in meteorology .[1] However, alternative techniques are common and are based on photography of mirror like hemisphere .[2] One of the first reported whole sky cameras was based on series of pictures with lens inclined to the horizon at an altitude of 45 degrees, with the lens that covers an angular field of 90 degrees, such camera revolves about a vertical axis. .[3]
Another application is that of hemispherical photography to study plant canopy geometry and to calculate near-ground solar radiation.
Meteorological applications
In meteorological applications the whole sky camera is used to study cloud cover, UV index, timelapse photography of clouds, cloud fractional coverage, sky polarization, the computation of cloud base height, as well as wind speed at cloud heights. Whole sky camera may have sun tracking device to block sun which is too bright for typical dynamic range of photographs. Sun tracking allows for reliable estimates of cloud fractional coverage in Sun proximity. There are techniques such as HDR which allow to make high dynamic range photographs without a sun tracker.
Cloud stereoscopy
Whole sky cameras in stereo configurations [4] can be used to derive cloud base height and cloud base motion. First work on this topic was done in 1896. .[5]
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Simple whole sky camera based on Canon A75 located north of Kennedy Space Center during meteorological experiment close to the MCR radar. -
Whole sky camera based on reflecting (mirror) dome with sun tracker. Constructed by K. Markowicz.
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Baltimore, Md., Sept. 16, 1914, 7:45am. Taken from Mueller's inclined camera. -
N. of Kennedy Space Center, Fl. on July 24, 2009. Taken from Flatau's camera. -
Sky image based on K. Markowicz's design. Black stripe covering the sun (sun tracker) is visible.
Notes and references
- ^ Hill, R. (1924) [1924]. "A lens for whole sky photographs". Quarterly Journal of the Royal Meteorological Society. 50 (211): 227–235. Bibcode:1924QJRMS..50..227H. doi:10.1002/qj.49705021110.
- ^ Depermann, C. E. (1949). "An improved mirror for photography of the whole sky". Bulletin of the American Meteorological Society: 282–285.
- ^ Fassig, Q.L. (1915). "A revolving cloud camera". Monthly Weather Review. 43: 274–275. Bibcode:1915MWRv...43..274F. doi:10.1175/1520-0493(1915)43<274:arcc>2.0.co;2.
- ^ Kassianov, E., C.N. Long, and J. Christy, 2005: Cloud-Base-Height Estimation from Paired Ground-Based Hemispherical Observations. J. Appl. Meteor., 44, 1221–1233.
- ^ Koppe, C. (1896). Photogrammetrie und Internationale Wolkenmessung. Braunschweig, Germany: Druck und Verlag von Friedrich Vieweg und Sohn. p. 108.