Mueller whole sky camera (ca. 1905) modified by Fassig. Reported in the 1915 issue ofMonthly Weather Review
Awhole sky camera is a specialized camera used in meteorology and astronomy for capturing a photograph of the entire sky. Another application is that ofhemispherical photography to study plant canopy geometry and to calculate near-ground solar radiation.
Whole sky cameras typically use afisheye lens that takes in an extremely wide, hemispherical image. Such lenses were originally developed for use in meteorology.[1]
However, alternative techniques are based on the photography of a mirror-like hemisphere which are more common.[2]One of the first reported whole sky cameras was based on a series of pictures with lenses inclined to the horizon at an altitude of 45 degrees. With a lens that covers an angular field of 90 degrees, such camera revolves about a vertical axis.[3]
In meteorological applications, whole sky cameras are used to study cloud cover, the current level of UV radiation, fractional cloud coverage, sky polarization, the computation of cloud base height and wind speed at cloud heights. Other uses include creating time-lapse photography of clouds. Whole sky cameras may be equipped with a sun tracking device to block sunlight which is too bright for the typical dynamic range of photographs. Sun tracking allows for reliable estimates of cloud fractional coverage, including cover in the part of the sky close to the Sun. There are techniques such asHDR which permit the taking of high dynamic range photographs without a sun tracker.[citation needed]
Whole sky camera also popularly known as an all-sky camera in the astronomical field is used for meteor, fireball, and spacecraft reentry recording and identification. While mostly identical to the meteorological application, the system for astronomical use tends to have a more sensitive night camera and much longer exposure due to the night-use nature of the camera.[4]
Whole sky cameras instereo configurations[5] can be used to derive cloud base height and cloud base motion. The first work on this application ofphotogrammetry was done in 1896.[6]
^Kassianov, E., C.N. Long, and J. Christy, 2005: Cloud-Base-Height Estimation from Paired Ground-Based Hemispherical Observations. J. Appl. Meteorol., 44, 1221–1233.
