Accession Number : ADA518985


Title :   Measuring Overcast Colors with All-Sky Imaging


Descriptive Note : Journal article


Corporate Author : NAVAL ACADEMY ANNAPOLIS MD MATHEMATICS AND SCIENCES DIV


Personal Author(s) : Lee, Jr, Raymond L


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a518985.pdf


Report Date : Apr 2008


Pagination or Media Count : 11


Abstract : Digital images of overcast skies as seen from the earth's surface open new windows onto the angular details of overcast colors and visible-wavelength spectra. After calibration with a spectroradiometer, a commercial CCD camera equipped with a fisheye lens can produce colorimetrically accurate all-sky maps of overcast spectra. Histograms and azimuthally averaged curves of the resulting chromaticities show consistent, but unexpected, patterns in time-averaged overcast colors. Although widely used models such as LOWTRAN7 and MODTRAN4 cannot explain these characteristic patterns, a simple semiempirical model based on the radiative transfer equation does, and it provides insights into the visible consequences of absorption and scattering both within and beneath overcasts.


Descriptors :   *PHOTOHELIOGRAPHS , *RADIATIVE TRANSFER , *COLORIMETRIC ANALYSIS , *CHROMATICITY , *SPECTRORADIOMETERS , *CLOUD COVER , IMAGES , CALIBRATION , SKY , ABSORPTION , MEAN , EQUATIONS , CHARGE COUPLED DEVICES , COLORS , SPECTRA , TIME , SCATTERING , SPECTROHELIOGRAPHS , DIGITAL SYSTEMS , MEASUREMENT


Subject Categories : Meteorology
      Electrical and Electronic Equipment
      Test Facilities, Equipment and Methods
      Miscellaneous Detection and Detectors
      Atomic and Molecular Physics and Spectroscopy
      Astronomy


Distribution Statement : APPROVED FOR PUBLIC RELEASE