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K. S. J. Anderson, J. Brinkmann (NMSU and Apache Point Observatory), M. Carr (Princeton University), D. Woods (NMSU and Apache Point Observatory), D. P. Finkbeiner, J. E. Gunn (Princeton University), C. L. Loomis (NMSU and Apache Point Observatory), D. Schlegel (Princeton University), S. Snedden (NMSU and Apache Point Observatory)
Cloud cover at Apache Point Observatory is monitored by an all-sky camera system which images clouds in the thermal infrared. Even thin clouds, illuminated by thermal emission from the ground, can be detected. These same clouds are almost invisible at visual wavelengths, especially on moonless nights at this dark-sky observatory site. Our camera system uses an aluminum hyperboloidal mirror to provide a wide-angle view covering most of the sky; it is sensitive to radiation in the 8 to 12 micron wavelength interval. A cloud free atmosphere is fairly transparent in this window; clouds appear as bright structures against the darker sky background. Images are recorded at video rates, then summed and averaged in software to increase system sensitivity. Current all-sky images are available to on-site observers or through the Apache Point Observatory web pages. Cloud information is used to plan observing, make real-time observing decisions, and can provide useful estimates of atmospheric extinction and sky brightness at other wavelengths.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.