Center for Astrophysical Research in Antarctica
A Brief Atlas of Atmospheric Characteristics
Infrared Sky Brightness
Sky emission abouve the South Pole in µJy
1.5-2.5 µm (upper) and 2.9-4.1 µm (lower), obtained
with 1% spectral resolution through the IRPS CVF. These are the
median of all the "darkest sky" spectra obtained during the winter
of 1995. Calibration
was performed using a black body source at 0 degrees Centigrade, and fluxes
short of 2.1 µm use a nominal clibration factor for the instrument. Note
that the upper plot uses a linar, and the lower plot a log, intensity scale.
For more information, see
Phillips et al. 1999.
Click each image for a larger, readable version.
In these plots, we present a comparison of the measured sky brightness
at zenith between the South Pole and Siding Spring (Australia) from
2-4.3 µm. In the first figure
(2-3 µm), the South Pole
spectra was collected on 31 May 1994 when the ambient temperature
was -62 °C, while in the second figure (3-5 µm) the
South Pole spectra was collected on 2 June
1994 when the ambient temperature was -66 C. In both plots, the
Siding Spring data was collected on 9 December 1993 at +10 C.
The units on the vertical axis of the left-hand plot are micro-Jy
Note the large dip in the South
Pole sky brightness between 2.25-2.5 µm compared to the temperate
latitude site. The South Pole sky is 20-100 times darker at these
wavelengths than any other sight on earth which is accessible for
large telescopes. CARA specifically designed the so-called K_dark
(2.29-2.43 µm) filter to exploit this atmospheric window.
The units on the vertical axis of the right-hand plot are milli-Jy
Note that between 2.9-4 µm, the South Pole sky is
more than 10 times darker than at a temperate latitude site.
For more information, please see Ashley et al.
Water vapor dominates the sub-mm spectrum, but "dry air" oxygen lines
are also important. Site intercomparison is complicated by
constituent variation, by measurement characteristics, and frequency.
For more information, see the site testing section of
the Stark et al. decadal
Click to retrieve readable version
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Last modified Thursday, 15-Apr-1999 11:16:24 CDT