CARA Science:
A Brief Atlas of Atmospheric Characteristics

Infrared Sky Brightness

Sky emission abouve the South Pole in µJy arcsec^-2, from 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.


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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 arcsec^-2. 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 arcsec^-2. 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. 1996.

Sub-millimeter Opacity


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 report and this site.

Millimeter Transmission

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