Marton G. Hidas, Michael G. Burton, Matthew A. Chamberlain, John W.V. Storey, PASA, 17 (3), 260.
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Title/Abstract Page: Infrared and Sub-millimetre Observing
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Conclusions
Modelling the infrared and sub-millimetre sky fluxes and atmospheric transmission at the South Pole, and examining their sensitivity to temperature, water vapour content and aerosol level, we reach the following conclusions:
- 1.
- At near-IR wavelengths atmospheric temperature has the dominant effect on flux levels in astronomical observing windows. The temperature at the top of the inversion layer, rather than at ice level, determines the amount of the thermal emission. The amount of aerosols, however, has a significant effect on both the atmospheric flux and the transmission. Water vapour content, over the range of values encountered on the Antarctic plateau, plays little role in determining these levels.
- 2.
- In the mid-IR windows, up to and including the 20
m window, aerosol content plays the primary role in determining flux and transmission levels for the atmosphere. Temperature plays a secondary role in determining the flux levels. Water vapour content has a marginal role. - 3.
- In the 30m mid-IR window, the far-IR windows at 200m and 230m, and in the sub-mm, water vapour content determines the atmospheric transmission. Aerosols play a negligible role. Flux levels only show a small range of variation with water vapour content, instead being set by the temperature. Flux levels are directly proportional to absolute temperature.
We stress that these conclusions are valid only for exceptionally cold, dry sites, such as those on the Antarctic plateau. The important qualities of an Antarctic observing site are high altitude, and a dry, stable and cold atmosphere, clear of cloud and aerosols. Our results show that these factors affect different wavebands to different extents. Therefore, the choice of optimum site within the continent may depend upon the type of observation being considered. Minimising the aerosol content can clearly be an important factor in this choice.
Future work
Several questions regarding the source of emission in the mid-infrared remain unanswered. It is clear that aerosols play a vital role. However, the exact nature of these aerosols, including their origin and distribution throughout the atmosphere, is still unknown. A better understanding of these details may help to identify possible sites where the effect of aerosols is minimised, thus improving observing conditions.
One possibility is to use a LIDAR to measure the altitude at which aerosols are located. This instrument uses backscattered laser light to probe the atmosphere. It could also help determine the origin of the aerosol particles, and whether they are related in any way to visible cloud.
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Title/Abstract Page: Infrared and Sub-millimetre Observing
Previous Section: The effect of aerosols
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