Measuring the infrared sky background from the high Antarctic plateau [thesis]

Matthew Freeman
The high plateau of Antarctica is known to be the best site on Earth for infrared astronomy. The extremely low levels of water vapour there open up new atmospheric windows, making ground-based infrared and terahertz observations possible. In particular, at the site Ridge A in Antarctica the atmospheric water vapour level regularly drops below 0.1 mm, lower than any other site on Earth. The low temperatures, stable atmosphere, and clear skies also contribute to the superb observing conditions at
more » ... this site. For most near-infrared observations the limiting factor is the background emission, which primarily comes from the atmosphere. To conclusively demonstrate the quality of a site, it is necessary to take measurements of the background in-situ. This has been performed for the first time away from the South Pole with the installation of the Near Infrared Sky Monitor (NISM) at Ridge A in 2015. NISM has taken measurements of the spectral radiance of the atmosphere in the Kdark band, at 2.4 microns. These measurements can determine how much infrared noise will be present in astronomical observations, and hence the quality of Ridge A as an observatory site. In this thesis, the data sent back from NISM are analysed to determine the zenith spectral radiance of the atmosphere at Ridge A. This analysis posed a challenge, as a number of problems occurred with the instrument, including problems with a motor used to set the beam altitude, and ice forming on the black body calibrator. As NISM is completely inaccessible for most of the year, these problems had to be diagnosed remotely, and dealt with in software. Ultimately, it was determined that there may be a long-wavelength leak in NISM's Kdark filter, and that it would be necessary to recover the instrument in order to characterise the leak. The team was not able to reach the site in the 2017/2018 season due to the poor condition of the skiway. A definitive measurement of the infrared sky background will have to wait until NISM is recovered in a future mission, when inspect [...]
doi:10.26190/unsworks/20985 fatcat:dnj7rvkgyvcznffk22ybc6b6pi