Statistics – Applications
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21347431z&link_type=abstract
American Astronomical Society, AAS Meeting #213, #474.31; Bulletin of the American Astronomical Society, Vol. 41, p.433
Statistics
Applications
Scientific paper
Astronomers have been plagued for centuries by "atmospheric extinction” - scattering and absorption of light as it travels through Earth's night-time atmosphere for the last millisecond of its often billion-year journey. This effect is the principal limiting factor to the precision and accuracy of observations made with ground-based telescopes. In an effort to significantly enhance the precision of observations we have initiated a program to quantitatively measure the atmosphere in the direction a nearby astronomical telescope is pointed, and to do so contemporaneously with its scientific observations.
The first instrument we have fielded to address this problem is the Astronomical Lidar for Extinction (ALE), a 527nm eye-safe elastic backscatter lidar that provides high precision extinction measurements when the atmosphere is clear and the majority of astronomical observations are being made. ALE is thus a "clear air lidar” primarily designed to make sub-1% measurements of atmospheric extinction every minute of time, and to make these measurements through an optical path sensibly the same as that through which astronomical observations are being made.
The bulk of temporal and spatial variability that affects ground-based astronomical observations originates in the troposphere where aerosols and water vapor exhibit large variation. Therefore, ALE principally monitors the Rayleigh backscatter from the relatively stable stratosphere, and from the stratospheric measurements we deduce the transmission of lower layers. ALE was designed to gather approximately one million photons from above 20km per one minute scan under clear conditions, enabling the high precision we require.
We describe ALE and present results from the first year of operations. We further discuss its astronomical applications and investigate the contributions to understanding Earth's atmosphere.
Development of ALE was funded by NSF Grant 0421087.
Fitch Jonathan J.
Gimmestad Gary G.
McGraw Jason
Roberts Dale
Smith Jeffrey J.
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