Progress in Astronomical Radiometry: Demonstration of Precise Lidar-based Real-time Atmospheric Extinction Corrections

Details Progress in Astronomical Radiometry: Demonstration of Precise Lidar-based Real-time Atmospheric Extinction Corrections Progress in Astronomical Radiometry: Demonstration of Precise Lidar-based Real-time Atmospheric Extinction Corrections

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21942206m&link_type=abstract

American Astronomical Society, AAS Meeting #219, #422.06

Astronomy and Astrophysics

Astronomy

Scientific paper

We demonstrate atmospheric extinction corrections to a precision of 0.25% per airmass at one minute cadence using the Astronomical Lidar for Extinction (ALE). The lidar tracked within or near the 0.7 degree by 1.0 degree field of view of a 300mm diameter astrograph acquiring imaging radiometric data of stars. The field included a target star, often a short-period variable star, and several comparison stars. Extinction corrections are simultaneously derived from the lidar returns and by differential radiometry amongst the comparison stars.
ALE is an alt-az mounted bistatic elastic backscatter lidar operated at 527nm transmitting 24 ns pulses at 1500 Hz with a 305 mm transmitter, 100 mm short range receiver and 670 mm long range receiver. Both receivers use photomultipliers as detectors and extinction corrections derive from pulse counting the stratospheric Rayleigh backscatter return from approximately 15 km to 30 km altitude.
We show that:
• Nightly mean extinction coefficients do not adequately represent the time and angular variability of extinction and can introduce systematic errors of at least one percent even on "visually photometric” nights.
• Extinction corrections must be derived by measurement of the column of atmosphere through which astronomical observations are being made.
• The ALE lidar provides precise extinction corrections through atmospheric transmission variations of at least 50% (0.75 mag of extinction).
• Lidar extinction corrections depend only upon instrumental parameters, principally lidar power, thus provide precise extinction corrections for the column of atmosphere through which the supported telescope observes, independently of the (e.g. stellar) content of the field.
We assert that lidar-based atmospheric extinction corrections obviate atmospheric extinction as the major source of radiometric error for ground-based telescopes.
This research is supported by NIST Award 60NANB9D9121 and NSF Grant AST-1009878.

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