EDP Sciences
Free access
Volume 373, Number 2, July II 2001
Page(s) 746 - 756
Section Instruments, observational techniques and data processing
DOI http://dx.doi.org/10.1051/0004-6361:20010611

A&A 373, 746-756 (2001)
DOI: 10.1051/0004-6361:20010611

Optimization of heterodyne observations using Allan variance measurements

R. Schieder and C. Kramer

I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany

(Received 11 January 2001 / Accepted 26 April 2001)

Stability tests based on the Allan variance method have become a standard procedure for the evaluation of the quality of radio-astronomical instrumentation. They are very simple and simulate the situation when detecting weak signals buried in large noise fluctuations. For the special conditions during observations an outline of the basic properties of the Allan variance is given, and some guidelines how to interpret the results of the measurements are presented. Based on a rather simple mathematical treatment clear rules for observations in "Position-Switch" , "Beam-" or "Frequency-Switch" , "On-The-Fly-" and "Raster-Mapping" mode are derived. Also, a simple "rule of the thumb" for an estimate of the optimum timing for the observations is found. The analysis leads to a conclusive strategy how to plan radio-astronomical observations. Particularly for air- and space-borne observatories it is very important to determine, how the extremely precious observing time can be used with maximum efficiency. The analysis should help to increase the scientific yield in such cases significantly.

Key words: instrumentation: miscellaneous -- methods: data analysis, observational -- space vehicles: instruments -- techniques: spectroscopic -- telescopes

Offprint request: R. Schieder, schieder@ph1.uni-koeln.de

© ESO 2001