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R.J. Maddalena (NRAO), C.H. Johnson (Breck School)
The traditional methods for calibrating data from cm-wave single-dish telescopes have problems in that the methods seldom obtain an accuracy better than 10%. Higher accuracy usually requires a significant outlay of telescope time and someone very familiar with the instrument. Also, the traditional assumption that the telescope has a narrow bandwidth no longer works when calibrating data from today's wide bandwidth receivers and backends. Any scientific project that needs to compare data from multiple radio telescopes is compromised at some level by the inaccuracy of the calibration. The high-dynamic-range, high-fidelity data from telescopes like the NRAO-GBT beg for better calibration.
We have modified and developed calibration methods that can obtain an accuracy of well under 5%. The new methods require very few ancillary observations but do not require of the observer any special expertise. The techniques include better models for atmospheric opacity and air mass and better models of the calibration noise diodes used in cm-wave radio telescopes. We will present data taken with two very different telescopes (the GBT and the NRAO-43m) using completely different hardware which, when calibrated using our new technique, have a relative calibration accuracy of 3%.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.