12 Meter Atmospheric Model

Until the end of the 2003-2004 season, spectral line data taken with the KP 12m telescope were converted to temperature units using a nominal fixed value for the calibration scale temperature. This value was relatively accurate for typical atmospheric conditions and frequencies not very close the edges of the different atmospheric windows accessible by the current facility receivers.

To improve the calibration precision for observations under varying weather conditions, covering wide ranges in elevation and for lines close to the edges of the atmospheric windows, we have implemented a real-time calibration system based on the ATM atmospheric model. Weather data (%RH, Tamb, Pamb, tipper tau) at the time of each calibration is sent to a program that calculates, for a given frequency and telescope elevation, a more accurate value for the calibration scale temperature. Tests of this procedure at the start of this season have shown a higher stability and repeatability of the intensity scales in the final calibrated spectral data.