### Data calibration

The telescope is regularly switched on and off source. It can be shown (see e.g. Kramer, 1997) that the brightness temperature of the source can be related to the measured counts (on and off-source) by

(12)
where , the calibration factor, is given by

|  |  |  | (13)
|  |  |  | (14)
|  |  |  | (15)
|  |  |  | (16)

If the cosmic background power ( ) is negligeable compared to the atmospheric emission ( ), then the last equation reduces to
(17)
From the previous steps, all the parameters are known to compute and thus .