In the online estimator (to be used for proposal preparation), the
is interpolated in frequency, airmass, amount of precipitable water vapor,
and ambient temperature from tabulated values (see
Fig.
). The airmass is estimated using the maximum
elevation of a source at the chosen Declination. The values are different
for summer and winter due to the different atmospheric
characteristics. Moreover, the chosen amount of precipitable water vapor
depends on the receiver band (in addition to the season) because the NOEMA
operation team schedule the different receiver bands according to the
actual weather (high frequency bands are scheduled only during the best
weather conditions).
The system temperature for a given LO frequency can be computed using an
atmospheric model in ASTRO (ASTRO
ATMOSPHERE command) with
ambient temperature and precipitable water amount as input. The overall
computing time of the continuum system temperature would be prohibitive
because of the computation of the atmospheric model over the
GHz IF bandwidth sampled every 100 MHz. Instead the
computation is done off-line on a grid of LO frequency sampled every
1 GHz.