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In the online estimator (to be used for proposal preparation), the
is interpolated in frequency and airmass from tabulated values (see
Fig. 1). 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).
In the ASTRO detailed sensitivity estimator, the system temperature is
computed using an atmospheric model (ASTROATMOSPHERE command)
with ambient temperature and precipitable water amount as input.
The
can vary significantly over the large bandwitdh of the 2SB
NOEMA receivers. Figure 2 shows the minimum and maximum
system temperature inside the IF bandwidth for all possible local
oscillator tunings. As a result, for continuum estimation, a frequency
averaged
is interpolated from a pre-computed table. The relevant
frequency in that case is the LO frequency of the tuning (see
Fig. 3). The averaging is done such as
.
This is not implemented in the ASTRO detailed estimator, due to the
prohibitive computing cost of the atmospheric model over the
GHz.