Spectroscopists may need to consider separately two different
sensitivities--the sensitivity to spectral
features in the individual line channels and the accuracy with which
the continuum can be estimated from the line-free channels. The need
for individual channel sensitivity normally
dominates, however. The calculation uses Equation 3, with
replacing 
. It may also be appropriate to express
the sensitivity in terms of brightness temperature by converting from
mJy per beam area to temperature units assuming a Gaussian beam of
area 
.
Use of narrow channel bandwidths often implies that
sensitivity, rather than u-v coverage, considerations determine 
for high-resolution synthesis spectroscopy, so that observations >12
hours long may be needed. Spectroscopic observations may also need
long integrations on the calibration sources to achieve enough sensitivity.