  Diagnostics of MHD waves in the solar atmosphere is a topic which often
encounters problems of interpretation, due partly to the high complexity of the
solar atmospheric medium. Forward modeling can significantly guide
interpretation, bridging the gap between numerical simulations and
observations, and increasing the reliability of mode identification for
application of MHD seismology. In this work we aim at determining the
characteristics of the fast MHD sausage mode in the corona on the modulation of
observable quantities such as line intensity and spectral line broadening.
Effects of line-of-sight angle, and spatial, temporal and spectral resolutions
are considered. We take a cylindrical tube simulating a loop in a low-{\beta}
coronal environment with an optically thin background, and let it oscillate
with the fast sausage mode. A parametric study is performed. Among other
results, we show that regardless of the ionisation state of the plasma, the
variation of spectral line broadening can be significant, even for low
intensity modulation. The nature of this broadening is not thermal but is
mostly turbulent. This places spectrometers in clear advantage over imaging
instruments for the detection of the sausage mode. The modulation of all
quantities is considerably affected by the line-of-sight angle, and especially
by the spatial and temporal resolution when these are on the order of the
mode's wavelength and period. This places high constraints on instrumentation.
