The time required to achieve the requested sensitivity depends crucially on the spectral setup, particularly the Representative Frequency (this sets, amongst other things, the atmospheric opacity) and the spectral resolution. If the sensitivity is requested in temperature units, the angular resolution will also have an effect. The Representative Frequency should have been chosen to reflect the most important spectral feature that is to be imaged, although in parts of the spectrum where the opacity is well behaved, which spectral window is chosen will actually make very little difference to the time estimate.
How the entered sensitivity is interpreted also depends on whether a rectangular area has been selected in the Field Setup. If so, the sensitivity entered should be that required in the final mosaiced map, not that corresponding to a single pointing. As the pointings in a mosaic usually significantly overlap, the combined sensitivity is higher and thus requires less time per pointing to be achieved. For Nyquist sampling, and assuming a Gaussian beam shape, the sensitivity of a mosaic is 68 per cent better than that of a single pointing and the time required per pointing is reduced by a factor 2.8. The OT will calculate this factor and use it when estimating the time for the project. Note, however, that if the requested sampling is significantly greater than Nyquist, the sensitivity becomes increasingly less uniform and thus a validation and TA Flag Sheet warning is triggered for separations greater than 0.8 times the antenna beam size.
It is also necessary to define the bandwidth over which the sensitivity should be calculated. This will depend on the scientific goals, but usually refers to the full bandwidth for continuum observations or to some fraction of the line width. The OT provides a number of shortcuts for completing this parameter, including ``AggregateBandwidth'' for continuum projects (the sum of all the defined spectral windows) and ``FinestResolution'', this referring to the highest (Hanning-smoothed) resolution of any spectral window (and the default for Spectral Line setups). Finally, a user-defined value is possible. Single continuum setups enforce the bandwidth for sensitivity to be equal to the total bandwidth i.e. 7.5 GHz. Once this parameter has been set, the OT's estimate of the time required for the project can be checked.