Unlike most other radio/mm/submm telescopes, instead of asking for a specific amount of time, an ALMA proposal states a sensitivity that needs to be achieved. The OT then, using an internal version of the ALMA Sensitivity Calculator, produces an estimate of how long this will take, based on the typical atmospheric conditions in which the project will likely be observed.
Clicking on the ``Time Estimate'' button will bring up a dialogue (Figure 5.10) that contains information relevant to the time estimation calculation. This includes the requested sensitivity and Representative Frequency, the total number of pointings, whether the ACA is required, the calibration requirements and other overheads. For Cycle 1, the time required for the ACA has been determined from simulations to be equal to three times the 12-m array time and the OT assumes this multiplication factor, even if the Total Power array will not be used i.e. for continuum observations.
The time required for calibration is calculated assuming the following, per SB and tuning solution:
Various overheads are included in the time estimate and cover various software and hardware latencies e.g. those caused by changing source/scan and starting and stopping an SB execution.