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Why are some Cycle 2 time estimates greater than they were for the same observations in Cycle 1? - Knowledgebase / ALMA Observing Tool (OT) - ALMA Science

Why are some Cycle 2 time estimates greater than they were for the same observations in Cycle 1?

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The time estimates for Cycle 2 are calculated in a different way to Cycle 1 and this has lead to significant differences between the time estimates calculated for each cycle. The main difference is that the integration and cycle times for each calibrator type are based on the defaults used during SB generation and are often significantly longer than what was assumed at Cycle 1. We also now include more accurate estimates of the various hardware and software overheads and latencies. This new approach has been based upon actual operations and should be a much more realistic estimate of how long it takes to complete a project.

The actual time on sources may also be slightly higher in Cycle 2 than Cycle 1, particularly for targets transiting at low elevations as the increasing sky temperature with decreasing source elevation was not being properly taken into account in Cycle 1. This can overcompensate the slight reduction in time that would be expected due to the larger number of antennas assumed for Cycle 2 (34 instead of 32). Overall, the Cycle 2 time estimates are thought to be much more realistic than those computed by the Cycle 1 OT, which often underestimated the total time needed to complete a project.