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Sensitivity versus Time and Early Science

Please remember that for ALMA observations, you do not request anamount of time, but rather a sensitivity. This is because it isdifficult to predict what sensitivity will be achieved based on anamount of observing time, mainly due to the fact that mm/submmobservations are greatly affected by the weather conditions, as wellas by the usual instances of antenna and other hardware failures. Asthe sensitivity was presumably chosen by the user for a good reason,ALMA will observe until the sensitivity is achieved (up to areasonable maximum limit). The Time Estimate button on theControl and Performance form will report how long it is expected totake to achieve the requested sensitivity.

A caveat of this is that for Early Science, the ($u,v$ ) coverage willbe relatively poor compared to the completed ALMA array, althoughstill excellent compared to other mm/submm interferometers. However,as ALMA's very large instantaneous sensitivity is so good, it ispossible that bright sources will have very short estimated times andthis might have consequences for the imaging performance due to theshort ($u,v$ ) tracks. If this is the case, it is possible to request alonger amount of time in your Scientific and Technical Case where itshould be rigorously justified. This can be signalled to the proposalreview committees by ticking the ``More Time'' box. As more antennasare added to ALMA, the need for this should vanish as even thesnapshot ($u,v$ ) coverage becomes superb.


next up previous contents index
Next: Representative Frequency Up: Control and Performance Previous: Control and Performance   Contents   Index
The ALMA OT Team, 2011 May 20