Scheduling the ATNF at millimetre wavelengths - a discussion paper

Background

When the ATNF is upgraded to 3 mm operation in 2000-2001, we can expect that only about 50% of the observing time will be suitable for millimetre operation. In order to make efficient use of the telescope, we will have to change the way we allocate and schedule observing time. This discussion paper considers some of the options, in order to initiate a discussion over how we should do this.

It should be noted that this same decision is being made for similar reasons at other observatories, and we should follow those discussions closely. We have one constraint which other observatories tend not to have which is that, because Australia is geographically isolated, our desire to encourage observers to visit us is probably greater than that at other observatories.

I assume for the purposes of this document that by the time the ATCA is operational at millimetre wavelengths, there will be instruments at Narrabri capable of characterising the weather conditions, and determining whether they are suitable for millimetre observing. These might include water vapour radiometers (either stand-alone or integral to the ATCA receiver package) and/or a dedicated interferometer continuosly measuring the phase on a geostationary satellite

Option 1: Just allocate the time and let the observers take the risk

This is essentially the way that optical telescopes (e.g. AAT) are allocated at present. In the case of the AT, we might nominate periods in the winter months as being the millimetre observing times, allocate tracks to different observers, and if the weather is not suitable then they just have to re-apply the following year. However, we differ from optical telescopes in that, even if the weather is unsuitable for millimetre observing, it is probably suitable for centimetre observing.

Pro

• Simple to administer

Con

• An inefficient use of observing time and resources

Option 2: Full dynamic queue scheduling

In this option, local staff (or software) make the decision as to which observation to make, in real time, on the basis of current weather conditions. As the schedule is continuously changing, it is impracticable for observers to come to the telescope for their observations, and so all observations have to be done in an absentee observing mode, which in turn implies hiring staff to make the observations.

Pro

• the most efficient use of observing time

Con

• The ATNF could not afford to hire the necessary staff unless other areas were cut
• Narrabri would not have so many astronomical visitors, thus increasing isolation.
• Epping, and other Australian sites, would not have so many astronomical visitors, so reducing the number of colloquia etc from outsiders.
• Difficult to schedule - would need sophisticated scheduling software (possibly available from elsewhere).
• With no need for observers to come here for the observations, there is a possibility that we would be swamped by non-Australian proposals. These could be limited by a quota system, but they would all still need to be ranked, thus increasing the workload on the time assignment committee and related staff.

Option 3: Dynamic queue scheduling for part of the year

This is essentially the same as option 2, but the dynamic scheduling would be operating for only part of the year (e.g. 3-6 winter months). Outside that time, operations would continue as at present.

Pro

• Efficient use of observing time, but without the full impact of the cons listed in Option 2

Con

• As in option 2, but reduced in severity of impact

Option 4: Observers propose backup programs

This is similar to the option exercised by some optical telescopes for projects that need photometric conditions. Each proposal is accompanied by a backup proposal that the observers will switch to if conditions become unsuitable for the prime proposal.

Pro:

• Telescope time is not completely wasted in poor observing conditions
• Does not involved the complexities and other disadvantages (see option 2) of queue scheduling

Con

• Experience suggests that these backup programs are often of little value and would not on their own rank high enough to win telescope time, so observing time and resources are still wasted.
• Observers still need to resubmit proposals for the next term.

Option 5: Override queue scheduling

This is a compromise between the options above. Observers would be expected to come for their observations as at present. However, if the weather became bad then millimetre programs would be halted and a centimetre project (selected from a backup list of such projects) observed instead. The millimetre project then goes on a queue of projects and will be observed by local staff, the duty astronomer, or other observers, when conditions permit. The millimetre observer is guaranteed to obtain the observing time by the end of the term.

When the observations switch to centimetre wavelengths, a choice has to be made of which centimetre project to observe. If the millimetre observer chooses to submit a centimetre backup project, and this is ranked high enough, then this backup project will be given priority over other centimetre observing projects. Otherwise, a project will be selected from a list of such projects, which may include some long-term survey projects chosen expressly for this purpose. The millimetre observer will be asked to help make these observations in return for his/her millimetre observations being handled by someone else.

There are two ways in which the required extra time for the queued millimetre observations could be obtained:

• Option 5a: some time at the end of each millimetre configuration (or weekly?) would be allocated for observing remaining millimetre projects in the queue, and these observations would be taken by the duty astronomer and local staff.
• Option 5b: There could be an override on centimetre observations. Thus if a centimetre observer were observing in a suitable configuration, and the weather became suitable for millimetre observing, then the array could be switched to millimetre observing and the centimetre project would then be placed in the backup queue for observing by millimetre observers when conditions became appropriate.

In either case, the millimetre or centimetre observer would be guaranteed his/her observing time by the end of the term.

The decision as to when to switch from millimetre to centimetre observations (or vice-versa) could be made in one of two ways:

• It could be left to the observer to make the decision, on the understanding that if he/she continues to observe in sub-optimal conditions, then he/she cannot request that data to be re-observed.
• It could be left to an impartial body such as the duty astronomer, a member of local staff, or a piece of software which has, as input, factors such as water vapour content, cloud cover, and phase on a test interferometer looking at a geosynchronous satellite.

Pro

• Makes efficient use of telescope time while still attracting visitors
• Does not require additional staff

Con

• The most complex of the options, requiring considerable thought and care to set up correctly
• Will result in disconnected chunks of data for both millimetre and centimetre data which then have to be concatenated.

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Last updated: 19 Sept 1997