Queued Service Observations with CFH12K:

Semester 2002A Report



A - Introduction

The Queued Service Observing (QSO) Project is part of a larger ensemble of software components defining the New Observing Process (NOP) which includes NEO (acquisition software), Elixir (data analysis) and DADS (data archiving and distribution). About 57 QSO nights (or more generally, NOP nights) with CFH12K were scheduled for the semester 2002A. This report presents some statistics and comments on this third semester of the queued service observing mode.

B - General Comments

We have been very severely affected by weather during this semester: about 24 nights of 57 nights were completely lost (that's 42%) and several others were affected by bad seeing or cirrus. That about 12-15 nights lost more than expected! In particular, of the 14 nights in May, 11 were completely lost. The best run was in June (shortest nights....) and we were able to catch up on several programs. It is then surprising to look at the statistics on the programs: the completion level for all the time for A programs reached 92 % !!! Statistics on B programs are not as good, of course, but not too bad either. And, all of the data taken during the semester have also been photometrically calibrated. To get that much data out while losing so much telescope time to weather shows that the queue mode IS working...

1. Technically, the entire chain of operation, QSO --> NEO --> TCS, is very efficient and robust. This is a complex system and the time lost to glitches now is basically negligible. Almost 13000 exposures have been taken through the QSO/NEO system since 2001A...

2. The QSO concept is sound. With the possibility of preparing several queues covering a wide range of possible sky conditions in advance of an observing night, a very large fraction of the observations were done within the specifications. The ensemble of QSO tools allows also the quick preparation of queues during an observing night for adaptation to variable conditions, or in case of unexpected overheads. The observing tool offers the possibility to load a pending queue and prepare it (for instance, by including the focus sequences) while another one is being executed so that the transition between queues is done rapidly. The new version of the tool is also very flexible and allows the selection of specific observations within the queue resulting in a greater observing efficiency.

3. QSO is well-adapted for time-constrained programs. The Phase 2 Tool allows the PIs to specify time constraints. We had one difficult monitoring program with those constraints during 2002A and we were able to carry out the observations in a timely manner. However, the impact of these programs on the other regular QSO programs cannot be understated. The number of time-constrained programs should be restricted during a semester.

4. Very variable seeing and non-photometric nights represent the worse sky conditions for the QSO mode. During 2001A and 2001B, we did not have enough programs requesting bad seeing or non-photometric conditions. Also, not enough programs requesting bright time were available. In 2002A, we had two "shapshot" programs available (programs requesting mediocre conditions) and we used them quite frequently during the bad weather conditions (both programs were done at about 25%). The availability of Skyprobe and real-time measurements of the transparency is extremely valuable and regularly used do decide what observations should be undertaken.

5. A very severe constraint for the QSO model is the limitation on the number of filters that can be mounted in the wheel of CFH12K at the same time. A filter must be mounted for at least three nights to make sure that the necessary detrend calibrations can be obtained. Thus the number of filter changes during a run is limited. This introduces an additional, restricting parameter in the selection of the programs to be carried out. Due to this constraint, a target might not be observed with all the filters required during the Phase 2 during the same run. We always try to achieve this for minimizing pointing discrepancies and slight rotations between the frames but this is not always possible. This constraint is more severe even for "non-standard" filters. Since those are generally less requested than the BVRI set, observations cannot be always performed during sky conditions specified by the investigators. In fact, for 2001A and 2001B, most of the observations with the non-standard set were done in better conditions than requested. This is good because it respects the queue concept. However, this can be frustrating for scheduling other programs using the standard set and requesting precisely these conditions since these observations could not be done because the filters needed were not mounted at the time. This constraint also has severe implications for the completeness of certain programs. For 2002A, this has continued to be a problem, limiting observations for one A program and one long B program.

7. Precise Agency time accounting is possible but not realistic on a short timescale basis. Several constraints dictate what programs should be executed. We have implemented a dynamic statistical tool so we can follow the progress of the programs for each agency and adjust the program selection for the queues. But, in reality, since not all the possibilities in sky conditions are equally represented by the programs of the different agencies, trying to adjust the time distribution on a short timescale (for instance, within a short QSO run) does not make sense. For 2002A, we were able to balance the Agency time within about 3%. This is not too bad, considering the bad weather conditions.

C - Global and Program Statistics

The following table presents some general numbers regarding the queue observations for 2002A (C, F, H, K, time, excluding snapshot programs):

Total number of Nights
Nights lost to weather
~24 (42%)
Nights lost to technical problems
~1 (<<2%)
Nights considered photometric
23 (41%)
QSO Programs Requested
QSO Programs Started
QSO Programs Completed
Total I-time requested (hrs)
Total I-time observed (hrs)
Total I-time validated (hrs)
Queue Validation Efficiency



D - Agency Time Accounting

Balancing of the telescope time between the different Agencies is another constraint in the selection of the programs used to build the queues. The figure below presents the Agency time accounting for 2002A. The top panel presents the relative fraction requested by the different agencies, according to the total I-time calculated from the Phase 2 database. The bottom panel represents the relative fraction for the different Agencies, that is, [Total I-Time Validated for a given Agency]/[Total I-Time Validated]. As showed in the plots, the relative distribution of the total integration time of validated exposures between the different was well balanced at the end of the 2002A, within 3%. We aim for 2% but considering the weather conditions, it is not bad at all. When A programs alone are considered, the balance is within these 2%.



E - Additional Remarks

Our third semester with the queue mode was quite successful, despite some considerable time lost to weather. To be able to get almost all of the A time done is quite significant. There are several issues that need to be addressed for 2002B. We will particularly focus on these issues: