Queued Service Observations with CFH12K:

Semester 2001B 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 48 QSO nights (or more generally, NOP nights) with CFH12K were scheduled for the semester 2001B. This report presents some statistics and comments on this second semester of the queued service observing mode.

B - General Comments

Despite a few technical problems and considerable time lost to weather, our experience with QSO mode has been quite positive during 2001B. The following comments address the main issues related to the QSO/NOP system for this semester:

1. Technically, the entire chain of operation, QSO --> NEO --> TCS, is very efficient and robust. This is a complex system and some glitches have been found and fixed during the previous semester. In general, the entire operational software chain has proved very satisfying. Almost 8000 exposures have been taken through the QSO/NEO system since 2001A... Basically, no time was lost during 2001B to technical problems related to the QSO/NEO/TCS system.

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. Our initial estimate of the general integration-time available for a given night (6.5 hr) proved to be correct (see below). However, this value depends strongly on the complexity of the queued programs to be performed. During the semester 2001B, we have been generally able to do MUCH more than 6.5 hours per night, even during the shorter summer nights. The main operational overheads are: focus sequences, pointing checks and dome rotation. As much as possible, the queues are always prepared to minimize the overheads.

4. QSO is well-adapted for time-constrained programs. The Phase 2 Tool allows the PIs to specify time constraints. We had several programs with those constraints during 2001B 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.

5. 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. We hope that more diversity will be found in programs for 2002A... Unfortunately, there is no seeing monitor available for Mauna Kea. We only get the seeing value after the readout of an exposure. This lack of reference for the image quality resulted in some observations being done in worse conditions than requested and those were not validated. However, the availability of Skyprobe and real-time measurements of the transparency is extremely valuable and regularly used do decide what observations should be undertaken. Starting in 2002A, the "snapshot" programs, that is programs requesting IQ > 1.2", will not be charged to the Agencies so we hope that this will help covering periods of mediocre conditions.

6. 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.

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 2001A, we were able to balance the Agency time within about 2%. For 2001B, we were able to reach the level of telescope time allocated for each agency, except for the Canadian Agency, by the end of this semester. The extremely bad weather and sky conditions encountered during the last run of 2001B resulted in a larger discrepancy than we had hoped for.

8. Semester boundaries are restrictive to the QSO mode. In a queue mode, targets can generally be observed on several runs, sometimes during the entire semester and more. The completion level of certain programs could be higher if the semester boundaries were removed, or at least , if some recycling of the programs completed at a certain level could take place. Balancing the Agency telescope time would be also much easier and would not have such a strong impact on the completion level of programs.

C - Global and Program Statistics

The following table presents some general numbers regarding the queue observations for 2001B (C, F, H, K, and D-time):

Total number of Nights
Nights lost to weather
~13 (27%)
Nights lost to technical problems
~1.5 (3%)
Nights considered photometric
~21 (42%)
QSO Programs Requested
QSO Programs Started
QSO Programs Considered 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 2001B. 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 French, UH, and D Agencies was balanced at the end of the 2001A, The situation is different for the Canadian Agency. The time spent for Canadian programs is off by about 12 hours. This is entirely due to the bad weather and mediocre seeing conditions during the December run since a long, highly-ranked program with only one target visible at the end of the semester, could not be done. Nevertheless, a balance of telescope time between the Agencies is surely possible in our QSO operational system!



E - Additional Remarks

Our second semester with the queue mode was quite successful, despite some considerable time lost to weather. There are several issues that need to be addressed for 2002A. We will particularly focus on these issues: