Gemini Observatory tracks completion rates for queue programs, open shutter efficiency, acquisition times and weather losses for both telescopes. In addition, the Observatory has investigated how observing conditions and program length may affect the probability of a program getting data. The results of these investigations may be particularly useful for PIs with programs in band 3. Information on RA distributions as well as the demand for the various GMOS gratings in semesters 2006B-2008A is also available. The following summarizes current status of these Science Operations Statistics. The graphs and this web page will be updated as time allows. Last update May 2009.

 

• Weather loss and delivered science nights
• Completion rates for queue programs
• Acquisition times
• Open shutter efficiency
• The effect of requested observing conditions and the program length
• GMOS gratings - demand and execution
• Long-term RA distributions and details for 2009A

 

Weather loss and delivered science nights

Each semester at the time of the Call for Proposals, the Observatory with input from the Operations Working Group decides on the number of offered science nights. The science queue (and classical nights) are filled using this number of science nights. The actual delivered number of science nights can either be larger (if planned engineering or commissioning tasks did not happen) or smaller (if engineering or commissioning tasks take longer than planned or if unforeseen events happen). In addition, the weather loss for a given semester will affect the completion rates. Figure 1a shows the weekly weather loss during semesters 2007A-2008B, while figure 1b below shows the use of available time.

Gemini North suffered an unusually high amount of weather loss in the period from late December 2008 to late April 2009. Further details can be found here.

Figure 1a: Weekly weather loss at Gemini North and South during the semesters 2007A, 2007B, 2008A and 2008B. Each bar on the histogram represents a week in the semester. The total weather loss for a semester in this period varies considerably (see the red lines). It is also clear that in some semesters the weather loss is very unevenly distributed through the semester contributing further to the challenge of completing the scheduled queue programs.

Figure 1b: Use of available time for Gemini North and South during semesters 2005A to 2008B. Shutdown time for Gemini North in 2008A includes the coating of the primary mirror in July 2008. On average, scheduled science nights make up 88% of all nights. The long term (2005-2008) weather loss amounts to 24%.

Completion rates for queue programs

The completion rates of queue programs is closely tracked and queue planning is carried out to optimize the completion rates. Full multi-instrument queue planning was put in place at Gemini North starting in semester 2005A, with Gemini South following in semester 2005B. This change combined with better reliability of instruments and telescopes has led to a significant improvement in the completion rates across all scientific ranking bands. Further, in semester 2004A the sizes of the ranking bands were changed from equal size to roughly 20%, 30%, and 50% for band 1, 2, and 3, respectively. At the same time the national TACs were given the option of granting band 1 programs rollover status such that it would be active in the queue for a total of three semesters. Starting in 2007A, the ranking bands were adjusted to roughly 30%, 30%, and 40% for band 1, 2, and 3, respectively.

Figures 2 and 3 show the queue completion rates for 2003A-2008B for both sites. The completion rates for 2003A-2004B exclude ToO (Target of Opportunity) programs. For semesters 2005B and later, ToO programs are included in the completion rates. A ToO program's completion is defined as the executed time relative to the triggered time. If a ToO program has used all allocated time, it is counted as completed independent of the amount of triggered time. ToO programs that do not trigger any observations are excluded from the statistics.

The completion rates in band 1 and 2 in semesters 2005A-2006A were 90% and 73%, respectively. In 2006B-2007A these decreased to 81% and 54%, respectively. In 2006B the earthquake at Gemini North significantly affected the completion rates. The change in ranking band size in 2007A may have contributed to the decrease in the completion rates for 2007A, though other factors such as the RA distribution especially for the queue on Gemini North and the failure of GNIRS on Gemini South, also contributed. Other incidents that occurred in 2007B at Gemini North were Michelle cooling problems, laser issues, as well as weather loss.
It should be kept in mind that there are still active band 1 programs with rollover status from 2008A and 2008B, which can still reach 90-100% completion. See Figure 3 for details.

For band 3 programs the queue planning aims at getting a significant amount of data for the programs that are in fact started, rather than getting a little bit of data for many programs. The effect of this planning can especially be seen in Figure 3 for semesters GN-2005A and GN-2005B, where the completion rate for band 3 programs that got started is between 70% and 80%.

Figure 2: Summary of the completion rates over a range of semesters from 2003A to 2008B and for both sites, as of Feb 6 2009. The significant improvement of the completion rates in 2005A-2006A is, in part, due to the full multi-instrument queue planning now in place at both sites. The completion rates for 2006B-2007A were affected by the earthquake at Gemini North (2006B), the GNIRS failure at Gemini South (2007A), and a very overfilled queue at RA=12-14h in good conditions at Gemini North (2007A), see plots of the RA distributions. The Gemini North completion rates for 2007B were affected by Michelle cooling problems as well as laser problems and weather loss. Semesters 2008A and 2008B still have active programs with rollover status in band 1. Thus, the final completion rate for band 1 is expected to be higher than shown on this figure.

Figure 3: Completion rate requirements and goals, as endorsed by the Gemini Board and the Operations Working Group. Further details are given below.

Requirements	Goals
1   Band 1: 90% completion rate after rollover period 2   Band 2: 75% completion rate 3   Band 2: 85% of started programs should have 75% of data taken 4A Band 3: 80% of started programs should have 75% of PI defined minimum data taken	1   Band 1: 100% completion rate after rollover period 2   Band 2: 90% completion rate 3   Band 2: 100% of started programs should have 75% of data taken 4B Band 3: 80% of started programs should have 100% of PI defined minimum data taken 5   Band 3: 80% of started programs should have 75% of all data taken

Acquisition times

The acquisition times are tracked from the records in the observing database. From an earlier study of this, it is known that the median time to slew and acquire a guide star for a new target is about 6 minutes. The exact time of course depends strongly on the length of the slew. In the following, this time is excluded from the statistics. Figure 4 and tables 1 and 2 below summarize the acquisition times for all the spectroscopic modes, and for the only imaging mode (NIRI+Altair) that has significant acquisition time above the slew and guide star acquisition. For the spectroscopic modes, the measured acquisition time is the time it takes to image the target and align it in the spectroscopic aperture (slit, IFU or MOS mask). For NIRI+Altair the measured acquisition time is the time it takes to center the target on the NIRI array.
Comparison of the 2005B+2006A times, when the acquisition procedures for the various instruments were not homogeneous and not integrated with the rest of the software, and the 2008A times, after the procedures had been integrated, shows a marked improvement. The integrated acquisition software saves 3 minutes per acquisition, which adds up to 3 nights per semester per site.

Figure 4: Acquisition times for spectroscopic and imaging observing modes done in queue time for Gemini North and South. In all cases the improvement from semesters 2005B/2006A to 2008A due to the integrated acquisition procedures is clearly visible.

Table 1: Summary of the number of acquisitions as well as the acquisition times for spectroscopic modes and NIRI/Altair imaging, showing the improvement from semester 2005B/2006A to 2008A.

Table 2: Acquisition statistics for semester 2008A, showing a more detailed breakdown by instrument and observing mode.

Open shutter efficiency

The open shutter efficiency for Gemini instruments has been tracked since August 2004. For each night the open shutter time is extracted from the FITS headers of the obtained observations. Open shutter efficiency is defined as the sum of all science and calibration exposures obtained between evening and morning twilight, divided by the usable time available (hours between twilight less time lost to weather or technical faults).

Figure 5 summarizes the open shutter efficiency for two epochs, August 2004 - Feb 16, 2006, and semester 2008A. GMOS-N used to have about 5% higher open shutter efficiency than GMOS-S, which may have been due to the effect of consistent queue planning of all GMOS-N nights since its commissioning. However, in 2008A these differences are no longer present. There is a noticeable improvement in efficiency for the most frequently used instrument combinations. It can also be seen that multi-instrument night efficiency is a function of the mixture of demand for different instruments.

Figure 5: Open shutter efficiency for facility instruments at Gemini North and South for 2004-2005 and for semester 2008A. Open shutter efficiency is derived as the fraction of the usable time during the night, less any loss due to weather or technical faults.

The effect of requested observing conditions and the program length

Recently a detailed investigation was carried out to better understand how the requested observing conditions and program length affect the probability of a program getting the requested data. Only semesters 2005A-2006A were included in this investigation since these semesters closely reflect the current queue planning principles and methods, while this is not the case for the earlier semesters.

Figure 6: Comparison of the distribution of program lengths for scheduled programs (gray) and programs that got at least 75% of the requested data (orange). For band 1 and 2 the distributions are identical. Thus, the program length for these two ranking bands has no influence on whether the program gets data. For band 3 there is a tendency that more of the shorter programs get executed. This is as expected since the queue planning focuses on selecting programs from band 3 that have a fair chance of getting a significant faction of the requested data. The median program length in band 3 for scheduled programs is 9 hours, while the median program length for those that got at least 75% of the requested data is 6 hours.

In order to simplify the investigation of the effect of the observing conditions, six broad bins of observing conditions were defined as follows based on the percentile bins used by the PIs to specify the required observing conditions. (IQ=Image quality, BG=Sky background, CC=Cloud cover)

IQ<= 70%, BG<= 50% (dark), CC=50% (photometric)

IQ<= 70%, BG> 50% (gray/bright), CC=50% (photometric)

IQ<= 70%, CC>=70% (cirrus, clouds)

IQ= 85%, CC=50% (photometric)

IQ= 85%, CC>=70% (cirrus, clouds)

IQ=Any

 

All the science observations in the observing database for the semesters 2005A, 2005B and 2006A were mapped onto these six broad observing condition bins. This was done both for the planned science observations and the executed science observations. Figure 7 shows the distribution by band and site.

As expected, the distributions of observing conditions for planned and executed observations in band 1 are very similar (due to the high completion rate), and the emphasis is on using the best conditions, specifically image quality of 70%-ile or better. The observations in band 1 shown at IQ=Any are primarily the Rapid ToO observations.

In band 2 the distributions of planned and executed observations are also very similar to each other. A larger fraction of IQ=85% observations are present in band 2 than in band 1.

For band 3 observations almost none are planned for the very best observing conditions (bin "1") and almost none get executed in these conditions. Further, 58% of the planned observations can be done in IQ=85% or worse. It is important to note that more than 70% of the executed band 3 observations are in fact observations that can tolerate IQ=85% or worse. Thus, the single most important condition for band 3 PIs to consider relaxing (if possible) is the image quality requirement.

Figure 7: Distribution requested observing conditions of planned (top) and executed (bottom) observations in the semesters 2005A, 2005B and 2006B at both sites. The observing condition bins are explained above.

GMOS gratings - demand and execution

Because the two GMOSs can carry only three gratings simultaneously, it is of special interest to PIs with programs in band 3 to know which gratings are in highest demand and therefore will most often be in the instruments. Figure 8 shows this information for semesters 2006B-2008A.

Figure 8: GMOS gratings: Total planned time in science observations as well as the executed time are shown for the six gratings for GMOS-N and GMOS-S.

Last update: May 14 2009 by Michael Hoenig