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 the distribution of the real observing conditions. This information may be used in the future to better match the queue filling to the expected distribution of the observing conditions. 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 information on weather loss and delivered science nights, as well as the completion rates for queue programs is updated regularly. The remainder of the information originates from specific requests from committees or from internal analysis of operations questions. This information will only be updated as time allows or as the need for updated analysis arises. Last update: February 2013.
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 1 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 1: Use of available time for Gemini North and South during semesters 2005A to 2012B. On average, scheduled science nights make up 87.6% of all nights. The long term (2005A-2012B) weather loss amounts to 23.5%.
Distribution of observing conditions
In order to simplify the investigation of the effect of the observing conditions, six broad bins of observing conditions were defined as shown in table 4, based on the percentile bins used by the PIs to specify the required observing conditions.
Table 4: Observing condition bins, based on the percentile bins used by PIs to specify their required observing conditions.
All the science observations in the observing database for a number of semesters were mapped onto these six broad observing condition bins. This was done both for the planned science observations and the executed science observations. Figure 6 shows the distribution by bin.
Semesters 07B+08A are shown for both sites, and compared to the 18 weeks of winter at Gemini North in 2008/2009 - a prolonged period of poor weather, on which more details can be found here. The proportions predicted by the model currently used for filling queue time are plotted as well.
Figure 6: Fraction of useful time, sorted by observing condition bin, for three different time periods. The model fraction is shown in gray. The red bars correspond to the prolonged period of poor weather in winter 2008/09.
Completion rates for queue programs
The completion rates of queue programs are 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.
Figure 2 shows the queue completion rates 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. It should be kept in mind that there are still active band 1 programs with rollover status from the past two semesters, which can still reach 90-100% completion.
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 be seen in Figure 2. The fraction of started band 3 programs that get at least 75% of the requested data is typically 70%.
Figure 2: Summary of the completion rates over a range of semesters from 2002B to 2012B and for both sites, as of Feb 8, 2013. Semesters 2012A and 2012B 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.
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
Table 1: Completion rate requirements and goals, as endorsed by the Gemini Board and the Operations Working Group.
Completion expectations for queue programs
Here we give a guide to expectations for the completion of Band 1, 2 and 3 programs. The three bands are best described as (i) top priority, intended to be executed and if possible completed (ii) lower priority, but intended to be executed to some reasonable completion rate and (iii) fillers, which should, in order to get data, be able to take worse observing conditions and be particularly aware of other constraints that may affect their execution.
We fill the queue to a level consistent with the above descriptions in a semester with reasonable weather. In case of a semester with poorer-than-normal conditions or significant instrumental or telescope problems, we attempt to protect programs in Band 1 as best we can (in the sense that any good weather will go to those programs). It is a clear signature of bad weather that Band 3 completions exceed those in the other two bands, and in such cases, programs in Band 2, which still tend to have tight observing conditions requirements, often lose out. The above analysis excludes target of opportunity programs, for which the completion rate depends on the rate of triggers and which we cannot therefore control, and block-scheduled instruments or observing modes, where statistics vary a lot (up and down) due to coincidences between observing blocks and weather.
The figures below show completion statistics in the regular queue, over the period since the commencement of multi-instrument queue observing in 2005. Grey lines represent the ratio of the total usable time in the semester to the total advertised time in the call for proposals (this line has a mean level corresponding to weather loss). The blue histograms represent the fraction of programs achieving a completion rate of 80% or above, and the white dots show the corresponding fraction of programs which achieved a completion rate of 100%. These figures should serve as a guide to what to expect in terms of completion rate. They exclude Target of Opportunity programs, and those executed in "schedule blocks".
The significant recent feature at Gemini North was the shutter failure of 2013B and 2014A; Band 1 completions were protected against this, but Band 2 suffered badly.
- Grey: Ratio of total usable time in the semester to the total advertised time
- Blue: Fraction of queue programs reaching 80% complete
- White dots: Fraction of queue programs reaching 100% complete
- Same as figure above.
- Same as figure above.
The significant recent feature at Gemini South has been a combination of weather loss, earthquakes and laser problems in 2015B and 2016A; even Band 1 was not immune to these problems.
- Same as figure above.
- Same as figure above.
- Same as figure above.
Breakdown: good and bad semesters
As seen above, Gemini North in 2014A presented a particularly bad semester, with shutter failure and weather reducing the amount of available time significantly. 2014B represented a more "average" semester, with good Band 1 completion rate and an understandable distribution between Band 1,2 and 3. Note that in a "reasonable" semester, a good fraction of programs reach 100% completeness.
Overheads Associated with Gemini Observations
When submitting a proposal for Gemini telescope time, all overheads associated with science observations must be included, except for those associated with the default set of baseline calibrations.
Each instrument page lists specific overheads associated with the instrument, in the "ITC, Sensitivity and Overheads" sections. These include: target acquisition, instrument configuration, detector readout, and telescope offsetting. The instrument overhead pages are:
Information on target acquisition times is included on the Observatory's statistics page. Typically optical and infrared imaging observations are set up in 6 minutes, and spectroscopy in 12 - 18 minutes. Use of GNIRS with the P2 wavefront center requires an additional re-acquisition about every 45 minutes due to flexure. Coronography with NIFS adds 5 minutes to the set up time. Altair adds 5 - 8 minutes to the set up time. GeMS laser AO observations take longer to set up, approximately 30 minutes. Additional overhead must be included if the observation is long (more than about 2 hours duration) such that more than one acquisition is likely. Please use the instrument links to obtain up to date information on specific overheads.
Figure 1: Acquisition times for Gemini North and South instruments during semesters 2005B to 2012A. These values do not include the typical 6 minute slew and guide time. The improvement from 2005B+2006A is due to unifying the acquisition software for the facility instruments.
Instrument component changes take around 20 seconds for GMOS, GSAOI, NICI and NIRI filters, and up to 100 seconds for FLAMINGOS-2 filter, grating and mask changes, GMOS mask and grating changes, and NIFS grating changes. Please use the instrument links to obtain up to date information on specific overheads.
The detector readout time depends strongly on the instrument and readout mode. For GMOS, the readout time is 18 - 150 seconds, depending on detector area and pixel binning used. Nod and shuffle observations require an additional 200 seconds. For FLAMINGOS-2, GNIRS and NIRI the readout time can be up to 20 seconds, depending on the brightness of the target and S/N required. For NIFS and GSAOI this time can be up to over one minute. Please use the instrument links to obtain up to date information on specific overheads.
Telescope offsets take 10 to a few-tens of seconds per motion, depending on the size of the offset.
Observing Tool Time Estimates
The timeline in the Observing Tool (OT) shows the estimated duration for the initial target acquisition and each subsequent exposure. The initial acquisition time is determined by instrument mode, and the exposure durations are broken down into the time required for integration, mechanism moves, readout and telescope offsets. The time charged to the partner or program is the actual time used and not the OT estimate. The actual time used is measured from the first telescope slew to the end of the last exposure for each observation. Note that the OT time estimate assumes a single acquisition, so that additional overhead must be allowed for when completing your Phase II if the observation is long (more than about 2 hours duration) and more than one acquisition is likely.
Starting in 2017B the Phase I Tool (PIT) automatically adds the time required for baseline calibrations to the observation request.. This time needs to be included in the total time request, but it is charged to the relevant Gemini participant. However, any calibration beyond this basic set does need to be included explicitly in the proposal and that time will be charged against the program. The time charged is the actual time used and not the time estimated by the Phase II Observing Tool. The partner-charged telescope time used in calibrations at night varies with instrument and the mode (e.g. imaging vs spectroscopy). For GMOS, calibrations add about 5% to the program time, for NIRI 10%, for GNIRS, FLAMINGOS-2, and NIFS 25%.
The overheads per instrument are:
The baseline calibrations are:
- GMOS: bad pixel masks, darks, biasses, fringe frames, GCAL and twilight flat fields, arcs and flux standards.
- Near-infrared instruments: bad pixel masks, darks, GCAL flat fields, arcs and photometric or telluric spectral calibrators. In addition, for GNIRS cross-dispersed data a pinhole mask spectrum is obtained with the flatfields; for NIFS a "Ronchi" calibration mask spectrum is provided for each wavelength setting. For near-infrared spectroscopy a telluric standard is obtained for each 1.5 hours of science, in the thermal regime this is increased to one for every hour of data; if tellurics are needed more frequently then that time will be charged to the program.
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 4 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 4: 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 program length
An investigation was carried out to better understand how the requested program length affects the probability of a program getting the requested data. Only semesters 2005A-2009B 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 5: 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.
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.
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 3 and tables 2 and 3 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 3: 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 2: 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 3: Acquisition statistics for semester 2008A, showing a more detailed breakdown by instrument and observing mode.
User demand for Target-of-Opportunity programs
Figure 7 shows the percentage charged for Gemini's Target of Opportunity (ToO) programs, sorted by band. It is readily apparent that we are using 20-25% of band 1 time on ToOs. ToOs come in two varieties:
- Rapid ToOs: response times vary from a few minutes up to 24 hours. In 2010A, there were 10 triggers per month per site.
- Standard ToOs: response times greater than 24 hours. in 2010A, there were 20 triggers per month per site.
Figure 7: Fraction of time charged for Target of Opportunity programs, by band.
Figure 9 shows the fraction of time allocated to non-sidereal programs, from 2010A to 2011B. On average, Gemini North has about 9% of its time allocated to non-sidereal programs, with an even higher fraction in 2011B. Gemini South currently features less non-sidereal programs. The reason for this discrepancy is currently not well understood, although it should be noted that Gemini North's host, the University of Hawaii, is involved in many non-sidereal programs.
Figure 9: The fraction of time allocated to non-sidereal programs.
The figures on this page summarize the RA distributions for planned and executed queue programs during semesters 2006B-2008B at Gemini North and South. Only science observations are included in the distributions of planned and executed observations. The distributions show the number of hours worth of observations at each RA. Programs that were withdrawn have been excluded from the distributions. Template observations for ToO (Target of Opportunity) programs are not included as these in general contain no RA information.
On each figure the approximate available time (number of hours) is shown. This is the absolute maximum number of hours that can be executed, without any loss to weather or technical problems, and no time for calibrations or engineering on the sky. The sum of the average weather loss, technical loss and engineering time accounts for around 40% of the total time - see figure 1 on the main statistics page for details. While the science observations typically can be executed within an hour angle of +- 3hours, it is quite clear that in some cases the planned observations cannot realistically be executed within the available time. This is particularly the case for GN2006B-2008B at RA=12-14h. This RA range includes both the North Galactic Pole and the HDF-N.
PIs with programs in band 3 and with flexibility in target selection are encouraged to use the information in these figures for selection of alternative targets at RAs in less demand from band 1 and 2. As for all target change requests, these need to be submitted for approval to the local Head of Science Operations, see the change request page for details.
- Figure 1: GN2006B-2008B planned and executed science observations
- Figure 2: GS2006B-2008B planned and executed science observations
Figure 1: RA distributions of planned and executed science observations for GN2006B-2008B. Note the concentration around RA=12-14h, corresponding to the North Galactic Pole.
Figure 2: RA distributions of planned and executed science observations for GS2006B-2008B.
Table 5 presents the number of new Gemini users, where a "new" user is defined as a PI name with no programs on Gemini in any prior semester (starting with 2000). The numbers are relatively stable, with on average 50 new PIs each semester, representing 21.9% of all Gemini PIs.
Table 5: The number of new Gemini PIs over the past few semesters.
Demand for Gemini Telescope Time
The figures below show the total demand in hours from each partner, host institution and staff, as well as the summed demand. The UK ceased to be a partner in 2013A. Requests for Exchange time are not included. The ratio of the total demand to the time available is given in the Over-Subscription page. Note that the requested time does not include time required for calibrations, unless the calibrations are non-standard. The Observing Overheads page summarises all overheads associated with Gemini observations. The standard, baseline, calibrations are described on the GMOS Baseline Calibrations webpage, the NIR Baseline Calibrations webpage, and the Mid-IR Baseline Calibrations webpage. Telescope time used in program calibration varies by instrument. For GMOS, calibrations add about 5% to the program time, for NIRI 10%, for GNIRS and NIFS 23%. For the typical instrument distribution across the sites, the additional overhead due to calibrations is 9% for Gemini North, and 5% for Gemini South.
The figure belows show the average (weighted by participating country (Participant) share) over-subscription of the Gemini telescopes between semesters 2005B and 2015B. The over-subscription shown on the left axis is calculated as the ratio of the total Gemini time requested to the total advertised available science time. Requests for Exchange time are not included. The available Gemini science time includes all three science bands 1, 2 and 3, and the requested time does not include program calibrations. From 2013A, the UK ceased to be a Gemini partner, increasing the amount of time available to the other partners by about 20%.
Typically the Observatory executes about 65% of the advertised science time in the Call for Proposals, the remaining time going primarily to weather loss. Currently, the available time advertised in the Call for Proposals is filled to the 80% level with classical and queue bands 1, 2 and 3 programs, to avoid overfilling the queue and disappointing band 3 investigators. Poor weather programs are designed to use any remaining very poor but useable telescope time.
Telescope time used in program calibration varies by instrument. For GMOS, calibrations add about 5% to the program time, for NIRI 10%, for GNIRS and NIFS 23%. The standard, baseline, calibrations are described on the GMOS Baseline Calibrations webpage, the NIR Baseline Calibrations webpage, and the Mid-IR Baseline Calibrations webpage. The Observing Overheads page summarises all overheads associated with Gemini observations.
Allowing for the 80% queue filling factor and adding a 9% overhead for calibrations at Gemini North, and 5% for Gemini South, for the typical instrument distributions, the effective over-subscription rate is 1.4 times the values shown in the plots below for Gemini North, and 1.3 times the value for Gemini South. The values along the right axis show the effective over-subscription rate allowing for calibration overheads and the 80% queue filling factor; currently Gemini North is over-subscribed by about a factor of three and Gemini South about a factor of two.
The Demand for Gemini Telescope Time page shows the demand in number of hours, without the division by available time. The over-subscription for each Participant, calculated as described above, is also available. Note that the y-axis scales differ.
- Over-subscription for Participant Argentina
- Over-subscription for Participant Australia
- Over-subscription for Participant Brazil
- Over-subscription for Participant Canada
- Over-subscription for Gemini Staff
- Over-subscription for hosts Chile and the University of Hawaii
- Over-subscription for United Kingdom (no longer a Participant)
- Over-subscription for Participant United States
Figure 1: Average over-subscription of Gemini North and South telescope time between semesters 2005B and 2020B, as the queue is filled to 80% to reflect typical semester loss rates.
Figure 2: Over-subscription of Gemini North and South telescope time between semesters 2005B and 2015B, for partner Argentina. The over-subscription is the ratio of the total requested time to the total available science time in classical and bands 1, 2 and 3 for the Participant, as advertised in each semester's Call for Proposals. The effective over-subscription rate is 1.4∗ the values shown for Gemini North, and 1.3∗ the values shown for Gemini South, as the queue is filled to 80% to reflect typical semester loss rates and calibration overheads are not included.
Figure 4: Over-subscription of Gemini North and South telescope time between semesters 2005B and 2015B, for partner Brazil. The over-subscription is the ratio of the total requested time to the total available science time in classical and bands 1, 2 and 3 for the Participant, as advertised in each semester's Call for Proposals. The effective over-subscription rate is 1.4∗ the values shown for Gemini North, and 1.3∗ the values shown for Gemini South, as the queue is filled to 80% to reflect typical semester loss rates and calibration overheads are not included.
Figure 5: Over-subscription of Gemini North and South telescope time between semesters 2005B and 2015B, for Participant Canada. The over-subscription is the ratio of the total requested time to the total available science time in classical and bands 1, 2 and 3 for the Participant, as advertised in each semester's Call for Proposals. The effective over-subscription rate is 1.4∗ the values shown for Gemini North, and 1.3∗ the values shown for Gemini South, as the queue is filled to 80% to reflect typical semester loss rates and calibration overheads are not included.
Figure 7: Over-subscription of Gemini North and South telescope time between semesters 2005B and 2015B, for the Gemini South host Chile and the Gemini North host University of Hawaii. Hawaii has not reported full over-subscripton statistics in recent years. The over-subscription is the ratio of the total requested time to the total available science time in classical and bands 1, 2 and 3 for the host, as advertised in each semester's Call for Proposals. The effective over-subscription rate is 1.4∗ the values shown for Gemini North, and 1.3∗ the values shown for Gemini South, as the queue is filled to 80% to reflect typical semester loss rates and calibration overheads are not included.
Figure 9: Over-subscription of Gemini North and South telescope time between semesters 2005B and 2015B, for Participant US. The over-subscription is the ratio of the total requested time to the total available science time in classical and bands 1, 2 and 3 for the Participant, as advertised in each semester's Call for Proposals. The effective over-subscription rate is 1.4∗ the values shown for Gemini North, and 1.3∗ the values shown for Gemini South, as the queue is filled to 80% to reflect typical semester loss rates and calibration overheads are not included.