Public SCOC meeting minutes

(note: earlier meeting minutes were collected in this post)


The SCOC met on Friday 10/28 to finalize the preparation ahead of 11/2-3 workshop and discuss the four simulations that were released to the public on 10/25.
We discussed which elements of our recommendation should be seen as final and which are still expected to be refined and identified a need for clarity about how much space there is to refine each piece of the recommendation, to help focus community efforts.
We agreed to move into 2023 with a few simulations, instead of just one, which may be small variations on the present four. We discussed the role of each simulation in the suite of four that was released and which ones are candidate surveys vs which are instead illustrative modifications to stress the parameter space of possible choices and identified the need to be clear on this point during the presentation of the simulations at the 11/2-3 workshop. In the past week the SCOC has reviewed drafts of a report describing our simulations asynchronously. The structure of the report was discussed.

The SCOC met on Monday 11/7 to discuss and review the feedback collected through the SCOC third workshop (11/2-3) and plan the details of the release of simulations and reports through 2022, ahead of the upcoming SCOC members’ rotation. Looking at the best strategy to deliver our recommendation to the next SCOC and to the public, the SCOC decided to 1) explore a few variations of the current simulations before we identify the one that best incarnates our recommendations: this include decoupling some properties of the roll_early simulations to see the separate effects of early rolling revisit cadence, correcting the Twilight NEO current implementation to align it to the recommendations of the SCOC, and some other tweaks on filters and footprint. These simulations should become available to the SCOC in the next 2-3 weeks. 2) Reconfirmed our intention to release our recommendations in the form of a report in December 2022, explicitly isolating the elements of the recommendations yet to be made, and those that still need finalizing, into a separate section for clarity.

The SCOC has scheduled meetings for the next two mondays

The SCOC met on 11/14. We discussed the draft report that is reviewed by all SCOC members and converged on changes to the introduction. Sections describing individual recommendations are still under review. The SCOC discussed new simulations that correct some implementations that were inconsistent with the SCOC recommendations in the set of four v2.99 simulations released before the November workshop: this includes correcting the implementation of the Twilight microsurvey and starting rolling after Y1. The new simulations also implement filter swapping differently as suggested by the DESC to increase the availability of the z filter (swapping u/z/y instead of only u/y). We decided to stop simulating strength 0.5 rolling, as the recommendation is for rolling at strength 0.9. We identified the need to investigate what in the new simulations suppressed the number of observations falling in time gaps 1-14 hours and 14 hour-1 day, which were identified as important time scales for several time-domain metrics. Additional simulations were commissioned to understand what parameter changes caused these drop in observation numbers.

The next meeting of the SCOC will be 11/21

The SCOC met on 11/21 and discussed the set of v2.99 simulations and isolated two simulations that implement the recommendations of the SCOC including:

  • Implement a correct version of the twilight survey (the 4 v2.99 simulations initially released were implementing the twilight survey inconsistently with the SCOC recommendation)

  • Are compliant with SRD (with a sufficiently high number of observations in the WFD),

  • Implements rolling at 2strips, 90% but

  • Rolling only starts after Y1 (~near Y1.5),

  • Implements suppress-repeat and triplets only once every several nights to enable coverage of short time scales (<=1 day).

We currently have 2 simulations that are compliant with this scheme. In addition one of the two new simulations implement filter swaps to increase access to the z band filter which has advantates for SN Ia cosmology at high redshift (as suggested by the community in the November ⅔ workshop) but the impact on the time gaps between observations propagate to all filters (not just z, y, and u) so this new implementation has space for further exploration.

The SCOC will decide in a mail-in ballot if one of these two simulations should be tagged as the new baseline and if so, in a separate vote the SCOC will choose which of the two.

The SCOC still intends to continue to explore possible variations and has commissioned additional simulations to the opsim team including additional studies of the filter swapping scheme simulations that modify the fraction of time spent on special programs.

The committee will meet again on 12/1/2022


The SCOC met on 12/1/2022 and approved a ballot to select an existing OpSim as Baseline v3.0. A subsequent mail ballot led to the selection of the current baseline as reported in PSTN-055 to be released on December 31


The SCOC met on January 23rd. New committee members were introduced to the team. A plan for assigning liaisons to the SCs was made and we expect the liaisons assignments to be completed early in February. The committee discussed Phase 2 report PSTN-055. We will work asynchronously leading up to our next meeting at the end of February to organize the recommendations that remain to be finalized in a prioritized list (Section 4 of PSTN-055), after which the SCOC will establish associated timelines and deliverables for the priority items and share them with the community.


The SCOC committee met on 2/27. The committee reviewed the 9 outstanding tasks as described in PSTN-055 (SCOC phase 2 recommendations, section 4) and prioritized them by urgency. At this time, the SCOC will prioritize the creation of two subcommittees: one dedicated to make progress in the decisions related to the DDF strategy, and the other to rolling cadence strategies – to balance the need to make uniform coadds with time domain needs, and investigate the feasibility of implementing rolling strategies that would lead to more uniform coadds. Additional items from Section 4 of PSTN-055 that the committee expects will progress soon with either added input from the community or new simulations are: filter swaps schemes (awaiting input from simulations), ToO (workshop plans moved to later in 2023, but advancing), Galactic plane cadence refinement (the committee is tasked with closing the loop with the community who was actively working on this through November 2022). New simulations should await the implementation of the new OpSim version which is expected in the coming weeks.

The committee chair is arranging meetings with the chairs/spokespersons of each SC and their liaisons to identify the best way to support each SC’s needs.

The committee will continue to hold office hours on the last Monday of the month and meetings of the full committee will continue for now on a monthly cadence on the last Monday of the month.


The committee met on March 27th.

With nine topics identified in PSTN-055 (Section 4) for the SCOC activities in 2023 and their prioritization agreed upon by the SCOC on February 27 (see earlier notes), the committees will reach out to authors of white papers and cadence notes within and outside of the SCs to ensure we correctly and comprehensively identify within them the community concerns and desired data that can influence decisions on these nine topics.

The committee approved the creation of a task force to discuss optimization of the uniformity of coadds in the presence of rolling. The SCOC members that share concerns on uniformity are invited to join the discussion on slack and to recruit members of their SC to contribute to the slack conversation. A description of the issues will be shared by the SCOC liaisons with their SCs to ensure all SC with a vested interest in uniformity of the coadds produced as part of Rubin data releases are aware of the discussion.

The observing strategy team updated the SCOC on necessary changes to the OpSim software and baseline simulations, including (a) updates to the software that incorporate the newest version of the rubin_sim, (b) updates to the start date of the survey following Monthly Updates | Rubin Observatory, (c) small modifications of the footprint that would improve alignment with the Euclid footprint on the LMC and SMC (<0.5% change in the footprint), and (d) updated DM requirements for templates as an input to the optimization in the feature based simulator. Pending SCOC approval, a new baseline with the aforementioned changes incorporated within it will be released. Some unexpected impact on some science metrics was noted by the SCOC and will be investigated. The observing strategy team is also working on updating the simulator with as-measured throughput curves for filters and camera - updated simulations that incorporate these changes are expected in April.

The SCOC has invited the Rubin Operations Early Science team to the next SCOC meeting at the end of April to plan coordination on early science decisions.

The SCOC reminds the community that, in addition to the liaisons who are the designated point of contact for the SCs, the SCOC holds regular office hours at 7AM PST on the last Monday of the month.


The SCOC met on April 27th.

The SCOC invited the Rubin Commissioning and Early Science team to discuss coordination on early science recommendations. As per SIT-COM-TN-10 - members of the SCOC will be invited to join the commissioning team as ex-officio members to facilitate advising the commissioning team where needed. Areas of relevance where the SCOC interfaces with the commissioning team may include: suggestions for technical studies that inform survey strategy, for design of Science Validation Surveys in the context of overall Early Science planning, and synthesis of technical inputs to inform survey strategy. The Early Science decisions will impact the design of the survey strategy in year 1, and thus they should be made in coordination with the SCOC. Where input from the community may be needed to refine Y1 operations, the SCOC is best placed to solicit and receive this input. The committee thanks Drs. Keith Bechtol and Leanne Guy for their interactions with the SCOC.


The committee gathered on June 5th. We reviewed progress on the work of the task force established to assess the impact of non-uniformity due to rolling based on extragalactic and cosmological science goals. We were pleased to hear that if commissioning and the first year of observations proceed as expected, then rolling should have minimal to no impact on photometric calibration. Work is underway to establish cosmological metrics quantifying the impact of rolling cadence on issues other than photometric calibration.
The committee reviewed changes in the OpSim current set of baseline simulations: a few improvements have been introduced in the opsim (a description is upcoming on community). Most of the proposed changes induce a significant impact on science metrics or they improve their throughput. New simulations that explore filter availability on the filter wheel and swap u with z/y based on moon phase were presented. The simulations produce significant improvements in SN cosmology. The impact of these changes on short time scale sampling, however, could not easily be assessed with existing metrics. The Opsim team is working on metrics for the assessment of changes of strategies on hour to 1-day time scale observations, and to understand what drives the significant improvement on SN DDF metrics. The SCOC expects to refine this updated baseline before the PCW. The SCOC continues to hold office hours on the last Monday of the month.


The SCOC met on June 26th and began reviewing the feedback received via this form requesting updates on concerns regarding the observing strategy and in particular the points identified in PSTN-055 as decisions that remain to be finalized: Filter balance (if the as-built throughput changes from what is expected); Intranight cadence in the Deep Drilling Fields (DDF); Galactic Plane/Bulge footprint and filter balance optimization; Uniformity of coadds within a rolling cadence; 2x15 vs 1x30 second snaps per exposure; Early Science; Availability of filters on the filter wheel. 14 responses were received. We thank the community for their continued engagement and thoughtful suggestions! Review will continue through July.

The SCOC has opened a slido to enable questions from the community to be answered and discussed at the PCW 2023 Updates on Survey Strategy Optimization (see Questions portal for "Updates on Survey Strategy Optimization" session at PCW 2023).

The next office hour will take place on July 31 at 7AM Pacific (as usual on the last Monday of the month) and the next SCOC meeting on Jully 31 as well.


The SCOC has convened on 9/11/2023 and reviewed the outcomes of the PCW. Particularly, we noted a significant interest from of the community in the timeline for the SCOC recommendation to adopt 2x15 snaps vs 1x30 sec with emphasis on having all science arguments pertaining to this decision available to the SCOC before commissioning feasibility tests of 1x30 sec exposure are complete. Having reviewed its calles for input, including the most recent form that solicited community input in June 2023, which contained questions about the scientific impact of a potential switch to 1x30 sec, the SCOC believes to have collected a significant amount of scientific input on this topic and we will begin a systematic review of it in early 2024.

The SCOC recognizes the need of better/more metrics to evaluate strategies to collect templates in the context of the survey strategy as a whole and supports and encourage ongoing work on assassing schemes for collecting template images and building templates for DIA, including ongoing work by Eric Bellm.

The SCOC was informed of a proposed change for the coating of the system mirrors and switching from Al-Ag-Al to Ag-Ag-Ag (or 3xAg). The survey strategy team is preparing simulations that incorporate the new expected throughput and they will make simulations and associated notebook available to the SCOC in the next few weeks.


The SCOC convened on 10/02/2023 and reviewed the impact of the change in plan on the coating material for the mirror: the current plan is to move to silver coating for M1 M2 M3 (Agx3) which leads to a ~15-20% increase in survey efficiency compared to Al-Ag-Al.
The SCOC acknowledges that the throughput of the u band filter is impacted negatively (30% loss in coadded depth) and will involve relevant community members in the assessment of the scientific impact and potential mitigations (e.g. changing the filter balance or exposure time for different filters)

The SCOC is still identifying the best days for the SCOC-community workshop targeting the first quarter of 2024 and for the ToO workshop.

The Milky Way task force has presented to the survey strategy team a set of requested simulation parameters for new MW simulations.


The SCOC met on 10/31/2023 and finalized the dates of the next SCOC-Science Collaborations workshop to January 17 and 19th 2024 (online only, see The Fourth SCOC-Science Collaborations Workshop (virtual) | The Fourth SCOC-Science Collaborations Workshop (virtual))

The SCOC is also finalizing the dates and details for the ToO meeting (March 2024. Exact dates will be announced ASAP, pending venue and room block confirmation)

The SCOC is identifying key members of the Observatory and community to solicit their participation into the ToO meeting and preparing a template for the report to be delivered at the end of the ToO workshop. The template will be available to the community at least two weeks prior to the workshop.

The SCOC is preparing to review the current filter balance in light of system throughput throughput updates included in the new OpSims (see Baseline v3.3 Run released!). While the existing metrics largely improve due to the increased survey efficiency, we are seeking community expertise to identify scientific cases that may be impacted by the changes and that are not currently monitored through existing metrics. In particular, studies of the impact on photo-z are underway and community contributions to understand the impact on stellar metallicity and associated science (halo formation history are welcome).

The SCOC wishes to remind the community that office hours are available every last monday of the month at 7 AM Pacific, and that the community is always welcome to contact the SCOC via the Science Collaboration liaisons, the SCOC chair, or directly at


The SCOC met on 11/27/2023. We refined the agenda for the upcoming SCOC and Science Collaborations workshop The Fourth SCOC-Science Collaborations Workshop (virtual) | The Fourth SCOC-Science Collaborations Workshop (virtual). The SCOC continues to discuss the impact of system throughput updates. While most science cases benefit from the added efficiency and increased depth in g through y band, we identified science cases where the new simulations show gains in some filters to be weighed against a loss in u band. Where needed, the SCOC will reach out to community members to aggregate by-filter metrics into a single figure of merit that can speak to the overall scientific impact of survey depth changes in different bands. Preliminary assessments of the impact on some science cases (photometric redshifts and stellar metallicity) have been reviewed and will continue to be discussed asynchronously.


The SCOC met on 12/18/2023 to finalize the schedule for the January SCOC-Science Collaborations workshop and discuss the format of the March ToO workshop ahead of the release of the workshop’s registration opening. Due to travel and holiday the SCOC will not have a committee-wide meeting in January


The SCOC met on 1/29/2024. The timeline of SCOC discussions and deliberations through Fall 2024, when the Third SCOC recommendation is planned to be delivered, was discussed. The SCOC is scheduled to release the Third SCOC Recommendation at the end of September, to present the content of the recommendation at the 2024 Rubin Community Workshop, and to have a complete draft of the deliberation available to the community before the beginning of September. The SCOC also commits to share any recommendations with the community as they are finalized on

The updated throughput of the Rubin system (incorporated into OpSim v3.3) offers an opportunity to reevaluate what filter balance provides the maximum overall scientific throughput for LSST. In the light of PSTN-055 Recommendation 2.3, and in consideration of the concerns of the community about decreased u-band depth (especially concerning its effect on photo-z and Galactic Halo science) the SCOC commissioned simulations that vary u-exposure time and u-band number of exposures. On 1/29/2024 the SCOC identified a set of viable options to increase u-band depth. These simulations will be released to the community in February.

The SCOC began reviewing the information gathered during the Fourth SCOC-SC Workshop (1/17 and 1/19 2024), with particular attention to community contributions.

The SCOC met on 2/26. After brief updates from the task forces, the meeting focused on preparation for the upcoming ToO workshop. The SCOC discussed the framework for enabling ToO responses, revised the workshop plan and template for the report to be written by workshop participants, and the workshop schedule.

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The SCOC met on Monday 3/25. The SCOC discussed the outcome of the RubinToO24 workshop and expectations for the workshop report, which is due on 4/14. The workshop was a successful event from the point of view of the SCOC which led to positive and effective collaboration on survey strategy ideas that the SCOC plans to review in April-May.
The Taskforce on Uniformity reported back to the SCOC. We reviewed promising modifications of the rolling strategy that deliver increased uniformity for data releases planned to be used for cosmological results by the DESC with minimum to no impact to other science metrics. We plan to investigate in detail the causes of the (possibly small) impact these survey strategy changes have seen on some science metrics (fast transients) in the upcoming weeks. Members of DESC have also submitted pull requests for multiple metrics that measure uniformity of coadds. Those pull requests are under review by the Survey Strategy team. Pull requests · lsst/rubin_sim · GitHub
The SCOC has agreed to submit a session proposal for Rubin Community Workshop 2024 to discuss the status of its phase 3 recommendation.

The SCOC met on 4/29/2024

Leading up to the July 2024 Rubin Community Workshop, the SCOC will increase the frequency of its regular meetings to every other week.

An analysis of the impact of u-band throughput changes and potential mitigations by increasing u-band exposure and/or number of images was reviewed. The SCOC, with the support of the Observing Strategy team, had identified a few options to mitigate losses in photo-z observed with the new throughput change without impacting other science areas. A motion was approved to vote (by email) on increases in u-band exposure time and number of images compared to baseline v3.3. The outcome of the vote will be tallied at the next SCOC meeting and shared in the next meeting minutes.

The SCOC has received the report from the RubinToO24 meeting on April 19th, which makes recommendations for the Rubin Target of Opportunity program for different science cases. The SCOC has organized three subcommittees to review the report with the goal of incorporating it into the SCOC recommendations and plans to discuss sections of the report at the May 13th meeting.

The SCOC has identified a few simulations produced over the past few months to be officially released as Opsim v3.4 with a community post that describes each simulation. The Opsims were released on 5/2 with this community post Release of V3.4 Simulations