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.
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 invited the Rubin Commissioning and Early Science team to discuss coordination on early science recommendations. As per SIT-COM-TN-10 - https://sitcomtn-010.lsst.io/ 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 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 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 fbianco@udel.edu, or directly at lsst-scoc@lists.lsst.org.
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 community.lsst.org.
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.
2/26/2024
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.
3/25/2024
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.
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
The SCOC designed a set of simulations relating to the ToO program that reflect the community recommendation in https://lssttooworkshop.github.io/images/Rubin_2024_ToO_workshop_final_report.pdf, as well as down and upscoped versions of the recommendation. These simulations, together with the scientific motivation for the ToO described in the report, will enable the incorporation of the ToO program in the Phase 3 survey strategy recommendation due September 2024.
The SCOC identified a parameter in the implementation of a rolling strategy that was previously not explicitly discussed, namely, the number of rolling cycles. A rolling cycle is defined as (roughly) 2-year period over which each rolling region receives alternate high- and low-intensity coverage. While the SCOC has made explicit recommendations on the sky rolling regions (recommending a 2 sky region split, see PSTN-055 Section 2.5.2) and on the strength of the rolling (0.9, see PSTN-055 Section 2.5.2), the number of rolling cycle was never explicitly discussed and deliberated on. Since, like the parameters discussed earlier, the number of cycle rolling strategies impacts uniformity and time-domain science, the SCOC is preparing to deliberate on it in its Phase 3 recommendation.
The SCOC has voted affirmatively on extending the u-band exposure to 38 seconds per visit and boosting the number of u-band observations by 10% compared to Baseline v3.2. This compensates for the relative throughput loss associated with the Triple-Silver mirror coating (discussed here) while preserving the increased survey depth at bands redder than g.
The survey strategy team has recently released a new set of simulations (v3.4) that include variations on the exposure time and number of u-band visits and modified rolling strategies for the community to review and share feedback on.
The next meeting of the SCOC, scheduled for May 27th, would fill on a US holiday and will be postponed to ensure sufficient attendance.
The SCOC met to review simulations that represent the community recommendation of the Target of Opportunity program formulated during the ToO workshop https://lssttooworkshop.github.io/. The simulations of the program showed little to no impact on the science to be conducted with the Wide Fast Deep survey, but took a smaller fraction of the survey time than expected. The Survey Strategy team is investigating this issue and the SCOC will reconvene to reevaluate the impact of the ToO program as more information becomes available.
6/17/2024
The SCOC reviewed updated ToO simulations. The impact of the addition of a ToO program implemented as per the recommendation of the Rubin ToO24 participants (https://lssttooworkshop.github.io/) as well as with down and upscoped implementation was reviewed. A statistically significant impact in the metrics tracking SN Ia number at low redshift and parallax is observed with the introduction of the ToO program. For other metrics (e.g. Brown Dwarfs) the observed impact is within the 1-sigma uncertainty determined by weather predictions. The SCOC will vote on ballots regarding the implementation of the ToO program within the first week of July. The observing strategy team prepared supporting material for this decision including notebooks reviewing the ToO program simulations can be found at sims_featureScheduler_runs3.4/maf/ql_too_com.ipynb at main · lsst-sims/sims_featureScheduler_runs3.4 · GitHub and survey_strategy/fbs_3.4/v3_4_too.ipynb at main · lsst-pst/survey_strategy · GitHub
The SCOC agreed to meet every monday in July leading to the Rubin CW to advance discussions on the recommendations for Galaxy survey strategy, DDFs, and rolling strategies.
7/1/2024
The SCOC discussed the report of the Galaxy Survey Strategy task force including recommendations on footprint details, rolling, coordination with Roman and filter balance. While some details of the filter balance in special regions remain to be defined, the SCOC has prepared ballots to vote on the recommendations of the Task Force. The outcome of the vote is expected by 7/15.
The SCOC heard a preliminary report from the Deep Drilling Field Task Force. The TF has ready recommendations for a variety of aspects of the DDF strategy including observation properties, dithering, and field prioritization over the 10 year survey. More work remains to be done on the nightly cadence and on balancing season length with cadence requirements.
The SCOC approved unanimously the endorsement of the ToO recommendation provided by the community in https://lssttooworkshop.github.io/images/Rubin_2024_ToO_workshop_final_report.pdf and foresees recommending the implementation of the program as described within. The SCOC ToO recommendation will also include a recommendation to have a new workshop before the start of O5.
The SCOC discussed the sensitivity of our recommendations to the outcomes of Y1. Over the next few months, we will commission simulations that examine the 10 year survey plan with different results from Y1, primarily due to different amounts of required engineering time.
The SCOC discussed the uniform rolling strategy simulations produced with the support of the Uniformity Task Force (see notes from 5/18/2024) as well as newly received feedback from the DESC which quantified the merits of these simulations for cosmology. It was also emphasized during the meeting that the Galaxies Science Collaboration favours uniformity of coadds as well.
These rolling implementations brought to light a new tunable parameter in the simulations: the number of cycles of rolling which, until now, the SCOC was not exposed to explicitly. Because rolling is not implemented in Y1, there can be up to 4 cycles of rolling in the 10 year survey. The uniform rolling implementation limits the number of cycles to 3 in order to intersperse the rolling with uniform observations to achieve better uniformity at key data releases. We note that the time-domain impact of implementing 3 vs 4 rolling cycles is felt primarily in the ~24 hours time scales (while shorter time scales are controlled by the presence of observations in triplets) and longer time scales still see most of the benefits of rolling even if rolling is limited to three cycles. The SCOC agreed this new rolling implementation is promising and affirms the importance of finding solutions that enable robust analyses for cosmology and galaxy science at intermediate years between 1 and 10 (see PSTN-055 section 2.5.2) . However, two concerns arose: first, the SCOC wants to ensure that before a recommendation is made the changes are understood and evaluated by the broad community, and will encourage these activities at the Rubin Community Workshop. Second, the current uniform rolling strategy has tight constraints around the start date of rolling (early in Y2). The ability to roll early in Y2 is however subject to the outcomes of Y1.
The SCOC is also aware that the Phase 3 recommendation pertains to the start of LSST and Y1 survey strategy, while rolling will not be initiated until Y2. This appears to be an opportunity to continue to investigate optimal rolling strategies such as uniform rolling and potential variants on it and to evaluate sensitivity to Y1 outcomes.
The SCOC will meet again on 7/15/2024 to continue rapid progress on our recommendation ahead of Rubin2024
The SCOC prepared a ballot to vote on the current recommendations of the DDF task force (see notes from 7/1/2024), to be voted on by Friday 7/19. The SCOC discussed the needed refinements and additional recommendations for the DDF survey strategies, including balancing intranight cadence and season duration and prioritization of different fields, and is preparing a roadmap to complete recommendations for minimal and optimal Y1 DDF observations within the SCOC Phase 3 report.
The SCOC revisited the benefits of moving from 2x15 second snaps to a single 30 seconds exposure. A few science cases that could benefit from snaps were presented to the SCOC in 2018 white papers, 2021 cadence notes, and responses to the 2023 SCOC feedback form. Snaps would enable studies of sub-minute variability. However, science cases that would benefit from measuring flux differences between snaps (which would be delivered as the only snap-related data product if snaps were implemented) are limited, and other, dedicated surveys may be capable of exploring these time scales (including potentially microsurveys within LSST). While the snaps slightly decrease the saturation limit of the survey, decrease is minimal, and only impacts a limited number of sources (compared to the wealth of sources observed by LSST). The SCOC does not see scientific advantages that could compete with the increased survey efficiency (7-9%) delivered by removing the overhead associated with the snaps. The potential for 15 second snaps to also help rejection and correction of glints and streaks from LEO satellite was also suggested and will be further investigated by the SCOC. With these considerations, the SCOC prepared a ballot to vote on moving to a single exposure per visit if the commissioning feasibility studies confirm that cosmic ray rejection is technically possible with a single exposure.