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.
The SCOC reviewed a new set of simulations designed to represent the upcoming Phase3 recommendation and include different system effects (e.g. the new uniform rolling) + system effects (e.g. down-time simulations specific for Y1 and the effect of jerk on slew time and scheduling). These simulations also include bug fixes (primarily increasing the fraction of visit pairs that are completed). The ToO simulations in this set still need improvements and are not integrated into the baseline (but included in a separate simulation).
The SCOC and Observing Strategy team agreed to produce a similar set of simulations with further updates and integration of features like jerk and downtime in the baseline as well as ToOs to better represent the SCOC upcoming recommendation and expectations for system performance. These simulations are now in the making and will be released shortly under the tag 3.6 for review by the community before the release of the Phase 3 recommendation (September 30th 2024). A draft of the Phase 3 recommendation will also be released in the first week of September.