2020-06-29 DM SST Agenda and Meeting notes

Leanne Guy

Zeljko Ivezic

Survey Cadence Optimization Committee (SCOC) stood up

• Led by Rubin Operations Head of Science (Željko) with representation from across LSST science pillars 
• Working on a report to describe what was learnt from the 100 or so simulations done in response to the cadence white papers
• Will be socialized internally before being presented at the PCW 
• SCOC will produce and initial survey cadence and recommendations on early science (very commissioning dependent). They are also charged with studying the best cadence to adopt during commissioning. This will be strongly based on the time available for commissioning (as well as other factors). 
• Charged with getting information from all the stakeholders, including PST and commissioning team
• SCOC looking to adopt an  iterative and data / analysis driven approach. 

SDA (Space Domain Awareness)  (Zeljko Ivezic)

• Project asked to give presentations to the JASON group on the impact of LEO satellite and on the Space Domain Awareness risk (i.e describing how good will LSST be at discovering government assets that the government don't want to be discoverable. 
• Project position put to the JASONs  is that delaying PVI release by 7 days will be catastrophic for science but that 1 day (24h) is will not have a major impact on science. This is consistent with the current baseline plan to release all prompt data products within no more 24h. An embargo period of 6 hours was added some time ago in anticipation of this issue. Hope that this strategy will be acceptable. 
• If this is not acceptable,  then the additional strategy proposed was to go for a longer delay (> 1 day) for images close to the geo-belt only.  (Currently 20% of all images for a 20 degree wide zone)
• A final proposed mitigation is to censor those alerts that are on streaks longer than the length corresponding to a fraction of the sidereal angular motion rate. 
• An earlier proposal to randomize observing times has been dropped; there was strong opposition from SSSC and it is also possible to determine the time from images with known SSOs.
• We have been asked not to bring these issues to the public domain yet, NSF/DOE want to get their ducks in a row 
• This is the proposal that has been presented, the JASONs will study it over the summer, we don't expect feedback for a few months. 
• Tangentially coupled to the selection of the data facility, that is, they might decide to run initial processing at trusted location.  

Simon Krughoff

Observations on the course: 

• Instruction was  varied, intro to LSP contained too much to go over in 1 session  and was overwhelming. Needed a more sedate pace for beginners 
• 20+ simultaneous logons revealed a bug  and made login time very slow, 15 mins+ for the first several weeks. The bug is now fixed. This shows need to have users!
• Less questions received than expected but the feedback was positive.
• Some students expected to do all their work through the portal.  Different data sets were exposed via the Portal and NB Aspects. This also reflects the feedback from the LSP FDR. 
• Attendance was consistently good, 17/18 of 20 throughout. 
• Not much visibility on the Zoom breakout rooms. Covered LSB, deblending, ingesting DPs and flare stars, SSOs.  Would be good to get a better view on what people worked on. 
• Would be useful to go through the NBs to understand how people did things and provide more pedagogical info on how to do things. 
• 13 branches on the repo. 
• Thanks to the support from all DM staff who gave talks and were on call. 
• Many people did not get as far as they wanted to  – there is  hope for continued involvement in the weekly stack-club meet ups. 

The lack of a formal definition of bright stars that can be applied consistently throughout the project has been a longstanding problem

• LIT-118 - Getting issue details... STATUS  
• What is being used in the pipelines at the moment?
• DM-22138 - Getting issue details... STATUS
• Robert Lupton suggests defining bright stars in terms of S/N such that the object photon noise >> S n_eff
• Also consider the definition of "isolated" (several requirements mention "bright, isolated stars".

• Need to choose a cut that is high enough that we are into the systematic floor rather than being dominated by photon noise – SNR cut of a few hundred.
• Definition is mostly in the SRD but there are there are different ways to capture signal-to-noise, so the definition needs to be clear.
• What ever is decided, it needs to be explicitly written into the definition of the metrics and the SRD - anywhere that design thresholds are specified, this influences the definition of the metric
• Need to have the flexibility to separate the metric that we want to use from the metric that we will use at any given time. E.g HSC exposures that are deeper that those of LSST — things will change when we start applying these definitions in practice
•  Definitions should include reference to the flags that we will cut on — an understanding of the theoretical and technical aspects is needed — we are throes of validation and verification right now.
• A related issue is how we define a given image as being of survey quality; the definition of bright stars is somewhat coupled to some of these other practical issues that we'll face when we actually go on Sky variable quality images that are delivered.
• Željko proposes not to have binary cuts but rather suggests to compute this in a continuous manner whereby for each image one computes effective exposure time given nominal depth expected for the survey, i.e if observing conditions are as assumed, one would have the same observing time. Then look at the distributions and make the cuts. This effective exposure time will also be used at the system level by systems engineering to track the integrated étendue of the survey.
• What are the practices of other current large scale surveys?
  • DES:  Section 4.7 of https://ui.adsabs.harvard.edu/abs/2018PASP..130g4501M/abstract . Contains information relevant to characterizing an exposures’s usefulness… those types of numbers form the underlying basis for whether observations meet quality cuts for the survey. They also are available (along with slightly more detailed measurements) for the DES Collaboration.
• Can define 2 different scopes: 1) Choose some standard reasonable definition of bright stars so that we have a consistent definition across all metrics, thereby simplifying future discussions, and 2) a more detailed scientific understanding of what is meant by the definition. Can potentially gain a lot with a reasonable definition and agreement of a first.

• Leanne Guy Keith Bechtol to form a plan for  how to engage the commissioning team to think about a) how to define bright isolated sources and b) image quality in general 25 Sep 2020 

Leanne Guy