DESC White Paper Drafts on WFD and DDF

Hi - on behalf of the DESC Observing Strategy Task Force, we wanted to share our white paper drafts publicly to further engage in discussion and collaboration with the LSST community.

These papers are still in the review process, and thus are changing, so we share the overleaf documents here.


Please comment in the comments below, or send emails to and

Michelle Lochner and Dan Scolnic

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Thanks for sharing! We looked at the WFD footprint as part of our “Peaceful Solutions” hack at the Cadence workshop in NYC in September, and recognize the figure in your paper as based on Peter Yoachim’s OpSim run after the workshop. Eric Gawiser and Humna Awan led the way in proposing the footprint, so we share roots. We’re writing up the hack as a white paper. No complaints here!

It’s certainly an excellent set of white papers, well argued with supported details.

I would like, however, to understand what the WFD paper in particular represents for sky coverage. Am I correct that this is a formal recommendation by the DESC, representing some one thousand astronomers including most of the LSST Project leadership, that the main LSST survey be designed to exclude as many stars and as much of the Galaxy as possible?

Thanks for those kind words, John!

The way I hope the Science Advisory Committee will read the DESC papers is as the recommendation of several hundred cosmologists who are fairly single-mindedly looking to make the best cosmological measurements they can, with LSST - and then I would expect the SAC to recommend cadence simulations that enable both cosmology and Milky Way science (as well as transient science, and solar system science, etc). Having said that, while it’s the extragalactic sky we are after, we have attempted to propose a WFD survey that is as efficient as possible, so as to leave more time for special programs like a Galactic plane survey.

The Project leadership have been careful to stay out of our discussions during the writing of these papers - like the SAC, I think they want to know what the rest of the science community thinks!

@dscolnic: A concern about the proposed filter pattern for the DDFs: you suggest a sustained pattern of gri/zy/off. But any time u-band is loaded one of the grizy filters will be missing.

I don’t think you were suggesting swapping u-band in and out every third day (and for the “grizy every night” simulation this isn’t possible at all), so you might comment on your assumptions or preferences for how often the u filter is loaded, for how long, and what filter it should replace.

Thanks Eric! Yes we should specify this - our thinking is to have u band during dark time on the order of 3 days, and y band time the rest of the time. So the switching will always be between u and y. I’ll add this in (unless you have some additional thinking on this point). Thanks!

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