Fix Version/s: None
Epic Name:KPM: AM1, FY15
Team:Data Release Production
This will be measured on precursor data (almost certainly from HSC, via
DM-2380) using the following procedure:
- Run visit-level processing (i.e. ProcessCcdTask, probably via the new HSC driver ported on
- Run relative astrometric calibration (i.e. meas_mosaic,
- Select bright stars and match across visits (new scripts, mostly delegating to existing code). Just selecting the stars used for PSF determination would probably work.
- Generate pairs of objects with separation near the target (5' for this issue, 20' or 200' for
DM-3064and DM-3071). Bin widths will have to be determined, as that's not included in the requirement specification. Will require new code.
- Plot separation deltas (difference from per-pair mean separation) vs. magnitude; measure RMS and outliers in magnitude bins.
This requirement is specified only for r and i band.
The same procedure will be used for the AM1 (
DLP-310), AM2 ( DLP-311, DM-3064), and AM3 ( DLP-312, DM-3071) measurements for this cycle.
Vishal Kasliwal [X], thanks for reminding me! Regarding Mike's comment – we've been aware of that for a while but didn't have the time to act on it yet.
If he's right (and I think he is), it will necessitate a tightening of the SRD. That makes it first my problem (to prove this needs to be done), and then a PST problem (to further review it and assess whether it can be done, given what we've built so far). I'll add it on my TODO list (I'd expect to be able to take it up sometime early next year).
Zeljko Ivezic, take a look some ~three comments up, this is about having to tighten the astrometry requirements to ~3mas (just FYI at this point).
Yes, Robert already mentioned this new 3mas goal to me some time ago. Before we can
propose to change the SRD, we need to understand quantitatively how whatever metric
was used depends on the actual value of that spec. I am puzzled by the following result.
To get to 3mas, and using error ~ FWHM/SNR, we need SNR ~ 200 or larger. The faintest
galaxies in our gold sample (i<25) will have SNR~20. So we need to go 2.5 mag brighter
to even theoretically be able to achieve 3mas. But if you go 2.5 brighter, and the cumulative
counts go down as logN = 0.31*(i-25), only about 15% of galaxies in the gold sample could
theoretically have relative astrometric errors as small as 3 mas. Hence, based on this simple
initial analysis, I conclude that 3 mas is an overkill. To convince me that I am wrong, we will
need a more quantitative description of the origin of this 3 mas requirement.
I'll try to look at this. I hadn't realized there was progress on this front since Bremerton. It would be useful to have the code that is being used to derive these metrics.
David Nidever [X] The code used to generate the plots is attached to this ticket.
jimBoschScript.py does the matching and generates ListOfLists.pkl which is a python pickled object consisting of the required data for all the matches.
KPMScript_hist.py & KPMScript_scatter.py produce the required scatter plots and histograms from ListOfLists.pkl i.e. you can avoid re-running the jimBoschScript.py and just directly use the .pkl object. This may be your best bet because the jimBoschScript.py needs HSC data to run anyway. You can change the matching parameters in the two KPMScripts to make the plots for the required annulus etc...
Hope this helps
John Swinbank et al., the methodology looks sound, but before we close:
In general, I think David should audit proposed ways to measure KPMs (sorry David ) – it's always good to have another pair of eyes there, as these tests ultimately determine whether we've passed or failed. We'll probably have to have an independent review of them in sometime near the end of construction.
PS: If it's better from the scheduling point of view, it's fine with me to make the above tasks for FY16 KPM measurements.