12/1/2014 (Peter, Chris, Michael)
· Pixels from camera are large and also many sources detectable by LSST will form “sky brightness” for the camera
· Camera: we measure two components, one is sky brightness that is just sky background that is function basically of source identification algorithm, we do not measure this well
o Instead, we can measure component that depends on moon-light / man-made light that scatters off of clouds (can measure time-variable part of sky brightness, not static)
o Goal is to produce a background sky model
§ Static background sky level as function of RA and dec (after remove sources)
§ What is sky brightness as function of lunar phase, angle from moon, latitude of moon
§ Need to separate cloud / time-variable part from static part
o Also have the sun brightness measurements as proxy for moon
· OpSim: Given the position of the moon and the sky, how bright is it at each point on the sky?
o What about the Milky Way? What is ratio of LSST sky brightness to all-sky camera sky brightness as a function of stellar density?
§ Under the assumption that we will take the same exposure to all fields, as a function of time, what is the sky brightness at all fields you care about throughout the night?
§ For each RA and Dec, find a dark-time sky brightness at that position. Can subtract off that number from all subsequent exposures.
§ Take all measurements of each source, figure out the dark time measurement for each source, plot as function of RA/dec
§ What will this plot look like? Should increase with zenith angle.
§ Correct for area per pixel, pixels have measurements in adu/arcsec
§ Flat fielding for point sources and for surface brightness are different
§ Also how to go from RGB in camera to LSST u,g,r,i,z,y (paper involving Tyco stars)
o Currently only uses photometric or closed dome
§ How is the implementation for somewhere in-between?
· Currently has some implementation
· Talk to Kem
· To do:
· Sky brightness as function of RA/Dec as a function of time
· Generate time-history of sky brightness for fields in file regardless of positions.
6/6/2014 (Simulations Telecon):
- B, G are not well-calibrated, but can give sky-cover. photo-diode well calibrated.
- CTIO water vapor absorption vs. time (no spatial dependency), up for several months
6/3/2014:
- DES tie-in
Michael to-do for scatter:
- compare short exposures
05/30/2014:
- Talk with Andy to figure out what output they want
- Convert pixels to RA, Dec for each image and then add it all together. Use to make a template and search for transients.
- Things to fix / look at: secant, stars that have magnitude issues (look constant)
- Make the deltax, deltay plots
05/29/2014:
Attendees: Michael and Chuck
2. [coughlin@lsst-dev ~]$ pwd
/lsst/home/coughlin
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
PATH=$PATH:$HOME/allsky/bin
PATH=$PATH:$HOME/wcstools-3.8.7/bin
PATH=$PATH:$HOME/fisheye
PATH=$PATH:$HOME/sextractor-2.19.5/bin
PATH=$PATH:$HOME/tphot
PATH=$PATH:$HOME/tonrytools
PATH=$PATH:$HOME/ffmpeg
PATH=$PATH:$HOME/ImageMagick-6.8.9-0/bin
PATH=$PATH:$HOME/cfitsio
https://github.com/mcoughlin/fisheye.git
- CS: There are existing catalogs of stars, for example the paper I sent you with bright stars and their griz-band magnitudes. It's better to get an external catalog
4. Abi (dophot) can fit individual images to extract magnitudes (compare with tphot/source extractor)
7. Can see milky way in cloud plots -> problem with sky brightness in photometry. Fix!