1/8/2015 (Peter, Chris, Michael)
Plot sky brightness as a function of extinction
- As cloud extinction increases, sky brightness increases (they are probably correlated enough that if you know one, you know the other)
- Likely knowing the lunar term is enough because it will dominate the term that is constant in time (due to the stars' placement in the sky)
Update the files on a daily basis
- Currently stuck at a month ago
Grab spectra from ESO model to try to predict magnitudes
- There have been some weird discrepancies (ESO slope not matching observed slope)
- Also of course twilight and cloud cover
- Can just fit to the available sky brightness data
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):
- Sky brightness, single value for sky at zenith as a function of time (to go into evolution of sky model)
- B, G from all-sky channel, R, Y, and Z from photo-diode
- B, G are not well-calibrated, but can give sky-cover. photo-diode well calibrated.
- Cloud model
- Check that the cloud model is appropriate
- Hard to fill-in the structure function scale (up to 1 degree) -> all-sky camera scale (5-10 degrees)
- Format for sky brightness time-series
- OpSim: Altitude and azimuth, not really high resolution, break sky into quadrants
- Healpix! (email Peter)
- Break up data into eighths and classify nights into eighths
- Compare our camera cloud cover to the telescope operator values
- Stick it in a database that we can query (few week time-frame)
- Night timestamp, observation timestamp, B/G/R/Y/Z (at zenith)
- Michael needs to remember that each pixel maps out the same solid angle
- CTIO water vapor absorption vs. time (no spatial dependency), up for several months
September: paper titled "Dynamic real-time scheduling of optical systems"
- Write down merit functions
- 5 sigma zero point magnitude of stars
- Include seeing model
Field FOM x SSM x DSM = IFM
Field FOM is a function of time
SSM is static airmass associated term (everything computable in advance)
DSM is sky brightness and clouds and like
- NCSA disk
- Photometric scatter
- Photometric transfer equations
- Transform from our R,G,B to G,R,I,Z,Y (stars on Wiki can be used to generate )
- Internal Reference Catalog
- Convert FITs files to healpix
- To observatories in real time (web server with FITs image and contour map with RA/Dec lines laid on top)
- LSST simulation guys
- Tier in to IR All Sky Camera
- Dome flat
- Sky flat
- Making Reference catalog
- Correction to LSST sky
- Stelar density dependent correction to sky brightness because LSST can resolve many of the stars that we cannot
- Pixel and time dependent
- Sky brightness model
- Check assumption that the solid angle subtended per pixel is same across entire image
- Take white teflon sheet behind point source and rotate lens and ask if the number of counts per pixel insensitive to rotation info of lens
- Daytime contrails
- Real-time to SOAR and Gemini
- Calibrated sky brightness w/ PD's
- Dome free sky obs to calibrate dome scatter
- New dome?
- Overall plan for calibration + schedule
- DES tie-in
Michael to-do for scatter:
Excess noise (non-Gaussian)
- take darks in lab
- subtract pair of darks
- plot dm vs. dx,dy
- m vs. t
- dm vs. m
- m_i vs m_j,
- m_R vs m_G
- residuals vs. dx, dy
- resid vs dm
- resid vs chi/N
- compare short exposures
- 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
Attendees: Michael and Chuck
1. Create a public fits files directory
2. [coughlin@lsst-dev ~]$ pwd
# User specific environment and startup programs
3. Create master catalog for all stars by looking at photometry over all the nights
- Then will not have to recreate mapping for each night
- TODO: Michael and Jamie
- 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
with excellent astrometry than to make our own, I think.
4. Abi (dophot) can fit individual images to extract magnitudes (compare with tphot/source extractor)
5. Search for transients with image subtraction (pixel by pixel image difference)
-> Convert (x,y) to RA/Dec (w/ fisheye)
- CS: Converting to RA, DEC is not enough. We'd have to rotate the images about the celestial pole, match PSF and sky, and then subtract.
6. For a given star, plot the magnitude differences vs fractional pixel remainder of the centroid (1024.35 -> 0.35) -> probably worst for R/B due to 1 pixel, different for x and y
7. Can see milky way in cloud plots -> problem with sky brightness in photometry. Fix!