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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
   - Deliverables
      - 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
   - Jacobians
      - 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:

   - m_i vs m_j,
   - m_R vs m_G
   - residuals vs. dx, dy
   - resid vs dm
   - resid vs chi/N

   - compare short exposures



  1. Talk with Andy to figure out what output they want
  2. Convert pixels to RA, Dec for each image and then add it all together. Use to make a template and search for transients. 
  3. Things to fix / look at: secant, stars that have magnitude issues (look constant)
  4. 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.
Sounds hard.
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!

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  1. How about we make the output discussion the subject of next week's (June 6th)  simulations phone con?