pachon sky camera christopher stubbs chuck claver jan 25, 2014
TRANSCRIPT
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Pachon Sky Camera
Christopher StubbsChuck Claver
Jan 25, 2014.
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Motivation• OpSim and ImSim can both benefit from actual sky
brightness and attenuation data.• Although some instruments exist in Chile, we consider
it advantageous to measure what we care about: optical sky brightness and optical transmission through clouds.
• Goal is to provide a map of m5, the 5 sigma point source magnitude, across the sky vs. time
• This should evolve into an agile scheduling system for LSST operations, that accounts for clouds in real time.
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Instrumentation• We installed at Pachon, on Jan 13 2014, a Canon
digital SLR camera with a 15mm fisheye lens. • Instrument resides in an atmospheric sciences
building, looking out through a hemispherical plexiglass dome.
• We acquire 1 sec and 10 second images each minute.
• Data is 3 band 14 bit dynamic range, lossless raw data, at 2888 x 1928 resolution.
• ~3 arcmin/pixel• 180 degrees of sky coverage from corner to corner
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Analysis Pipeline• Convert .CR2 raw Canon files into FITS files:– monochrome (add all flux)– B,G,R
• Perform photometry on all of these files• Extract sky brightness estimate at zenith, from
200 x 200 pixel box at zenith.• We can get a 3 arcmin resolution of sky
brightness by taking median filtered (point source-suppressed) image.
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Towards All-sky Astrometry
RMS fitting error ~60arcsec (~1/3 pixel) with 7th order polynomial
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More work to do on the photometry
dM = M_SAO - M_tphot + ZP
dM
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Photo-diode measurements3.5 deg FOVNIST calibrated diodes
Extends zenith measurements to the red with LSST ‘z’ and ‘y’ band filters.
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Goals• Finalize astrometric aspects, x,y to Ra, Dec• Refine photometry over full sky• Deploy photodiodes permanently• Map out attenuation in magnitudes• Determine 2-d profile of 5 sigma point source
magnitudes• Obtain this information for all nights • Continue to obtain nightly m5 maps• Transmit this information to OpSim and ImSim