DRI Photoacoustic Instrument

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DRI Photoacoustic Instrument
Pat Arnott, DRI, pat_at_dri.edu.
PA in operation, sampling from a dyno. Consists
of laptop, tan colored box where instrument is
housed, and black 19 equipment rack for
electronics. Aircraft version will be smaller
and able to fit in 19 rack.
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Status

• Ground based unit ready. May have 2 wavelength
  operation ready for IOP (532 nm, 675 nm and or
  1047 nm).
• Trying to reduce the size of instrument for
  aircraft use. Parts are being machined for the
  reduced size unit. Will probably use 523 nm or
  675 nm laser. 675 nm would go well with NASA
  CRD.
• Could use existing unit if necessary for aircraft
  use.

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Summary of Current SGP Measurement by NOAA What
to expect aloft and at the ground (purple).
Boxes are 25, 50, and 75 values, whisker ends
are 5 and 95.
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Interesting reduction of Single Scatter Albedo
with height from the NOAA CMDL data set (Pat
Sheridan)
Altitude in meters, Extinction is on left in
Mm-1, and single scatter albedo on the right. AOS
ground based values are in purple
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Estimated Leg lengths as a function of altitude
for good Photoacoustic Data
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Estimated Leg Lengths The numbers
Median Babs values aloft from NOAA were used to
estimate the time necessary to achieve good
photoacoustic measurements at different
altitudes. Clean or dirty days could change the
picture dramatically. These are integration
times for a SINGLE good measurement. Decide the
number of measurements needed at each level, and
multiply the times by this value. These
estimates are based on experience, should be
realistic.
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ISSUES

• RH conditioning? Are we going to take the
  aerosol at whatever RH appears, or measure the RH
  in each instrument? (scattering and extinction
  measurements especially need thought).
  Filter-based light absorption instruments should
  be presented with DRY aerosol (RH lt 30 ideally).
• Leg durations need to be much longer as the
  altitude increases to get good data, likely from
  all aerosol instruments.