OLYMPEX Cloud Microphysics

This data set consists of data collected from four instruments on the UND
Citation aircraft, the PMS Two-Dimensional Cloud probe (2D-C), the SPEC
Two-Dimensional Stereo probe (2D-S), and two SPEC High Volume Precipitation
Spectrometers (HVPS-3).  All instruments are two-dimensional optical array
probes which record images of particles that travel through their sampling area.
The recorded images are then analyzed to produce particle size distributions
from 50 microns to 3 centimeters in diameter.  


Probe specifications:

2D-C:    32-element diode array, 30 microns per pixel
2D-S:    Two 128-element diode arrays, 10 microns per pixel
HVPS-3:  128-element diode array, 150 microns per pixel

The 2D-S records particles from two separate arrays, one with a vertical (top
view) orientation, and one with a horizontal (side view) orientation.  They are
treated as two separate instruments in this data set.

There were two HVPS-3 instruments on this payload.  The probe named "HVPS3A" was
oriented horizontally, and the probe named "HVPS3B" was oriented vertically.
The HVPS3A probe was rotated to the vertical position on the two flights on 
December 18, 2015 for comparison with the HVPS3B probe. 

The 2D-C was oriented vertically for all flights.


Processing details:

Particle size distributions are given in terms of particle diameter, which is
defined as the diameter of the smallest circle than can completely enclose the
particle image.  Images that touch a side of the array are allowed.  The
technique described in Field et al. (2006) has been applied to mitigate
shattering artifacts on the 2D-C and 2D-S.  The 2D-C and 2D-S also had modified
probe tips to minimize the amount of shattering.  Optical depth of field for the
2D-C follows the manufacturer's specifications.  Depth of field for the 2D-S and
HVPS-3 follows Lawson et al. (2006).

For each flight a "comb.spectrum" file has been produced, which is a combination
of a small-particle instrument (2D-S) for particles smaller than 1mm in diameter, 
and a large-particle instrument (HVPS-3) for particles larger than 1mm in diameter.  
The vertically-oriented instruments (2D-S[v] and HVPS3B) were used for this product.

Bulk ice water content (IWC) is derived in the size distribution files for the
convenience of data users, using a mass-size parameterization of
mass=0.0061*(D^2.05) from Heymsfield et al. (2004).  Note that this has been
indiscriminately applied, and will not be valid in cases of rain, graupel, or
ice habits that are not well represented by this mass-size parameterization.

The total number concentration (Nt) given in the files is for particles larger
than 100 microns for the 2D-C and 2D-S, and larger than 1mm for the HVPS-3.  


File naming convention:

The size distributions are written in ASCII files (using the NASA Ames format
specification) with each instrument's data in a separate file.  The two arrays
on the 2D-S are identified by an 'H' for the horizontal array, and a 'V' for the
vertical array.  Files are named with the following convention:

    YYYYMMDD_HHMMSS.2DC.1Hz
    YYYYMMDD_HHMMSS.2DS_H.1Hz
    YYYYMMDD_HHMMSS.2DS_V.1Hz
    YYYYMMDD_HHMMSS.HVPS3A.1Hz
    YYYYMMDD_HHMMSS.HVPS3A.1Hz
    YYYYMMDD_HHMMSS.comb.spectrum.1Hz

The particle image files are named with the following convention:

    YYYYMMDD_HHMMSS_2DC7.png
    YYYYMMDD_HHMMSS_HVPS3A.png
    YYYYMMDD_HHMMSS_HVPS3B.png
    YYYYMMDD_HHMMSS_2DS_H.png
    YYYYMMDD_HHMMSS_2DS_V.png

where

    YYYYMMDD = year, month and day
    HHMMSS = hour, minutes, and seconds at data start time
    comb.spectrum = combined spectrum (2D-S, HVPS-3)
    png = portable network graphics, a raster graphics file format


References:

Field, P. R., A. J. Heymsfield, A. Bansemer, 2006: Shattering and Particle
Interarrival Times Measured by Optical Array Probes in Ice Clouds. J. Atmos.
Oceanic Technol., 23, 1357–1371.

Heymsfield, A.J, Aaron Bansemer, Carl Schmitt, Cynthia Twohy, and Michael R.
Poellot, 2004: Effective Ice Particle Densities Derived from Aircraft Data. J.
Atmos. Sci., 61, 982–1003.

Lawson, R.P., Darren O’Connor, Patrick Zmarzly, Kim Weaver, Brad Baker, Qixu Mo,
and Haflidi Jonsson, 2006: The 2D-S (Stereo) Probe: Design and Preliminary Tests
of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe. J. Atmos.
Oceanic Technol., 23, 1462–1477.