PMS-2D Processing Software

Overview

For the most part data are distributed in raw format. Starting with DYCOMS-II in mid-2001, RAF will be producing 1D histograms from the 2D probes. Two sets of histograms will be produced. The "1DC" arrays will emulate the 260X ("Entire-in"). The "2DC" arrays will use a "Center-in" approach to reconstruction.

Definitions:

h = height along the diode array.
w = width along the flight path.

"1DC/P" Histograms ("Entire-in")

These histograms will emulate the 260X probe where particle size is determined as the maximum particle height. Rejection criteria are as follows:

Reject particles which occlude either end diode.
Reject particles with a height of zero (zero area images).
Reject particles where h * 4 < w).

A particle is determined to end at the first blank slice encountered, this has the effect of shortening or removing many shattered particles.

The Sample Volume per bin per second is determined as follows:

2D-C:

Data processed prior to June of 2006 used the following DOF:

   DepthOfField[i] = { 1.56, 6.25, 14.06, 25.0, 39.06, 56.25, 61.0, .... 61.0 }

   DepthOfField[i] = { 61.0, 61.0, 61.0, .... 61.0 }
   EffectiveAreaWidth[i] = 6.0 - (0.2 * i-1)

2D-P:

Data processed prior to June of 2006 used the following DOF:

   DepthOfField[i] = { 145.203, 261.0, ...., 261.0 }

   DepthOfField[i] = { 261.0, 261.0, ...., 261.0 }
   EffectiveAreaWidth[i] = 0.75 - (0.025 * i-1)

   SampleArea[i] = DepthOfField[i] * EffectiveAreaWidth[i]
   SampleVolume[i] = TAS * SampleArea[i] * 0.001 * (((float)1000 - deadTime) / 1000)

where deadTime is the number of milliseconds the probe is shutdown (overload) plus the amount of time consumed by rejected particles.

Variables associated with this method are labeled:

A1DC_xxx is the raw particle count histogram.
C1DC_xxx is the corresponding concentration histogram.
CONC1DC_xxx is the total concentrations.
etc is *1DC_xxx

"2DC/P" Histograms ("Center-in")

These histograms use a center-in(1) method of reconstruction, that is, if the center of the particle is in the diode array, then the diameter can easily be determined. Any particle which touches an end diode and who's height is less than or equal to half the width is considered to have be "center-in". Diameter for all particles under this algorithm is the maximum of height vs. width. Rejection criteria are as follows:

Reject particles where w > 121.
Reject particles where h < 24 and w > 6 * h.
Reject particles where h < 6 and w > 3 * h.
Reject particles with a height of zero (zero area images).
Reject particles wich touch an edge diode and where w <= 2 * h).

Projects processed after December 2006 also had an Area Ratio Rejection criteria where the actual area (count of occluded diodes) divided by the smallest bounding box was less than 50% were rejected.

Reject particles where area / (h * w) <= 50%.

A particle is determined to end at the first blank slice encountered, this has the effect of shortening or removing many shattered particles.

The Sample Volume per bin per second is determind as follows:

2D-C:

   DepthOfField[i] = { 1.56, 6.25, 14.06, 25.0, 39.06, 56.25, 61.0, .... 61.0 }
   EffectiveAreaWidth[i] = 0.8

2D-P:

   DepthOfField[i] = { 145.203, 261.0, ...., 261.0 }
   EffectiveAreaWidth[i] = 6.4

   SampleArea[i] = DepthOfField[i] * EffectiveAreaWidth[i]
   SampleVolume[i] = TAS * SampleArea[i] * 0.001 * (((float)1000 - deadTime) / 1000)

where deadTime is the number of milliseconds the probe is shutdown (overload) plus the amount of time consumed by rejected particles.

Variables associated with this method are labeled:

A2DC_xxx is the raw particle count histogram.
C2DC_xxx is the corresponding concentration histogram.
CONC2DC_xxx is the total concentrations.
etc is *2DC_xxx

1) More information on "Center-in" and reconstruction algorithms can be found in: Heymsfield, A.J., Parrish J.L., 1978, A Computational Technique for Increasing the Effective Sampling Volume of the PMS Two-Dimensional Particle Size Spectrometer. J. Appl. Meteor, 17, 1566-1572.