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Default SODA2 Processing Settings

Linkage scripts within ADPAA pass parameters to the included SODA2 software which determine the particle sizing method and additional sizing corrections, the method of processing partially captured particles, and other corrective procedures to be used during processing. The default settings and their alternatives are described below.

Methods for Processing Particle Size [method]

default: fastcircle; 
alternatives: WaterProcessing, xsize, ysize;  

• fastcircle - the smallest possible circle is fit around a particle image and the circle diameter is used at the particle diameter. A computationally efficient method which helps produce a simple comparison of particle area to the area of a circle or "area ratio". Particles are rejected if the area ratio is less than 0.1, or the particle size is outside of the size-bin range.

• WaterProcessing - a method of applying "fastcircle" with the addition of stricter roundness criteria to only process particles that are liquid water, as well as a particle size correction factor based on the size of Poisson spots generated when imaging liquid particles. Poisson spots develop due to particle magnification as a result of improper particle placement within the probe's depth of field. When a Poisson spot is detected the area of the spot is measured and compared to to the total particle area. The resulting ratio produces a correction factor which reduces the measured particle size to that of the actual particle (without Poisson magnification). More information on Poisson spot size correction can be found in Korolev (2007), DOI https://doi.org/10.1175/JTECH1980.1. Particles are rejected if the area ratio is less than 0.4 (or less than 0.5 if the particle is 10 or more pixels in size), if the size is greater than 6 mm, or if the corrected particle size is outside of the size-bin range.

• xsize - the maximum difference between shaded pixels is measured across the array (the x plane). Xsize is particularly useful for spinning disc calibrations.

• ysize - the maximum difference between shaded pixels is measured along the direction of airflow (the y plane).

Methods for Processing Partially Captured Particles [processingtype]

default: reconstruction; 
alternatives: allin, centerin;

• reconstruction -

• allin - particles are only processed if they are fully imaged and do not touch an array edge.

• centerin -

Other Settings and Corrective Procedures

• fixedtas - the true air speed of the plane is set to a specific value rather than read in from the data files, default off.

• inttime_reject - apply a particle shattering correction using particle interarrival times, default on.

• project - the name of the project to be used in the particle images and idl routines, default 'UND-North Dakota'.

• stuckbits - correct for errors generated by diodes that are continuously on or off using their neighboring diodes, default off.

• timeoffset - the time in seconds to be added to the probe data if the data acquisition computer clock was incorrect, default 0.