On board the T28 aircraft was a Hail Spectrometer. The probe output 1D data for ?all? of it's flights. The probe had an array of 126 image elements .9mm in size. For the 1D outputs, if say a particle were to block four consecutive image elements, then the system would record the top and bottom blocked diode as the size of the particle and output a sized particle based on that. There is no size dimension along the width of the particle or the direction of travel. Once the diodes were no longer blocked, then the probe would “?refresh?” and wait for the next particle to pass through. Because the probe was made for larger particles, it can be assumed that coincident particles are rare. However, in the event there were coincident particles, unless the probe knew to filter them out and ignore them, then an erroneously large particle could be recorded.

Here is an example of what the data file looks like,

Time is at 1 hertz, and the counts are in 1-14. The size ranges become more spread apart as the channels get larger since there are less large particles.

Size ranges are,

• 01 : 0.40 - 0.50 cm
• 02 : 0.50 - 0.60 cm
• 03 : 0.60 - 0.70 cm
• 04 : 0.70 - 0.80 cm
• 05 : 0.80 - 0.94 cm
• 06 : 0.94 - 1.10 cm
• 07 : 1.10 - 1.30 cm
• 08 : 1.30 - 1.56 cm
• 09 : 1.56 - 1.86 cm
• 10 : 1.86 - 2.17 cm
• 11 : 2.17 - 2.61 cm
• 12 : 2.61 - 3.21 cm
• 13 : 3.21 - 4.00 cm
• 14 : 4.00 - 5.00 cm

With the counts, concentration can be calculated. The basic formula used to calculate concentration is,

  Conc (#/m^4) = Counts / (SA * Airspeed * Binsize change)
  

Where,

• SA is sample area which is (probe arm length * height)
  • Height is (number of diodes * diode size)
• Binsize change is the (Max_Size - Min_Size) for each channel.
  • For channel 1, this would be 0.50 - 0.40 = 0.10

For the 1D data from the Hail Spectrometer, the variables are,

• Probe arm length: 0.93 m
• Diode size: 0.009 m
• Diodes: 126
• Airspeed: ~100m/s
• Binsize change: 0.001, 0.001, 0.001, 0.001, 0.0014, 0.0016, 0.002, 0.0026, 0.003, 0.0031, 0.0044, 0.006, 0.0079, 0.01
• Sample counts data from flight 757, June 22, 2000,

Plugging all of those numbers into the formula, the concentration is calculated for each second and for each channel (where the corresponding binsize change is used for their respective counts).

A plot showing what the 1D Hail Concentration looks like