This note applies to the FSSP-100 instrument introduced in about 1976 and which was the standard instrument for measurements of cloud droplet size distributions for about 30 years. These notes come from analysis of old GENPRO routines (g2inp - part of Xanadu) conducted by Al Cooper. The last recorded change to these routines was 1995.
Note that FSSP data from 1981 to 1993 have been converted from GENPRO format to NetCDF.
No bin sizes were recorded with the FSSP data originally stored in GENPRO format. Instead, what was recorded was a range in a variable named FRNG, that had one of the following four values. The meaning was:
range 1: 3 um bins, sizes (bin midpoints) 3 ,6, 9, 12, 15, ... ,45
range 2: 2 um bins, sizes (bin midpoints) 2, 4, 6, 8, 10,..., 30
range 3: 1 um bins, sizes (bin midpoints) 1, 2, 3, 4, 5, ..., 15
range 4: 0.5 um bins, sizes 0.5, 1, 1.5, 2, 2.5,... 7.5
NOTE: Range numbers varied in different processors. For the 'DAP" processing that was common long ago the range convention was [0,1,2,3] instead of [1,2,3,4]. This translation applied to RAF GENPRO files. There is some ambiguity regarding Wyoming N2UW files, which used GENPRO format at one time but, I think, may have used the [0-3] range convention.
It is suggested that when you download this data, you extract the variable FRNG and try to determine if it spans the range [0-3] or [1-4], then apply the ranges above as indicated.
Some analyses done by Darrel Baumgardner and others used variable size bins, but this apparently was not included in the GENPRO files but was applied in data analysis. Darrel in particular had variable sizes that accounted for Mie-scattering variability, but this was not part of the archived data.
For more information, see Miller, E.R., R.B. Friesen, "RAF Bulletin 9: Standard Output Data Products from the NCAR Research Aviation Facility" Feb 1989 Pp D.22 (Be sure to find the version with the correct publication date.)
Internal users: Code can be downloaded from http://svn/svn/dmg/stewardship/GENPRO/g2inp