A 2D-S instrument is a cloud particle probe that contains two orthogonal open path optical array probes, which image cloud particles between about 10 microns - 2 mm in size as they pass through the instrument sample volume.  This imagery is used to calculate the concentration and cross-sectional area size distributions, and to estimate the mass size distribution of the observed cloud particles.  These variables are integrated across the size bins to obtain the total concentration, extinction, and estimated total water content over the observed size range, and is provided at a frequency of 1 Hz.  The particle imagery can be utilized to infer cloud particle phase.  This data does not cover the full size range of cloud particles, and should be analyzed in conjunction with complementary cloud probes, such as the CDP, HVPS, etc.  This dataset contains Fast 2D-S imagery collected aboard the NCAR C-130 during the CAESAR project.