The CPI can image and count particles in the size range of 15-2500um, with the images having a nominal 2.3um resolution. Image analysis and data processing software provided with the probe takes particle size information (including area and volume) and ice crystal habit classification from the images to produce histograms etc. The CPI is especially suitable for use in ice and mixed phase clouds which typically have relatively low (compared to water clouds) particle concentration of 1000/L. The CPI may be used in much higher particle concentrations, but under these conditions while particle spectra are reliable, absolute particle concentrations are not due to coincidence errors in the particle detection system. While designed for aircraft use, and able to operate at any aircraft speed and altitude, the CPI, with the use of a suitable aspiration device may also be used for ground based, or lab studies. The University of Manchester and UFAM (Universities' Facility for Atmospheric Measurements) operated this instrument.