The Particle Habit Imaging and Polar Scattering (PHIPS) is an airborne single-particle cloud probe that combines two measurement systems. A stereo-microscopic imager captures two bright-field images of individual cloud particles. The two images are taken with a separation of 120° and they have an optical resolution that ranges between 7.2 and 2.35 μm depending on the magnification settings. Individual images are later analyzed for the particle properties that include projected area, perimeter, area equivalent diameter, maximum diameter, the diameter across the maximum diameter, aspect ratio and roundness for both images respectively.
The second measurement system is a polar nephelometer where the light scattered by single cloud particles is collected by 20 detectors placed at equidistant angular distances of 8° in the angular range from 18 to 170°. The polar nephelometer uses a 532nm laser light for the measurements. The scattered light intensity is given as unit counts that can be roughly be converted into nano watts with a calibration coefficient. More details of the instrument setup and a comprehensive calibration can be found in the references.
Schnaiter, M., Järvinen, E., Abdelmonem, A., Leisner, T., "PHIPS-HALO: The airborne particle habit imaging and polar scattering probe - Part 2: Characterization and first results.", Atmospheric Measurement Techniques, 11, 341-357, 2018, doi:105194/amt-11-341-2018.
Abdelmonem, A., Järvinen, E., Duft, D., Hirst, E., Vogt, S., Leisner, T., Schnaiter, M., "PHIPS-HALO: The airborne particle habit imaging and polar scattering probe - Part 1: Design and operation.", Atmospheric Measurement Techniques, 9, 3131-3144, 2016, doi:105194/amt-9-3131-2016.