First correlated measurements of the shape and light scattering properties of cloud particles using the new Particle Habit Imaging and Polar Scattering (PHIPS) probe

摘要

Studying the radiative impact of cirrus clouds requires knowledge of therelationship between their microphysics and the single scattering propertiesof cloud particles. Usually, this relationship is obtained by modeling theoptical scattering properties from in situ measurements of ice crystal sizedistributions. The measured size distribution and the assumed particle shapemight be erroneous in case of non-spherical ice particles. We present here anovel optical sensor (the Particle Habit Imaging and Polar Scattering probe,PHIPS) designed to measure simultaneously the 3-D morphology and thecorresponding optical and microphysical parameters of individual cloudparticles. Clouds containing particles ranging from a few micrometers toabout 800 μm diameter in size can be characterized systematically withan optical resolution power of 2 μm and polar scattering resolution of1° for forward scattering directions (from 1° to 10°) and8° for side and backscattering directions (from 18° to 170°). Themaximum acquisition rates for scattering phase functions and images are262 KHz and 10 Hz, respectively. Some preliminary results collected in two icecloud campaigns conducted in the AIDA cloud simulation chamber arepresented. PHIPS showed reliability in operation and produced sizedistributions and images comparable to those given by other certified cloudparticles instruments. A 3-D model of a hexagonal ice plate is constructedand the corresponding scattering phase function is compared to that modeledusing the Ray Tracing with Diffraction on Facets (RTDF) program. PHIPS is ahighly promising novel airborne optical sensor for studying the radiativeimpact of cirrus clouds and correlating the particle habit-scatteringproperties which will serve as a reference for other single, ormulti-independent, measurement instruments.