The Particle Habit Imaging and Polar Scattering probe PHIPS – A novel instrument for cloud research

To get an in-depth understanding of the radiative impact of ice clouds we need to know the link between the morphology of single ice crystals and their angular light scattering function. Up to date this question has been addressed by developing and improving numerical optical models with increasing degree of microphysical detail. However, the results from optical particle models are still questionable especially when it comes to the effects of ice crystal complexity like hollowness and surface roughness. This was the motivation for the development of a specific airborne cloud probe to address the initial question by an experimental approach.

The Particle Habit Imaging and Polar Scattering (PHIPS) airborne probe is a combination of a cloud particle imager and a polar nephelometer. Two microscopic units take 120° stereo images of single cloud particles that allow for an unprecedented view of the ice crystal morphology as well as the deduction of the crystal orientation with respect to the scattering laser beam of the instrument. The latter information is a prerequesite for any modelling attempts of the simulatneously measured angular light scattering function. This function is measured for the imaged crystals in the angular range from 18° to 170° with a resolution of 8°.

In this contribution we explain the operation principle of the PHIPS instrument and present data from three airborne field campaigns. A unique and comprehensive data set of microphysical properties and correlated angular light scattering functions of single ice crystals is now available that will be discussed. We also give insight into further instrument development plans.