Simultaneous Cloud Particle Imaging and Angular Light Scattering Measurements with the Novel PHIPS-HALO Probe

To understand the radiative impact of ice clouds we need to know the link between ice particle microphysical and single-scattering properties. Up to date this has been done by creating and improving numerical models that try to accurately represent the ice crystal geometries found in in-situ measurements. However, there are still considerable uncertainties in the scattering properties of the modeled ice particle geometries. A direct way to measure the ice crystal scattering properties is with a polar nephelometer, although to get enough signal the in-situ polar nephelometers need to integrate over a cloud particle ensemble. There has been attempts to link the measured ensemble angular scattering function to cloud particle microphysical measurements but until now it has not been possible to simultaneously measure the microphysical and scattering properties of single ice crystals with an in-situ instrument.

To improve the knowledge of single-scattering properties of atmospheric ice crystals and to provide an unique data set to aid the validation and improvement of scattering models led to the development of the particle habit and polar scattering probe (PHIPS-HALO). The PHIPS-HALO is a combination of a particle imager and a polar nephelometer. Two cameras take stereoscopic images of single cloud particles that can be used to reconstruct the particle morphology (or shape) and orientation with respect to the laser beam - an information important for the modeling aspects. Simultaneously the angular scattering function from 18° to 170° is measured with the angular resolution of 8°.

In this contribution we will show the operation principle of the PHIPS-HALO instrument and discuss the first results from cloud chamber tests and from field campaigns. The PHIPS-HALO was successfully operated onboard the German HALO aircraft during the ACRIDICON-CHUVA campaign in Brazil in 2014. We will present an unique dataset of the combined microphysical and scattering properties of tropical ice crystals. We will also discuss the application of the instrument to discriminate between ice particles and liquid droplets in mixed-phase clouds and give an insight to the plans for further instrument developments to broaden the knowledge of the optical properties of cloud particles.