Abstract

The ICEMET-sensor is a novel cloud droplet and particle imaging instrument which measures icing conditions by determining the number and sizes of the supercooled droplets in a known air volume. The sensor captures digital holograms from 0.5 cm 3 sample volume with a maximum rate of 3.0 cm 3 /s. This lensless imaging instrument uses a computational imaging method to reconstruct the shadow images of the objects in the measurement volume. The size, position and shape descriptors of the individual particles and droplets are calculated and saved into a database. This data can be used to separate between cloud droplets and other particles. The calculated features are used to determine the two essential parameters needed for ice accretion modeling according to the ISO 12494 icing standard: liquid water content (LWC) of the air and median volume diameter (MVD) of the droplets. The basic working principle of the sensor and the image processing method are described. The performance of the sensor was tested in a wind tunnel under mixed-phase icing conditions. The measured LWC and MVD values were used to model ice accretion using the ISO 12494 icing standard for rotating cylinders. The modeled ice accretions were compared with weighed ice masses obtained from the wind tunnel with the same sized cylinder. The results show that accurate droplet size measurement and separation between droplets and ice crystals are essential for estimating the ice accretion rate properly. Without filtering out the ice crystals, the calculated accretion rates were overestimated by 65.6 % on average.