The supercooled liquid water content (SLWC) sensor is a device which can be used to measure the supercooled liquid water content of clouds. The sensor operates by measuring the buildup of ice on a thin vibrating wire. The mass of the ice changes the vibration frequency of the wire. The rate of change of vibration frequency can be used to quantitatively determine the supercooled liquid water content of the cloud.
The sensor is primarily intended to be flown on sounding balloons and used at such velocities (3-5 m/s). Other configurations of the sensor are possible for surface-based, extended operation, and UAV applications; please contact us for details.
This version of the SLWC sensor has been generally but not completely replaced by a single-wire version of our Universal Water Content sensor. We understand some users prefer this type and will keep it available as long as we can.
The SLWC sensor is designed to pair with any radiosonde capable of accepting the XDATA digital data format. The vibration frequency of the wire is reported to 0.02 Hz every 3 seconds.
The rate of change of vibration frequency (df/dt) is one part of the SLWC determination. Additional information which must be known or estimated includes the rise rate of the balloon (or airspeed of the platform) and the median volume diameter (MVD) of the cloud droplets. Complete data reduction procedures and equations are given on our Cloud Sensor Resources page. Another example of complete data reduction is given by Serke et al.1
Simply observing the rate of change of vibration frequency (df/dt) enables the detection of ice buildup on the wire. This can be useful for the sensitive and rapid detection of icing conditions which could adversely affect the operation of a UAV or icing-sensitive instruments. In typical clouds at low airspeeds (balloon ascent rates of 3-5 m/s), the df/dt change is visible within several seconds. At higher airspeeds, the rate of change will be noticeably faster.
1Serke, D. et al. "Supercooled Liquid Water Content Profiling Case Studies with a New Vibrating Wire Sonde Compared to a Ground-Based Microwave Radiometer." Atmospheric Research 149,77-87(2014). DOI: 10.1016/j.atmosres.2014.05.026.