The liquid water content (LWC) sensor is a device which can be used to measure the above-freezing liquid water content of clouds. The sensor operates by measuring the buildup of water on a thin vibrating wire which is coated with a collection medium. The mass of collected water changes the vibration frequency of the wire. The rate of change of vibration frequency can be used to quantitatively determine the liquid water content of the cloud.
This sensor is very similar to the supercooled liquid water content (SLWC) sensor and, in fact, will also accumulate ice buildup in the event it encounters supercooled liquid water. It is our recommendation that the LWC sensor only be flown when above-freezing conditions are expected. Alternatively, it would be our recommendation that the LWC sensor be flown with the SLWC sensor so that any effects due to the presence of supercooled water may be recognized and dealt with appropriately in the data.
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.
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.