This instrument is part of the Wave Experiment Consortium (WEC) on Cluster.
Its objectives are to:
* measure the electron density via active sounding of plasma resonances; and,
* record via passive wave analysis the natural wave emissions in the high-frequency range, from 4--80 KHz.

    An active sounder can provide the total local electron density, including the cold component, which is the dominant one in many of the regions to be explored. Most of the time, this cold component cannot be obtained from particle experiments, owing to the satellite's electric potential and photoelectron sheath disturbance. The sounder consists of three main parts: 
    
    * a sensitive double-sphere antenna, measuring the AC electric field, provided as part of the EFW experiment; 
    * a transmitter, a receiver, a digital spectrum analyzer, and a controller unit, which form the WHISPER instrument itself; 
    * command and data processing systems, which are part of the DWP experiment.