Wind/Waves Antenna Length Determined Using Quasi-Thermal Noise Spectroscopy

The Wind/Waves instrument has been collecting in situ electric field measurements in the solar wind as well as Earth's magnetosphere and geotail since 1994. The Thermal Noise Receiver (TNR) sub-instrument uses a wire dipole made of very long and thin whip antennas, highly convenient for Quasi-Thermal Noise (QTN) measurements. The instrument team has determined that twice during the mission, in 2000 and 2002, one of the antenna arms broke, changing the antenna response to plasma fluctuations. In this note, we use the QTN spectroscopy method developed specially for the TNR to determine the antenna length after each of these breaks. By parametrically varying the value of the antenna length used in the QTN calculation, we find that initial 50 m long antenna arm was initially shortened to ∼25.5 m in 2000, and then to ∼20 m in 2002.