HADES-Hydrophone for Acoustic Detection at South Pole

The South Pole Acoustic Test Setup (SPATS) is located in the upper part of the optical neutrino observatory IceCube, currently under construction. SPATS consists of four strings at depths between 80 and 500 m below the surface of the ice with seven stages per string. Each stage is equipped with an acoustic sensor and a transmitter. Three strings (strings A-C) were deployed in the austral summer 2006/2007. SPATS was extended by a fourth string (string D) with second generation sensors and transmitters in 2007/2008. One second generation sensor type HADES (Hydrophone for Acoustic Detection at South Pole) consists of a ring-shaped piezo-electric element coated with polyurethane. The development of the sensor, optimization of acoustic transmission by acoustic impedance matching and first in situ results will be discussed.