  In this paper acoustic transmitters that were developed for use in underwater
neutrino telescopes are presented. Firstly, an acoustic transceiver has been
developed as part of the acoustic positioning system of neutrino telescopes.
These infrastructures are not completely rigid and require a positioning system
in order to monitor the position of the optical sensors which move due to sea
currents. To guarantee a reliable and versatile system, the transceiver has the
requirements of reduced cost, low power consumption, high pressure withstanding
(up to 500 bars), high intensity for emission, low intrinsic noise, arbitrary
signals for emission and the capacity of acquiring and processing received
signals. Secondly, a compact acoustic transmitter array has been developed for
the calibration of acoustic neutrino detection systems. The array is able to
mimic the signature of ultra-high-energy neutrino interaction in emission
directivity and signal shape. The technique of parametric acoustic sources has
been used to achieve the proposed aim. The developed compact array has
practical features such as easy manageability and operation. The prototype
designs and the results of different tests are described. The techniques
applied for these two acoustic systems are so powerful and versatile that may
be of interest in other marine applications using acoustic transmitters.
