GITEWS (German Indonesian Tsunami Early Warning System) is a project of the German Government at the reconstruction of the tsunami-prone region of the Indian Ocean. Aim was to create an early alert system to protect the countries around the Indian Ocean, that were affected by the disastrous Tsunami in 2006. The sensors of this system needed to comprise seismometers, GPS instruments, tide gauges and buoys as well as ocean bottom pressure sensors.
After extensive benchmarking of various international competitors, the develogic HAM.NODE Hydro Acoustic Modem was chosen as the sole subsea communication system for transmitting sensor data from the ocean bottom to the surface data buoys.
The HAM.NODE surface modem is installed in a custom mooring frame below the data buoy and relays sensor data from the bottom modem to the buoy controller.
For lower operating cost the surface modem is powered from re-chargeable NiMH batteries. Charge management is handled by the optional HAM.NODE Power Management Module.
The bottom modem is mounted to an ocean bottom unit and directly interfaces to a Paroscientific precision depth sensor and a SEND Geolon MTS seismic recorder system. The bidirectional transmission of sensor data between bottom and surface modem is per-formed using OFDM-mDPSK modulation with MF directional transducers. Typical net user data rates up to 3,400bps can be achieved with this setup across near vertical channels of up to 6,500m depth.
Besides conducting data transmission, the customizable application layer of the HAM.NODE bottom unit also records pressure data and is responsible for detecting tsunamis on the recorded pressure data.