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Software Development for the Tsunami Buoys and Tide Gauges

The Tsunami Early Warning System comprises four different kinds of sensor systems:

  • offshore GPS buoys including an associated Ocean Bottom Unit,
  • tide gauges including high resolution GPS receivers,
  • GPS "only" stations, and
  • seismic stations partially combined with GPS stations

STI supported GFZ in creating operational concepts and the final implementation of offshore buoys and tide gauges. Both sensor systems have some common requirements as listed below:

  • autonomous operation
  • fault-tolerant on component/subsystem level - derived from reliability and performance considerations
  • provide real-time measurements and observations for the Warning Centre
  • handle parallel and/or redundant usage of satellite communication facilities
  • recognise anomalies (e.g. tsunami wave)
  • monitor and coordinate subsystems within the sensor station
  • perform various tasks necessary for proper station operation

Below an excerpt of software components including some of their main features is provided. All these software components are developed by STI for the German Indonesian Tsunami Early Warning System:

Buoy/Station Management Daemon

A management software to operate autonomous sensor stations in the Tsunami Early Warning System context was needed. Starting from the buoy managment SW the functionality was extended to cope with tide gauge and GPS stations specific requirements. This required a stable, robust and flexible core system which had to be able to cope with faults, anomalies and to provide auto-recovery capability with active health state reporting.

SpaceTech supported GFZ in development of the Station Manager and Buoy Manager Daemon (BMD) respectively. The features include, but are not limited to:

  • manages autonomous field sensor stations
  • observation dependant operation mode switching
  • power management and power dependent operation mode switching
  • commands and controls all subsystems
  • extendable via Plugins with own API
  • data compression and transmission to Warning Centre
  • TCP/IP command and control interface to Warning Centre
  • controls all satellite links to Warning Centre
  • forwards tsunami warnings
  • near real-time data streaming in tsunami mode
  • internally parallel non-blocking task execution
  • programming language C
Buoy/Station Management Daemon structure
Buoy/Station Management Daemon structure

Ocean Bottom Unit Daemon

The Ocean Bottom Unit (OBU) is a measurement device deployed on the sea floor in a depth of up to 6000m. There, it registers

  • seismic events generated by earthquakes and
  • sea level pressure and anomalies e.g. generated by tsunami waves.

Therefore, each OBU is equipped with a broadband seismometer, one differential and one absolute pressure sensors to measure the corresponding data, a datalogger for storage, batteries as a power supply and an acoustic anchor releaser with a dedicated battery.

Both, the buoy and the nearby deployed OBU are equipped with an acoustic underwater modem. In principle, the communication is performed via sonic signals similar to dolphin communication. This communication link is mainly used for sending tsunami warnings to the buoy and data retrieval from the OBU.

The following tasks have been carried out by SpaceTech:

  • driver software for interfacing underwater modems between OBU and buoy
  • command and control of Ocean Bottom pressure sensor and seismometer
  • data acquisition from underwater sensors
  • low and high data rate acqusition (later for tsunami mode)
  • sophisticated timeout and retry mechanisms for communication
  • TCP/IP command interface for Buoy Management Daemon
  • programming language C++

The acoustic link and the complete system has been tested by SpaceTech near Toulon (south of France in the Mediterranean See) in 2008. The OBU was deployed in a depth of 2200m. A tsunami buoy was acting as relay station for data transmission between the OBU and the nearby island via 900Mhz radio transceivers.

The SpaceTech activities (contracted by IFM Geomar institute) included:

  • establishment / debugging of Toulon test configuration and performance of test preparation in Hamburg
  • interface agreement and planning alignment with French institute IFREMER, Toulon
  • negotiation of deployment vessel conditions with local shipyard
  • installation of RF link station on nearby island, Île du Levant
  • coordination of team and deployment of test configuration
  • data retrieval and software adaptations during the test period of 4 month

Battery Management Library and Command Line Tool

Every buoy and tide gauge is equipped with a Battery Manager device. It provides up to 16 power lines to power all measurement and communication devices of a field station. SpaceTech developed the software for this Battery Manager and provided updates for upgraded hardware:

  • driver software for interfacing Battery Manager (e.g. for switching up to 16 power lines)
  • watchdog interface
  • power level based switching of power lines
  • command line tool as well as library implemenation
  • programming language C

Solar Array Daemon

Every buoy and tide gauge are powered by batteries which are charged from solar panels. The charging is controlled by solar controllers (two independent, fault-tolerant strings). SpaceTech designed and implemented an interface software for these solar controllers with the following features:

  • gather data like power income, usage and battery capacity
  • control of different charging models
  • power generator control (for tide gauges)
  • highly configurable data acquisition for ~200 measurement values
  • programming language C

Tide Gauge Daemon & Campbell Research Daemon

The tide gauges collect water level data via two pressure sensors (one located just below the water surface and a second some metres below) and a radar sensor measuring from above the sea surface. All these devices are connected to a datalogger which converts analog signals to digital information. SpaceTech developed the initial software which gathers data from the datalogger via a serial interface:

  • data acquisition software for interfacing different types of data loggers
  • API for live data analysis for scientific algorithms (e.g. tsunami detection)
  • self-test functionality
  • different data acquisition modes
  • programming language C/C++

In the meanwhile, the software has been extended by the GFZ for instant tsunami detection algorithm processing.