How the system works
The system has two operation modes - 'standard' and 'event'. It generally operates in 'standard' mode, where it routinely collects sea level information and reports via satellite at relatively low frequency transmission intervals (i.e. every 15 minutes). This helps to save battery life and hence extend the deployment life. The tsunami buoy is triggered into 'event' mode when the pressure sensor first detects the faster moving seismic wave propagating through the sea floor. It then commences reporting sea level information at one minute intervals to enable rapid verification of the possible existence of a tsunami. The system returns to standard mode after 6 hours if no further seismic events are detected.
Data from Envirtech's tsunami buoys, via the Control Center (Download Specifications) are made freely available to the international community and the tsunami warning centres of other countries in real-time using the World Meteorological Organization's dedicated Global Telecommunication System (WMO GTS).
Standard operation Mode
In Standard Operation Mode the sea level is transmitted to the surface every 15 minutes and reach the control centre in few seconds via Inmarsat communications. On the right, the chart shows the tide in the Andaman Sea as collected by the UM2 of the Thailand Tsunami Warning System during the last 15 days of 2010. The underwater module UM2 has been deployed on a seabed 2,640 meters deep and its pressure sensor has an accuracy of 1 part per million so it is capable to detect 1 mm of sea level variation in 1 thousand meters of water column. Meteorologic weather and sea waves cannot influence the measure cause the water column acts as a low pass filter (Courtesy NDWC Thailand).
Event Operation Mode
The Underwater Module detects by itself the presence of a "special" event and starts to operate in Event Mode. The sea level is acquired every 15 seconds and collected data are transmitted to the surface each minute. In few seconds data arrives to the Control Centre and an alarm procedure is raised.
Next chart shows the October 2010, Sumatra event, as collected by an Envirtech Tsunami buoy deployed in South China Sea, 2,600 Km far the earthquake epicenter on a seabed 4,400 meters deep. The seismic waves reached the Underwater Module few minutes after the earthquake, setting it in Alarm mode (Courtesy SOA - China). No tsunami followed the event in South China Sea.
Envirtech tsunami detection buoys (Download Specifications) are designed, built and deployed to assess the tsunami waves accurrence. These buoys measure the sea level out in the deep ocean. This enhances the capability for early detection and real-time reporting of tsunami before they reach land, to support public authority to raise an evacuation command.
The tsunami buoy system comprises two components: the underwater module (UM), anchored to the sea floor, and the surface buoy. The sensors on the sea floor measure the change in height of the water column above by measuring associated changes in the water pressure. The water column height is communicated to the surface buoy by acoustic telemetry and then relayed via satellite to the tsunami warning centre.
The buoy, is a SPAR buoy with high stability to maintain a good horizontal plane also in case of big waves. To increase the data throughput the acoustic modems have been installed at the end of the underwater pole. Each buoy has two completely separated payloads to implement redundancy. It is well known that most of issues at sea can be solved with a complete single redundancy. So each buoy has 2 acousitc Rx/Tx modems, 2 CPUs, 2 Inmarsat-C transceivers etc. Both systems are in warm back-up and powered by an high insulation power supply based on batteries and solar panels. The system development required more than 8 years of test and tune to reach the 100% of real time collected data in a 2 years unmanned operational cycle. At present Envirtech buoys are the most reliable Tsunami buoys available on the market.
Tsunami Event at Envirtech BPR
Next chart shows a Tsunami crossed the Envirtech BPR in Andaman Sea, on a sea bed 3,200 m deep, on September 2007. In this case after recorded the seismic P-Waves the BPR also transmitted the Tsunami waves data. To better show the event, the TIDE has been filtered (Courtesy NIOT - India).