Measuring the shortest change, to give the longest warning – how it works
A tsunami wave in deep water creates a small (a little as 3 cm) but measurable change in pressure that can be maintained in excess of 20 minutes.
The sensitive pressure sensor in the BPR detects the small, but continuous change in water pressure, which triggers transmission of a series of warning messages to a surface buoy moored above it. This means that the first message warning of a tsunami, caused by a small variation in water pressure on the seabed thousands of miles from shore, can be in the office of the monitoring organisation within minutes, if not seconds.
The Tsunami Early Warning System (TEWS), developed by MSM Ocean and Sonardyne, centres around a sophisticated Bottom Pressure Recorder (BPR) deployed on the seabed. This modified Compatt 6 transponder works in conjunction with a surface buoy and onshore control centre to create a comprehensive tsunami detection network.
The BPR operates at depths up to 7,000 m and features impressive longevity, running for four years on standard power or up to nine years when housed in a glass sphere configuration. Operating in the LMF band (14-20 kHz), the device samples water pressure every 15 seconds and typically transmits data hourly to the surface. The system is compatible with various surface transceivers, including our Ranger 2 USBL system.
The detection process is both sensitive and precise. The BPR can identify pressure changes as small as 3 centimetres, using the NOAA DART® algorithm to compare measured pressure against predicted values. When two consecutive variations exceed the preset threshold (typically 3cm), the system enters alert mode. Data is then transmitted acoustically to the surface buoy, which relays the information via dual Iridium satellites to the shore. This entire alert process takes only minutes to complete.
System management is streamlined through the NETCOM-TS web application, which provides comprehensive control and monitoring capabilities. The data is shared with NOAA’s National Data Buoy Center, ensuring broad distribution of critical warning information. The system can be configured remotely, and maintenance is straightforward thanks to an acoustic release mechanism that allows for simple recovery and redeployment. Unlike some competing systems, this solution requires no underwater cables, making it particularly reliable and easy to maintain.
This integrated system serves as a crucial link in the chain of tsunami detection and warning, providing coastal communities with vital advance notice of potential threats. By combining robust hardware with sophisticated detection algorithms and seamless communication protocols, the system delivers a dependable early warning solution that can save lives and property in vulnerable coastal areas.
