Envirtech Tsunami Warning System
 

(This paper has been extracted by presentation to United Nation - Unescap - High Level Expert Group meeting  on technical options for disaster management systems - Bangkok June 22, 2005 and further improvements following best practice).

Introduction

In this technical sheet an innovative and reliable system able to forecast and measure the arrival of a tsunami is described. It is the result of several experiences of the Italian company Envirtech S.p.A. in marine project combining the company competence in the scientific/environmental field, the newest offshore technologies, the more advanced electronics and data management and communication solutions and the knowledge of logistic/operational aspects related to the installation of sea surface buoys, underwater systems, control centre and geographical scale alarm systems. This page concerns only  the ocean side segment.

Architecture

The system is composed of the following main parts:

1. In underwater monitoring module (UM) installed at the seabed;

2. a surface buoy (SB) moored in the area of the UM;

3. an “in water” communication segment connecting the UM with SB;

4. an onshore centre (OC) hosting a standard PC server;

5. a satellite communication segment connecting SB and OC.

Two different classes of underwater modules have  been developed to comply with different types of applications. Basically the two Classes differ for the instrumentation embedded, in consideration of the distance between the  tsunami-genic sources and the most close coastal regions.

Poseidon Class   UM

(see test at sea  video stream), (see also deployment of DS2 in the Andaman Sea)

Are standard deep ocean real time Tsunami monitoring systems based  on sea levels measures. The systems are deployed in free-fall assured to their buoyancy line, after a brief survey of the seabottom in the deployment area. Typically the system fall speed measured is 1.6 meter/sec, so to cover 4000 meters the system will need about 40 minutes.

This devices can be used when the distance between the coast and the tsunamigenic source consent at least one hour of early alarm after that the tsunami waves have been  measured. Tipically the deployment distance is more than 1000 Km off shore. The maximum deployment depth is 5000 meters.

Respect to competitors  devices  the systems have been improved using a robust stainless steel frame hosting all components  in titanium vessels. A new, very low power consumption, computer (Arm Technology) and a  very powerful litium power pack capable of two years authonomy have been used.  One paroscientific pressure sensor has been used for tsunami waves measure.

The Poseidon class UM have been designed to be always recoverable using an indipendent system for ballast release. In this manner, avoiding to use the same device both for acoustic transmissions and ballast  release, the operators will be sure to have always a chances to recover the unit after an eventual system failure or for routine maintenance.

After that a Ballast release command has been dispatched the underwater module will pop-up from the ocean bottom at a speed of  1.2 meter/sec - An optional radio beacon could be used in addition to the embedded radar reflector to speed-up  recovering of the device when the ocean surface will be  reached.

Vulcan Class   UM

The devices in the vulcan class are basically realtime seafloor observatories with high performance and capability to collect many different parameters transmitting them to the surface with high throughput.

These equipments should be used when the coastal region to protect is too close to the tsunami-genic source. In fact in these cases should be acquired any precursor of  tsunami-genic event. The Vulcan Class seafloor observatories have the same basic performances of the Poseidon Class devices but are also capable to collect data coming from broadband seismometers, Hydrophones, Adcp and water quality probes. These devices are deployed using a mooring line (not freefall) and represent by themselves the dead weights for the surface buoys used for satellite data relay.

Surface Buoy

The SB  is composed by a metallic pole and a foam body having a diameter of 1.45 m. The main parts installed on the buoy are: 

1. the electronic box containing the SB Data Acquisition and Communication System (SB-DACS) relied on the same type of electronics of the UM;

2. an autonomous power supply system composed of 3 photovoltaic panels (12V- 50W each) and a gel battery pack (12V- 400Ah);

3. a magneto-inductive surface modem or the acoustic modem for the data link with the underwater unit;

4. a satellite modem Inmarsat C for reliable data connection with the Onshore Centre (OC);

5. a meteorological station (optional);

6. a multi-parametric probe to monitor the main physical/chemical properties of the surface water layer (optional).

System Functionalities

The TWS provides the main basic functionalities listed below:

1. F001: continuous measurement of the sea bottom pressure with a rate of 15s, 30s, 1min, 2min, 5min selectable be the user in the OC. Optional monitoring of earthquakes occurence.

2. F002: on line processing of the pressure data with a digital Kalman filter to detect a frequency component typical of a tsunami: the thresholds for the detection of tsunami waves can be configured by the OC user.

3. F003: the beginning of a possible event is automatically triggered by the pressure sensors (able to detect earthquake waves) and also by the hydrophone/seismometer if installed in UM.

4. F004: the UM can start the tsunami detection algorithm also on user request from the OC in case of identification of seismic activity in the interested area.

5. F005: daily synchronisation of the SB and UM clock with the GPS.

6. F006: self-diagnostic and periodical notification to the OC.

7. F007: internal logging in UM and SB of all acquired data, all detected events, all diagnostic status and exchanged messages (black box).

8. F008: remote configuration of the UM (change of communication settings, filtering parameters, on/off of sensors and devices, software updating).

9. F009: reception of commands from OC and notification of its execution;

10. F010: reception of data request from OC and reply with the requested data.

The main scenario in case of detection of an anomaly in the pressure signal is the following: 

1. the UM-DACS in its standard operating mode IDLE MODE detects an unexpected variation in the pressure signal;

2. a notification message is sent to the OC and the UM-MODULE changes in the new status ALARM MODE;

3. in ALARM MODE the UM sends periodically a message to the OC: on request the user in the OC can transfer all pressure data acquired in ALARM MODE.

4. In case of detection of a tsunami events (frequency component in the range 0.01..0.0005Hz) an TSUNAMI DETECTION message is sent to the OC.

5. The user in the OC can verify the pressure data acquired during the ALARM MODE to validate the alarm condition and to verify its amplitude.

6. After the decrease of the tsunami wave components under some minimal threshold (parameter remotely configurable by the OC user) and after a period of some hours (parameter remotely configurable by the OC user), the UM chages from ALARM MODE to IDLE MODE.

Comparison with NOAA DART system

Respect to the NOAA DART system, the Envirtech TWS implements more reliable and robust technologies/solutions: the main differences are summarised here below.

In the Envirtech TWS a dedicated mechanical frame for the UM has been designed and developed: in the DART system the supporting frame for sensors and electronics is a sort of simple table not able to protect adequately the devices;

Envirtech TWS does not use glass spheres that can be dangerous during the installation and recovery phase: the implosion of a glass sphere can damage the other devices;

Robust titanium vessels are used in Envirtech TWS.

High reliability and energy capacity primary Lithium battery are used in Envirtech TWS respect to the standard Alkaline D-Cell powering the DART.

The electronics of Envirtech TWS system is relied of ARM microprocessor with RISC architecture whereas the DART uses a Motorola 68332 that is becoming obsolete.

In the Envirtech solution a well integrated seismometer can be used to implement event driven solutions capable to increase alarm reliability and tsunami-genic events  models tuning.

In the Envirtech TWS,  reliability of the whole system during the installation/recovery phases and during the working period at the sea bed is not comparable with Noaa Dart. Taking into account the type of application of these systems (they are installed to save human life) and the high logistic costs for their installation and maintenance in open sea, a significant increase in the system reliability deserves higher priority respect to an initial partial reduction of materials expenditures.