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The Sea Level Station Monitoring Facility: examine the
performance and delay of 430 tsunami warning stations
Vanhoorne Bart1, Hernandez Francisco1
Flanders Marine Institute (VLIZ) Belgium - Wandelaarkaai 7 – 8400 Ostend – Belgium
– [email protected]
1
Keywords: real-time, satellite, network, sea-level, tsunami, Global Telecommunication
System (GTS)
The Intergovernmental Oceanographic Commission (IOC) together with the Flanders
Marine Institute (VLIZ) is hosting and developing a public accessible website
(http://www.ioc-sealevelmonitoring.org/) that brings together more than 430 sea-level
stations globally.
The objective of the website is:
 to provide information about the operational status of global and regional
networks of real-time sea level stations
 to provide a display service for quick inspection of the raw data stream from
individual stations
A sea-level station consist of one or more of sensors (pressure, radar …) that are housed
near the coast or on a buoy. The sensors are measuring the sea-level on a fixed interval
varying from a second to several minutes or hours. The frequency depends on various
parameters like tsunami risk, power consumption, satellite cover, …. While measuring,
the station transmits the data in real-time to a satellite.
The Global Telecommunication System (GTS)
After the data has been transmitted to a satellite, a ground station picks up the data and
distributes the data through the GTS. The GTS is a global network for the transmission of
meteorological data from weather stations, satellites and numerical weather prediction
centers connected via various point-to-point, point-to-multipoint and multipoint-to-point
circuits. The circuits are composed of a combination of terrestrial and satellite
telecommunication links. Meteorological Telecommunication Centers are responsible for
receiving data and relaying it selectively on GTS circuits.
The use of satellites is preferred above other communication channels like the internet or
cell phone networks, since they may be slow, congested or down. Also, sea-level stations
are often located in very remote places where no other option then satellite is available.
The Sea level Station Monitoring Facility website is one of the many receivers in the
GTS network. The facility decodes and displays the data (which consists different
messages) on the website in a user-friendly way. Graphs, performance and delay are
generated on the fly.
Very recently, the Sea level Station Monitoring Facility also became a supplier of data
towards the GTS system. A number of stations are now equipped with a BGAN
(Broadband Global Area Network) terminal. They are connected directly on the internet
via satellite (i.e. they have an unique IP address) and they transmit their data to the Sea
Level Facility via a web service (HTTP POST). The data is displayed immediately on the
website and the delay is close to 0 seconds, since the database insert is triggered by an
HTTP request and not based on a polling system. At the same time the data is put onto
the GTS.
Performance and delay
For various reasons messages can get lost or corrupted. For this, the performance of each
station is calculated. The performance is the ratio between the number of messages
expected divided by the number of messages arrived.
There is usually a delay between the data being sent by the sea level station itself, and the
data being received by the Sea Level Monitoring Facility. The goal is of course to
minimize this delay by looking at the different parameters and communication channels
in the network.
For doing this, a local database that holds the metadata of these stations is of course
crucial. By allowing any station operator to update his station parameters, we can ensure
that no erroneous delay or performance is reported.
Usage
The website has been used - and proven useful - by various authorities that issue tsunami
warnings. This was clearly visible during both for the last Chilean tsunami (end Feb
2010) and a smaller Indonesian tsunami (end October 2010). The hits on the website
were at least fivefold.