Case study: The Athenet networked seismic array

October 2006

Güralp Systems is assisting in the upgrade and testing of a networked seismic array in Greece, operated by the Seismological Laboratory of the National and Capodistrian University of Athens.

The Athenet seismic network contains 8 stations based around CMG-40T instruments with 30 s – 50 Hz response, which are located up to 150 km from the university's central Athens campus.

The upgraded instruments have been retro-fitted with the latest DM24 digitizer modules.

Data from the instruments will be transmitted over the Internet to the laboratory using Güralp Systems' CMG-DCM and CMG Serial Server units.

Sample hardware has been installed at Güralp Systems' factory for testing, and has been running continuously for some weeks.

Depending on operational conditions, each installation either has a Güralp Systems Serial Server or DCM data communications module to connect it to the network.

Digital streams in GCF format are output direct from the sensor to the network module's serial input port. A number of different telemetry methods are used to transmit the data across the Internet and the Greek academic network, GUNET, to a data centre in Athens. These include terrestrial phone lines, GPRS over 3G mobile phone networks, radio-frequency and VSAT links.

In Athens, data is received and archived in several formats for the use of clients. Real-time monitoring and analysis can be performed in Scream!, SeisComP, or custom programs written in the graphical programming language, Processing.

Test results

Two of the CMG-40TD sensors were set up in the Güralp Systems factory after the new digitizers were fitted.

One of these was connected to a SSU and the Internet. The second was connected to a DCM.

In Athens, a PC running Scream! connected to both installations and was able to receive data reliably.

Data received at Athens from the test installations, generated using Güralp Systems' drumplot software.

Using Scream!, clients can view sensor outputs and mass positions in real time. Comprehensive status information is also transmitted from the digitizer, including GPS status, timing accuracy and internal temperature.

In this test phase, Scream! received data continuously for over a week with no loss of data.

In the next phase, the DCM installation was remotely reconfigured to provide a SeedLink server in addition to the Scream! server. Data was successfully received by SeisComP installations in Athens over this link. Engineers at Güralp Systems worked closely with the seismologists in Greece to identify areas of improvement and eliminate data gaps.

Viewing real-time data in SeisComP.

Data from the installations with Serial Servers can be converted to MiniSEED format in Scream! and imported into the SeisComP system locally.

Next steps

The Seismological Laboratory is currently evaluating operational conditions at each site, and considering plans for future expansion to decide on its exact hardware requirements.

At some sites, accelerometers or other additional instruments are planned for connection to the network. The 40 Gb backup data capacity of the DCM will be used, where available, to record locally at multiple sample rates.

Serial Servers

To connect a simple, single digitizer installation directly to a local area network, Serial Server modules are a robust and cost-effective choice.

The Serial Server.

Connecting to a remote TCP server.

The Serial Server module provides direct access over TCP/IP to the serial data output by the digitizer. Multiple clients running Scream! can connect to the Serial Server's output port and receive streams. Scream! uses a robust block recovery protocol to make sure data blocks are not lost if the TCP link is disconnected.

The SSU allows full configuration and control of digitizers over the network. An RS232 monitoring port also allows data streams to be viewed by a local Scream! installation.

The SSU is designed to give your installation the greatest possible autonomy. An optional internal UPS allows the system to operate for up to 72 hours from an internal battery. Serial Servers of all kinds can operate from either 10 – 24 V DC power or 110 / 240 V AC mains (outlet) power without additional hardware. The unit can also be equipped with a wireless network interface, enabling you to communicate with installations over distances up to 500 m.

DCMs

Stations with several digital instruments, those requiring extended backup capacity, and those with connections to the Internet or other networks will be equipped with CMG-DCM modules.

The CMG-DCM.

SeedLink options.

The CMG-DCM is a custom-designed low power computer running a full Linux operating system.

The unit can receive data from multiple sources and make it available to clients using a number of seismic data protocols, including CD1.1, DSS, Scream! and SeedLink.

Configuration is easily done over a comprehensive Web-based interface, or by connecting directly to the unit and issuing commands. The DCM can also control attached digitizers and sensors, or make them available for control by Scream!. Local users can connect to the DCM using a network hub, or over a serial link, and perform configuration tasks.

The CMG-DCM can be connected directly to the Internet through a firewall, with support for secure HTTP and SSH tunnelling. PPP and advanced modem and telemetry links are also fully supported.

Installation ideas

The DM24 digitizer module can be retrofitted to any Güralp Systems analogue instrument, of any age. Existing 3TD, 40TD or 5TD instruments can also be upgraded to use the new digitizer technology, providing a highly cost-effective route to building state-of-the-art seismic arrays.
The DCM is available as a stand-alone unit as depicted above, or integrated with a DM24 digitizer in a single weatherproof box.
For borehole installations, the DCM and DM24 digitizer can be combined in a single downhole unit, which replaces the strain relief mechanism used in analogue boreholes.

Because data can be emitted directly from the borehole ready for transmission across the network, surface enclosures can be reduced in size.
Installations requiring authenticated data benefit from the strong cryptographic capabilities of the CMG-AM, a data unit based on CMG-DCM technology.



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Sample hardware has been installed at Güralp Systems' factory for testing, and has been running continuously for some weeks. Depending on operational conditions, each installation either has a Güralp Systems Serial Server or DCM data communications module to connect it to the network. Digital streams in GCF format are output direct from the sensor to the network module's serial input port. A number of different telemetry methods are used to transmit the data across the Internet and the Greek academic network, GUNET, to a data centre in Athens. These include terrestrial phone lines, GPRS over 3G mobile phone networks, radio-frequency and VSAT links. In Athens, data is received and archived in several formats for the use of clients. Real-time monitoring and analysis can be performed in Scream!, SeisComP, or custom programs written in the graphical programming language, Processing. Test results Two of the CMG-40TD sensors were set up in the Güralp Systems factory after the new digitizers were fitted. One of these was connected to a SSU and the Internet. The second was connected to a DCM. In Athens, a PC running Scream! connected to both installations and was able to receive data reliably. Data received at Athens from the test installations, generated using Güralp Systems' drumplot software. Using Scream!, clients can view sensor outputs and mass positions in real time. Comprehensive status information is also transmitted from the digitizer, including GPS status, timing accuracy and internal temperature. In this test phase, Scream! received data continuously for over a week with no loss of data. In the next phase, the DCM installation was remotely reconfigured to provide a SeedLink server in addition to the Scream! server. Data was successfully received by SeisComP installations in Athens over this link. Engineers at Güralp Systems worked closely with the seismologists in Greece to identify areas of improvement and eliminate data gaps. Viewing real-time data in SeisComP. Data from the installations with Serial Servers can be converted to MiniSEED format in Scream! and imported into the SeisComP system locally. Next steps The Seismological Laboratory is currently evaluating operational conditions at each site, and considering plans for future expansion to decide on its exact hardware requirements. At some sites, accelerometers or other additional instruments are planned for connection to the network. The 40 Gb backup data capacity of the DCM will be used, where available, to record locally at multiple sample rates. Serial Servers To connect a simple, single digitizer installation directly to a local area network, Serial Server modules are a robust and cost-effective choice. The Serial Server. Connecting to a remote TCP server. The Serial Server module provides direct access over TCP/IP to the serial data output by the digitizer. Multiple clients running Scream! can connect to the Serial Server's output port and receive streams. Scream! uses a robust block recovery protocol to make sure data blocks are not lost if the TCP link is disconnected. The SSU allows full configuration and control of digitizers over the network. An RS232 monitoring port also allows data streams to be viewed by a local Scream! installation. The SSU is designed to give your installation the greatest possible autonomy. An optional internal UPS allows the system to operate for up to 72 hours from an internal battery. Serial Servers of all kinds can operate from either 10 – 24 V DC power or 110 / 240 V AC mains (outlet) power without additional hardware. The unit can also be equipped with a wireless network interface, enabling you to communicate with installations over distances up to 500 m. DCMs Stations with several digital instruments, those requiring extended backup capacity, and those with connections to the Internet or other networks will be equipped with CMG-DCM modules. The CMG-DCM. SeedLink options. The CMG-DCM is a custom-designed low power computer running a full Linux operating system. The unit can receive data from multiple sources and make it available to clients using a number of seismic data protocols, including CD1.1, DSS, Scream! and SeedLink. Configuration is easily done over a comprehensive Web-based interface, or by connecting directly to the unit and issuing commands. The DCM can also control attached digitizers and sensors, or make them available for control by Scream!. Local users can connect to the DCM using a network hub, or over a serial link, and perform configuration tasks. The CMG-DCM can be connected directly to the Internet through a firewall, with support for secure HTTP and SSH tunnelling. PPP and advanced modem and telemetry links are also fully supported. Installation ideas The DM24 digitizer module can be retrofitted to any Güralp Systems analogue instrument, of any age. Existing 3TD, 40TD or 5TD instruments can also be upgraded to use the new digitizer technology, providing a highly cost-effective route to building state-of-the-art seismic arrays. The DCM is available as a stand-alone unit as depicted above, or integrated with a DM24 digitizer in a single weatherproof box. For borehole installations, the DCM and DM24 digitizer can be combined in a single downhole unit, which replaces the strain relief mechanism used in analogue boreholes. Because data can be emitted directly from the borehole ready for transmission across the network, surface enclosures can be reduced in size. Installations requiring authenticated data benefit from the strong cryptographic capabilities of the CMG-AM, a data unit based on CMG-DCM technology.