Specifications Seismic System as part of the LOFAR Project Report: GeoLOFAR-004 (DRAFT) Version: 5.0 Date of issue: May 2012 Contact person: Dr. Guy G. Drijkoningen Dept. of Geotechnology Stevinweg 1 2628 CN Delft The Netherlands Tel: + 31- 15 - 278 7846 Fax: + 31- 15 - 278 1189 Email: g.g.drijkoningen@tudelft.
Contents 1 2 3 Introduction ............................................................................................................................... 3 Overview seismic system .......................................................................................................... 4 Local (sensor) fields .................................................................................................................. 6 3.1 Geometry of sensors .......................................................
1 Introduction This document specifies the design and implementation of the seismic system within the LOFAR project. This document results from extensive testing at the Exloo test-site of LOFAR. From the “Project Plan of the Seismic Application in LOFAR” [1] this document refers to tasks 1.1 and 3.6. The structure of this document is as follows: first an overview of the total seismic infrastructure will be given, before zooming in into the different components.
2 Overview seismic system In this section an overview of the total seismic system is given and described. It shows the different subsystems which are described in further detail in subsequent sections. This section describes in a general manner how the sensor network LOFAR is implemented for seismic applications. In Figure 2.1 a drawing is shown which gives the over-all structure. The data start to be sensed by the sensors in the field.
- data-storage and retrieval sites (TNO, KNMI) - data access for users (e.g., TU Delft) This will be done in the following, noting that the discussion on the first item, the local sensor fields, will be the most extensive one.
3 Local (sensor) fields In this section the local sensor fields are further described in detail. First, the geometries as being used within the framework of LOFAR will be described. Next, the hardware will be discussed where its actual specifications are mostly given in appendices. Finally the software active on the local fields will be described. 3.1 Geometry of sensors Two seismic geometries are planned: 1.
Figure 3.1 Configuration of 4C sensors for province-scale network at each antenna field (3 shown here) For the local/km-scale geometry, the sensors will not be placed on any of the antenna fields but somewhere on top of a producing gas field where induced seismicity is occurring. In the horizontal direction, the total seismic wavefield needs to be properly spatially sampled, and this requires a horizontal spacing of 12 m (Drijkoningen [2]).
Figure 3.2 Configuration of 4C and 1C sensors for local/km-scale network. For the final systems, most of the electric and electronics is housed in one cabinet. The hardware components are described in subsection 3.2. From a software point of view the systems are approached in the same way, and are described in subsection 3.3.
3.2 Hardware Most of the electric and electronics is housed in one cabinet. An overview of a system is given in Figure 3.3. GPS-antenna output LAN (optical) control Local Seismic Controller AD controller 10 kHz HC control Analog-to-Digital signal converters control data 10 kHz HC 48 V = AC-to-DC converter 48 V = ( 220V~ to 48V= ) 220 V ~ 220 V ~ 380V separator 4-component seismic sensor 4-component seismic sensor Figure 3.3 Overview of the province-scale network.
AD controller This is a local piece of electronics that is supplied by a vendor so it is off-the-shelf. In the case for the test-site at Exloo, this was supplied by Geometrics Inc. This controller controls the AD converters and makes sure the data is properly transported. A specific task of the AD controller is to use a GPS clock to time-synchronize all AD converters on a common time-base. Local Seismic Controller This is the computer system from TNO on which the local software runs.
over 10 years and that they need to be below the frost region which is often taken as 60cm below the surface. Also, a cable placed at the surface is prone to damage, e.g. due to farming, and also therefore it is desired to bury the cables. Still, one would like to be able to retrieve and/or repair any damaged cable, so the cable should not be too deep. Therefore, it was decided to bury the cables at 1 meter depth.
3.3 Local software components Locally on a sensor field, the different software systems that are running are: - Local Control System - Local Data System - Local Meta-data System Local Control System (LCS) Each site has it own Local Control System (LCS). By means of the LCS the geophones at the site can be configured and monitored. The Local Seismic Controller presented in the hardware description performs all the functions of the LCS.
Local Meta-data System (LMS) At every LOFAR field, meta-data about the local (specific) AD-converter configuration can be entered and queried from the internet by means of the Local Meta-data System (LMS). The LMS also provides meta-information to other local systems like LDS and LCS in a standardized and consistent way.
3.4 Power consumption In this section a summary of the power consumption for the two configurations is given.
4 Central LOFAR network In this section, the bandwidth that is needed for the transportation over the LOFAR network is specified. To this end, a separation is made between two types of measurements: - time-lapse seismic measurements, requiring higher bandwidths temporarily, and - continuous monitoring for seismic interferometry and making use of events.
5 Central System (Rekencentrum Groningen) The central system where all data from all sensor fields come together is at the Rekencentrum at Groningen. At Groningen, TNO has installed its own servers with separate LINUX-based machines. An overview of the different components is given in Figure 5.1.
Figure 5.1. Pictorial overview of the different components, centralized at Groningen.
Central Processing System (CPS) This system is responsible for processing the collected data from the sites. The following processes on this system can currently be identified. - Data reduction/Seismic Interferometry - Event detection Currently, no more processing steps are taken into account. However, because of the very little experience in interferometry, it might be needed, in future, to add extra processing steps to make the results better.
6 Data storage and retrieval sites (TNO, KNMI) The data are only temporarily stored on a storage server at the Rekencentrum Groningen. The ultimate storage will take place at TNO and the KNMI. On the system of TNO, the following software systems will run: - Global Data services System - Global Control System - Global Meta-data System Global Data services System (GDS) After processing the data on the Central Processing System the identified events can be stored permanently.
7 Data access for users (e.g., TU Delft) This section describes the data access from remote sites. Since a lot of seismic data is constantly measured and stored by the LOFAR-network and because many data consumers want to use these data again at any arbitrary moment in time, a graphical tool has been developed that allows the user to get easily certain selections of measured seismic data for further processing at the user’s own local site.
- Query data-function: the query data function helps us to find data files of a certain period in time. We have the possibility to formulate two types of queries: o All data files around a certain event in time or o All data files with a certain time interval. For the use of the website, the reader is referred to appendix H.
8 References [1] Drijkoningen, G.G. et al., 2007. Project Plan of the Seismic Applications in LOFAR. Report GeoLOFAR-002. [2] Drijkoningen, 2007. Design of Seismic network in LOFAR: Testing at Exloo test-site. Report GeoLOFAR-006 [3] Drijkoningen, G.G., J. Brouwer and H. Haak, 2003. Veldtest Meetnet nabij Annerveen, 2003: Metingen, Resultaten en Implicaties, pp.24.
Appendix A: AD converters: The “GeoEel” GeoEel: This system is the system supplied by the vendor Geometrics Inc. It is an off-the-shelf system which is designed for seismic monitoring and not specifically for GeoLOFAR. It contains digitizers, DC/DC power supplies, timing control mechanisms and output over Ethernet lines. It is designed as a field-deployed distributed system. As such it has internal power supplies and processors, and is packaged in a rugged housing, if needed.
Hardware Description The GeoEel system consists of 3 boards in a set, 8 channels per set. The GeoEel consists of the analogue board, the DSP board, and the Ethernet board. Analogue board: - Calibration and reference DAC - ADC converters, with integrated programmable gain pre-amplifiers - Output: serial data stream, each channel read through a MUX - Required input: many registers to be written to set up clock, sample rates, gains, inputs and so on.
Figure A.2. Photo of GeoEel-boards, with 14 8-channel boards. (On the left (white): 48V power supply).
Appendix B: 220V AC to 48V DC converter The Xantrex HPD Series stands for “High Power Density”, providing 300W in a quarter-rack wide chassis. The HPD uses switch-mode technology combined with linear post regulation to provide performance comparable to an all-linear design. (Webpage: http://www.xantrex.com/web/id/84/p/1/pt/27/product.asp) Model: HPD 60-5 M2, with locking knob M13.
En500781-2, EN50082-1 and IEC 1010-1, NRTL/C, CSA certified Analog Programming: Remote On/Off and Interlock Remote Monitoring Over Voltage Protection Trip Range Tracking Accuracy 2-25V signal or TTL-compatible input, selectable logic 0-10VDC for 0-100% or rated vo9ltage or current ±1.0% 3V to full output + 10% ±1% for series operation Figure B.2 Photo of converter of 220V AC to 48V DC.
Appendix C: Sensors and housing C.1. Geophone: SM-6 geophone from Sensor b.v. Specifications SM-6/U-B 4.5Hz 375 Ω (B-coil) Frequency Natural Frequency fn Tolerance Maximum tilt angle for specified fn Typical Spurious Frequency 4.5 Hz ±0.5 Hz 0o 140 Hz Distortion Distortion with 0.7 ips p.p. coil-to-case velocity Distortion measurement frequency Maximum tilt angle for distortion specification < 0.3% 12 Hz 0o C Damping Open-circuit damping Open-circuit damping tolerance 0.
C.2. Hydrophone: Benthos PreSeis 2520 General Characteristics Impedance DC resistance Sensitivity Change vs. frequency Change vs. depth Change vs. temperature Natural frequency Distortion Mechanical Resonance Leads Polarity 1730 Ω nominal at 100 Hz 350 Ω ± 5% at 20o C -206.8 ± 1.5dB re 1V/μPa (4.58μV/μbar) Less than 3.0dB from 10Hz to 1000 Hz Less than 1dB fro 0.3m to 200m Less than 1.5dB from 0o to 50o C 10Hz ± 15 % at 5mV rms output (not specified) Greater than 2.
Figure C.2. Frequency response curves of PreSeis hydrophone C.3. Holder The 3C geophone is put in a special holder as shown in Figure C.3.
Figure C.3. Drawing of the holder for the 3 components of the SM-6 geophone. Photo of holder of 3C geophone, with two components of the geophone partly shown.
C.4. Housing of 3C geophone and hydrophone. In Figure C.4 the drawing of the 4C sensor (geophone + hydrophone) housing is shown. Figure C.4. Drawing of the housing for the 4C (geophone + hydrophone) sensor.
Figure C.5. Photo of housing of 4C sensor. C.5. Casting material As casting material for the housing, Scotch-cast® No.815 Resin is used. It is an unfilled solvent free two component Epoxy Resin for room temperature curing. It is one of a system of products available from 3M Electrical Specialties Division. This product has been used extensively for hydrophones deployed at sea. Its features are: - Good adhesion on metals and different plastics; - Highly flexible; - Low viscosity; - Re-enterable.
Appendix D: Cables The cables chosen needed to be waterproof for duration of 10 years. Poly-urethane (PUR) material is the material which is often used in the offshore industry so are well suited for land applications. The cable from Ehrbecker-Schiefelbusch was chosen: S 200 series.
- Characteristic acc.
Appendix E: GPS antenna GPS antenna, from D.D.S. Electronics. (Webpage: http://www.d-d-s.nl/gps-antenne.htm) Specifications Size Weight Cable Length Connector Type Mounting Power Current consumption Gain 48mm (width x 15 mm (height) x 58 mm (length) 65 grams 3 meter BNC-M Magnet or screws 3 mm 2.5 – 5.0 V DC 6 mA ± 15 % ± 27 dB Figure E.1.
Appendix F: Different scenarios of data rates In this appendix, different scenarios are worked out. For the continuous monitoring 2000 Hz is used. Field type 1 Province-scale field 2D cross (km-scale) # Fields 17 # sensors 6 * 4 component 126 * 4 comp. # channels 24 504 Data transport 1 site of province-scale geometry # channels #Bytes 24 24 3 4 Sample rate (Hz) 2000 2000 MBytes/sec GBytes/day 0.14 0.18 11.59 15.
Appendix G: GeoLOFAR Seismic Control software The following screenshots provide an overview of the web application. Figure 0.1 Main menu This is the main menu for the web Application. From here the user can navigate to the different parts of the application.
Acquisition control Figure 0.2 Acquisition control In this screen an overview is presented of all the configured devices and their state. There are buttons for Connect Establishes a socket connection to every device and activates the selector process that monitors the sockets for traffic and handles it. Start After the socket connections have been established the user can start the acquisition with this button.
Operational settings Through the next 3 screens the user can respectively change general settings, AD-controller (SPSU) settings and AD-converters settings. Figure 0.3 General settings Nr of blocks per sample file: This is the number of sample blocks that are written to one sample file. When this number is reached the current sample file is closed and a new sample file is created. Length of SEGY trace in millisecond: On every site a SEGY file is generated on the fly for monitoring purposes.
Figure 0.
Figure 0.5 AD-converter settings These settings apply to all the AD-converters of a site. Arm mode Calibrate Gain Channel length Coupling Sample rate Continuous or Triggered Not applicable Gain factor Nr of samples per block of data received from the AD-converter Selects AC or DC coupling Frequency with which samples are recorded. 2000Hz means that the device takes 2000 samples per second.
Structural information Figure 0.
Figure 0.7 Overview of structural data for the AD-converters Before an AD-converter can be used in the acquisition process on this site, its structural data has to be configured through this screen. This screen provides an overview of all the AD-converters of the site. It offers the following possibilities Edit opens the edit screen where the different attributes of the structural data of the can be changed.
Figure 0.8 Structural data for a AD-converter In this screen the structural attributes for AD-converters can be changed. This screen is also used for adding a new AD-converter. Identifier IP Address Port Nr X Y sourceDepth waterDepth enabled An identifier that is unique for this site.
Appendix H: Description of the GeoLOFAR-web site Hereafter one can find a functional description of the GeoLOFAR -web site, a description of the data functionality that the web site offers and a brief description of the infrastructure that is used. The GeoLOFAR-web site can be used in a Microsoft Internet Explorer 7 web browser. Other web browser may function as well. The URL of the web site is: http://geolofar.nitg.tno.nl.
Zoom-out, for zooming out of the map by means of a rubber box (mouse drag) or according to a fixed step size; Pan, for moving the map to the right, to the left or up or down (mouse drag); Zoom-full-extent, for zooming to the full extent of the map; Zoom-Lofar-field, for zooming to a particular LOFAR field; Identify, for identifying Seismic sensors and LOFAR fields on the map by showing meta data of these objects and for applying data functions.
selecting the Geophone (mouse click), the corresponding Meta-data will appear in a Popup window. By activating other layers we can select elements of those layers at the map and Meta-data of the elements will appear in the popup window. When we further zoom in to the Exloo field and after we set the City layer to invisible, we get the following screen and we can see the exact position of the available Geophones in the Exloo field.
As we can see in the popup window above, we selected the Exloo field, the status is test and we see that 48 Geophones are connected to the LOFAR network. The number attributes of the LOFAR field entity can be extended in the Meta-data database if desired. H.1. Data-functionality of the GeoLOFAR-web site By means of three buttons in the popup window that has been described in the previous paragraph, we are able to apply three data functions to allow us to get measured data from the selected LOFAR field.
After pushing the data function button, the screen above appears which gives us an overview of all the data files of the selected LOFAR field. This screen allows us to look further for data files of a certain date, by selecting a day in the list (mouse click). Finally we can download the data files by selecting and downloading the files to our local work station. Also it is possible to look for data files in a Windows file explorer.
View-function, the view function gives us a graphical over view of all recently measured data. The overview appears in a popup window and is being refreshed automatically every six seconds. In the overview all measurements of all available data channels are taken into account. Query data-function, the query data function helps us to find data files of a certain period in time.
For the quick retrieval of the desired data file according to the given search criteria, a GeoLOFAR Meta-data database is has been developed. In this database all aspects of the measured data and all the attributes of each data file are being stored. An overview of the structure of the file meta-data-table that is being used to store the Meta-data is given in the next screen. Finally the file meta-data-table will contain many of millions of meta-data attributes of all stored data files.
In this table we can browse through all data files that are adopted in the result. Also it is possible to create an overview from this table with the layout like the one that is being used at the data-button functionality described earlier (Get data (FTP)). The result can also be transformed to a SEGY-format table (Get SEGY Data), so that the data can be used directly in PC-desktop applications that work with the SEGY format. H.2.
CDS (Central Data Storage) Storage QueryServer Groningen.nitg.tno.nl LDS (Local Data System) Viewer GDS (Geo Data System) WebServer Geolofar.nitg.tno.nl Astronbuinen.nema.rug.nl http 80, ftp 21 internet MapServer Kochab.nitg.tno.
Appendix I: Failover and recovery To create a reliable server infrastructure each server type has his own failover system that fits to his purpose. The following Raid options are implemented. Description: RAID 1 is usually implemented as mirroring; a drive has its data duplicated on two different drives using either a hardware RAID controller or software (generally via the operating system). If either drive fails, the other continues to function as a single drive until the failed drive is replaced.
Appendix J: Computer Hardware In this network we identify two types of servers. Depending on the server task a system configuration, failover and recovery plan is made. In a later stadium we may have to reconsider the system configurations storage size depending on the life time of the data.
