Introduction

The MSU VolcanoSRI Seismic Monitoring Network consists of:

  • Base station composed of the following components:
    • Base station box
    • 900 MHz transceiver antenna
    • USB cable
  • One or more Seismic nodes composed of the following components:
    • Seismic processor node
    • 1-axis Geophone
    • GPS antenna
    • 900 MHz transceiver antenna
    • Battery case
    • Sealed Lead Acid Battery
    • Power cable to connect processor node with battery case
    • Solar Panel (optional)
  • AC Charger

The components making up a Seismic node, once assembled, are contained in two water proof boxes. Both cases are water proofed to an IP67 Rating which protects from dust and against the effects of immersion in water to depth between 15 cm and 1 meter. These cases have been tested for extended periods of time in torrential rain downpours over a period of several days with no evidence of water incursion.

The radios used in the seismic node use the Digi International digital mesh protocol. Nodes in the network can be configured as one of the following types:

  • Coordinator - establishes the network. There should only be one coordinator per network. The basestation is configured as a coordinator.
  • Router - routes messages through the network. Can also originate messages to other nodes.
  • End Node - Originates messages, can not route messages for other nodes.

The radios contained in the processor boxes are configured as Routers. This allows a node within communications range of the basestation to forward messages from nodes that can not directly communicate with the basestation.

Basestation Setup and Software Installation

The base station (show to the right with its 900 MHz antenna attached and provided USB cable) provides communications between a laptop running the Network Monitoring application and the nodes comprising the monitoring network.

The base station connects to the Windows 7 laptop using a standard USB cable (provided). Before plugging in the base station the FTDI USB driver must be installed. This driver can be found here. This executable unpacks the drivers and runs an installation procedure.

Once the FTDI USB driver has been installed the base station may be plugged in using the supplied USB cable. Windows should automatically recognize the device and prepare the driver.

The base station can be used with two different pieces of node management software:

  • XCTU - DIGI International, manufacturer of the radios used, provides this node management software which is used to update the radio firmware as well as viewing/editing any of the radio configuration parameters. This software can be installed using installer found here.
  • SeismicNetworkMonitor - MSU developed software that displays a node connectivity diagram and interprets messages received from the seismic nodes. This software has only been tested on a Windows 7 64 bit system and requires Microsoft .NET 4.0. The Seismic Network Monitor software can be installed using the setup program found here. This installation will automatically download and install .NET 4.0 from the web if it isn't already installed on your system.

Seismic Node Setup and Installation

Installation of a Seismic Node consists of the following steps:

  • Battery installation
  • Processor Box positioning/mounting
  • GPS antenna positioning/mounting
  • Solar Panel positioning/mounting
  • Cable installation

These steps are described in the following sections.

Battery Installation

The Battery Box contains the main battery, a 7ah sealed lead acid rechargeable battery, and a charge controller. The charge controller ensures the solar panel does not over charge the battery.

The battery must be placed in the Battery Box and connected to the charge controller by two push on connectors.

  1. Begin this process by orienting the battery box as shown in the photograph with the black latches toward you and the box hinge facing away from you.
  2. Open the box cover by first releasing the three black latches. The cover should open away from you.
  3. Place the battery in the box positioned in the upper right corner away from you with the terminals facing to the left.
  4. Attach the red wire with the red connector by pushing the connector on the red colored battery terminal.
  5. Attach the black wire with the blue connector by pushing the connector on the black colored battery terminal.
  6. Carefully close the battery box lid ensuring that the internal wires are not crimped by the box lid.
  7. Close the three black latches to secure the cover.

This completes battery installation.

Prior to use the battery should be fully charged. This can be done by attaching the solar panel or through the use of the supplied AC Charger. In either case the battery should fully charge after about 3 hours. You can check the charge state by openning the battery box and observing the LED found on the Charge Controller. If the LED is bright RED the battery is charging. If the LED is has a green tint the battery has reached full charge.

Processor Box positioning/mounting

How the processor box is positioned depends on the distance between nodes and the physical terrain. When the distance between nodes is < 50 meters over flat terrain the boxes can simply be placed on the ground and the radio antenna directly attached to the box. For installations where the distance between nodes is > 50 meters or the terrain is hilly it may be necessary to elevate the antenna to ensure reliable communication. The antenna can be elevated using one of two methods:

  1. Connect the antenna directly to the processor box and mount the entire assembly to a short post driven into the ground. The "Typical Installation" shows this type of mounting.
  2. Attach the antenna to a bracket mounted on a post driven into the ground. The processor box can then be placed on the ground with the antenna connected to the box using a coax extension cable (not included). This cable should have the appropriate RP-SMA connectors on each end. This cable should have a RP-SMA Female Jack with male pin on one end and a RP-SMA male plug with female socket on the other end. Ensure that the connectors are properly waterproofed.

GPS antenna positioning/mounting

The GPS receiver contained in the processor box has an internal chip antenna. If the processor box is mounted horizontally (clear cover facing the sky) and the unit has a clear view of the full sky, this internal antenna may be sufficient for the GPS receiver to track a sufficient number of satellites to obtain an accurate position fix. If the terrain is rugged or the unit does not have a clear view of the sky the external GPS antenna (see photo) should be used. This is an active antenna that boosts the satellite signals by 24 dbm. This external GPS antenna has a built in magnet allowing it to be attached to any bracket (not included) with magnetic properties. If the processor box or antenna is attached to a pole it is convenient to attach this bracket to the same pole. This type of mounting is shown in the "Typical GPS Antenna Mounting" picture. This antenna has an 18 foot cable allowing it to be placed substantial distance from the processor box if needed.

Solar Panel positioning/mounting

If the seismic node is going to be operated for extended periods of time exceeding 2 days a solar panel should be used to keep the battery charged. A 20 watt solar panel is sufficient to maintain battery charge even on relatively cloudy days. The solar panel should be set at a slight angle facing south to maximize the amount of solar radiation it receives. If the antennas or processor box is attached to a short pole to provide elevation the solar panel can be leaned against this pole as shown in the photograph. For long term installations a bracket (not included) should be used to attach the solar panel to the pole ensuring that it doesn't shift positions in adverse weather conditions.

Cable installation

Once all of the components have been position it is time to connect the various cables to the boxes. When refering to the connectos on the processor box it is assumed that the box is oriented as shown in the "Processor Box" picture.

NOTES:

  1. The polarity of the GPS and radio antenna connectors are different so it is not possible to attach them to the wrong connector.
  2. The power and Geophone use the same type of connector. DO NOT MIX THESE TWO CONNECTIONS.

Cable the units as follows:

  1. Begin by attaching the external GPS antenna to the processor box by inserting the RP-SMA connector to the right most gold receptacle. Ensure that the connector is tightened sufficiently.
  2. Next attach the radio antenna by attaching it to the left most gold recepticle. Ensure that it is tightened sufficiently.
  3. Attach the geophone to the processor box by inserting its cable plug into the right most black connector (the one closes to the GPS antenna connection) aligning the white arrows. Press the Geophone spike firmly into the ground to ensure good mechanical coupling with the ground. It may also be desireable to bury the geophone a few inches below the surface.
  4. Attach the solar panel to the battery box. Either connector on the battery box can be used. Make sure the white arrows are aligned.
  5. Attach one end of the gray power cable to the other connector on the battery box. Make sure the white arrows are aligned.

As soon as the last power cable is attached the node will initialize and begin operation.

Typical Seismic Node Installation
Typical Node Installation
Basestation and USB Cable
Basestation with USB Cable and Attached Radio Antenna.
Battery Box with Battery
Battery Box and Battery
Battery Box Internal View
Internal View of Battery Box with Battery Installed
Processor Box with Radio Antenna
Processor Box with Radio Antenna
External GPS Antenna
External GPS Antenna
Typical GPS Antenna Mounting
Typical GPS Antenna Mounting
Node Cabling
Node Cabling

Operation

Configuration and operation of the Seismic Network is controlled by two pieces of software:

XCTU Node Management Software

XCTU is a utility produced by Digi International for use with the XBEE radio modules used in the MSU VolcanoSRI seismic nodes. It provides the following node level functions:

A user guide describing the use and operation of the XCTU software can be found here.

Seismic Network Monitoring Software

Seismic Network Monitoring Application Main Screen
Seismic Network Monitoring Application Main Screen

The Seismic Network Monitoring (SNM) Software was developed by Michigan State Univerity Department of Computer Science and Engineering using Visual Studio 2010. It provides a graphical representation of the seismic network nodes and communication paths as well as displaying messages send by the seismic nodes. When first started the user is presented with a dialog box allowing them to select the communication port the basestation is attached to. Once connected to the base station the main screen will appear. This screen is divided into two panels. The left panel displays the seismic network while the right panel is used to display messages from the nodes. Initially both panels will be empty.

As nodes come on-line the following messages should appear:

This application initiates a network discovery process upon initial startup and at 5 minute intervals. The lines connecting nodes on the network diagram represent the communications paths. Near the center of these lines are numbers that show the signal strength on the communications path between those two nodes.

Positioning the cursor in the left panel and right clicking brings up a context menu with the following operations:

Positioning the cursor in the right panel and right clicking brings up a context menu with the following operations:

Seismic Node File Formats

When running each Seismic Node samples its attached geophone a 100 samples per second. These samples along with detected p-Phase events are stored in a files on the node's SD card. These files can be found in the \seismic directory. They are named:

where YY is the 2-digit year, MM is the current month and DD is the current day of the month

Both files are text format Comma Separated Value (CSV) files. Each record in the Seismic sample file represents one sample and has two fields: 64 bit UNIX timestamp in milliseconds the sample was obtained; the reading. The readings saved in the file are the raw geophone reading after being filtered by a 2hz to 10hz band pass filter. This filter rejects frequencies outside this band pass to -80db.

The p-Phase event file has one record for each seismic event detected. Each record has two fields: address of the node in 16 digit hexadecimal format, 64 bit UNIX timestamp in milliseconds the event occurred.