PI: |
Ralph J. Archuleta
Institute for Crustal Studies University of California, Santa Barbara ralph@crustal.ucsb.edu |
Project: | Portable Broadband Instrument Center (PBIC) |
Associates: |
Aaron Martin, aaron@crustal.ucsb.edu
Peter Rodgers, rodgers@crustal.ucsb.edu |
Institution: | Institute for Crustal Studies
University of California, Santa Barbara 93106 |
The PBIC took delivery of our first three Guralp CMG-40T sensors in early June. The PBIC was active in Web and software development, response calibration and outreach programs. The PBIC has also been looking at telemetry options for the portable recorders.
Dates | Institution | PI(s) | Experiment |
---|---|---|---|
01/01/96-02/27/96 | UCSB | Archuleta/Steidl | GVDA Rock site |
10/17/96-02/27/97 | UCSB | Archuleta/Nicholson | CLC/SCEC UCSB Hazard Study |
03/04/97-11/21/97 | UCLA | Kohler/Davis | LA Basin Passive Seismic Exp. |
05/13/97-05/15/97 | UCSB | Archuleta/Steidl | CLC Borehole |
08/18/97-current | SDSU | Day/Astiz | Northern Baja Broadband depl. |
At the lowest end of the telemetry spectrum, the DAS would broadcast its status to a central site. This one way communication allows the user to know the operating state of the site. This can be accomplished through use of the ARGOS satellite system. An on-site satellite transmitter broadcasts the DAS status at selected intervals to the polar orbiting ARGOS satellites. The transmitters have requirements similar to the GPS receivers. They need to point towards the sky. Interference should be minimal and typically will not matter since data integrity is not critical for this information. The on-site transmitter costs about $1500 per DAS. The access fee for the ARGOS system would be approx. $5-10/day. This fee gets the data sent to the user automatically at preselected intervals. If the fee has to be paid for each DAS, long-term deployments could become expensive. The benefits of this system are simplicity, flexibility and ease of access.
The next level would be two-way, low-speed communication with the DAS. This could be accomplished via spread spectrum technology or possibly by digital cellular modems. This level of telemetry allows the user to interrogate the DAS, check disk status, event status, and to change parameters. The bandwidth would probably not allow any significant transfer of data. The DAS would record in triggered or continuous mode normally. While the radio links may be somewhat susceptible to noise and interference, this shouldn't pose too much of a problem. For interrogation purposes, the transmission is not critical. If the user wants to send parameters, any interference becomes much more important. Costs of digital cellular phones have been dropping recently as availability has increased. The hardware cost of the major pieces of equipment should be less than that for the ARGOS system, but there may be connectivity issues that require specialized hardware to interface to the DAS.
Yet another level of telemetry would be a high speed one-way or two-way link to send continuous data directly to a central receiving system. The Reftek arrays in Anza and northern Colorado currently use this type of telemetry. Again, spread spectrum technology or digital FM radios could be used. The built-in IRIS/PASSCAL software wasn't originally designed for telemetry, doesn't perform adequate error checking, and has no retransmission ability. Therefore, the IRIS/PASSCAL EPROMs in the Refteks must be replaced with EPROMs that adequately support telemetry. The two existing arrays mentioned earlier use software developed by UCSD. Once this reprogramming is done, the Refteks can only be used in telemetry mode. Because of transmission bandwidth limitations, this mode is more suited to low sample rate data, such as arrays of long period seismometers. The two existing arrays maintain a total throughput of about 423 samples per second for all channels and data streams. In this telemetry only mode, any interference or transmission problems are critical since it means losing data. There is also the question of site locations. Certain sites may be unsuitable for radio transmission due to nearby interference, range or line-of-site limitations. Site location may then be driven by telemetry considerations rather than scientific objectives. This type of telemetry typically requires a longer "hardening" time and more preparation time. It may require radio surveys to be done prior to deployment to find suitable sites. Also range and line of site limitations may require that the signal be retransmitted. It is probably only appropriate for sites that will be deployed for a minimum of six months or so. The benefits of this type of system include complete access to data on-line.
In the past the PBIC has worked with principal investigators on balancing the frequency of site maintenance with data loss from failed sites. Having a method of checking the site remotely will be a huge benefit for the PI's, since they will have a way of seeing if the site is running as expected or not. The PBIC sees the most benefit in an intermediate form of telemetry at this time. One that allows the user to interrogate the DAS about its status. The user can then judge when the site needs to be visited. Future technological advances should allow us even more capability for reducing the cost of operating an experiment while maximizing the uptime of the equipment.
Current | Model | Description | |
---|---|---|---|
9 | 72A-02 | 16 bit data acquisition system (DAS) | |
9 | 72A-08 | 16/24 bit data acquisition system (DAS) | |
24 | 72A-05/PBIC | External hard disk subsystems (200Mb-1Gb) | |
18 | 111A | GPS units | |
18 | L4C3D | 1Hz velocity transducer | |
16 | FBA23 | Force Balance Accelerometer | |
3 | CMG40T | Intermediate period 3 component sensor | |
1 | CMG40T interface/calibration unit | ||
2 | 72A-03 | Portable exabyte tape system | |
1 | Portable DAT tape system | ||
2 | 2Gb Portable Data transfer disk | ||
4 | Zeos style palmtop computer | ||
2 | HP style palmtop computer |