2.6 Hardware and Software Development in Support of Data Acquisition

Monuments and Antenna Mounts

Monumentation is fundamental to the selection and installation of a continuous station. A substantial effort has been invested by the UNAVCO Community to address the monument stability issue and at present the "preferred" monument is the deeply anchored/braced monument designed by Frank Wyatt, Hadley Johnson, and Duncan Agnew. (See Improved stability of a deeply anchored geodetic monument for deformation monitoring, Geophysical Research Letters, Vol. 22, No. 24, Pages 3533-3536, December 15, 1995.) To serve as a clearinghouse for this important information, the Boulder Facility has developed a section on the UNAVCO Home Page dedicated to monumentation information with links to Scripps for information on the drilled/braced monument and to the USGS Pasadena Field Office for monument designs in support of the SCIGN network. Examples of GPS Geodetic Quality Benchmarks, taken from various sources including the NOAA manual NOS NGS 1, Geodetic Bench Marks, U.S. Department of Commerce, September 1978 are also listed.

In addition to the dissemination of pre-existing information, UNAVCO supported requests for monument consultation and design on a per project basis. Jim Normandeau supported the Southwest Pacific project by locating three stations for Mike Bevis in the countries of New Caledonia, Vanuatu, and Fiji. A monument was also designed by Jim to support a project in Greenland (Figure 2-17) (GPS and absolute gravity observations of crustal motion in Greenland, 1996 Science Snapshots). A specially designed Invar rod was used for this monument to meet the climate extremes of Greenland. Invar, a Nickel-based metal, has a low coefficient of thermal expansion, does not rust, and is affordable at $13.02 / lb for Invar 36. Chuck Meertens has used the design on other projects, such as Yellowstone.

Figure 2-17. Monument at the Greenland Permanent Station.

Antenna mounts are also important to the long-term stability of the antenna position. To meet requests for a long-term stable antenna mount, Curt Conquest, Senior Technician, developed the leveling mount and the 0.5m and 1.0m spike mounts, (Figures 2-18 and 2-19). The specification table on the UNAVCO continuous station Home Page provides further information about these mounts.

Figure 2-18. Schematic Drawing of the 50-cm UNAVCO Spike Mount.

Figure 2-19. Schematic Drawing of the UNAVCO Leveling Mount.

Continuous Station Monitoring System

The continuous station monitoring system was developed by George Liu, Field Engineer, and Curt Conquest in 1996. The microcontroller-based system monitors and controls the operating parameters of a continuous station using Trimble 4000 SSE/SSi receivers. It uses a Blue Earth microcontroller and various sensors to monitor the operating parameters of the receiver system including battery voltage, system load, solar power charging currents, temperature inside the battery and system boxes, and the outside ambient air temperature. The microcontroller has the capability of controlling two digital power systems, which allows routine power cycling of modems, software resets of the receiver, and the ability to turn communications devices on for limited periods to conserve battery power and reduce solar panel requirements.

Figure 2-20. Continuous Station Monitoring System Board.

The microcontroller takes samples from the various sensors every five seconds and writes averaged measurements once every fifteen minutes to the GPS receiver data file as a comment statement. The microcontroller power-cycles the radio modem daily and the receiver weekly to prevent the equipment from freezing up due to transient voltage or misinterpreted modem noise. The microcontroller clock is synchronized with the receiver GPS clock once per week. The monitoring system can act as an interface to a variety of sensors including solar radiation meters, precision barometers, precision humidity sensors and tilt gauges. Showrmk, the data extraction program, currently operates on Trimble .dat files and is compiled for both UNIX and DOS systems. The monitoring system is currently in operation in the eighteen station Basin and Range network. Information about the monitoring system can be found on the UNAVCO Home Page.

Power

Providing long-term, reliable power is a determining factor for siting continuously operating stations. As scientific requirements determine station locations, DC power is often required as part of the support infrastructure. Testing, training, documentation, and consultation on power-related issues have been an important development role for the Facility. In March 1995 Oivind Ruud, Engineer, participated in a training class on photovoltaics for tradespeople and professionals conducted by Rocky Mountain Solar Electric, Inc. The purpose of the class was to provide training in determining power requirements, connection techniques, installation strategy for large solar panel arrays, AC inverters, configuring and installing battery backup, and lightning protection. Using this information, solar panel and battery configurations have been designed to meet power requirements for a "standard" station configuration and for specific project needs.

Continuous stations powered by AC power have also undergone development to meet specific project or location requirements. Uninterruptable power supplies, surge suppressors, low voltage disconnects for battery backups, and intelligent battery chargers for long-term use have been identified and evaluated for use in AC configurations. Facility staff have also provided consultation on these issues to investigators developing budgets for proposals, purchasing hardware, or who have power problems with previously installed stations. For example, Roland Burgmann installed a station about 150m from the power source which would not operate because the light gauge wire used to run the DC power to the site had too large a power loss. Warren Gallaher, Technician, identified the problem and provided a solution that will support the installation of an AC station up to 600 feet from the power source. The solution included vendor sources and schematics for the installation of a 40 Watt, 115V AC to 24V DC power supply, solid or stranded 14 AWG wire in a conduit from the power supply to the receiver, a DC to DC converter to step the power down to 12V, and a power line filter for noise problems.

Communications Testing

Reliable communications allow for automatic system monitoring, data download, data management, data processing and data archiving. The cost of providing communication is often the determining factor in locating and operating a continuous station as the high cost of data downloading can be prohibitive. System reliability and maintenance are also important considerations as most communication systems consist of several components including modems, repeaters, computers, and the Internet. A failure in any single component can interrupt the communications link.

Boulder Facility staff, primarily Oivind Ruud, George Liu, and Software Engineer Deborah Martin, have conducted numerous tests of various modem configurations including baud rates and various register settings such as modulation protocols and flow control to optimize the communication speed for Trimble 4000 SSE/SSi receivers. These tests began during FY95 when numerous download tests were conducted in support of the ARI purchase. Further tests were conducted through FY96 in support of continuous station networks, driven by the timing of the Basin and Range Phase I installation. During this time, the Telebit T3000, Telebit Worldblazer, ZyXel U-1496P cellular modem, and the Freewave DGR-115H radio modems were tested as stand alone systems, with repeaters, and in combination using different modems (e.g. radio modem with telephone modem). Results from these tests were used to determine the most reliable, cost effective settings for downloading Trimble 4000SSE/SSI receivers. Oivind Ruud recorded the recommended settings from these tests which are posted on the UNAVCO Home Page. Examples are shown in Figures 2-21 and 2-22. Additional information regarding short haul modems and satellite communications is also included at this Web location.

Figure 2-21. Remote Download Wire Diagram.

Figure 2-22. Sample Phone Modem-to-Radio Modem-to-Repeater Configuration.

Several antennas for radio and cellular phones were also tested. A description can be found at http://www.unavoc.uar.edu/equipment/Continuous_stations/telcom/antennas.html. A corner reflector antenna, which is designed for reflecting the back lobe of the antenna signal, has been used at the Facility and was subsequently installed at the Basin and Range COON site to prevent the cellular modem signal from interfering with the reception of the GPS receiver.

Enclosures

Identification of enclosures for long-term, outdoor protection of the electronics equipment to support a remote GPS station and the design of the components within the enclosure was begun in 1995 with a final design published on the Home Page in 1996. Designs for sheltered, outdoor, and underground locations have been used on various projects including Arenal Volcano, Popocatepetl Volcano, and the Basin and Range network. National Electrical Manufacturers Association (NEMA) standards were followed to meet different design needs for size, cost and performance. To provide a variety of fabrication options for investigators, Curt Conquest worked with a local vendor to allow them to support fabrication (e.g., Basin and Range project), worked with technical support staff from other institutions to support their fabrication efforts (e.g., Yellowstone/Wasatch project), and fabricated several systems in house (e.g., Arenal Project). Schematics, assembly instructions, bill of materials and vendor information for the UNAVCO "standard" data collection system is on the UNAVCO Home Page. Future plans include adding similar information for other GPS receiver types to the Web.

Lightning Protection

Many continuously operating GPS stations are located in areas with severe storms and high lightning activity. To avoid damaging the equipment and interrupting data flow, it is advisable to use surge and lightning protection to dissipate the energy from lighting strikes or surges in the power grid. Electro-magnetic pulses (EMPs) induce high voltage in unprotected coaxial cables, antennas, data communication cables, power cables and telephone lines which connect to expensive receivers, computers or modems. To increase staff knowledge regarding these issues, Bruce Stephens, Manager of the Equipment Services Group at the beginning of FY96, and Curt Conquest attended a "Grounding, Shielding and Surge Protection of Electronic Equipment for Instrumentation and Control" class conducted by Austral Control Systems Inc. This class was designed to provide engineers and technicians with a practical reference for the correct grounding of electronic equipment used for industrial control to meet North American (ANSI) and International (IEC) practices.

Lightning protection for coaxial antenna cables have been tested for radio modem, cellular modem and GPS receiver protection. Adding in-line protection between the GPS antenna and receiver was also tested for any potential signal degradation. Two lightning protection devices, the Alpha Delta R-T/N used by the CORS network and the Huber Suhner used on other radar installations, were tested. A network analyzer was used to test for group delay, insertion loss, and impedance matching. Zero baseline tests were also conducted and the data were processed using Bernese software. Based on test results, UNAVCO recommends the Huber Suhner EMP Protector. The results are written in a UNAVCO technical report, Effects of LEMP Protection on GPS Signals by C. Conquest, B. Stephens, and T. Van Hove, found on the Home Page. This same model is also used for radio and cellular modem protection.

Currently, Telco line protection is provided for telephone lines using the Iso-Tel 4 which can be used with RJ-11 or RJ-45 connectors. This protects against surges coming through the telephone line and damaging the modem. This has been a problem for the telephone modem at the Arenal Volcano, Costa Rica base station. Since the installation of this protection there have been no problems with this part of the communications link. At the time of this report the Facility is investigating lightning sponges, which provides multi-stage protection and will reset themselves unless taking a direct lightning hit.

Software Support

Data download software has been developed since 1994 to assist with both manual and automatic downloading of GPS data. The manual download tools have been used on many UNAVCO supported campaigns since 1995. Numerous continuous stations and networks have been supported using UNAVCO download and data management software including the Wasatch, Nepal, Hawaii, Basin and Range, Popocatepetl Volcano, Montserrat Island, Tien Shan, and CASA projects.

In 1995, a menu-based interface for manual downloads of both Trimble and Turborogue receivers was developed by Deborah Martin for the DOS operating system. This MENUASST program has been used on numerous campaign-style projects for data download and management. Initial development of continuous station data download and management software began in early 1995 by Stephanie Perry, Myron McCallum, and Deborah Martin. A prototype software was developed to run on DOS under Win 3.X, using Trimble's DOS-based R-utilities download software. This beta program was deployed to the Arenal Volcano project in May 1995. Trimble's download software and protocols are proprietary and are supported on DOS and SUN-Solaris platforms. Subsequent to the Arenal deployment, the UNAVCO continuous station download software was migrated to the Perl script language to run under SUN-Solaris and the Automated Data Retrieval (ADR) program has been installed at the other sites listed above.

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