2.1 Short-term Loans and Servicing of Equipment

Eighty four community receivers are supported by the Boulder Facility. The Facility maintains a full-time pool of 39, and half-time pool of 15, GPS receiver systems which includes the ancillary equipment (e.g., tripods, tribrachs, solar panels, download PCs and cables) necessary to make precise GPS measurements in the field (Table 2-3). Figure 2-2 shows the major components of a receiver system. An inventory of over 8,000 pieces of ancillary equipment, including three types of GPS antennas, is also maintained for community use. In addition, the Facility continues to be responsible for maintenance of an additional 30 receivers purchased using NSF funds and located at universities, as long as those receivers have useful research value. The Facility receives, tests, calibrates, repairs, upgrades, packages, ships, and documents this equipment to support GPS data collection activities worldwide. In FY96, 84 receiver systems were loaned to the community with an additional 20% of the projects requesting only ancillary equipment.

Table 2-3: UNAVCO Community NSF Hardware Pool

Figure 2-2. Major Components of a Receiver System as Deployed for Campaign Use.

Equipment Handling

A procedure has been developed for handling dedicated and shared GPS equipment to provide reliable, well-calibrated equipment for support of high-precision GPS data collection. When equipment arrives at the Facility from either a member university or a field project, the Facility logs information about the equipment into a database, checks the functioning of all of the pieces, calibrates and repairs equipment as necessary, and cleans and packages the equipment for the next project or return to owner. On average, this process takes two days per system, with efficiency gains for preparation of multiple systems. These tasks are conducted by trained technicians in the Equipment Services Group, which is managed by Ed Manzanares, an electrical engineer. Additional types of equipment support are also provided including the design of special packaging to reduce weight and to protect new types of equipment (e.g. Trimble chokering antenna), and assistance with equipment purchase to community members (e.g. ARI).

To track the equipment, the Facility has used a combination of a Filemaker Pro database along with copies of UNAVCO-generated manifests. The manifests contain key information (serial number, part number, manufacturer, value and description) necessary for customs importation and exportation and have been successfully used for shipments around the world. When equipment arrives at the Facility from a project, the equipment owner, or a vendor, all of the equipment listed on the manifest is accounted for and the database is updated. Unique Facility serial numbers are used to cross reference items and are added to all equipment handled by the Facility. This is currently done manually and, although time consuming, is an important part of tracking equipment. Long term plans to improve the system include updating the database to a SQL compatible database and using a bar code system. To check in a single system takes approximately an hour.

Once a system is checked in and each piece of equipment accounted for, the equipment is tested and calibrated. Components that directly affect the GPS data quality (receivers, antennas, and tribrachs) are checked first in a test and calibration lab. A minimum of eight hours of data at a 30-second sample rate is collected from each GPS receiver. A specially designed test rack, which can accommodate 32 receivers is used for this purpose. Eight antennas are mounted on the UNAVCO roof for testing purposes. The receiver data are analyzed to determine clock drift, multipath levels, cycle slips, signal-to-noise ratios, and usable data percentages using UNAVCO's QC program[1]. A copy of the test results is placed in a log book that accompanies the receiver. The memory board of each receiver is tested for any defects that may cause the loss of data in the field. The Trimble receivers are equipped with a self memory test program, which is activated from commands that are entered using the front panel keys. The receiver writes and then reads a 5 volt DC signal to every block and sector of the memory board. If the receiver is unable to write or read any of the signals, the receiver notes the bad block or sector on the screen. The results are documented and filed for future reference. Technicians spend approximately one hour, not including the eight hour survey, to test and document the test results of each receiver.

Each antenna is tested for electrical operation and ground plane run-out (warp). To test the electrical operation, the antennas are connected to a receiver and the signal-to-noise ratios calculated by the receiver are recorded for each channel. An identical set up and receiver is used for each antenna and the receiver is programmed to track the same satellite on every channel to allow for an unbiased comparison of signal-to noise ratios. Any of the satellites may be used for the test. The signal-to-noise ratios are then compared to assess performance. The signal-to-noise ratios should not vary more than 10% between channels. The antennas are then tested for ground plane run-out. Because the ground plane run-out determines the flatness of the ground plane, a granite surface plate is used to assure accurate measurements. The antenna is mounted to a precision-machined fixture, which sits on the granite surface plate and rotated 360 degrees. A dial indicator, which also sits on the granite surface plate, is used to measure the run-out as the antenna is rotated. The indicator measures to a precision of +/- 0.01mm and the antennas must be within 2mm of total run-out. These measurements take approximately one hour per antenna.

The optics and level bubble of each tribrach are tested and calibrated next. It is crucial that the optics and level bubble are calibrated properly, so that the antenna can be precisely centered over the mark on the ground. Calibrating the optics and level bubble can be a very lengthy process due to the careful setup and iterative nature of the process. A technician sets the tribrach on a tripod and aligns the cross hairs of the optics with a mark on the ground. After the tribrach is rotated 180o, the technician verifies that the cross hairs are still lined up on the ground mark. If the cross hairs are not on the mark, the optics are adjusted using two set screws to move the optics along the x and y axes. After an adjustment is made, the alignment process is started over. Several adjustments may be required before the tribrach is calibrated properly. A calibration puck with a 1 minute level bubble is used to calibrate the Wild tribrachs, which have a 5 minute bubble. If the tribrach bubble is not level, it is adjusted using two set screws to move the bubble into the center of the bull's-eye. The average tribrach calibration takes approximately two hours.

The UNAVCO pool receivers currently have 5 or 10 MB of memory, which will store several days to several weeks of data depending on the desired data rate (e.g. 5 MB memory will store three to four days of 24 hr, 30 sec data). For a standard project, the data are downloaded from the receiver to a backup medium - this is highly recommended for safeguarding the data in all cases. Field computers are used to perform the download to the secondary storage device such as floppy disk, zip drive or optical drive. All download computers are thoroughly tested for performance. A DOS utility program, ScanDisk, is used to scan the hard-disk drive for bad sectors. The serial ports are tested for operation by using a loop back plug in conjunction with the Norton Utilities program. The loop back plug allows the computer to transmit data out the transmit pin and then read the data on the receive pin. The Norton Utilities program is also used to scan the Central Processing Unit (CPU) for any defects. The computers are connected to a receiver to verify communication and data transfer which allows the communication cable to be tested for proper operation. A file located on the receiver is transferred to a floppy disk in the computer to ensure that the floppy drive is operating correctly. The AC adaptor is plugged into an AC wall plug to verify proper operation. The DC adaptor is connected to a deep-cycle battery to assure that the computer can be powered by a DC power source. Before the computers are deployed to the field, the batteries are charged, old data files are erased, and the computers are cleaned. Source disks that contain the DOS program and receiver download program are included with every computer. Testing and preparing the computers for field deployment takes approximate two hours per PC. Due to increasing unreliability with the aging PCs, the Facility has made replacing them a high priority.

Each receiver system comes with two 10Ah batteries and a Xenitronix 1.7Amp charger. Solar panels and more powerful chargers are also available for projects. Solar panels for battery charging are a standard project request item. Although the solar panels used in the pool are fairly durable and special packaging has been designed, they receive a lot of wear. A break across just one cell will reduce the current output by 33%. Before the solar panels are deployed, they are tested for voltage and current output. Curt Conquest, a senior technician, built a load tester that eliminated the need of a battery for testing the solar panels and reduced the amount of time to test them from one hour to half an hour. The load tester is a high current resistor that is placed between the regulator output and a multi-meter. The resistor draws current from the solar panels, and the multi-meter measures the current draw. The multi-meter also measures the voltage of the solar panels. The panels are tested outdoors in natural sunlight. Finally, the panels are connected to a solar regulator and all of the connectors are checked for loose connections or corrosion.

There are many small pieces of equipment that contribute to the success of a project. These include height rods, compasses, tape measures, voltmeters, surge suppressors, battery chargers, and flashlights. Height rods, compasses, and tape measures are important items for measuring the antenna height and orientation and are calibrated before they leave the Facility. Surge suppressors, battery chargers, voltmeters, and flashlights are tested for proper operation. Extra fuses, flashlight and volt-meter batteries, survey tape, and electrical tape are included with all systems.

The Facility has always worked to customize packaging to protect the equipment from the extensive shipping and rough handling. With each new receiver purchase the packaging has been redesigned around the new equipment sizes and to reduce the weight and subsequent shipping costs. The most recent changes resulted from equipment purchased under the ARI award. The antenna case was downsized to reduce weight and redesigned to accommodate the new Trimble choke ring antenna and minimal ancillary equipment. The Facility worked closely with the many community members who purchased equipment under the ARI to assure that equipment was properly packaged before deployment. The Facility continues to work with the community, as necessary, to assist with their equipment needs and has implemented an area on the UNAVCO Home Page that contains pertinent information on packing, including approved vendors, instructions on preparing foam inserts, and pictures of how the equipment can be configured (Figure 2-3).

Figure 2-3. UNAVCO Packaging Configuration for the Recent ARI Trimble Equipment Purchase. (Select to enlarge)

Equipment Repair

The Facility is able to repair all of the equipment included in a GPS system. Facility staff have had specialized training from manufacturers to repair receivers, antennas, tribrachs, optical plummets and tripods. Facility staff also have extensive experience with repairing PCs and other electronic equipment. This ability to repair equipment in-house results in tens of thousands of dollars of cost savings yearly.

In FY96, the Facility repaired eleven, and modified another ten, Trimble SSE receivers including both pool and community-owned receivers. Several examples of receiver repairs include:

• During the Eastern Mediterranean project and on a University of Texas at Austin project, the operators were unable to download data. UNAVCO diagnosed a memory board failure in both cases. Unfortunately, neither UNAVCO nor Trimble were able to recover the data from the failed boards. Both receivers received new memory boards.
• Filter boards (back panel of the receiver) were diagnosed as the problem for two pool receivers, one from the University of Wisconsin and one from the University of Washington returning from Antarctica. The Wisconsin receiver was unable to track satellites reliably and had a short on the antenna port. The Washington receiver would not track satellites and had a blown antenna port which appeared to be the result of a power surge caused most likely by someone trying to plug power into the antenna port. Both receivers were successfully repaired.
• Two processor boards were replaced, one for a receiver used on the Eastern Mediterranean project and another sent from the University of Texas at Dallas. The project receiver would only track on 16 of the 18 channels, but it had been used during the project to track up to eight satellites. The University of Texas receiver would not boot up when powered. Both received new processor boards.

The ten receiver modifications were necessary to repair a defective inductor on the power supply board. This was identified by a UNAVCO technician, Warren Gallaher. Warren identified this problem in a receiver that was under test on the UNAVCO test rack. He contacted Trimble and learned that an entire batch of inductors were bad and needed replacing, which UNAVCO proceeded to do. The inductor is part of the power circuit that supplies power to the memory board. Normally repairs are done at the board level. When a receiver malfunctions, a technician or field engineer diagnoses the problem to a specific board. The bad board is removed, replaced with a spare, and sent to Trimble for repair. There are times, however, that technicians trouble-shoot to the component level, such as the replacement of the defective inductors. The warranty arrangement on the community and pool Trimble SSE receivers provide free board replacements with UNAVCO providing troubleshooting and repair support.

All UNAVCO technicians and field engineers have been trained to repair Trimble receivers. Trimble has sent service personnel to the Facility several times to train staff in the repair and operation of its receivers including SSTs, SSEs, and SSIs. In addition, Ed Manzanares has been trained at Trimble to trouble-shoot SST, SSE, and SSI receivers to the component level. He has been authorized by Trimble to train new staff members to trouble-shoot and repair receivers. Trimble has also trained staff on antenna repair and UNAVCO is authorized to replace broken Low Noise Amplifiers (LNA) in the antennas. Specific staff are also authorized to repair Turborogue and Ashtech receivers.

Cables (antenna, power, and communication), tribrachs, and battery chargers commonly need repair in the field or upon return. Damaged cables usually require new connectors, with the average cable repair taking approximately one hour. Tribrachs are usually repaired at the Facility, although, there are times when a field engineer must repair one in the field. Tribrach repairs take from 15 minutes to a couple of hours.

Agent Projects

UNAVCO's goal for pool equipment is to keep it off the shelf and in the field as much as possible. Historically, requests for one to two receivers are often used to support new areas of research. For example, in 1994 the Facility loaned a receiver to John Labelle for ionospheric studies (GPS Helps Unravel Ionospheric Instability, 1996 Science Snapshots)[2]. Chris Alber's doctoral work on improved measurement accuracy and slant path atmospheric measurements have been supported for the last several years at a modest level (Improved GPS surveying using pointed radiometers; Slant path water vapor measurement using GPS, 1996 Science Snapshots). EAR-funded projects in the last year also used the community pool equipment to augment university-owned resources, meet emergency responses, or provide unique resources such as processing software keys. During this time, the Facility saw an increased number of requests for ancillary equipment, primarily from investigators who obtained receivers under the ARI award. The term "agent project" is used to refer to projects that request equipment support from the Facility but have no UNAVCO field engineer in the field during data collection. From a Facility perspective, an agent project encompasses the same level of equipment services provided to a campaign, without a field engineer in the field to take care of the equipment.

The equipment services group normally acts as the point of contact for agent projects, with additional consultation provided by field engineers as needed. Facility staff, primarily Ed Manzanares, consult with investigators to determine equipment required for the project, manage the necessary shipping and training, and provide information and documents for data management to ensure data are returned to the UNAVCO archive. The demand on technician and archiving staff often increase for an agent project as tasks normally handled by the field engineer must be handled by these staff. These tasks include budget development, equipment consultation, financial management, logistical and technical support, shipping, agent training, equipment repair, and data management and coordination for archiving. New users often require training in equipment operation and data management, and come to the Facility for agent training at the beginning of the equipment loan.

During FY96, the UNAVCO Boulder Facility has supported nineteen agent projects, with PIs requesting varying levels of support. As shown in Table 2-4, some of the projects requested complete systems, whereas others only requested ancillary equipment (e.g., solar panels, tribrachs, computers, and data processing software keys). For example, one of the larger agent projects, the Nepal project (Strain rates in the Indian-Eurasian collision zone, 1996 Science Snapshots), requested six complete systems and the Tien Shan Project (A GPS Study of the Tien Shan of Kyrgyzstan and Kazakhstan, 1996 Science Snapshots) requested only one. UNAVCO has worked to coordinate requests for equipment from NASA and NSF-funded projects regardless of ownership of the equipment. For example, in 1995 the NASA-DOSE New Zealand project (Kinematics of the New Zealand Plate Boundary and GPS, 1996 Science Snapshots) was able to use fifteen Trimble receivers from the NSF pool. The Facility also supports projects which are joint NASA and NSF-funded, such as the Seafloor Geodesy project (GPS geodesy using sea floor monuments, 1996 Science Snapshots).

Table 2-4: Agent Projects Funded by NSF or Using NSF Pool Resources in FY96

Note: Discussion of support to specific projects may include reference to an associated Science Snapshot which can be found on the UNAVCO Home Page. Snapshots shown below are referenced in the report text.

Most agent projects use the equipment for less than two months. However, some projects request equipment for longer periods of time and the Facility has seen an increase in requests for long-term loans of over a year. Yehuda Bock's Indonesia project (Southeast Asia plate kinematics, 1996 Science Snapshots) borrowed one SSE almost two years ago and has it installed at a continuous site in Indonesia.

In FY 1996, the Facility supported one request for an RTK system. There has been an increase in requests recently, however, of up to four for FY97. The Facility has access to one RTK system purchased by the NSF Office of Polar Programs for five months each year. This system is part of the Antarctica equipment pool and is used in Antarctica during the summer field season. Another system is currently on loan from Trimble. Dr. Duncan Agnew's San Clemente project (Space-geodetic measurements of crustal motion in central and southern California, 1996 Science Snapshots) has used this system for several years in the spring.

There are occasions when the Facility handles equipment that is not part of the community pool. For example, Dr. Bob King purchased four Trimble SSI receivers, antennas, computers, solar panels, and ancillary equipment for use by his Chinese colleagues. The Facility tested, inventoried, manifested, and shipped the equipment to China (Geological, Geodetic, and Geophysical study of southwest China: A test of Cenozoic tectonic models for Eurasia, 1996 Science Snapshots) at Dr. King's request. The Facility has a long history of supporting this project and has migrated from using pool receivers and field engineers to providing just equipment support. Chinese collaborators have received extensive training from UNAVCO and MIT on data collection methods and data processing.

[2] 1996 Science Snapshots can be found at http://www.unavco.org/.

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