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The 46th meeting of the Civil GPS Service Interface Committee (CGSIC) was held in September 2006 in Fort Worth. The big news at this meeting was the apparent death of the Nationwide Differential Global Positioning System (NDGPS) network. While good news for such companies as OmniStar and StarFire, which have complained for years about the federal sector competing with the private sector, pulling the plug will not impact the precise community. Not heavily used by the precise community because of its accuracy (±1-3 meters), the only downside I see is the cessation of work on the High Accuracy NDGPS, which can provide centimeter-level real-time accuracy at great distances from a single tower, accuracies that the space-based augmentation systems mentioned above cannot at this time provide. Even so, the system is being mothballed in such a way that if the need arises in the future, the $54 million invested so far will not be entirely wasted. Many of the federal agencies at the meeting for example the Forest Service, which is using it extensively for such things as wildfires expressed displeasure when it was announced that the Federal Railway Administration (which had provided the bulk of the funding) decided that GPS is not needed for positive train control. One of the early proponents of NDGPS, DeLaine Meyers from the North Dakota DOT bitterly complained, and said that many people are using the system, and hinted that there could be legal liabilities if the system is terminated. But without safety-of-life providing the impetus for FRA funding, NDGPS funding is curtailed for now.
But even though the FRA is moving a different direction for its needs, the DOT announced that it will increase funding for GPS. This is because the nation’s traffic woes are getting worse year by year, and money spent on alleviating congestion will pay big dividends in the future. NDGPS employs many of the old Air Force ground wave antennas, and its signals are not as affected and degraded by terrain as are other systems. Because NDGPS works so well, DOT might resurrect it in the future for its intelligent transportation initiative. On the other hand, Intelligent Transportation Systems (ITS) needs ±30cm, and DOT is looking at a space-based WAAS approach rather than NDGPS.
Even though the EU program developed a problem with the second test satellite, Galileo is proceeding, as is GLONASS which, with Russia’s new-found oil money, has launched several satellites recently. Several speakers at the meeting alluded to looming difficulties with the Galileo system, including a desire by some of the EU countries to include a military signal, something which the US would oppose. Also, some feel that EU cost-recovery methods for Galileo might raise trade issues. But the most strident criticism of Galileo came during a panel session in which the participants strongly denounced ESA’s failure to release the Interface Control Document which is needed for the manufacturers to produce equipment. Panel members said that specs are non-existent and much of the language is vague. When GPS was created, documentation was quickly made available for free, and the world has benefitted from the free and open system. The panel members urged ESA to drop its plans to make the precise community pay for the signals and one indignantly added that the precise community in Europe has made money from the free GPS, so why should the world precise community have to pay to use Galileo? It was noted that the price of chipsets is falling, which might make the plan to exact a royalty from Galileo boards difficult to implement. In a dramatic display of the fallibility of encrypting the signal, it was announced that a US university team had cracked the code within one day of the launch of the first Galileo test satellite. The general sense of the panel was that competition is good, and that Galileo should join with GPS and GLONASS in making these life-altering navigation signals freely available to the world, just as GPS has been.
State & Localities Subcommittee
Christa von Hillebrandt, Director of the Puerto Rico Seismic Network, made a fascinating presentation on Puerto Rico Seismic Network and Tsunami Warning Center. Most people probably don’t think of the Caribbean as being a hotspot for earthquakes, but history has shown just the opposite, and the effects of a large earthquake in the Caribbean Basin would have a great impact on the East Coast. The Pacific Warning Center is quite advanced, but much work needs to be done for the southern and eastern sides of the country. GPS is being used throughout the Caribbean on tide gauges and buoys. Interestingly, nearshore buoys are no help for tsunami detection, and many more open-ocean buoys are needed around the world. Seth Gutman, from the NOAA Earth System Research Laboratory in Boulder, Colorado reported on activities that use GPS to determine atmospheric water vapor. The potential impact for the precise community lies in modeling the tropospheric delay, which, with the errors introduced by the ionosphere, is one of the two largest error sources in GPS. The benefit for humanity lies in the ability to create better climate models and weather predictions. Something the future holds is the introduction of OPUS Rapid Static. This new technique will only require 15 minutes of observations as opposed to the two hours currently required, and it will implement the new tropo model (NOAATrop) being developed by Gutman’s team. The crew from NGS gave an update on CORS, which now has more than 1,000 stations. Recently, the first of ten GPS/GLONASS receivers was added to the network. CORS will also be added to six additional tide gauges to help determine absolute sea level. should be ITRF 2005 is coming, and will do away with NAD 83. The entire northern half of the western hemisphere is now covered by CORS. In addition to OPUS Rapid Static mentioned above, other major enhancements are underway for OPUS. First is OPUS DB, which will allow users to store their information in a database on an NGS server and share results. Second is OPUS Projects, which will allow users to perform more than one adjustment at a time. Finally, OPUS GIS will allow less-expensive single-frequency GIS-grade receivers to be used by people that don’t need survey accuracy. Here are the specifics for each new enhancement:
OPUS Database
• Streamlined method for users to publish their results
• User registration (ID & password, validation process)
• OPUS solutions can be integrated into the NGS database
• Data elements from OPUS, additional metadata
• Submission review by user and NGS
OPUS Projects
• Managers can define a project
• Process any number of stations under a project, project can span several days to weeks, contract work
• Project processing
• Each dataset goes to OPUS but is identified with a project, results returned to submitter a few minutes later, manager can monitor processing and submission
• Final adjustment
• Entire project adjusted as one campaign, review & submission to NGS
OPUS Rapid Static
• User requests, single frequency capability, rapid static solutions (10 15 minutes of data), will be processed with carrier phases
• Accurate to several centimeters, need more accurate ionospheric and tropospheric modeling, in development at OSU and NGS
OPUS GIS
• Compute a differential pseudorange solution for less expensive GPS receivers
• Aimed at those in the GIS community who do not require cm level accuracies
• Allows processing in a consistent approach and "certifying" their l
ocations in the NSRS
• Generate rapid static solution from seconds or minutes of data
• Accuracies: A few decimeters to a meter horizontally
RTN
The biggest buzz at the meeting swirled around real time networks. Contributing Writer Gavin Schrock gave a presentation about OnGrid (see Gavin’s article in our December 2006 issue). Several Europeans were there to lend their knowledge about RTN. The Germans have pioneered the use of Ntrip, a transportation protocol for RTCM messages that provides a receiver with a hack-proof IP address, thereby eliminating the need for multiple server ports. According to the German BKG website: Networked Transport of RTCM via Internet Protocol (Ntrip) stands for an applicationlevel protocol streaming Global Navigation Satellite System (GNSS) data over the Internet. Ntrip is an RTCM standard designed for disseminating differential correction data (e.g., in the RTCM-104 format) or other kinds of GNSS streaming data to stationary or mobile users over the Internet, allowing simultaneous PC, Laptop, PDA, or receiver connections to a broadcasting host. Ntrip supports wireless Internet access through Mobile IP Networks like GSM, GPRS, EDGE, or UMTS. Look for a future installment about Ntrip in Gavin’s RTN-101 series.
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