GPS : Global Positioning System
Do You think that the GPS device in your hand, or in your vehicle tells you your exact position?
How about the GPS navigation system in the cockpit of that commercial jet that your are aboard. Should you trust it?
GPS - Not as Accurate as you might think: " It ain't necessarily so" is part of a line from one of our favorite operas. The line can also be apropos when one relies upon the GPS Positioning System to tell you your location. Maybe you are where the little box says you are or maybe you ain't. A change in the position of a switch or a change in a couple of lines of code can throw your measurement way off. And, that can be a deliberate throw of a switch to falsify GPS accuracy.
As amateur radio operators, the changes mentioned above are irritating. When errors in reported positioning are the result of atmospheric changes including refraction, absorption, solar wind streams, etc. hams usually want to know why, how much, for how long, what is the significance to propagation, and how are the factors measured.
Discrepancies in THE GPS positioning system are reported to us as subscribers for data reports from the "GPS Space Weather Service " and other sources. The GPS Space Weather Service is a division of the "Solar Influences Data analysis Center ( SIDC ) - RWC Belgium ". Historically, we have tried to advise the amateur radio community when we have received A "RED error code Alert". We do not assume the responsibility for being an official source for any type of critical alert.
We give space weather, geomagnetic and related data on the Web Site primarily as a convenient source of current information when readers want up-to-date data while reading an article or working a sample problems and formulas.
Discrepancies in data reported by the "Global Positioning System" are not rare. They are a result of geomagnetic and ionospheric aberrations from geomagnetic storms, high speed solar wind streams and others sources including those mentioned above.
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The "SIDC ESA Space Weather Pilot Project, the Royal Observatory of Belgium and the Royal Meteorological Institute of Belgium are developing new services for the users of GPS." |
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The Klobuchar model, the Official Correction Model, is broadcast by GPS Satellites. The Model corrects for predicts the ionosphere Total Electron Content (TEC). The TEC is used to measure ionospheric error. A discrepancy can exist between the predicted TEC and the actual TEC during active space weather. The measured TEC is compared with the predicted TEC by the SIDC ESA (European Space Agency) Space Weather Pilot Project at the Royal Observatory of Belgium. The Positioning Error is reported by a Error Color Scale. A RED error code indicates a > 5 meter error. Other codes include Green (00 to 2.5 meters) error on the color scale and Orange (2.6 to 5 meter) error. |
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Errors in calculating one's position when using a single receiver and the GPS positioning system include : Dithering errors caused by intentional manipulation of the satellite's clock frequency, Ionospheric Refraction, Tropospheric Refraction, Multi-path signals, Orbit Error, Epsilon Error, Receiver Noise, Total Electron Count (TOC), and other factors. |
RTK : Trimble's Real Time Kinematic
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RTK = Trimble's Real Time Kinematic (RTK). This system gives GPS position accuracy down to the centimeter level. Differential GPS requires two or more receivers that cooperate to find a highly accurate positions.
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The United States of America has the Only Fully Functioning GPS System USA and GPS At this time, the United States of America has the only fully functioning GPS System. There is a lot more to the GPS System than just finding your location on a map. Technology involving the GPS system expands into numerous fields (hidden functions). ESA and GPS The European Space Agency (ESA) is in the process of negotiating among member countries to put their own GPS System into operation. Updated news on ESA advances into the global positioning field.
A URL that can get the interested reader more information includes : http://gpsatm.oma.be/Ionospheric-Products/General-Product-Description.php . |
U.S. Agencies Monitoring GPS Function:
Functioning of the United States' GPS system is monitored by U.S. Agencies including:
The U.S. Coast Guard
NOAA
U.S. Air Force
Federal Railroad Administration
U.S. Army Corps of Engineers
The Federal Highway Administration
D.O.T.
National Geodetic Survey
Functioning of the GPS system is dependent on space weather conditions, with associated events such as changes in the Earth's geomagnetic field, and the proper functioning of equipment. Equipment failure rate is low but data is often incorrect.
In October and November 2003, the Sun produced the largest and most violent solar flares man has ever recorded originating from that body. Space weather news for many month referred to the solar storms experienced that fall. NOAA contacted a number of its sources - including the Web Site - soliciting information concerning storm damage from readers that experienced problems and equipment damage as a result of the intense solar flare activity and the resulting geomagnetic storms.
Most of the topics of Space Week 2004 (Sponsored by NOAA's Space Environment Center (SEC) ) concerned the effects of the solar storms of the fall of 2003 (See Superflare) on equipment and the need for better solar weather forecasting models.
It is known that intense solar weather and severe geomagnetic conditions can cause great injury or kill satellites and their on board equipment. A section of the Web Site's "NOAA Scales" page lists some of the dangers that face communication devices as a result a intense storms (example data from NOAA).
During Space Weather Week 2004, it was disclosed that surprisingly little actual damage was done to satellites during the rein of solar terror this past fall. SEC
The "how" and "why" questions for the most part go unanswered. The the past, much smaller storms have caused considerable damage to the "power grid", to gas pipelines, navigation systems, communications systems and equipment and to sensitive electronic and magnetic devices. The fact that such massive storms can occur while the 11-year solar cycle is on the down swing has not gone unnoticed. Even today, much of the talk in space weather circles revolves around the events of October and November of 2003.
The push is on to develop a better understanding of how data can be applied to better solar and geomagnetic forecasting. Space weather and geomagnetic forecast need to be more accurate and be accurate for longer intervals of time. Accurate data then needs to have practical application in improving the safety and well-being of man and machine.
Efforts are being made to improve existing models used forecasting solar and geomagnetic behavior. The accuracy and sophistication of models used in space weather forecasting is said to be some 40 years behind the kind of data and forecasts that we get concerning atmospheric weather. The same agency is responsible for the civilian forecasts of both types of weather, the National Oceanic and Atmospheric Administration (NOAA).
New indices are being studied to determine if they have anything significant to add to the improvement of solar weather forecasting. The "T-Index" from IPS and the "E-Index" derived from the Solar 2000 program are examples.
One measure of a good forecasts includes the degree of confidence that can be put into it. Space weather model development is intended to replace generalities with more specific forecasts. The Familiar statements such as " isolated periods of minor geomagnetic storm levels may occur during the next 48 hours", can become more useful with the advent of forecasts with specific data involving the time of day, latitudes and longitudes involved, etc.
Better forecasting models need to be accurate for long periods of time to give space workers a higher degree of protection. Predictability of radio wave propagation at all frequencies needs improvement. A high degree of importance has been given to developing the means of being able to predict solar and geomagnetic storms well enough in advance that satellite owners and operators can take corrective action to protect their satellite and the equipment aboard the satellite from the environmental damage that can occur with solar and geomagnetic storms.
The GPS system is the most sophisticated satellite system in existence.
Monitoring the GPS system and providing real-time solar conditions data and solar weather forecasts is among the responsibilities of the National Geodetic Survey. Having the two responsibilities in a single agency is expected to generate better ionospheric models because the right hand knows what the left hand is doing.
Software available through the National Geodetic Survey
An on-line interactive version is also available from the Geodetic Tool Kit
Check on the GPS constellation status at the U.S. Coast Guard's Web page.
NOTE: Readers that are sticklers for individual privacy are advised to stay away from subscribing to any lists that sends e-mail reports on the accuracy and failures of systems that might even remotely be considered as militarily sensitive.
(We get a number of "military" and other "government" visitors due to the nature of the Web Site).
To be continued:
The European Space Agency's (ESA's) Global Positioning System
31 Dec 2002, 02:44 UTC : ESA Dismayed. The European Space Agency (ESA) announced a mid-December breakdown in negotiations concerning their proposed geo-positioning satellite system, Galileo.
"23 December 2002, ESA PR 83-2002. Despite the determined efforts of the European Space Agency’s Executive at a meeting of the ESA Council a little under a fortnight ago (on 11 and 12 December), it has not proved possible to obtain unanimous agreement on ESA’s participation in the Galileo project".
"Although 13 of the Agency’s Member States were ready to accept a compromise solution in the common interest, two (Germany and Spain) were unable to do so. In the words of Antonio Rodotà, ESA Director General, 'This is a hard blow for Europe. The entire space industry in Europe will badly suffer from this break in the negotiations.”
"He went on to say that, 'While keenly aware of the economic, industrial and strategic importance of satellite navigation, our Member States failed to reach an agreement, thereby delaying the start of the project’s development and validation phase.”
"The ESA Executive will be renewing its efforts to get the Galileo project back on track immediately after the Christmas break". Above text: Courtesy of the European Space Agency
At the present time, the entire world depends on the U.S.'s "Global Positioning System" (GPS). The proposed European Galileo Satellite System would serve many of the same navigational uses now being supplied by the U.S. funded and administered GPS satellites.
According to the European Space Agency News Release, the European system
would consist of 27 functioning and 3 reserve satellites to be fully operational
by 2008. Two operation systems located at undisclosed locations in Europe
would administer the navigational system. Information courtesy of
the European Space Agency. Text by KC4COP
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The Following is taken directly from the European Space Agency Web Site
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GSTB-V2/A satellite (artist's impression)
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First Galileo satellites six months from launch
9 June 2005
Two experimental satellites are being developed for the Galileo System Test
Bed – Version 2, which will make up the first phase of in the 'in-orbit
validation' of the Galileo system. Both spacecraft are now approximately six
months away from launch.
The main mission of these first Galileo satellites is intended to secure the
Galileo frequency filings, validate new technologies for operational use,
characterise the radiation environment of medium earth orbit that the
operational satellites will occupy and enable experimentation with live Galileo
signals. To ensure the success of this phase, two satellites have been ordered
from industry, currently known as
Precise Positioning Service (PPS)
Note Key words: " Authorized users", cryptographic equipment and keys,
A billionth of a trillionth of a watt.
"On April 28, 2001, a weak radio signal reached Earth from beyond the orbit of Pluto. It was NASA's Pioneer 10 spacecraft, struggling to communicate with ground controllers, its message riding on a radio signal that registered just a billionth of a trillionth of a watt."
"How do you listen to a transmission that couldn't make a lightbulb glow in a billion years? It's all in a day's work for NASA's extraordinary Deep Space Network (DSN)."
"The DSN is a global system for communicating with interplanetary spacecraft. The largest and most sensitive scientific telecommunications system in the world, it also performs radio and radar astronomy observations for the exploration of the solar system and the universe."
"Communicating
with missions in deep space is difficult," said Joseph Statman, Manager of
the Deep Space Mission System Engineering Office at NASA's Jet Propulsion
Laboratory (JPL). "It requires extremely large antennas, huge transmitters
and very sensitive receivers." Click on image in enlarge
Above: A 70-meter antenna at the Deep Space Network Goldstone complex in California. NASA
"The DSN consists of three clusters of antennas spaced approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. "The strategy here is, no matter where the spacecraft is, you're always in contact with it," explained Statman. Each complex is situated in semi-mountainous, bowl-shaped terrain to shield against radio frequency interference."
"DSN locations in Spain, Australia, and California are approximately 120 degrees apart in longitude, which enables continuous observation and suitable overlap for transferring the spacecraft radio link from one complex to the next."
"The centerpiece of every DSN facility is an enormous 70-meter diameter antenna (230-foot) capable of tracking spacecraft more than 16 billion kilometers (10 billion miles) from Earth. Arrayed around that dish is an assortment of 34-meter, 26-meter, and 11-meter antennas. The 26-meter antennas feature a double-axis astronomical mount that allows them to point low on the horizon to pick up fast-moving, Earth-orbiting satellites as soon as they come into view. These can track at up to three degrees per second."
"DSN antennas communicate with far-flung spacecraft at radio frequencies of 2.2 GHz, 8.4 GHz, and 32 GHz. For comparison, the lowest frequency, 2.2 GHz, is about the same as radio waves that cook food inside household microwave ovens."
"All of the antennas communicate directly with the Deep Space Operations Center at JPL in Pasadena, CA. The center staff directs operations, transmits commands and oversees the quality of spacecraft telemetry and navigation data delivered to network users."
"We're getting ready for a crunch period beginning in November 2003," said Rich Miller, head of planning and commitments at JPL. That's when the U.S., Europe and Japan all will have missions arriving at Mars. These include NASA's 2003 Mars Exploration Rovers, the ESA Mars Express Mission, and the Japanese Nozomi spacecraft. At the same time Stardust and Deep Space 1 will be encountering comets and a third comet mission named "CONTOUR" will launch. And, of course, other ongoing missions will have continuing communications needs."
"[These new] missions all happen to lie in the same part of the sky," said Statman, who described the area where the spacecraft will cluster as a slice of the sky with Mars in the middle. "We need to track them but we don't have enough antennas."
"Madrid will receive a new 34-meter antenna that will increase available spacecraft-tracking time by about 105 hours per week when Mars is in view. The Madrid complex's current capacity is 315 hours"
"Goldstone already supports as many as 420 hours per week of deep space communication, a figure that will balloon to 525 hours when an existing antenna comes online in 2003. "Both the Japanese and the Europeans have tracking antennas in Australia," says Statman, so they can help with the communications load at that longitude."
"As part of the upgrade, older hardware and software systems will be phased out and replaced with ones that are more reliable and, in some cases, automated. Also, Madrid and Canberra will receive processing equipment that will allow operators to combine signals from multiple on-site antennas, increasing their sensitivity to distant transmissions. Goldstone can already do that."
The fortunate hams that can afford to obtain the surplus equipment have DX locked-up for years!
"Every bit of extra sensitivity is welcome, says Statman. The total signal power arriving at a network antenna from a spacecraft transmitting from the outer solar system is 20 million times weaker than the power level from a modern digital watch battery!"
Edited from aericle by NASA