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Tag Archives: GPS

Feb 22, 2010

Solar Activity May Impact GPS Users

A solar flare that occurred on February 12, 2010 may signal a return to high solar activity after several months of sustained low activity. Intense solar flares can cause temporary disruptions in GPS signals due to the high levels of radiation they release into the Earth’s atmosphere.

Solar activity generally occurs in eleven-year cycles, with the next peak expected by 2012. Increased solar activity is particularly troublesome for the navigation devices many drivers reference in their vehicles. GPS blackouts may last for a number of minutes during periods of peak solar activity and may occur several times each year. In addition to GPS blackouts, the atmospheric charge can impact the amount of time it takes for a GPS signal to make it to a GPS receiver, which causes inaccurate readings. Positioning may be off by as much as thirty feet during these periods, which will have the greatest impact on GPS survey equipment.

For iPhone users that want to keep track of solar activity, NASA has helped implement a new app called “3D Sun” that allows users to access a live global view of the sun. Data is provided in near real-time fashion by NASA’s STEREO mission, a pair of satellites that provide coverage of both sides of the sun simultaneously. More information on the app is available at http://3dsun.org/.

A high resolution 2D image of the sun taken by NASA's STEREO mission. STEREO is monitoring solar activity that may interfere with GPS and other signals. (Public domain image courtesy of NASA.)

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Jan 22, 2010

The Third Point in China’s Compass

By Mary L. Johnson

China launched the third satellite in its Compass Navigation Satellite System on January 17, 2010. This satellite is one of five planned geostationary satellites that will ultimately provide navigation coverage within the Asia-Pacific region. An additional 30 non-geostationary satellites are expected to be in place by 2020 in order to bring the Compass constellation to full global coverage.

Also known as the Beidou system, the geostationary satellites will provide free open service within the local service area. A second level of service will provide greater accuracy to authorized users only.

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Jan 21, 2010

24+3 = Greater GPS Coverage

By Mary L. Johnson

GPS geometry dictates that a minimum of 24 satellites is necessary to provide complete global coverage. Properly configured within the GPS constellation, more satellites would mean improved coverage and ostensibly greater accuracy. Although the United States currently has 30 satellites in orbit, several of these are riding shotgun with older satellites and serving strictly in an auxiliary capacity, so the working constellation has remained steady at 24. However, things are about to change dramatically.

On January 11, 2010, following extensive feasibility studies, the U.S. Strategic Command (USSTRATCOM) announced that three of the augmentation satellites would be moved to new locations within the GPS constellation, thus effectively increasing the number of individually positioned satellites from 24 to 27. The main thrust of the reconfiguration is to increase coverage in previously degraded areas, such as the mountainous regions of Afghanistan, for military purposes. However, the changes will benefit civilian and commercial users as well.

The new “Expandable 24” configuration will take approximately two years to implement fully, but the first satellite is already on the move. Space Vehicle Number (SVN) 24 began its journey on January 13 and should arrive in its new position sometime in January 2011. The other two satellites have shorter journeys ahead of them. SVN 49 will begin its journey on January 21 and is expected to be in its new position by May 2010. SVN 26 will being its journey on February 8 and should also be in its new position sometime in May 2010.

From the mountainous regions of Afghanistan to the urban canyons of the United States, GPS users should begin to notice gradual improvements in GPS coverage over the next two years as the number of satellites visible from any location on earth begins to increase. I find it especially intriguing that two of the three satellites being moved are expected to be in place in May 2010, exactly 10 years after Selective Availability (SA) officially ended and GPS first became readily available to non-military users.

SVN 24, a GPS IIA satellite similar to the one in this image, is currently on the move to provide enhanced GPS coverage to users worldwide. The satellite is expected to arrive in its new location within the GPS constellation sometime in January 2011. (Public domain image courtesy of http://pnt.gov/public/images/.)

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Jan 18, 2010

Galileo Moves Forward

By Mary L. Johnson

The European Commission has awarded a contract for the first 14 satellites in the burgeoning Galileo constellation. The first satellite is scheduled for delivery in July 2012, with one satellite every 1.5 months thereafter until the last satellite is delivered in March 2014. Additional contracts were awarded for system support services and launch services.

Bringing the Galileo constellation closer to reality will require the collective efforts of several nations in and beyond the European Union. Companies in Germany (OHB System AG) and the United Kingdom (Surrey Satellite Technology Limited) will be providing the satellite components, an Italian company (Thales Alenia Space) will provide the system support services, and a French company (Arianespace) will provide launch services that will use both French Ariane-5 and Russian Soyuz launchers.

The announcement was made on January 7, 2010, and contracts are expected to be signed within the next few weeks. The European Commission anticipates initial navigation system services by early 2014. The final completion date of the 30-satellite constellation has not been announced.

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Jan 12, 2010

GPS in 2010: Facing the Competition

By Mary L. Johnson

In my last blog post, I reported on issues with the existing GPS constellation that may cause signal disruptions, performance degradation and a decline in positioning accuracy for GPS users worldwide. A desire for independence, as well as concerns about United States control over system access and an aging satellite infrastructure have prompted other nations to develop their own Global Navigation Satellite Systems (GNSS) that could compete with and/or complement the existing GPS constellation.

The Galileo constellation, sponsored by the European Union (EU) and European Space Agency (ESA), was originally slated for full operation by the end of 2009. Though test satellites have been launched to verify orbits and time synchronization for the new constellation, delays in planning and lack of funds have postponed the first operational satellites from being launched until sometime in late 2010. The projected number of satellites in the Galileo constellation has already been reduced from 28 to 22 initially, due to cost overruns.

Russia’s GLONASS was fully operational back in 1995, but lack of funding due to the collapse of the Soviet Union eventually caused the system to fall into disrepair. A new commitment in 2001, including the announcement of a partnership with India, has put the program back on track, though still far behind its target date of restoring full world coverage by the end of 2009. Even after placing 3 new satellites in orbit in December 2009, GLONASS has only 19 working satellites in its constellation, which guarantees coverage only within Russian territory. A total of 24 satellites are needed to provide global coverage.

After initially expressing interest in assisting the EU with its Galileo constellation, the Chinese government is planning its own Compass constellation that will expand the existing Beidou Navigation System from regional China-only coverage to worldwide coverage. The target completion date is 2015. However, there were positioning issues with the first 2 satellites in 2009 that may ultimately delay or even prevent the Compass constellation from becoming a reality.

The Quasi-Zenith Satellite System (QZSS) is a proposed three-satellite system that would provide enhanced GPS coverage within Japan. The first satellite is scheduled for launch sometime in mid-2010. Full operation is anticipated by 2013. However, funding for the second and third satellites in the system is not expected until 2011 at the earliest, since it is contingent on the successful launch and operation of the first satellite. QZSS is intended to enhance rather than replace GPS, and is expected to provide improved reliability and usability to the entire South East Asian region.

The Indian Regional Navigational Satellite System (IRNSS) is a regional satellite system being developed by the Indian Space Research Organisation. A seven-satellite system is scheduled for completion by 2012, and will provide accurate coverage of India and a 2,000-kilometer perimeter around its borders. All space, ground and user components will be made in India.

As the United States moves to modernize its own aging GPS constellation in 2010 and beyond, interoperability with one or more of the new constellations will ultimately become possible. GPS receivers with dual capabilities will be able to get more accurate readings, and the addition of new satellites to any of these alternate constellations will provide needed back-up to the United States as its older satellites fail. I will be looking skyward in 2010 to monitor these conditions and providing periodic updates on each constellation as news becomes available.

Artist’s rendering of a GPS III-A satellite, part of the U.S. modernization of the existing GPS constellation. (Public domain image courtesy of http://pnt.gov/public/images/.)

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Jan 04, 2010

2010: A Pivotal Year for GPS

By Mary L. Johnson

GPS technology was in the news a lot during 2009. It was number one on the British Science Association’s March 2009 list of “Top Ten Inventions that Changed the World,” and number seven on a travel-related list of “Top Ten Inventions that Changed the World of Tourism” six months later. In October 2009, Google’s announcement about a free GPS navigation tool for smart phones sent shockwaves through the entire GPS navigation industry and caused stock prices to plummet for a number of existing GPS device manufacturers. In November, GPS World reported that the Dutch government was initiating a distance-driven tax to replace the existing road tax on cars. The new tax will be calculated by onboard GPS receivers and is intended to reduce carbon emissions and traffic congestion. In December 2009, GPS was on the ABC News list of “The Top Ten Gadgets of the Decade,” second only to the iPod.

However, a report on GPS issued in May 2009 by the Government Accountability Office (GAO) was much less favorable. The GAO concluded that if significant action was not taken by the Air Force to meet critical goals for modernizing the system, the older satellites in the GPS constellation will begin to fail in 2010, and it is likely that the total number of operational satellites will fall below the minimum number of 24 needed to provide the level of GPS service that the world has grown accustomed to. Currently, about half of the existing GPS constellation is approaching “single thread” operation status, where a critical system error could render could render a satellite inoperative.

It is possible this assessment is overly pessimistic, at least in the short term. The constellation is currently at its maximum number of 30 active satellites and has another five deactivated spares as well as satellites that are “in the barn” on the ground, ready to launch on short notice. However, the GPS III upgrade has been repeatedly delayed and further delays could endanger the integrity of the system. Colonel Brad Parkinson, the original architect of the GPS, recently testified to substantial concerns regarding the risk of a GPS “brownout” that could arise from reduced satellite numbers.

A reduction in operational satellites would cause performance degradations and a decline in positioning accuracy that would do more than simply reduce the accuracy of your car navigation systems or impact the ability of your GPS-enabled smart phone to find the nearest public transit station. For example, many Enhanced-9-1-1 emergency calls, particularly from mobile carriers, rely on GPS technology to determine and transmit caller location data to emergency dispatch centers. Power companies also use the precision timing of GPS to synchronize power plants and substations. Without it, they will lose the vital ability to trace back failures in the power grid in the event of a major blackout, and restoration of power could be significantly hampered. In addition, the airline industry may need to delay, cancel or reroute flights to allow for projected gaps in GPS coverage. Military operations would be impacted as well.

The United States controls the GPS constellation, and although civilian access has been allowed on a global scale since selective availability (SA) was discontinued in May 2000, there has been growing concern in other nations that some level of selective availability could be re-established in the event of another terrorist attack or hostile military actions against the United States. While the GPS III system will not include any SA capabilities, these fears, along with a desire for independence and concerns about the aging satellite infrastructure, have spawned the development of alternate Global Navigation Satellite Systems (GNSS) that would compete with and/or complement the existing GPS constellation. Unfortunately, these systems will not be operational in time to provide any back-up to the United States in the event of one or more satellite failures within the next couple of years.

I’ll have more information about the alternate GNSS in my next blog post.

A diagram of the existing GPS constellation showing 24 healthy satellites in orbit around the earth. Failure of any of these satellites could cause some level of performance degradation and a decline in positioning accuracy for GPS users worldwide. (Public domain image courtesy of http://pnt.gov/public/images/.)

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Aug 28, 2009

Geolocation: Followed, Not Just on Twitter

By Jeremy Heffner

We are truly at a tipping point in the ubiquity of geolocation technologies.

Take the browser for instance. With the latest version of Firefox a developer can ask your permission to triangulate your location based on your IP address and the WiFi hotspot signals in your area. Calling out to Google’s Location Services, the browser returns a reasonably accurate location to the website. Other browsers are also working to support the Geolocation API specification — iPhone’s Safari, Opera, and Chrome using Gears. Think of the possibilities for a dynamic localized news feed in Everyblock or highly targeted advertising.

When every website is location aware, how does this impact privacy? Already, we are leaving a fairly large trail as we browse the web, but being able to connect to our location could be downright creepy. The ad might read: “Hi Jeremy, care to come across the street and buy some French fries?”

The Electronic Frontier Foundation released a whitepaper this month covering the issue of locational privacy. While I tend to think that EFF can be a bit overly cautious, they make some good points. A lot of services can be implemented without associating a particular user with a particular location — completely anonymous search, for instance.

There are definitely uses for user specific data. Take Loopt or Google Latitude, the entire point of the products are to publish your location to your friends. In this regard, I don’t want the developer to jump through hoops to allow my friend to know that I am close but not reveal my actual location — it’s sort of the point.

Google Latitude on iPhone

The concept of a continuously published stream of locations for a user is immensely powerful. Imagine if the iPhone would publish updated geo-location which was shared with applications that the user granted access. Loopt could let me know that my friend is nearby without me having to open the application to update my location. Zillow could pop up a notice that I’m walking by a house that is for sale that meets my requirements. This concept of a geo-augmented reality is quite powerful, but must be done correctly so that it isn’t abused.

It will be quite interesting to see how Twitter’s API updates to include geolocation will play out. I like the idea of using Twitter as a central location feed and having other services pull from it. I’m sure we are going to see some location based spam start appearing — remember the French fries I was offered?

I was reading an article about ESRI’s solutions to manage GPS data for parolees. Analyzing parolee movement is brilliant for parole officers to keep touch on what their parolees are up to. I’d love to see a good case study in how this impacts reincarceration rates.

Contrast that with the iPhone Offender Application that was in the news. Publishing home addresses of sex offenders is commonplace, but having extremely ready access to the data is not. How does a rehabilitated individual start fresh when i can look up the offenders on my block in 30 seconds? Imagine the ramifications if we started publishing tracking data for parolees. The more that you think about it the less that is different between these two scenarios, one just has more detailed data.

Yes, we are being followed more and more as geolocation becomes tied into the services we consume. Let’s just hope its all implemented securely. And, no, I don’t want any French fries.

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