Mary L. Johnson | Azavea Atlas

Articles by Mary L. Johnson

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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Nov 10, 2009

Augmented Reality for Smart Phones

By Mary L. Johnson

Smart phones combine Internet access and camera capabilities with conventional cell phone functionality. The most recently released smart phones have global positioning systems (GPS), magnetic compass and accelerometer capabilities built in that determine where the phone’s user is standing, in which direction the phone is pointing, and at what angle the phone is tilted. This past summer, the Google Android and Apple iPhone platforms were enhanced to enable software developers to interface with the camera display controls and overlay additional information. Referred to as “augmented reality,” these new capabilities enable smart phone users to automatically access selected information about the world around them in order to augment their reality experience.

Augmented reality technology is extremely new, and its full potential still remains to be seen. Applications have already been developed to help users identify landmarks, learn about architecture, locate public transportation stops and even find their cars in crowded parking lots. Once an augmented reality application has been downloaded to a user’s smart phone, there is no need to access a traditional website or even enter a street address or other search criteria in order to use it. The augmented reality data simply appears on the smart phone’s camera screen in response to the phone’s location. For example, a smart phone user could point the phone’s camera at a local street scene and instantly access prices, room sizes and other information about available real estate within camera range. Depending on the application, the augmented reality data might appear as an overlay at the bottom of the camera display, or as lines of text superimposed directly on a selected site in the camera’s viewfinder.

Azavea recently assisted the Department of Records City Archives with a grant application that could bring augmented reality to the City of Philadelphia. If funding is approved, the proposed application will enable point-and-view access to designated historic photographs from the PhillyHistory.org website for selected locations around the City. The Department of Records believes that augmented reality will provide an innovative means of engaging students in the study of history, architecture and photography. A secondary benefit of this exciting technology would be the enhancement of local tourism, since tourists will be able to access archival photographs and background information about an historic building while literally standing at its doorstep. Best of all, users will be able to download the proposed augmented reality application at no cost directly from the PhillyHistory.org website.

The example image below is courtesy of Mobilizy/Wikitude World Browser (www.mobilizy.com).

Augmented reality applications, like the Wikitude World Browser shown here, allow users to access information about the world around them in relation to their locations. The augmented reality data appears as an overlay on the camera display and can be paged through much like standard web pages. The Philadelphia Department of Records is pursuing a grant that could provide point-and-view access to historic photographs of selected locations in a prototype augmented reality application. Users will be able to automatically access and page through the historic photographs by simply pointing a Smart Phone at the contemporary site.

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