Testing GPS Precision

Students in the forest surveying class tested the precision of Garmin 60 GPS receivers today. Nine teams two students recorded 25 sets of coordinates at five different points. Two points were in forested areas and three were in the open. Each team copied their data to a spreadsheet. After the data for each point is combined we will do statistical analysis of the results. More to come.

End of Selective Availability Anniversary

The June 2010 issue of  Forestry Source (subscription required) contains a short primer on GPS. Author Steve Wilent mentioned the tenth anniversary of the end of Selective Availability (SA) on May 1, 2000, following an executive order by President Clinton. Under the SA program deliberate error was introduced into the GPS signal so that the live signal would have an error of about 100 meters. This was done to protect national security during military operations. Only military GPS receivers had a chip to remove the error.

The policy was changed to promote the use of GPS in the general economy. The military agreed fully with the new policy. There were ways around SA, by using a supplemental FM correction signal broadcast locally by the US Coast Guard or by doing post-processing correction of field data in the office.

Now that the GPS signals has no more deliberately introduced error the use of GPS has grown dramatically  in all parts of the economy from cars to personal devices. The sport of geocaching would not be possible if SA were still in operation.

For foresters, the end of SA has meant that low cost, rugged, recreational grade GPS receivers can be used for most forestry operations. The accuracy of these receivers is more than enough for most forestry mapping  operations. The forest technology program at Penn State Mont Alto has been able to acquire sufficient receivers so that all the students can have one to use for field work. Collecting GPS data in the field and using it to create maps has now become a normal part of all fieldwork.

We should make the end of SA a national holiday!

New GPS Model

Today we started using the new Garmin GPS model 60 receivers. These units have USB connections in addition to the serial ports, which is nice. They seem to work quicker than the older model 76 receivers that we have been using. They also have better graphics. And they have GPS related games! We will continue to use the older GPS units, but it is nice to have the new equipment, too.

GPS satellite developments

GPS World discusses Russia's recent launch of three more GLONASS satellites. This brings the total available satellites to 18, enough for navigation in Russia. Russia hopes to have a complete constellation of GPS satellites working by 2009. There was a recent news story of President Putin with his dog showing how a GLONASS-based GPS tracking device was now possible.

This follows last week's successful launch of a new GPS satellite, also described in GPS World. The new GPS IIR-18 (M) satellite will replace an existing older unit. It provides a stronger civilian signal and some new capabilities for military navigation.

This news is exciting for anyone interested in GPS. Within a few years we will have the choice of receivers using NAVSTAR (American), Galileo (European), or GLONASS (Russian). There will certainly be combinations of the different systems for even better accuracy and reliability. The combinations may be subscription-based for the extra service. I am sure there will be intense competition among providers to provide good deals and packages.

Maybe they will even solve the problem of good reception under a closed forest canopy with a low cost receiver!

Russian GPS: GLONASS

Business / World Business

Russia Challenges the U.S. Monopoly on Satellite Navigation

By ANDREW E. KRAMER

Published: April 4, 2007

Russia plans to launch eight navigation satellites to compete with the Global Positioning System operated by the U.S.

This New York Times article describes the Russian effort to complete its own GPS system, called GLONASS, by launching eight more satellites. This would make it operational over the Russian land mass and nearby countries. The network is seen as a competitor to the US system and an effort to bolster Russia's prestige. Many countries fear reliance on an American system in case of problems in international relations. The article says that the European system, Galileo, is stalled over fears of unprofitability. The Chinese are also planning a system.

Conceivably a GPS receiver that could use multiple systems would be more accurate. It could also work even when one system or the other was unavailable. Even at the best of times the US system may work intermittently, although it is much better now than previously.

It would be great if the countries working on GPS could develop a universal system. Since that seems unlikely, they should at least cooperate on standards to benefit all users.

For now the systems we have work well in the forest, but every improvement is welcome.