The Birth of GPSBeginning in the 1960s, the U.S. military begandevelopment of systems to aide navigation. In 1973, all entities were directed to unify their systems using atomic clocks carried on satellites.

This program would be operated under the direction of the U.S. Navy.

Time is accurate to 150 billionths of a second!

GPS EmergesThe Navy developed the Navstar Global Positioning System – now known as GPS. Satellite launches began in 1978, and were followed by 2nd generation versions in 1989.Our current version of GPS achieved operational status in 1995 and consists of at least 24 - 29 operational satellites at any given time each with an orbit period of 12 hours.

Public vs. Military

Originally, GPS was designed so civilian users wouldn’t be able to achieve the same accuracy the military could. However, in 1983, followingthe crash of Korean Flight 007, President Ronald Reagan issued a directive that mandated GPS signals would be available to the entire world without charge.

How Does GPS Work?

GPS satellites transmit signals to equipment on the ground. The GPS receivers we commonly use only receive signals; they don’t transmit anything. Each satellite in the synchronized system transmits information about its position and current time. The signals are then received by an instrument on the ground.

The signals move at the speed of light, and since some satellitesare farther away than others, their signals are received at slightly different times. The receiver then calculates the distance to the satellites by estimating the amount of time it takes their signals to reach your receiver. When the receiver has estimated the distance to at least four satellites, you are ready to go!

GPS 101 – Top Things to Know! Info can tell you where you are, how fast you’re going, how to reach a certain place, etc. Information collected is completely FREE! No info is sent back to the satellites. You need to be outside for accuracy. You’ll need three satellites for navigation (latitude and longitude), but four for elevation.

The Garmin etrex Venture Receiver

Garmin Display Options

Satellite Page

Pointer Page

Graph of Time vs. Latitude

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Graph of Time vs. Latitude (2 Data Groups)

Websites to “Borrow” From• www.geocaching.com• www.gpsmaze.com• www.lovinfifth.com• www.mountainpeaks.net• www.garmin.com• www.uen.org• www.ion.org• http://teacherlink.org/content/math/activities

/gps-position/guide.html

More Helpful Websites• www.mathbits.com (look under math caching)• www.ahisd.net/campuses/cambridge/teacher

/GeocachingActivityTypes.pdf• www.sdgfp.info/Parks/Regions/Custer/Geocac

heScavengerHuntBooklet.pdf• http://teacherlink.org/content/math/activities

/gps-position/guide.html (also check out gps-area/home.html)