GPS

Doug Van Zee

Global Positioning System

The Global Positioning System is the most significant development in navigation since the compass.

A network of satellites that continuously transmit coded information, which makes it possible to precisely identify locations on Earth by measuring distance from the satellites.

Global Positioning System

Control segment: 5 ground stations tracking satellite positions, keeping the satellites in their proper orbits, and telling the satellites their exact positions and the exact time.

Space segment: 24 satellites (21 working 3 spares). User segment: GPS receiver including a radio receiver, quartz

clock, memory and a CPU to perform a wide variety of calculations.

GPS Signal Radio signals at 50 watt

transmission power Travel line of sight only,

i.e. through clouds and glass, but not mountains and buildings.

Space Segment 24 satellites cruising at an altitude

of 13, 670 miles 6 orbits with 4 satellites each Two complete orbits in 24 hours 2000 lbs, 17 feet in diameter, solar

powered Expected lifetime 10 years Any location on earth will have line

of sight access to a minimum of six satellites at all times

How it works Velocity X Travel Time = Distance

x

x

Triangulation•1st satellite -> sphere

•2nd satellite -> circle

•3rd satellite -> 2 points

•4th satellite -> 1 point

It takes at least 4 satellites to obtain a three-dimensional position fix

GPS errors

Ionosphere and troposphere delays Number of satellites visible Before 2000, there was an intentional degradation of satellite signal

Was turned off May 1st, 2000 (Operation Desert Storm) Allowed 10 times the accuracy for civilians

User Segment GPS receiver (parallel multi-channel)

Time of day Location (lat and long) Waypoints

Define: marked location Routes Distances Tracks Maps PC connectivity

Geocaching Hi-tech version of treasure hunting Caches typically consist of a waterproof container discreetly placed

within the local terrain. The container will include a logbook and any number of more or less valuable items such as toys, books, money, jewelry, trinkets, etc.

Rules: fill out the logbook take something out of the cache put something in the cache return the cache to the exact position and condition in which it

was found

Information about geocaching and the location of caches can be

found at www.geocaching.com