1. GPS BASICS

2. Developed by Oklahoma 4-H
What is GPS?
Developed by Oklahoma 4-H

3. GPS Global Positioning System Network of 24 satellites (with spares)
Developed by Department of Defense
Operational 24 hours/day
Available worldwide
Land, sea and air
Works in all weather conditions
It is FREE!!
GPS stands for Global Positioning System. It is a network of 24 satellites (with spares) placed into orbit by the Department of Defense (DOD). It works anywhere in the world, 24 hours a day, in all weather conditions, and on land, air or sea. GPS is based on the coordinate system. The best part is that it is FREE to use!

4. Satellite Constellation

5. Navigation Tools of the Past
Sextant Chronometer
How did we navigate before GPS? Early sailors and travelers used the sun, stars and landmarks to navigate. They used sextants to make precise observation of the sun, stars, and planets to chart their course. In the 18th century clockmaker John Harrison invented the chronometer. It allowed navigators to know what time it was in two places at once, which helped to determine longitude. In the 1930s radio beacons were used to navigate. Their accuracy level was several miles. The space race in the 1950s and 1960s was the beginning of the GPS navigation system. In 1957 the Russians launched Sputnik, which became the world’s first artificial satellite. The radio waves emitting from Sputnik allowed researchers to determine Sputnik’s location. This caused them to think they could determine a location on earth from a satellite in space.

6. Beginnings TRANSIT developed by Navy in 1960s
Used to track nuclear submarines
Air Force created own system
Used to locate vehicles on land or in air
The Navy developed TRANSIT in the 1960s to track their fleet of nuclear submarines. It consisted of three satellites. The problem with TRANSIT was it had low accuracy and was not available 24 hours a day. This technology was used until 1996 and was replaced by GPS. During this time the Air Force also created a system to accurately locate vehicles on land or in the air.

7. NAVSTAR Combined Navy and Air Force systems in 1973
NAVigation Satellite Timing And Ranging (NAVSTAR)
First used in combat during Operation Desert Storm – 1991
Full Operational Capability – April 27, 1995
In 1973, these two combined and formed NAVSTAR. NAVigation Satellite Timing And Ranging (NAVSTAR) is the official DOD name for GPS. The first GPS satellite was launched in It was first used in combat during Operation Desert Storm in The GPS system reached full operational capability on April 27, 1995.

8. GPS System Space Segment – Satellite Constellation
Control Segment– Monitoring Stations and Ground Antennas
User Segment – Receivers
A GPS system consists of three segments – Space, Control and User. The Space segment consists of the satellite constellation. The Control segment consists of the master control station located at Schriever Air Force Base in Colorado. There are also four stations that monitor the satellites and three ground antennas. The User segment consists of the receivers and antennas receiving the signal on Earth.

9. Map of Monitoring stations

10. GPS Satellite
GPS satellite

11. Satellite Information
Weighs approximately 2,000 lbs
Travels 7,000 mph
17 feet across with solar panels extended
Last 10 years
Orbit 12,500 miles above Earth
Circle the Earth twice daily
GPS satellites weigh approximately 2,000 lbs (1 Ton), travel 7,000 mph, last ten years and are 17 feet across when solar panels are extended. They are powered by solar energy but do have backup batteries for emergencies. Satellites are orbiting 12,500 miles above the Earth. Each satellite circles the Earth twice daily. The number of satellites in orbit changes, the following website gives information concerning the status of each satellite:

12. In the next lesson we will learn:
How GPS works
Coordinates – Latitude and Longitude
Creating and Finding Waypoints using a GPS receiver

13. How Does GPS Work?

14. How it works Satellite circles the Earth and transmits signal
Signal contains time it was sent and its location
All satellites send their signal at the same time
Difference in time to reach receivers is used to determine location
As each GPS satellite circles the earth, it transmits a radio signal called a pseudo random code. Each signal is encoded with information used to determine a receiver’s location. The signal transmission includes the time the signal was sent and the satellite’s location in space. Receivers on earth receive this signal. All the satellites in the constellation send their information at the same time. However, they arrive at different times due to the distance the signals travel.

15. Formula: Distance = Speed x Time
Signal travels at the speed of light – 186, miles per second
Speed and Time are known, use to calculate Distance
The signals travel at the speed of light which is 186, miles per second (mps). The formula Distance = Speed x Time is used to determine the distance between a satellite and a location on earth. This formula is used because the both the speed and time are known. For example, it takes a signal 1 second to reach a receiver. So, we know that the receiver is 186, miles from the satellite. However, the actual calculation is slightly more complicated than this.

16. Example of formula calculation

17. Trilateration
Process of measuring the distance from at least three satellites
Three satellites calculate 2D position (Latitude and Longitude)
Four or more satellites calculate 3D position (Latitude, Longitude, and Altitude)
GPS uses a process called trilateration to determine a precise location. Trilateration is the process of measuring the distance from at least three satellites to determine a location on earth. Three satellites calculate a 2D position while four or more satellites calculate a 3D position. 2D positions consist of latitude and longitude measurements. 3D position contains both latitude and longitude in addition to altitude measurements. The differences between the two is that a 2D position can track movement, while a 3D position can calculate speed, bearing, trip distance, distance to destination, sunrise/sunset, etc.

18. Trilateration
You have no idea where you are. You ask someone and they say you are 125 miles from Wichita, KS.
Someone else says you are 250 miles from Springfield, MO.
Another person tells you that you are 65 miles from Oklahoma City, OK.
Where are you? Stillwater, OK

19. One satellite can locate a receiver’s position somewhere on a sphere
Two satellites can locate a receiver’s position to a circle representing the intersection of two spheres
. One satellite can determine a receiver’s position somewhere on a sphere. Two satellites narrow the position down to a circle where the two spheres intersect. Three satellites locate the position to one of two points at the intersection of all three spheres. The second point is automatically ruled out because it is located somewhere in space.
Three satellites can locate a receiver’s position to one of two points represented by the intersection of three spheres.

20. Latitude Latitude lines run horizontal Equator is 0°
North and South Poles are 90°
GPS is based on the coordinate system using latitude and longitude lines. Latitude lines run horizontal with the equator being 0°. The North and South poles are each 90°. They are noted as north or south of the equator.

21. Lines of Latitude
Latitude lines

22. Longitude Also known as meridians, run vertical
The Prime Meridian in Greenwich, England is 0°
Lines range from 0° to 180°
International Date Line
is 180°
Longitude lines, also known as meridians run vertical. Longitude lines run from 0° to 180°. The Prime Meridian located in Greenwich, England is 0° and the International Date Line is 180°. They are noted as east or west of the Prime Meridian. Sometimes a negative is used to designate south or west instead of S or W. On a GPS unit this negative may show up as a zero in front of the coordinates.

23. Lines of Longitude

24. Now for the
fun part!

25. Click Stick Page Button Zoom In button Power Button Zoom Out button
Find button
Page Button
Power Button
Click Stick
This is a Garmin eTrex Legend GPS receiver. It has five buttons and a click stick. It is important to learn what these buttons are and their functions.
To turn the unit on, press the flat power button on the right side. The screen will show satellites trying to acquire a signal. GPS only works outside, to use inside, turn GPS off. When the screen pops up, “Use with GPS off?” push down on the click stick. The GPS will now stop searching for satellites. OR Using the click stick, move until the “On Screen Page” button is highlighted. Press click stick down to get a drop down menu. Select “Use with GPS off” and push joystick down.

26. Satellite Page Map Page Navigation Page
There are five pages. The first page is the satellite page. What you see is the sky view (the view if you were looking straight up). The empty circles are satellites and the filled in circles are satellites that have acquired a signal. The numbers in the circles is the satellite number. The first satellite to acquire a signal downloads an almanac of satellite information to help the GPS determine where it is at.
Hit the page button or big button on the right side. You are now at the map page. The filled in triangle is a “you are here” marker.
Using the click stick, highlight the “On Screen Page” button (top right hand corner, looks like single sheet of paper). Enter, then highlight pan map, then enter again. The arrow pointer tells you where you are as you fly around the world. Using the zoom in/out buttons and click stick, fly around the world. Zoom in and out on different places. At the top of that page, you will see the latitude and longitude for where your arrow is at. To exit, Pan Map hit the page or big button.
Hit the page/big button again and you are at the navigation page, it looks like a compass. With the GPS on, it will show you the direction you are going and the speed.
In order for this to work, you must be moving!

27. Trip Page
Main Menu
Hit the page/big button again. You are now at the trip page. It contains your travel information.
Hitting the page/big button again take you to the main menu. From here we will learn how to create and find waypoints. Waypoints are locations that are saved in you GPS. They may be home, school, a favorite place, etc.
First make sure all the units are all in the same format. To check this, from main menu go to setup, enter. Then to Units, enter. The Position Format should be hddd°mm.mmm’ or hddd.ddddd°. The Map Datum should be set to WGS 84. When making waypoints, have the students turn the units off and then back on once outside.
You see a man holding flag above his head labeled “Mark”. We are going to call the man “Mark”. By highlighting “Mark” and pressing the click stick, you create a waypoint. The page will show “Mark” holding the flag. Once “Mark” is pressed from the main menu, the waypoint is marked where you are at. Therefore, do not hit enter “Mark” until you are where you want the waypoint to be.
Each waypoint is assigned a three digit number. If you want you can name the waypoint. Use the click stick to highlight the number and press enter. A keypad will show, enter the name you want and then highlight OK. Select OK (bottom right) on the mark waypoint page. You have successfully created a waypoint! It is important to remind the students to remember the waypoint number that they marked.
Now we will want to find our waypoints. On the main menu page, select “Find”, “Waypoints”, and then “Nearest”. Select the waypoint you want to find (by number or name) and press enter. The waypoint page will show, select “Go To” on bottom left. The compass page will show, students will need to move in the direction of the large arrow.
Things to remind the students of: They must be moving in order for the receiver to know their location and the direction they are moving. The receiver will not be completely accurate. They may have to look around depending on the accuracy factor.

28. The next lesson we will talk about limitations and accuracy with a GPS receiver.

29. Limitations and Accuracy with GPS

30. Accuracy Problems Atmosphere Delay Signal Multipath
Receiver Clock Errors
Number of Satellites Visible
Satellite Geometry and shading
Selective Availability – Turned off
The atmosphere can have an effect on the accuracy. As the signal passes through the ionosphere and troposphere, the water vapor and particles can slow a signal down, therefore affecting the time.
Signal multi-path is caused by the satellite signal reflecting off of buildings, rocks, water, trees, etc. Accuracy tends to be better in open areas where the likelihood of reflection is decreased.
Receiver clock errors can also cause decreased accuracy. This is because the clocks within a receiver are not as accurate as an atomic clock. Satellites however are equipped with an atomic clock.
The number of satellites visible can also cause problems. The more satellites available or visible, the accuracy increases. At all times there should be at least 3 satellites visible.
Another variable is whether the satellites are bunched up or spread out. This is called satellite geometry and shading. The ideal positioning is when the satellites are spread out.

31. WAAS Developed by the FAA Wide Area Augmentation System
Increases the accuracy of GPS receivers
Full Operational Capacity on July 10, 2003
The FAA and Coast Guard have both developed programs to help increase the accuracy of GPS. Both are free to the public, but may require special equipment such as an antenna.
Wide Area Augmentation System or WAAS, was developed by the FAA to increase the accuracy of GPS. It consists of approximately 25 ground reference stations, two master stations located on either coast, and 2 geostationary satellites, designed to increase GPS accuracy in real-time. The surveyed ground reference stations collect GPS data, compare the calculated position with their known position, remove the error then send the corrected information to the master control stations to be uploaded to the WAAS satellites. The satellites then broadcast the corrected GPS signal. WAAS reached Full Operational Capacity on July 10, This is currently only available in North America, but other governments are developing this technology. Garmin claims with WAAS its receiver’s accuracy is three meters or less, 95% of the time. Newer GPS units have this capability which can be turned off.

32. Wide Area Augmentation System
WAAS
Corrected Signal
The surveyed ground reference stations collect GPS data, compare the calculated position with their known position, remove the error then send the corrected information to the master control stations to be uploaded to the WAAS satellites. The satellites then broadcast the corrected GPS signal  
WAAS Master
Station
WAAS Reference
Station
Receiver

33. Differential Correction
Developed by the Coast Guard
Also known as DGPS
Ten meter or less accuracy
Full Operational Capacity March 15, 1999
The Coast Guard developed Differential GPS or DGPS which is another correctional differential signal. It uses two receivers, a precisely surveyed reference station and a moving receiver (you). The stationary receiver works in reverse by using its location to determine the timing errors from the satellites. It figures what the time travel should be and compares it to what the satellite sends. It then sends out correction signal to the moving receiver. There are two control centers and 60 plus remote broadcast sites. It allows for one to three meter error typically but ten meter accuracy in all established coverage areas. It reached Full Operational Capacity on March 15, If this signal is being received, it will show up as D’s on the satellite page.

34. Differential GPS Correction Signal Stationary Receiver
The stationary reference receiver gets the signals from the satellites as does the mobile receiver (boat). The stationary receiver then works backwards to compute the errors. It computes how long it should take to receive a signal versus what it actually took. The difference is the error correction. It has no idea which satellites the roving receiver is using to compute its location. Therefore the stationary receiver computes error corrections for all visible satellites. It then sends this correction information to the satellites and mobile receivers.
Correction Signal
Stationary Receiver

35. Now what do we do with this information?
The next section discusses the uses of GPS

36. Uses of GPS

37. Uses of GPS Locating Tracking Navigating Mapping Timing
GPS is used in locating, tracking, navigating, mapping, and timing. Locating is determining a basic location of someone or something. Tracking is the process of monitoring something or someone as it moves. Navigating is determining where you are going or getting from one location to another. Mapping includes surveying and mapping locations around the world. Timing involves frequency, precise time measurements, and time intervals.

38. Using GPS What are uses you can think of? Boating Fishing
Hunting Camping
Hiking Biking
Rafting

39. Using GPS continued
Scouting from land or air, Horseback riding, Hot air ballooning, Aviation, Snowmobiling, Skiing, Search and Rescue, Four wheeling, Emergency Vehicle Tracking, Highway Driving
Geocaching, Surveying, Military, Precision Agriculture
keeps track of cargo containers as they are shuffled around Singapore’s busy port.
Geologists can measure the subtle shifts in the earths crust...movements of just a few millimeters
location of trucks as they transfer goods throughout the us....also keeps track of scheduled stops and time behind the wheel.
guides passenger cars along unfamiliar roads
guides pleasure boats between points.....
jet plane to determine its exact position
guides a cruse missile to its target
meteorologists measuring delays in gps signals caused by atmosphere to aid in forecasting weather.
farmers use it to help spread fertilizer on their fields so it can be distributed equally
experimental systems are leading blind people about
Locating pets and even people (kids)

40. Using GPS continued
Survey disaster areas, Map movement of environmental disasters (Oil spills, wild fires, floods, etc)
Mapping fallout shelters, sidewalks, streets, trees, trails, etc.
Measuring the growth or decline of mountains

41. How does GPS improve these activities?
Makes the location more precise
User Friendly
Mapping is easier
Universal system
Fun!
Ask the students if they can think of other benefits of GPS.

42. What can you do
with GPS?
Have the students brainstorm other uses of GPS. Ask how they or someone they know currently use GPS.

43. GPS/GIS and 4-H Potential Projects Youth Favorite Places Geocaching
Geocaching
National GPS / GIS Integration Team
The National Map Corps
National Map Corps – Works on issuing a new US map (Like the ones in classrooms). The current map is from 1967.

44. GPS/GIS and 4-H Community Atlas Environmental Impact Team
ESRI Grants
Environmental Impact Team
Waterwell Mapping
The Globe Project

45. GPS/GIS and 4-H Oklahoma Project Ideas Danger Signs
Historic Downtown Areas
Illegal Dump locations
Health and Wellness benefits
Storm Shelters
Nature Trails and/or Vegetation