Gk-12 Sensors!: Gps
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GK-12 Sensors!: GPS Brad Neumann and Eeva Hedefine The University of Maine
What is GPS? GPS – Global Positioning System Have you ever been in a shopping mall and relied on the directory maps with the “You Are Here” star? GPS works the same way, but on a global scale.
How does GPS work? Imagine that a GPS unit communicates with only one of these 24 satellites. Then, the GPS can only make a large and general “You Are Here” star.
www.stoller-eser.com
But, how does GPS work? Just as we depend on satellites for cellular phones and TV broadcasts, we also rely on satellites for GPS. In fact, GPS relies on 24 satellites that orbit the earth in very precise paths. www.stoller-eser.com
How does GPS work?
With two, and even three and four satellites to communicate with, the GPS unit can make the “You Are Here” star smaller and more precise.
How does GPS work? Communication with four satellites is usually enough to improve location accuracy to within about 10 meters. Some GPS units can provide location within a few centimeters!
Components of a GPS Three parts of a GPS: Space Segment • satellites
Control Segment • base stations
User Segment
www.aero.org/publications/GPSPRIMER/GPSElements.html
• fighter jet • surveyor • hiker
Space Segment
www.stoller-eser.com
24 satellites in 6 orbital planes. Satellites orbit at 11,000 nautical miles (12,659 statute miles) Each satellite orbits the earth in 12 hours. Each satellite broadcasts a signal.
Control Segment Base station receives signal and monitors each satellites exact location in space. Base station also maintains an atomic clock for precise measurements of signal travel time.
www.stoller-eser.com
User Segment To determine location, the receiver measures the time it takes for the individual signals to reach the unit. distance = travel time X speed of light Through communication with multiple satellites the receiver location can be “triangulated”
www.stoller-eser.com
How do I know where I am? The GPS receiver displays location in degrees of latitude and longitude. Latitude is measured north and south of the equator. Longitude is measured east and west of the prime meridian. www.stoller-eser.com
Global Positioning System Initially developed by the U.S. Department of Defense for military use. Still maintained by DOD today, but can also be for civilian use. Navigation in your car. Finding your favorite fishing hole. Mapping trails or roads.
GPS Accuracy For safety reasons the DOD only operated civilian GPS with selective availability – scrambling of signal Selective availability was turned off in May of 2000. GPS accuracy went from 100 m to 10 m in good conditions. The most accurate (and expensive) GPS receivers now have centimeter accuracy.
Accuracy depends on: Quality of equipment Time over which observations are made
GPS Accuracy
www.stoller-eser.com
Accuracy is best when the satellites used are widely spaced
GPS in the Real World Navigation Military, commercial, personal
Locational data collection Science • Relate a particular phenomenon to a place
Mapping • Geographic Information Systems (GIS)
Global Positioning Systems Let’s get out there and try one out! References www.stoller-eser.com. Environmental Surveillance, Education, and Research Program. Idaho National Engineering and Environmental Laboratory. www.aero.org. The Aerospace Corporation.
What is GPS? GPS – Global Positioning System Have you ever been in a shopping mall and relied on the directory maps with the “You Are Here” star? GPS works the same way, but on a global scale.
How does GPS work? Imagine that a GPS unit communicates with only one of these 24 satellites. Then, the GPS can only make a large and general “You Are Here” star.
www.stoller-eser.com
But, how does GPS work? Just as we depend on satellites for cellular phones and TV broadcasts, we also rely on satellites for GPS. In fact, GPS relies on 24 satellites that orbit the earth in very precise paths. www.stoller-eser.com
How does GPS work?
With two, and even three and four satellites to communicate with, the GPS unit can make the “You Are Here” star smaller and more precise.
How does GPS work? Communication with four satellites is usually enough to improve location accuracy to within about 10 meters. Some GPS units can provide location within a few centimeters!
Components of a GPS Three parts of a GPS: Space Segment • satellites
Control Segment • base stations
User Segment
www.aero.org/publications/GPSPRIMER/GPSElements.html
• fighter jet • surveyor • hiker
Space Segment
www.stoller-eser.com
24 satellites in 6 orbital planes. Satellites orbit at 11,000 nautical miles (12,659 statute miles) Each satellite orbits the earth in 12 hours. Each satellite broadcasts a signal.
Control Segment Base station receives signal and monitors each satellites exact location in space. Base station also maintains an atomic clock for precise measurements of signal travel time.
www.stoller-eser.com
User Segment To determine location, the receiver measures the time it takes for the individual signals to reach the unit. distance = travel time X speed of light Through communication with multiple satellites the receiver location can be “triangulated”
www.stoller-eser.com
How do I know where I am? The GPS receiver displays location in degrees of latitude and longitude. Latitude is measured north and south of the equator. Longitude is measured east and west of the prime meridian. www.stoller-eser.com
Global Positioning System Initially developed by the U.S. Department of Defense for military use. Still maintained by DOD today, but can also be for civilian use. Navigation in your car. Finding your favorite fishing hole. Mapping trails or roads.
GPS Accuracy For safety reasons the DOD only operated civilian GPS with selective availability – scrambling of signal Selective availability was turned off in May of 2000. GPS accuracy went from 100 m to 10 m in good conditions. The most accurate (and expensive) GPS receivers now have centimeter accuracy.
Accuracy depends on: Quality of equipment Time over which observations are made
GPS Accuracy
www.stoller-eser.com
Accuracy is best when the satellites used are widely spaced
GPS in the Real World Navigation Military, commercial, personal
Locational data collection Science • Relate a particular phenomenon to a place
Mapping • Geographic Information Systems (GIS)
Global Positioning Systems Let’s get out there and try one out! References www.stoller-eser.com. Environmental Surveillance, Education, and Research Program. Idaho National Engineering and Environmental Laboratory. www.aero.org. The Aerospace Corporation.
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