What is remote sensing?
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Collection of information about an object without being in direct contact with the object
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Medical examples
X-rays
Cat-scans
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A photograph
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An aerial photograph
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A satellite image
Lake Erie
Downtown Cleveland
Cleveland International Airport
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Highest resolution data available to the public – QuickBird 0.61m pixel
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How do imaging satellites work?
Satellite sensors “see” reflected and emitted radiation
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Principles of remote sensing
• Energy is detected by a sensor • All sensors are sensitive to specific areas of the electromagnetic spectrum
– The spectrum consists of electromagnetic radiation that occurs in various wavelengths
• Areas of the electromagnetic spectrum can be sensed = bands
– Broad bands – Narrow bands
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THE ELECTROMAGNETIC SPECTRUM
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What is GPS
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What is the Global Positioning System?
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html
• Department of Defense developed, worldwide, satellite-based radio navigation system • Consists of 24 operational satellites • Provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time • Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock 10/31/2008 12
The GPS constellation
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Satellites
• Each GPS satellite orbits the Earth twice a day • Each satellite transmits signals to Earth • GPS receivers measure the time between when satellites sent a signal relative to the GPS receiver receiving the signal
– Tells how far away the satellite is
• Signals from several satellites will give accurate results
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How do we locate ourselves in 2D space (Trilateration)
1 point of reference
625 miles from Boise
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Increasing accuracy
2 points of reference
625 miles from Boise 690 miles from Minneapolis
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Finding the location
3 points of reference 625 miles from Boise
690 miles from Minneapolis
615 miles from Tuscon
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How do we locate ourselves in 3D space using GPS
Trilateration in 3 dimensions
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GPS Position – 1 satellite
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Source: After Lusch 1996
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GPS position – 2 satellites
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Source: Garmin GPS Guide for Beginners
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GPS position – 3 satellites
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Source: Garmin GPS Guide for Beginners
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GPS accuracy
• < 1m to ~15m depending on technology • WAAS
– Wide area augmentation system – Consists of 25 ground reference stations positioned across the United States that monitor GPS satellite data – Only available in the USA
• • • • EGNOS now in Europe MSAS now in Japan BEIDOU now in China GAGAN now in India
– Gives accuracy to within 5 ft
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The Geographic Grid
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How latitude and longitude are measured
90°N
45°N
90°
Prime Meridian
45°
45° 90°
0°
45°S 90°S
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Moving over the grid
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Move up or down on a list (usually for setup)
Garmin trex
PAGE – Change screens ENTER – Change Settings
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Up
Down
Turn the GPS on with the PWR button on the right side
of the etrex.
Power (PWR) – ON/OFF
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Garmin etrex
• This is the Satellite View. • It is the first page that appears. • Wait until you see “Ready to Navigate.”
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Satellite Screen
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Garmin etrex Unit Immediately After Power is Turned On
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When at least 4 Satellites have been “locked in”, GPS can determine Coordinates.
Signal strength bars turn black.
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Important elements of the “Position Page”
• Latitude/Longitude • Time – E.S.T. – Daylight Savings – offset -5.00hr from Greenwich, England and the Prime Meridian.) • Elevation (Height)
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Move up or down on a list (usually for setup)
Garmin trex
PAGE – Change screens ENTER – Change Settings
•The etrex unit has been set up for you. •Wait for it to show READY. •Use the PAGE button three times to get to the Location Screen
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Up
Down
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Power (PWR) – ON/OFF
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