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dendrology
study of trees and how/where they grow
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cardinal directions
N, S, E, W
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bearing is expressed
N45W
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azimuth compass has degrees from...
0-360
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contour lines, all points on line have...
same elevation
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section has how many acres
640
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who created gps
u.s. military
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gps system elements
satellites, receivers, ground stations, software
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gps is used for
- navigating around the landscape
- mapping landscape features
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normal constellation of satellites and current
- 24+
- currently approx. 31
- six orbits, four satelites in each orbit
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altitude and orbit of satellite
11,000 miles and 12 hour orbit
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ground stations
- five ground stations
- master control station in colorado springs
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to find horizontal position you need
- triangulation
- at least three fixed objects
- knowing elevation requires a fourth
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gps satelites broadcast signals
- L-band of microwave spectrum
- 186,000 miles/sec.
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each satellite sends...
- ephemeris (own location)
- almanac (location of all others)
- signal indicating time sent
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secret to gps is...
time!
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receivers do what?
calculate distance to each satellite based on time required for signal to arrive
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3 types of signals
- coarse acquisition code- CA
- Carrier phase code- L1 & L2
- military- P code
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errors of gps...
- multipath error
- selective availability
- receiver clock
- atmosphere
- satellite clock
- ephemeris error
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geometric dilution of position
- better solution when widely spaced satellites over cluster
- lower GDOP value better the position
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differential collection
- allows improved accuracy through collected data
- receiving signals from 2 sources to compare and give corrections
- removes all errors except multipath
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WASS
- wide area augmentation system
- 25 ground stations administered by FAA
- only covers N. America
- transmits satellite corrections
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accuracy of receivers
- recreation grade- 1-3 meters
- mapping grade- 1m or less
- survey- 1-5cm
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waypoints...tracks...routes
- point with coordinates
- dynamic line following waypoints
- static multi reading points that create a track
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latitude and longitude
- lat- E-W 180 degrees
- lon- N-S 0-90 degrees
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UTM
- universal transverse mercator
- each zone has central meridian
- defines horizontal positions into 6 degree zones
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