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31 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Accuracy |
How close the device's calculated position is from the truth |
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Precision |
A set of numbers that is spread out, the higher the precision the more contained the numbers are, the lower the precision the more spread out they are |
Precision Choke |
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Multipath |
Multipath is where a satellite signal arrives at a receiver from more than one path or route |
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How to reduce Multipath |
Can be reduced by antennas with a gain pattern that filters low satellite elevations and absorbs radio frequencies |
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Error Minimisation |
Multipath is mitigated through advanced instrumentation, careful planning and good field procedures, Specialised digital signal processing techniques and external antenna's that choke or absorb stray multipath GNSS signal |
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Dilution of precision (DOP) |
Is a measure of the quality of the geometry of the satellite constellation. The accuracy of the data collected by a GPS or GNSS receiver at the time of use |
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Real Time Kinematic (RTK) |
Used to increase the Accuracy of GPS signals by using a fixed base station which wirelessly sends out corrections to a moving receiver |
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Static requirements |
The reference receiver must have a fixed known coordinates. Allows users to calculate the corrections for the satellite vehicles being tracked, applied to rovers position at post-processing stage. At least four common satellites must be tracked simultaneously by both the base and receiver. Post processing software is used to derive point positions for the rover setups |
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Real Time Kinematic (RTK) Requirements |
The reference (Base) receiver must have a fixed known coordinates. Need for a real time data link between the reference receiver and the rover. Minimum of 5 satellites must be tracked simultaneously by both the base and receiver. Provides instant positioning at the rover - no post processing required |
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Static Advantages and disadvantages |
-Higher accuracy can be achieved - no data link required between reference and rover receiver -larger areas cam be covered •slower/smaller amounts of work are achieved •Post processing required to obtain results |
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RTK advantage and disadvantages |
- instant positioning available - large volumes of work can be achieved - detail -Allows linking surveys more easy and quicker •lower accuracy (20-30mm) •Requires radio link with reference receiver •Range limited by radio signal and topography |
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What is GPS/GNSS |
Means of determining position and navigation |
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Segment of GPS (SPACE) |
•44 satellites •Orbit twice a day •Emit radio signals •Use their signals as a reference point for finding locations on earth similar to stars |
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Segment of GPS (USER) |
• Handheld GPS unit and person holding it • type and technique of the way you use the receiver determines the Accuracy of the results • Accuracy from (m to cm) |
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Segment of GPS (CONTROL) |
• Monitors GPS satellite from ground stations on earth Adjust the SV orbits due to solar winds and other small variables |
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GPS/GNSS TODAY |
• Broad range of activities • Easy to use • Greater improving functions • less expensive •ability to connect to internet for mapping service • Greater business applications and improvement of community services |
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Types of Systems |
• GPS developed by America for military use in 1970's • Public allowed access in 1980's • 1994 saw all 24 SV being used • Russia have the GLONASS • European Union Gilileo • Two levels public and defence (encrypted) |
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The Transit System |
• Developed by the US Navy • Consisted of 7 SV's • Approx 1100km above the earth • Used for geodetic surveying in the late 70's and 80's |
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Limitations of the Transit System |
• Limited number of Satellites • Low altitude - large forces hard model therefore disturbed the satellite orbits • Long periods of time where no satellites were visible • required several SV passes to determine a position • Accuracy of position measurements not as high as ideally recommended |
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GPS Components (Control Station) (Ground) |
• Responsible for the laughing, maintenance, repair and data validity of the SV's • Calcultes correction coefficients for the satellite clocks • Monitors the health and transfer of info. To the SV's • 5 locations aro around the world - Ascension Island, Colorado springs, Diego Garcia, Hawaii and Kwajalein.
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GPS Components (Master Control Station (MCS)) (Ground) |
•Located at Colorado Springs • known as Consolidated Satellite Operations Centre (CSOC) • Station where all orbit, correction parameters and health indicators are generated • other 4 station send info to the CSOC for processing • required info. Then transmitted back to stations for uploading to SV's
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GPS Components (Australia Fiducial Network (AFN)) (Ground) |
• 10 permanent GPS tracking stations in Australia • Each stations has a dual frequency GPS receiver • |
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GPS Components (Receiver) |
• Receiver is basically a radio that can tune into either of the 2 GPS carrier frequencies L1 and L2 • Consists of the antenna and antenna pre-amplifier, Radio Frequncy section(RF), Signal Tracking Loops, Microprocessor, Power Supply, Data Storage medium and the User Interface |
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GPS Components (Antenna) |
• converts the electromagnetic signal transmitted by the satellites into electric signals that can be utilized by the receiver electronics • Some systems only receive the L1 frequency • Dish helps eliminate the effects of multipath • Important feature of the antenna is the stability of the phase centre • Mechanical and electrical centre generally don't coincide • different antenna used in one Survey could cause problems |
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GPS Components (Antenna Pre amplifier) |
•Boosts signal from satellites as they are generally weak when they hit the receiver • Located in the bottom of the antenna • Powered by a voltage passing through the co-axial cable that transfers the signal to the receiver |
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GPS Components (Radio Frequency (RF)) |
• Termed from end of the receiver • Takes incoming signal and reduce its frequency to a more manageable frequency termed an intermediate frequency (IF) • information then passed ontothe signal tracking portion of the receiver
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GPS Components (Signal Tracking Loops) |
• Antenna receives signals from multiple satellites at a time • Signal amplified in the antenna reduced to an IF by the front end • Receiver then distinguishes the different SV signals • Once the receiver has distinguished each SV it can then lock onto the SV transmission |
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GPS Components (Microprocessor) |
• Controls operations such as initially acquiring satellites, tracking the code and carrier, interpretating the broadcast navigation message and compute satellite receiver coordinates • More powerful the processor the greater the functionality that can be supported by the receiver |
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GPS Components (Power Supply) |
• These days generally in the form of small DC power Sources • portable units (RTK) might need a couple of days • Static stations can run of larger power Sources |
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GPS Components (Data Storage) |
• Multiple forms • Internal, PCMCIA cards, etc. • All now are compatible with other software and survey equipment |
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GPS Components (User Interface) |
• Vary between companies • Offer multitude of functions and clear large colour screens |
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