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Digital Mapping > Lecture 4: Navigation Systems > Flashcards

Lecture 4: Navigation Systems Flashcards

1
Q

Name the 4 Global Navigation Satellite Systems(GNSS)

A
  • United States’ Global Positioning System (GPS)
  • Russia’s GLONASS
  • European Union’s Galileo
  • China’s BeiDou
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2
Q

What is GPS?

A

A system that uses satellites to provide geographic positioning

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3
Q

How does GPS get a location?

A

small electronic receivers determine their longitude, latitude, and elevation using radio signals transmitted from satellites

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4
Q

What is selective ability?

A

adds intentional, time varying errors of up to 100 meters to the publicly available navigation signals(to deny enemy the use of civilian GPS receivers for precision weapon guidance)

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5
Q

What is Trilateration?

A

method of determining relative positions using the geometry of triangles

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6
Q

What is a fix?

A

An absolute position of a receiver

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7
Q

What does Trilateration need for GPS?

A
  • known locations of two or more satellites

- measured distance between the GPS receiver and each satellite

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8
Q

What does accurate distance calculation need for Trilateration?

A

both the GPS receiver & satellite clocks must be precisely and continually synchronized

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9
Q

Why is accurate distance calculation for Trilateration impossible?

A

The clocks in GPS receivers are not as accurate as the atomic clocks in the satellites

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10
Q

How do you eliminate the clock errors in accurate distance calculation for trilateration

A

A fourth satellite is required

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11
Q

What does each GPS satellite constantly send to the Earth

A

Coded radio signals (pseudorandom code)

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12
Q

What do GPS satellite signals contain?

A

The satellite that is sending the info

Where the satellite is at any given time

Date and time it sent the signal

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13
Q

What does a GPS receiver have?

A
  • antenna tuned to the radio frequencies transmitted by the satellites
  • very accurate clock
  • a processor to decode the satellite’s signal
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14
Q

Name some GPS applications

A 
Navigation 
Autonomous Vehicles
Tracking
Recreation (fun)
Mapping
Location based social media 
Mapping
Accurate time
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15
Q

Satellite signals cannot pass through…

A

Objects that contain a lot of metal or water

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16
Q

Satellite signals can pass through…

A

clouds, glass, and plastic.

17
Q

What decreases the power of satellite signals?

A

solid objects such as buildings

18
Q

What is the minimum number of satellites for a full constellation?

A

24 operational 95% of the time

19
Q

Why 24 satellites for a full constellation?

A

ensures there are at least four satellites in view from virtually any point on the planet

20
Q

What do monitoring stations do?

A

track the location and health of each satellite (e.g., clock error, malfunctions, correct orbit)
Synchronize the atomic clocks onboard the satellites to within a few nanoseconds of each other

21
Q

Name some accuracy problems for a GPS

A 
Atmosphere delay
Signal multipath error
Receiver clock errors
Number of satellites visible
Satellite geometry
Orbital Errors
22
Q

What is a Multipath error?

A

GPS signal bounces off of objects (building, rocks) before it reaches GPS receiver.
(increases the travel time of signal)

23
Q

What is Satellite Geometry?

A

the relative position of the satellites at any given time

24
Q

When does the ideal satellite Geometry exist?

A
  • satellites are located at wide angles relative to each other
  • when overhead the earth
25
Q

When does bad satellite geometry result?

A
  • satellites are located in a line or in a tight grouping

- when near the horizon

26
Q

What is a jammer

A

radio frequency transmitters that intentionally block, jam, or interfere with lawful communications (Illegal in USA)

27
Q

What is Dead reckoning?

A

ancient method of planning and tracking the movements needed to navigate

28
Q

What must you know to use dead reckoning?

A
  • starting location
  • direction (bearing or azimuth)
  • speed and time (aka distance)
29
Q

What is path integration?

A

Animal dead reckoning

30
Q

What is a accelerometer?

A

motion sensors to measure speed

31
Q

What is a gyroscope?

A

rotation sensors to measure direction

32
Q

What is Internal Navigation System (INS)?

A

System that uses computers, accelerometers and gyroscopes to continuously calculate position, orientation and velocity

33
Q

What is INS used for?

A

used in ships, aircraft, submarines, guided missiles

34
Q

What is the method INS uses?

A

dead reckoning

Digital Mapping (5 decks)

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