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B4U3M1 > GNSS Basics > Flashcards

GNSS Basics Flashcards

1
Q

The process of finding your way from your current location to your desired destination is known as…

A

Navigation

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2
Q

What were the 3 early methods of navigation?

A

1) Piloting (maps/landmarks)
2) Dead reckoning (straight line)
3) Celestial (stars)

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3
Q

What is GNSS?

A

Global Navigation Satellite System

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4
Q

What are the 2 methods of electronic navigation?

A

Radio navigation & GNSS

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5
Q

What is the overarching term for satellite systems that provide global geospatial positioning?

A

GNSS

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6
Q

What are the 2 GNSS systems for position determination?

A

Triangulation & trilateration

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7
Q

Which GNSS system uses angles/azimuths from known landmarks to figure out your location?

A

Triangulation

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8
Q

Which GNSS system uses intersecting spheres to determine location?

A

Trilateration

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9
Q

The ~ range from an SV to a user’s receiver is known as…

A

Pseudorange

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10
Q

What do receivers use as the pseudorange?

A

The radius of a sphere, centered on the satellite’s location

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11
Q

How many circles are required to pinpoint a location in triangulation?

A

3

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12
Q

How many spheres are required to pinpoint a location in trilateration?

A

4

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13
Q

Errors in GPS signals that affect trilateration are collectively known as…

A

User Equivalent Range Error (UERE)

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14
Q

What are the 2 types of UERE?

A

1) User Range Error (URE)
2) User Equipment Error (UEE)

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15
Q

What 2 errors contribute to URE?

A

1) Satellite clock error
2) Satellite ephemeris error

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16
Q

What causes satellite clock error?

A

The drift of the SV clock from actual GPS time

17
Q

How do satellite clock errors affect different users?

A

Equally, regardless of their distance from the SV

18
Q

What causes satellite ephemeris errors?

A

The difference between actual SV location and the position predicted by SV orbital data in NAV message. Also, perturbations.

19
Q

How do ephemeris errors affect different users?

A

Differently, based on their distance from the SV

20
Q

What are the 4 contributors to UEE?

A

1) Ionosphere
2) Troposphere
3) Receiver noise
4) Multipath

21
Q

What are the 3 ways the ionosphere causes UEE?

A

1) Scintillation
2) Refraction
3) Group delay

22
Q

How does the troposphere cause UEE?

A

Refraction

23
Q

How does receiver noise cause UEE?

A

Interferes w/receiver performance (larger pseudoranges)

24
Q

How does multipath cause UEE?

A

Delays reception of reflected GPS signals

25
Q

What is DOP?

A

Dilution of Precision

26
Q

What would cause a poor (high) DOP?

A

Satellites being too close together

27
Q

What are the 4 essential elements of GNSS?

A

1) Timestamp
2) Ionospheric data
3) Clock correction
4) Satellite ephemeris (location)

28
Q

Which essential element is required to calculate pseudorange?

A

Timestamp

29
Q

Which access scheme is used in GNSS?

A

CDMA (Code Division Multiple Access)

30
Q

An SV’s signal is identified from many others in the same BW by use of what?

A

PRN codes

31
Q

What are the 3 scintillation effects that can impact GNSS signals?

A

1) Refraction
2) Group delay
3) Diffraction/scattering

32
Q

What are the 5 GPS channels and their uses?

A

1) C/A for civilian use
2) P/Y for military use
3) L3 for NUDET (nuclear detection) data
4) L4 for ???
5) L5 for safety of life

33
Q

Why can we obtain only pseudoranges and not precise ranges?

A

Because of clock errors and atmospheric refraction

34
Q

In what band does GPS operate?

A

L-band, which is heavily affected by scintillation

35
Q

Which countries are associated with the following GNSS systems?
1) GPS
2) GLONASS
3) Galileo
4) BeiDou
5) QZSS
6) IRNSS

A

1) USA
2) Russia
3) Europe (EU)
4) China
5) Japan
6) India

B4U3M1 (4 decks)

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