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Fundamentals of GIS > Chapter 5 - Global Navigation Satellite Systems > Flashcards

Chapter 5 - Global Navigation Satellite Systems Flashcards

1
Q

What are three of four satellites used for defining positions on Earth?

A
  1. NAVSTAR Global Positioning System; 2. GLONASS; 3. Galileo; 4. Chinese Compass Satellite Navigation
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2
Q

This global navigation satellite system was deployed by the United States Department of Defense

A

NAVSTAR Global Positioning System

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3
Q

This global navigation satellite system was deployed by the Russian government

A

GLONASS

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4
Q

This global navigation satellite system is under development by the European Union

A

Galileo

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5
Q

This global navigation satellite system is under development by China

A

Chinese Compass Satellite Navigation

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6
Q

This was the first global navigation satellite system

A

NAVSTAR Global Positioning System

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7
Q

How many phases were there in the development of NAVSTAR?

A

3

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8
Q

When was the first phase of NAVSTAR?

A

1973-1979

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9
Q

What two things occurred during Phase 1 of NAVSTAR?

A

Concept validation and first satellite launch

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10
Q

What year was the first NAVSTAR satellite launched?

A

1978

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11
Q

When was the second phase of NAVSTAR?

A

1979-1985

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12
Q

What occurred during Phase 2 of NAVSTAR?

A

Full development and testing

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13
Q

When was the third phase of NAVSTAR?

A

1985-present

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14
Q

What occurred during Phase 3 of NAVSTAR?

A

Production and deployment

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15
Q

What two levels of service does GPS provide?

A

Precise positioning and standard positioning systems

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16
Q

This level of GPS is available only to authorized users

A

Precise positioning system

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17
Q

Who is an authorized precise positioning system user?

A

US/allied military forces

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18
Q

What are two things that precise positioning systems require for use?

A

Cryptographic equipment and special receivers

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19
Q

Precise positioning systems are accurate to how many meters 95% of the time?

A

21 meters

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20
Q

This type of positioning system is available to all users

A

Standard positioning system

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21
Q

Standard positioning system accuracy was degraded by this until May 2000

A

Selective availability

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22
Q

Is the standard positioning system now roughly the same accuracy as precise positioning system?

A

Yes

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23
Q

What are the three segments of GPS?

A

Satellite segment, control segment, user segment

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24
Q

This GPS segment is a constellation of orbiting space vehicles

A

Satellite segment

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25
Q

This GPS sector is a network of ground stations

A

Control segment

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26
Q

This GPS segment is comprised of public and private users

A

User segment

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27
Q

How many active satellites make up the GPS?

A

31

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28
Q

How many inactive spare satellites are in the GPS?

A

2

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29
Q

At what height do the GPS satellites orbit?

A

20,000 km

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30
Q

How many orbital planes are in the GPS?

A

6

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31
Q

How many satellites are in each GPS orbital plane?

A

5

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32
Q

How many times per day do GPS satellites orbit?

A

Twice

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33
Q

GPS satellites contain these for positioning

A

Precise clocks

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34
Q

What are at least three of four types of navigation information constantly transmitted by GPS satellites?

A
  1. Pseudo-random ID code; 2. Time; 3. Ephemeris (precise orbit for the satellite); 4. Almanac (status information for constellation)
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35
Q

GPS satellites are tracked by these

A

USAF monitor stations

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36
Q

To what location is GPS data sent?

A

Schriever Air Force Base, Colorado

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37
Q

What are at least two of three regular navigational updates sent by each GPS satellite?

A
  1. All satellite clocks synchronize; 2. Ephemeris of each satellite is adjusted; 3. Health status of each satellite is given
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38
Q

How much money has the Department of Defense invested in GPS?

A

$19 billion

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39
Q

Since what year has the Dual Use System been in place for both civilians and military?

A

1985

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40
Q

What percent of GPS users are now civilians?

A

95%

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41
Q

What are at least two of three requirements for users to receive GPS?

A

Antenna, processors, stable clock

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42
Q

What are at least two of three factors to consider when determining surface position using GPS?

A

Range distance triangulation, dilution of precision, positioning errors

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43
Q

This uses distance from many reference points to pinpoint a location

A

Triangulation

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44
Q

What does GPS use as reference points for triangulation?

A

Satellites

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45
Q

These two types of data provide accurate satellite locations in range distance triangulation

A

Almanac and ephemeris data

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46
Q

Transmitted signals between satellites are used to determine this

A

Range distance

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47
Q

How many reference locations does triangulation use to position a point?

A

3

48
Q

This is the distance between a satellite and a receiver

A

Range distance

49
Q

The range distances from many satellites determines this

A

Receiver position

50
Q

How many atomic clocks does each GPS satellite have?

A

4 (2 cesium and 2 rubidium)

51
Q

What is the accuracy of GPS satellite clocks?

A

+/- 1 second per $30,000

52
Q

How much does each GPS satellite clock cost?

A

$100,000-$500,000

53
Q

GPS receiver clocks are similar to these

A

Quartz watches

54
Q

Is there never error between satellite and receiver clocks?

A

No

55
Q

Can atomic clocks be used in GPS receivers?

A

No

56
Q

What size are the atomic clocks in GPS satellites?

A

Computer-size

57
Q

Are GPS receiver clocks accurate only over short periods?

A

Yes

58
Q

Do GPS receiver clocks need to be reset often?

A

Yes

59
Q

Which satellite is used to recalibrate the receiver clock?

A

4th satelllite

60
Q

This is the measure of geometry of visible satellites

A

Dilution of precision

61
Q

Does high dilution of precision result in good or poor satellite spread?

A

Poor satellite spread

62
Q

Does high dilution of precision result in high or low positional uncertainty?

A

High positional uncertainty

63
Q

Does low dilution of precision result in good or poor satellite spread?

A

Good satellite spread

64
Q

Does low dilution of precision result in high or low positional accuracy?

A

Low positional accuracy

65
Q

What does PDOP stand for?

A

Position dilution of precision

66
Q

What does VDOP stand for?

A

Vertical dilution of precision

67
Q

What does HDOP stand for?

A

Horizontal dilution of precision

68
Q

What DOP value is considered ideal?

A

1

69
Q

What DOP value is considered very good?

A

1-3

70
Q

What DOP value is considered good?

A

4-5

71
Q

What DOP value is considered fair?

A

6

72
Q

What DOP value is considered suspect?

A

> 6

73
Q

What are at least 4 of 7 sources of positioning errors?

A
  1. Selective availability; 2. Satellite and receiver clock errors; 3. Ephemeris errors; 4. Atmospheric interference; 5. Receiver computation/noise; 6. Multipath errors; 7. Interference from radar/microwave/radio waves
74
Q

This is the intentional degradation of GPS for national security

A

Selective availability

75
Q

Selective availability results in how many meters of positioning error?

A

100 m (160 m vertical)

76
Q

When was selective availability of GPS turned off?

A

May 2000

77
Q

Satellite and receiver clock errors result in how many meters of positional errors?

A

1 m

78
Q

Ephemeris errors result in how many meters of positioning errors?

A

1 m

79
Q

Atmospheric interference results in how many meters of positioning errors?

A

10 m

80
Q

Multipath errors result in how many meters of positioning errors?

A

0.5 m

81
Q

Positioning errors create this in range distance

A

Range uncertainty

82
Q

These errors can be reduced with a special antenna and receiver

A

Multipath errors

83
Q

This is an enhancement to GPS that was created to improve the low accuracy by selective availability

A

Differential GPS

84
Q

Differential GPS uses this at known points

A

Ground station network

85
Q

DGPS stations asses satellite error by measuring differences between these two positions

A

Known and satellite-calculated position

86
Q

DGPS uses range measures from these two sources

A

Roving receiver and base station

87
Q

In DGPS, these are used to correct positions for the roving receiver

A

Base stations

88
Q

What is the positioning accuracy of GPS without DGPS?

A

10 m

89
Q

What is the positioning accuracy of DGPS?

A

2 cm - 2 m

90
Q

DGPS has the best results when the rover is within this many km from a base station

A

300

91
Q

In this form of DGPS, rover and base station data are put into a computer, then corrections applied to rover data

A

Post-processed DGPS

92
Q

In this form of DGPS, base stations transmit corrections made on the fly to a rover

A

Real-time DGPS

93
Q

How many stations are in the U.S. national DGPS network?

A

82 (128 planned)

94
Q

What are two kinds of GIS receivers?

A

Code-phase receivers and carrier-phase receivers

95
Q

These GIS receivers’ measurements use transmitted pseudo random code

A

Code-phase receivers

96
Q

What is the error range in meters for a single fix for a code-phase GIS receiver?

A

3-30 m

97
Q

Can code-phase receivers occasionally have errors greater than 100 m?

A

Yes

98
Q

How can accuracy be improved for code-phase GIS receivers?

A

By averaging many fixes

99
Q

These GIS receivers’ measurements use satellite carrier waves

A

Carrier-phase receivers

100
Q

What is the accuracy of carrier-phase GIS receivers?

A

A few cm

101
Q

These GIS receivers require continuous data collection over a long period

A

Carrier-phase receivers

102
Q

What is the accuracy of low-cost SPS GIS receivers?

A

100 m

103
Q

What is the accuracy of medium-cost DGPS SPS GIS receivers?

A

1-10 m

104
Q

What is the accuracy of high-cost DGPS carrier-phase GIS receivers?

A

1 mm - 1 cm

105
Q

What are at least two of three applications of GPS in the field?

A
  1. Field digitization; 2. Tracking/navigation; 3. Land surveying
106
Q

This type of data can be recorded directly in the field with GPS

A

Vector data

107
Q

Can attributes be obtained in the field from GPS?

A

Yes

108
Q

GPS data can be used to establish these in field digitization

A

Control points

109
Q

New field digitization GPS equipment combines these two devices to integrate data straight into GIS

A

Receiver and computer

110
Q

These aid in point collection during field digitization

A

Laser rangefinders

111
Q

Field GPS data collection can be hampered by this

A

Sky obstruction

112
Q

At what angle above the horizon does terrain become a serious problem in field digitization?

A

> 15 degrees

113
Q

What are two types of equipment to help field digitization equipment in difficult terrain?

A

Advanced receivers and range poles

114
Q

Real-time GPS tracking is used for managing these

A

Vehicle fleets

115
Q

New GPS receivers can be used to track this in the field

A

Wildlife

116
Q

GPS receivers can aid this in the land, sea and air

A

Navigation

Fundamentals of GIS (13 decks)

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