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GIS > GPS > Flashcards

GPS Flashcards

1
Q

GPS stands for

A

global positioning system

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2
Q

GPS

A

technology that broadcasts satellite signals for navigation and position determination on earth

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3
Q

examples of how are GPS receivers used

A
  1. in car navigation
  2. cell phones
  3. smart watches
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4
Q

is GPS free

A

yes

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5
Q

when and what was the first use of GPS

A

1964 with the NAVSAT system

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6
Q

what was NAVSAT used for

A

tracking the locations of commercial and military sea vessels

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7
Q

what was the origin of the GPS we use

A

the NAVSTAR system developed by USA

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8
Q

what was the first use of GPS outside of the USA

A

Soviet Union shoots down Korean Airline in 1983

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9
Q

what administration allowed worldwide access to the GPS

A

Reagan administration

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10
Q

GNSS

A

the overall term for technology that uses signals to find locations on Earth

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11
Q

what does GNSS stand for

A

global navigation satellite system

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12
Q

what are the three segments of GPS

A
  1. space segment
  2. control segment
  3. user segment
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13
Q

what segment(s) does the space segment send data to

A

control and user segment

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14
Q

how many satellites does GPS require

A

24

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14
Q

how many orbital planes are there for the satellites for GPS

A

six orbital planes

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14
Q

what is the orbit altitude of the satellites for GPS

A

20 200 km

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15
Q

how many degrees are the six orbital planes for the GPS satellites separated

A

60 degrees

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16
Q

how many satellites are visible from any point on earth

A

5 to 8

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17
Q

describe the data from the space segment of GPS

A

ephemeris

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18
Q

ephemeris data

A

information about the satellite’s status, orbit and precise location

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19
Q

what type of GPS data is sent to users from a satellite

A

ephemeris data

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20
Q

how is the data from the satellite sent to the control stations and users

A

done through digital pseudo-random codes

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21
Q

C/A code in satellite data

A

information accessible by ALL GPS Receivers

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22
Q

what is a frequency in C/A codes

A

L1 - navigation information (time and position)

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23
Q

what are P-codes

A

information from satellites that is accessible by MILITARY receivers

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24
Q

what L level data is received by P-code data

A

L1 and L2

25
Q

what does L2 measure

A

atmospheric interference

26
Q

Y -codes

A

encrypted version of P-code intended for MILITARY use

27
Q

what is the control segment of GPS

A

series of worldwide ground stations that monitor signals from GPS satellites

28
Q

where is the master control center for GPS satellites

A

Colorado

29
Q

what type of corrections are sent from the control station to a GPS satellite

A
  1. orbit correction
  2. time corrections
  3. atmospheric condition corrections
30
Q

what is the user segment of GPS

A

GPS receivers on the ground that pick up satellite signals

31
Q

what controls the number of satellites a GPS receiver will connect to

A

the number of channels (12 channels = 12 satellites)

32
Q

what are single frequency GPS receivers

A

receivers that only use the L1 frequency

33
Q

what type of data do single frequency GPS receivers have access to

A

time and position of satellite

34
Q

what type of data do dual frequency GPS receivers have access to

A

L1 and L2 (military recievers)

35
Q

what are dual frequency GPS receivers

A

receivers that use L1 and L2

36
Q

what is needed with GPS receivers for accurate readings

A

direct line of sight of the satellite

37
Q

what is trilateration

A

a method to find your position based on the distance from at least THREE known points

38
Q

how does 3D trilateration differ from regular trilateration

A

finding your position on earth’s surface, which is not flat but an ellipsoid

39
Q

what speed does the signal from the satellite travel at

A

speed of light

40
Q

what is pseudo-range

A

the distance between a GPS satellite and a GPS receiver

41
Q

how to calculate pseudo-range

A

speed of light * transmission time

42
Q

where is your location if two satellites are used

A

the location is somewhere along the boundary

43
Q

what happens when trilateration is done with 3 instead of 2 satellites

A

the location narrows to two points

44
Q

of the two points found with three satellites in trilateration, where are they

A

one is in space and the other is on earth

45
Q

what causes trilateration to NOT be accurate

A

time the signal takes to reach the receiver (if time is a little off from speed of light = huge distance on earth that’s off)

46
Q

what type of clocks do satellites use to reduce time errors

A

atomic clocks

47
Q

what type of clocks do receivers use to reduce time errors

A

quartz clock

48
Q

what is used in trilateration to account for time errors

A

a fourth satellite

49
Q

what are 5 sources of errors in GPS

A
  1. time dilution of precision
  2. position dilution of precision
  3. atmospheric interference
  4. multipath signals
  5. selective availability
50
Q

what is position dilution of precision

A

error introduced due to geometric position of satellite

51
Q

what results in higher position accuracy

A

a wider distribution of satellites

52
Q

where are two instances of atmospheric interference

A
  1. ionosphere (density and stratification variation)
  2. troposphere
    (atmosphere pressure and moisture)
53
Q

does the ionosphere cause larger error or the troposphere

A

ionosphere

54
Q

what is multipath signal error

A

an error caused by the reflection of GPS signals from surrounding surfaces

55
Q

what can be used to have the clearest signal to the satellite

A

antennas that raise the receiver so it has access to clear sky

56
Q

what is differential GPS

A

a method of using ground based corrections in addition to satellite signals

57
Q

where are base stations placed in DGPS

A

locations with known coordinates

58
Q

how do base stations work best

A

when built close to receivers

59
Q

what is real time kinematics

A

combination of GPS signals and a base station to provide real time corrections

60
Q

what is post processed kinematics

A

combination of GPS signals and a base station to correct location information POST data collection

61
Q

what is WAAS

A

a network of ground stations that measure variation in GPS signal

62
Q

importance of WAAS

A

reduces the error to 3 meters or less

GIS (5 decks)

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