Тест по Differential GPS (CES v5.0)

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Правильные ответы:
1

GLONASS is an alternative to what system?

Ваш ответ правильный:

Navstar GPS.
2

Global Navigation Satellite Systems (GNSS) provides three services known collectively as PNT, what are they?

Ваш ответ правильный:

Position, Navigation and Timing.
3

How can the adverse effects of the ionosphere and troposphere be minimized?

Ваш ответ правильный:

The effects of the ionosphere and troposphere can be reduced by not using the data from satellites below a certain altitude.
4

How does the Differential GPS improve the accuracy of the output position?

Ваш ответ правильный:

An error of position message is provided by a differential reference station and sent to the ship.
5

How does the Navstar GPS receiver finds a position using the calculated distances from satellites?

Ваш ответ правильный:

The intersection of spheres of position with the satellites at their centres.
6

In the Navstar GPS system there are normally 24 active satellites, how many different carrier frequencies are used for transmissions by all of the GPS satellites?

Ваш ответ правильный:

Each satellite uses 2 carrier frequencies.
7

In the Navstar GPS system there are normally 24 active satellites, how many different carrier frequencies are used for transmissions by all of the GPS satellites?

Ваш ответ правильный:

Each satellite uses 2 carrier frequencies.
8

In the Navstar GPS system, satellites orbit the earth at an altitude of approximately what distance?

Ваш ответ правильный:

20 200 km.
9

In the Navstar GPS system, satellites orbit the earth in approximately:

Ваш ответ правильный:

12 hours.
10

It is commonly recognised, that the Navstar GPS system consists of three main segments. What are these segments?

Ваш ответ правильный:

Space, Control and User segment.
11

It is recognized, that Global Navigation Satellite Systems (GNSS) transmit signals, that can be used to provide three different services. What are these?

Ваш ответ правильный:

Position, Navigation and Timing.
12

The Navstar GPS provides two levels of service. What are they?

Правильный ответ:

Standard SPS and Precise PPS.

Ваш ответ:

Special SPP and Standard SSP.
13

What actions should be taken by the Officer of the Watch when the Navstar GPS receiver is set to provide an output position of latitude and longitude using the datum of WGS 84, which is different to the datum on the paper chart?

Ваш ответ правильный:

Apply the corrections marked on the chart before plotting the latitude and longitude.
14

What are the dangers of the Officer of the Watch being totally reliant on the Navstar GPS?

Ваш ответ правильный:

It is always dangerous to be totally reliant on one navigational system, because no single navigational system is 100 % reliable.
15

What datum is used by the HO approved vector charts, as used by the Navstar GPS system?

Ваш ответ правильный:

WGS84.
16

What geographical factors can affect the accuracy of the Differential GPS produced position?

Ваш ответ правильный:

Distance between ship and Reference Station.
17

What is a “Multipath Error” when related to GNSS?

Ваш ответ правильный:

A multipath error is when the satellite signal is reflected off something before arriving at the receiver.
18

What is meant by the abbreviation RAIM?

Ваш ответ правильный:

Receiver Autonomous Integrity Monitoring.
19

What is the affects of selective availability being switched off?

Ваш ответ правильный:

More accurate positions.
20

What is the approximate strength of the GPS transmitted signal?

Ваш ответ правильный:

100 watts.
21

What is the difference between the speed of a radio signal and the speed of light?

Ваш ответ правильный:

Nothing.
22

What is the nearest approximation of the shape of the earth?

Ваш ответ правильный:

Spheroid.
23

What is the pseudo-random code with reference to the Navstar GPS?

Ваш ответ правильный:

The complicated digital code sent from the satellite and mirrored by the GPS receiver.
24

What is the reason for “clock error” with reference to the Navstar GPS system?

Ваш ответ правильный:

The difference between the time at the satellite clock and the time at the receiver clock.
25

What is understood by the abbreviation WAAS?

Правильный ответ:

Wide Area Augmentation System.

Ваш ответ:

Wide Augmentation Accuracy System.
26

What is “Jamming” when referred to GNSS?

Ваш ответ правильный:

Jamming is the intentional blocking of the satellite signals.
27

What output figure of HDOP indicates good accuracy?

Ваш ответ правильный:

Lower than 4.
28

What types of Global Navigation Satellite Systems (GNSS) receivers are used at sea for navigational purposes?

Ваш ответ правильный:

Navstar GPS, GLONASS, and combined Navstar GPS and GLONASS, while other GNSS are under development.
29

When a Navstar GPS receiver loses the satellite signals, it reverts to what mode of operation?

Ваш ответ правильный:

DR mode.
30

When considering GPS what is the main function of RAIM?

Ваш ответ правильный:

To assess the integrity of the GPS signals.
31

When considering GPS, a 3D position has three unknown parameters: latitude, longitude and altitude. Why are signals from four satellites required to find an accurate 3D position?

Ваш ответ правильный:

Because of the receiver clock error.
32

When considering GPS, how does the elevation mask angle influence the number of available satellites for position fixing?

Ваш ответ правильный:

Normally, the higher the elevation mask angle is set, the fewer satellites are available.
33

When considering GPS, what is the result of receiving multipath signals?

Ваш ответ правильный:

System accuracy decreases.
34

When considering Navstar GPS receiver, what is the minimum number of satellites, that must be available to calculate a 3 Dimensional (latitude, longitude and altitude) position?

Ваш ответ правильный:

4.
35

When considering Navstar GPS, what is the meaning of pseudo-range?

Ваш ответ правильный:

Initial calculated distance between the satellite and the receiver.
36

When considering Navstar GPS, what is the name of the common error, affecting the orbital satellite position information?

Ваш ответ правильный:

Ephemeris error.
37

When considering Navstar GPS, what is the safest operating mode to select?

Ваш ответ правильный:

Three dimensional.
38

When considering Navstar GPS, which DOP is most important for a maritime user when checking GPS accuracy?

Ваш ответ правильный:

HDOP.
39

When considering Navstar GPS, which coordinate system (datum) is recommended to be used at all time?

Ваш ответ правильный:

WGS-84.
40

When considering a Navstar GPS receiver the output course and speed, provided by the receiver, provides what information?

Ваш ответ правильный:

The course and speed over the ground.
41

When considering a Navstar GPS receiver, what control should be operated when a member of the crew falls over the side of the ship?

Ваш ответ правильный:

The “Man overboard” button.
42

When considering a Navstar GPS receiver, what is the minimum number of satellites, that must be available to calculate a 2 Dimensional (latitude and longitude) position?

Ваш ответ правильный:

3.
43

When considering a basic GPS, which of the following statements is true?

Ваш ответ правильный:

If own ship speed is low, the GPS calculated speed over the ground is of low accuracy.
44

Why are the calculated ranges known as “pseudo-ranges”?

Правильный ответ:

They are referred to as pseudo-ranges, because they are based on an estimate of time difference.

Ваш ответ:

They are referred to as pseudo-ranges, because they are not actually a measurement of range.
45

Why is it considered dangerous to totally rely on the Navstar GPS for obtaining positions?

Ваш ответ правильный:

Because it is not 100 % reliable.
46

With reference the Navstar GPS outputs, what does a low HDOP figure indicate?

Ваш ответ правильный:

A low HDOP figure indicates a probable accurate position, provided by broad angles of intersections between the position lines from the satellites in use.
47

With reference to Navstar GPS system used in conjunction with a Differential Reference Station, on what is the accuracy of the resultant position mainly dependant?

Ваш ответ правильный:

The distance between the observer and the reference station.
48

With reference to Navstar GPS system, what happens to the GPS radio signal speed when it passes through ionosphere?

Ваш ответ правильный:

The speed decreases.
49

With reference to Navstar GPS, how many ground based control stations are used to monitor the satellites?

Ваш ответ правильный:

The Master control station and 4 regional control stations.
50

With reference to Navstar GPS, why is the initial calculated range of the satellite call “pseudo-range”?

Ваш ответ правильный:

The initial range is calculated uses an assumption to make the calculation.
51

With reference to a standard ships Navstar GPS receiver, how would the probable accuracy of the output position be indicated?

Ваш ответ правильный:

HDOP.
52

With reference to the Navstar GPS system, how are the inaccuracies of position due to “clock error” removed?

Ваш ответ правильный:

By making use of the signal from one more satellite than the minimum required.
53

With reference to the Navstar GPS system, which statement is true?

Ваш ответ правильный:

GPS provides good global coverage.
54

With reference to the Navstar GPS, what are the effects on the ships position, resulting from an incident of “spoofing”?

Ваш ответ правильный:

Spoofing can deliberately produce a feasible, but incorrect position.
55

With reference to the Navstar GPS, what is the result of the height of the GPS antennae being incorrectly entered into the GPS receiver?

Ваш ответ правильный:

When in the 2 dimensional mode of operation the GPS position may be less accurate.
56

With reference to the Navstar GPS, what is the significance of the “pseudo-random code” of the satellite transmissions?

Ваш ответ правильный:

The signal is so complicated, that it almost looks like random electrical noise.
57

With reference to the Navstar GPS, what is “selective availability” and does it affect the GPS position accuracy at this time (2011)?

Ваш ответ правильный:

Selective Availability is when the GPS accuracy is intentionally degraded to a maximum of 100 meters, 95 % of the time. It ceased to be operational in the year 2000.
58

With the Navstar GPS system, how many monitoring stations are there?

Ваш ответ правильный:

4.
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