VOCABULARY

increased accuracy  более высокая точность

reference station  - референц станция  

range error correction поправки ошибок при определении дальности

pseudorange -  псевдодальность

in the vicinity  - в районе

ephemeris errors - эфемеридные (орбитальные) ошибки

satellite clock errors -  ошибки часов спутника

ionospheric errors – ионосферные ошибки

tropospheric errors – тропосферные ошибки

 

Find the answers to these questions in the following text:

1. What is the principle of the DGPS positioning?

2. What’s the difference between range and pseudorange?

3. Why are there inconsistencies between satellites?

4. What datum is the DGPS reference system?

5.  What are the sources of error?

 

Differential Global Positioning System (DGPS) has been conceived as a method of providing increased accuracy in positioning. DGPS is now the principal system used in hydrographic surveying to accurately determine the position of seabed features.

The principle of DGPS is that a single reference station at a known location can compute a range error correction for GPS satellites in view. The GPS consists of a network of 24 satellites launched by the USA. The error corrections are then broadcast to the ships in the vicinity. By applying the corrections to the signals received, a user can typically improve the accuracy in the order of 5 metres or less depending on the quality of the receivers.  Positions of a feature (e.g. sounding, navigation aids) should be referenced to the datum recommended as the World Geodetic System 84 (WGS 84), which is a geocentric reference system,

The first stage in the navigation process is to measure pseudorange, the distance between the satellite and the receiver (приемник). Pseudorange is obtained by multiplying the signal propagation time by the speed of light. Pseudorange differs from the actual range. It is corrected for many errors:

Satellite clock errors

Ephemeris errors (ephemeris - detailed orbit parameters)

Ionospheric errors

Tropospheric errors

 

ASSIGNMENT

1   Translate the words of the same root:

Available availability avail

Differ differential different

Err error erroneous

Refer reference referee referent referendum

Ephemeris ephemerial

 

2   Match the words in the box with their short definitions

 

the approximate distance to the satellite

 a body orbiting in space

 distance over which something has an effect

the time delay between the transmission of a signal from the satellite and its reception.

 

3   Match the opposites in the lines

Transmission, tenuous, transmit, corrections, high

Errors, reception, low, receive, dense

4   Are the following statements true or false? Agree or correct the false  ones

DGPS  is the measurement of the errors at a reference station and making them available to correct the readings of a mobile user (rover).

Differential Global Positioning System doesn’t know the position of the reference station.

Pseudorange is calculated by dividing the signal propagation time by the speed of light.   A user cannot improve the accuracy by applying corrections to the signals

 

5  Translate the sentences:

 

1  Псевдодальность,  полученная системой позиционирования,  отличается от истинной дальности.

2  Часы спутника являются причиной ошибок, они приводят к потере точности, если не внести поправки

3  Сигналы со спутников передаются на расстояние приблизительно двадцать тысяч километров 

4   На сигналы оказывает влияние атмосфера, причем основной результат - рефракция сигнала 

5  Тропосфера является важным источником ошибок позиционирования  для высокоточной съемки.