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The standard [[Work in Progress:DGNSS Fundamentals|DGNSS technique]] of the determination of the GNSS position for an accurately-surveyed position known as reference station. Given that the position of the reference station is accurately known, the deviation of the measured position to the actual position and more importantly the corrections to the measured pseudoranges to each of the individual satellites can be calculated. In classical DGNSS technology, only corrections to C/A code pseudoranges are being transmitted, which brings rover positional errors down to values about 1m. The remaining DGNSS error source is multipath, which can be reduced by the use of special multipath mitigation methods.
The standard [[Work in Progress:DGNSS Fundamentals|DGNSS technique]] of the determination of the GNSS position for an accurately-surveyed position known as reference station. Given that the position of the reference station is accurately known, the deviation of the measured position to the actual position and more importantly the corrections to the measured pseudoranges to each of the individual satellites can be calculated. In the classical DGNSS technology, only corrections to C/A code pseudoranges are being transmitted, which brings rover positional errors down to values about 1m. The remaining DGNSS error source is multipath, which can be reduced by the use of special multipath mitigation methods.


The main steps of DGNSS tecnique are:


--------------------
wikipedia:
*Operation
*Operation
A reference station calculates differential corrections for its own location and time. Users may be up to 200 nautical miles (370 km) from the station, however, and some of the compensated errors vary with space: specifically, satellite ephemeris errors and those introduced by ionospheric and tropospheric distortions. For this reason, the accuracy of DGPS decreases with distance from the reference station. The problem can be aggravated if the user and the station lack "inter visibility"—when they are unable to see the same satellites.


*Accuracy
A reference station calculates differential corrections for its own location and time. Users may be up to 200 nautical miles (370 km) from the station, however, and some of the compensated errors vary with space: specifically, satellite ephemeris errors and those introduced by ionospheric and tropospheric distortions. For this reason, the accuracy of DGNSS decreases with distance from the reference station. The problem can be aggravated if the user and the station lack "inter visibility"—when they are unable to see the same satellites.
DGNSS accuracy is in the order of 1 m (1 sigma) for users in the range of few tens of km from the reference station, growing at the rate of 1 m per 150 km of separation
 
The United States Federal Radionavigation Plan and the IALA Recommendation on the Performance and Monitoring of DGNSS Services in the Band 283.5–325 kHz cite the United States Department of Transportation's 1993 estimated error growth of 0.67 m per 100 km from the broadcast site[3][4] but measurements of accuracy across the Atlantic, in Portugal suggest a degradation of just 0.22 m per 100 km.[5]


*Post processing
*Post processing
Post-processing is used in Differential GPS to obtain precise positions of unknown points by relating them to known points such as survey markers. The GPS measurements are usually stored in computer memory in the GPS receivers, and are subsequently transferred to a computer running the GPS post-processing software. The software computes baselines using simultaneous measurement data from two or more GPS receivers.
Post-processing is used in Differential GPS to obtain precise positions of unknown points by relating them to known points such as survey markers. The GPS measurements are usually stored in computer memory in the GPS receivers, and are subsequently transferred to a computer running the GPS post-processing software. The software computes baselines using simultaneous measurement data from two or more GPS receivers.


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The improvement of GPS positioning doesn't require simultaneous measurements of two or more receivers in any case, but can also be done by special use of a single device. In the 1990s when even handheld receivers were quite expensive, some methods of quasi-differential GPS were developed, using the receiver by quick turns of positions or loops of 3-10 survey points. At the TU Vienna the method was named qGPS and adequate post processing software was developed.
The improvement of GPS positioning doesn't require simultaneous measurements of two or more receivers in any case, but can also be done by special use of a single device. In the 1990s when even handheld receivers were quite expensive, some methods of quasi-differential GPS were developed, using the receiver by quick turns of positions or loops of 3-10 survey points. At the TU Vienna the method was named qGPS and adequate post processing software was developed.
----------------------
 
*Accuracy
 
DGNSS accuracy is in the order of 1 m (1 sigma) for users in the range of few tens of km from the reference station, growing at the rate of 1 m per 150 km of separation The United States Federal Radionavigation Plan and the IALA Recommendation on the Performance and Monitoring of DGNSS Services in the Band 283.5–325 kHz cite the United States Department of Transportation's 1993 estimated error growth of 0.67 m per 100 km from the broadcast site[3][4] but measurements of accuracy across the Atlantic, in Portugal suggest a degradation of just 0.22 m per 100 km.[5]


==DGNSS funcionalities and performances==
==DGNSS funcionalities and performances==

Revision as of 09:30, 3 June 2011


FundamentalsFundamentals
Title DGNSS Fundamentals
Author(s) GMV
Level Basic
Year of Publication 2011
Logo GMV.png


The classical DGNSS technique technique is an enhancement to a primary GNSS system, that consists of the determination of the GNSS position for an accurately-surveyed position known as reference station. DGNSS accuracy is in the order of 1 m (1 sigma) for users in the range of few tens of km from the reference station.

The classical DGNSS technique

The standard DGNSS technique of the determination of the GNSS position for an accurately-surveyed position known as reference station. Given that the position of the reference station is accurately known, the deviation of the measured position to the actual position and more importantly the corrections to the measured pseudoranges to each of the individual satellites can be calculated. In the classical DGNSS technology, only corrections to C/A code pseudoranges are being transmitted, which brings rover positional errors down to values about 1m. The remaining DGNSS error source is multipath, which can be reduced by the use of special multipath mitigation methods.

The main steps of DGNSS tecnique are:

  • Operation

A reference station calculates differential corrections for its own location and time. Users may be up to 200 nautical miles (370 km) from the station, however, and some of the compensated errors vary with space: specifically, satellite ephemeris errors and those introduced by ionospheric and tropospheric distortions. For this reason, the accuracy of DGNSS decreases with distance from the reference station. The problem can be aggravated if the user and the station lack "inter visibility"—when they are unable to see the same satellites.


  • Post processing

Post-processing is used in Differential GPS to obtain precise positions of unknown points by relating them to known points such as survey markers. The GPS measurements are usually stored in computer memory in the GPS receivers, and are subsequently transferred to a computer running the GPS post-processing software. The software computes baselines using simultaneous measurement data from two or more GPS receivers.

The baselines represent a three-dimensional line drawn between the two points occupied by each pair of GPS antennas. The post-processed measurements allow more precise positioning, because most GPS errors affect each receiver nearly equally, and therefore can be cancelled out in the calculations.

Differential GPS measurements can also be computed in real-time by some GPS receivers if they receive a correction signal using a separate radio receiver, this is the case in Real Time Kinematic (RTK) surveying or navigation.

The improvement of GPS positioning doesn't require simultaneous measurements of two or more receivers in any case, but can also be done by special use of a single device. In the 1990s when even handheld receivers were quite expensive, some methods of quasi-differential GPS were developed, using the receiver by quick turns of positions or loops of 3-10 survey points. At the TU Vienna the method was named qGPS and adequate post processing software was developed.

  • Accuracy

DGNSS accuracy is in the order of 1 m (1 sigma) for users in the range of few tens of km from the reference station, growing at the rate of 1 m per 150 km of separation The United States Federal Radionavigation Plan and the IALA Recommendation on the Performance and Monitoring of DGNSS Services in the Band 283.5–325 kHz cite the United States Department of Transportation's 1993 estimated error growth of 0.67 m per 100 km from the broadcast site[3][4] but measurements of accuracy across the Atlantic, in Portugal suggest a degradation of just 0.22 m per 100 km.[5]

DGNSS funcionalities and performances

Notes


References