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In [[Real Time Kinematics|Real Time Kinematics (RTK)]], the compensation of the ionospheric delay between the base station and each of the roving users works for baselines up to 10-20 kilometers. When using a network of base stations, [[RTK Systems|Network RTK]] (NRTK), to mitigate atmospheric dependent effects over distance, the allowed distance between baselines and rovers increases up to 50-70 kms. In the late 1990s, the '''Wide Area RTK''' concept was introduced by the [http://www.gage.es/ Research Group of Astronomy and Geomatics (gAGE)] from the Technical University of Catalonia (UPC) to address these problems.


Differential GNSS (DGNSS) is a kind of [[GNSS Augmentation]] system based on an enhancement to primary GNSS constellation(s) information by the use of a network of ground-based reference stations which enable the broadcasting of differential information to the user – also named rover – to improve the accuracy of his position – the integrity is not assured.
==Wide-Area Real-Time Kinematics (WARTK)==
There are several DGNSS techniques, such as the [[DGNSS Fundamentals|classical DGNSS]] (or DGPS), the [[Work in Progress:Real Time Kinematics|Real Time Kinematics (RTK)]] and the [[Work in Progress:Wide Area RTK(WARTK)|Wide Area RTK (WARTK)]].
 
==Differential GNSS==
 
[[File:Claas_Baseline_HD.jpg|Transportable DGNSS reference station|thumb|250px]]


The classical [[Work in Progress:DGNSS Fundamentals|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. 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. These corrections can thereby be used for the correction of the measured positions of other GNSS user receivers.  
Starting in late 90's until nowadays, the group [http://www.gage.es/ gAGE/UPC] has developed the Wide-Area Real-Time Kinematics (WARTK) technique, which allows the extension of local services based on the real-time carrier phase ambiguity resolution to wide-area scale (i.e. baselines between the rover and reference stations greater than 100 km), for both dual-frequency (only GPS) and 3-frequency systems (also with Galileo and modernized GPS). The Wide-Area Real-Time Kinematics (WARTK) technique for dual and 3-frequency systems are based on an optimal combination of accurate ionospheric and geodetic models in a permanent reference stations network. The main factor limiting the range extension of the RTK technique beyond a few tens of kilometers is the differential ionospheric correction between the roving and the nearest reference GNSS station. Such ionospheric correction prevents the real-time ambiguity fixing, and therefore the corresponding accurate navigation at sub-decimeter level. The ionosphere produces ambiguity biases and correlations whose mitigation becomes the main problem to sort out. Even with the aid of multi-reference-station techniques, due to the baseline limitation (<20 km), several thousands would be required to cover such a service to the whole European region.<ref>[http://www.gsa.europa.eu/wartk-based-egnos-and-galileo-technical-feasibility-study WARTK-EGAL Project]</ref>


When GPS is the only constellation used for the Differential GNSS technique, the system is called DGPS. DGPS 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 main techniques supporting WARTK are related to an accurate real-time computation of ionospheric corrections, combined with an optimal processing of GNSS observables (carrier phases in particular) in both 2 and 3-frequency systems. The method increases the RTK/NRTK service area, with permanent stations separated by up to 500–900 kilometers — all while requiring 100 to 1,000 times fewer receivers covering a given region.<ref> Hernández-Pajares et al, ''Feasibility Study of a European Wide Area Real Time Kinematic System,'' invited talk in 4th ESA Workshop on Satellite Navigation User Equipment Technologies (Navitec), ESTEC, Noordwijk, The Netherlands, December 2008</ref>


The DGNSS term can be refer to specific implementations using DGNSS technique. It is often used to refer specifically to [[Work in Progress:DGNSS Systems|systems]] that re-broadcast the corrections from ground-based transmitters of shorter range. For instance, the [http://www.uscg.mil/ United States Coast Guard] and [http://www.ccg-gcc.gc.ca/ Canadian Coast Guard] run one such system in the US and Canada on the longwave radio frequencies between 285 kHz and 325 kHz. These frequencies are commonly used for marine radio, and are broadcast near major waterways and harbors. Australia runs two DGPS systems: one is mainly for marine navigation, run by  [http://www.amsa.gov.au/Shipping_Safety/Navigation_Safety/Differential_Global_Postitioning_System/Service_Status/index.asp Australian Maritime Safety Authority], broadcasting its signal on the longwave band; the other is used for land surveys and land navigation, and has corrections broadcast on the Commercial FM radio band.<ref>[[Wikipedia:DGPS|DGNSS in Wikipedia]]</ref>
Although its feasibility has been demonstrated with real data, no WARTK operational system has been deployed so far.


There are other DGNSS techniques used by high-precision navigation/surveying applications, based on the use of carrier phase measurements. These are the cases of  the [[Work in Progress:Real Time Kinematics|Real Time Kinematics (RTK)]] and the [[Wide Area RTK|Wide Area RTK (WARTK)]], where the differential GPS measurements are computed in real-time by specific GPS receivers if they receive a correction signal using a separate radio receiver.
==WARTK Related Articles==


==DGNSS Related Articles==
The following articles include further information about different important topics related to a WARTK:


The following articles include further information about different important topics related to a Differential GNSS:
* [[WARTK Fundamentals|WARTK Fundamentals]] introduces the recently-developed WARTK technique.
* [[Work in Progress:DGNSS Fundamentals|DGNSS Fundamentals]] introduces the classical DGNSS technique, its functionalities and the objectives of a DGNSS system.


* The [[Work in Progress:DGNSS Standards|DGNSS Standards]] article summarizes the international bodies in charge of the standardization of DGNSS systems, the principle applicable documents and its current status.  
* The [[WARTK Standards|WARTK Standards]] article summarizes some conventions, models and formats commonly used by WARTK.  


* [[Work in Progress:DGNSS Systems|DGNSS Systems]] sections provides a brief overview of the current existing DGNSS systems.
* [[WARTK Systems|WARTK Systems]] sections provide an overview of the potential WARTK systems and applications.


==Notes==
==Notes==

Latest revision as of 17:13, 18 September 2014


FundamentalsFundamentals
Title Wide Area RTK (WARTK)
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

In Real Time Kinematics (RTK), the compensation of the ionospheric delay between the base station and each of the roving users works for baselines up to 10-20 kilometers. When using a network of base stations, Network RTK (NRTK), to mitigate atmospheric dependent effects over distance, the allowed distance between baselines and rovers increases up to 50-70 kms. In the late 1990s, the Wide Area RTK concept was introduced by the Research Group of Astronomy and Geomatics (gAGE) from the Technical University of Catalonia (UPC) to address these problems.

Wide-Area Real-Time Kinematics (WARTK)

Starting in late 90's until nowadays, the group gAGE/UPC has developed the Wide-Area Real-Time Kinematics (WARTK) technique, which allows the extension of local services based on the real-time carrier phase ambiguity resolution to wide-area scale (i.e. baselines between the rover and reference stations greater than 100 km), for both dual-frequency (only GPS) and 3-frequency systems (also with Galileo and modernized GPS). The Wide-Area Real-Time Kinematics (WARTK) technique for dual and 3-frequency systems are based on an optimal combination of accurate ionospheric and geodetic models in a permanent reference stations network. The main factor limiting the range extension of the RTK technique beyond a few tens of kilometers is the differential ionospheric correction between the roving and the nearest reference GNSS station. Such ionospheric correction prevents the real-time ambiguity fixing, and therefore the corresponding accurate navigation at sub-decimeter level. The ionosphere produces ambiguity biases and correlations whose mitigation becomes the main problem to sort out. Even with the aid of multi-reference-station techniques, due to the baseline limitation (<20 km), several thousands would be required to cover such a service to the whole European region.[1]

The main techniques supporting WARTK are related to an accurate real-time computation of ionospheric corrections, combined with an optimal processing of GNSS observables (carrier phases in particular) in both 2 and 3-frequency systems. The method increases the RTK/NRTK service area, with permanent stations separated by up to 500–900 kilometers — all while requiring 100 to 1,000 times fewer receivers covering a given region.[2]

Although its feasibility has been demonstrated with real data, no WARTK operational system has been deployed so far.

WARTK Related Articles

The following articles include further information about different important topics related to a WARTK:

  • The WARTK Standards article summarizes some conventions, models and formats commonly used by WARTK.
  • WARTK Systems sections provide an overview of the potential WARTK systems and applications.

Notes


References

  1. ^ WARTK-EGAL Project
  2. ^ Hernández-Pajares et al, Feasibility Study of a European Wide Area Real Time Kinematic System, invited talk in 4th ESA Workshop on Satellite Navigation User Equipment Technologies (Navitec), ESTEC, Noordwijk, The Netherlands, December 2008
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