Efficient and accurate surveying with GPS/Glonass

Satref consists of: Permanent GPS/Glonass

reference stations situated almost all over Norway

Control centre, located at NMA, Hønefoss.

What SATREF does:The SATREF® services continuously model the size of the effects of different error sources in the GPS and Glonass systems We generate and distribute both real-time reference/correction data (RTCM) and post processing data (RINEX).

The reference stations PGS-B: 16 stations on the Norwegian mainland

+ Ny Ålesund, Jan Mayen, Höfn (Iceland) PGS-C: About 60 stations (continuously increasing)

The station coordinates are computed in two independent ways:

Precise point positioning (solution in ITRF2005, transformed to EUREF89)

GNSS baselines from the 4 closest EUREF89 benchmarks (landsnett, stamnett)

Satref services accuracy

22 metres or better for 95%

of the measurements

GPS onlyMPOS DPOS

CPOS

Your positionYour surveyed position

ETPOS

Possible to achieve

millimetre accuracy

3-5 metres or better for 95%

of the measurements

3 decimetres (30

centimetres) or better for 95%

of the measurements

5 centimetres or better for 95% of the

measurements

CPOS: Data flow

Reference data (RTCM)

SATREF® control centre GNSS position (NMEA) GNSS rover

GNSS raw observation(and ephemeris) data

fromthe reference stations

IGS

Predictedephemerisdata

Data processing Sofware: Trimble GPSNet Input:

GNSS raw observation data Predicted (and broadcast) ephemeris data Known station coordinates

Network processing between the stations error models (“network corrections”) are created

The VRS principle (I)Ref. station

Virtualref. station(VRS)

50km

The VRS principle (II) Network-RTK in CPOS are operated in the same

way as traditional RTK, but a mobile reference receiver is replaced by a virtual reference station (VRS). CPOS uses one of the first NMEA positions it gets from the user as a VRS.

The reference data from the VRS are based on the nearest physical stations.

The CPOS software takes the observation data from the nearest physical station, modifies them by the network corrections and transforms them to the VRS position.

The VRS principle (III)Ref. station

Virtualref. station(VRS)

GNSS rover

Connecting to CPOS Mobile phone

GSM

Internet NTRIP protocol

• This reduces telecom. costs• Most users today connect via GPRS on a

mobile phone, but there are alternatives

GPS only

GPS+Glonass (full coverage autumn 2008)

All combinations are possible

Reference data formatRTCM v2.3 (CPOS via mobile phone with GPS

only) Contents (in brief):

Pseudorange “measurements” Carrier phase “measurements” Position of the VRS + “antenna” description (“null-antenna”) Position of the nearest physical reference station

RTCM v3 (all other CPOS varieties) Contents (in brief):

Pseudorange “measurements” Carrier phase “measurements” Position of the VRS + “antenna” description (“null-antenna”) Position of the nearest physical reference station Residual messages from the model interpolation

What are the SATREF services used for?

Navigation

Land surveying

Registration

Retrieving

Machine guidance

Flight positioning for photogrammetry, laser scanning etc.

Documentation

Who are the users of CPOS?

MunicipalitiesEnergy

Governmental

Private surveying

Contractors

Quarrying/mining

Others

CPOS today Today there are more than 400 users

CPOS is offered to the entire country, but is only established when there is a sufficient market.

Establishing and management are financed by the users: 4 users per station established, 2 years commitment and 20000 NOK (approx. 2500

EUR) + VAT each year Discount for customers with several users:

• 3 – 10 users: 15000 NOK• >= 11 users: 13000 NOK

The SATREF services are non-profit services. This means that a possible profit in the short run is used to

reduce the prices upgrade existing reference stations establish more reference stations

CPOS coverage areas

Areas covered during 2008

CPOS in the future Goals for 2015:

Coverage area: The 95% most populated areas in Norway + important infrastructure areas (roads, rail)

1 cm 3D accuracy with a relatively high level of integrity

Additional use of the reference stations GNSS observation data from the stations are used in

Monitoring and analysing the performance of EGNOS at northern latitudes

Making a Norwegian ionosphere model Meteorology Monitoring crust movements

• Plate tectonics• Post-glacial rebound (land uplift)

Some stations give observation data to IGS, EUREF and other organisations/institutions

All this means that we have to make sure that the quality of the stations is as good as possible