AUSPOS - How it works

 

Question 3.1 - How does AUSPOS work?

All computations are undertaken using the Bernese Software System. Bernese is a high precision orbit and geodetic parameter determination software system. For more information see Bernese GNS Software.

The International GPS Service (IGS) product range is used in the computation process. Precise orbit parameters, Earth orientation parameters and coordinate solution IGS products are used.

NOTE: The IGS final orbit product is not available until approximately two weeks after the observation day. The rapid orbit product is available two days after observation. If both the final and rapid orbit products are unavailable, then the IGS ultra-rapid orbit product will be used.

Once a user has submitted a RINEX file, the nearest 15 IGS and APREF stations are used as the reference stations for the processing. That data is retrieved from Geoscience Australia’s GNSS Data Archive. A precise solution using a 'double difference' technique is then computed using these stations. The coordinates of the IGS stations are constrained with uncertainties of 1mm for horizontal and 2mm for the vertical.

Question 3.2 - How are observational errors accounted for?

The effects of observation error sources, such as receiver clocks, troposphere and ionosphere are taken into account, either through modelling, or estimation of related parameters. All the computations are undertaken according to IERS conventions.

A summary of the computation standards are provided as an appendix to all processing reports.

Question 3.3 - What Reference Frame is used?

All coordinates are computed in ITRF2008. For Australian users, Geocentric Datum of Australia 1994 (GDA94) coordinates are also provided in the report. GDA94 coordinates are determined by an AUSPOS derived ITRF to GDA transformation model. The accuracy of this transformation is sub-centimetre.

Question 3.4 - Does the system work with data collected anywhere on Earth?

Yes, the system was designed to work anywhere on Earth because the IGS network has global coverage. We download all IGS core station data and the APREF station data as soon as they are available in the Geoscience Australia GNSS data archive.