AUSPOS - GPS Antennas

Question 5.1 - Why do I have to specify the GPS antenna?

To achieve the highest quality processing results, attention needs to be paid to the type of antenna used. Using the incorrect antenna type can introduce significant bias (more than 10 cm in the vertical component) and noise into the computed coordinates.

The actual observation point on a GPS antenna is called the electrical phase centre. The location of this phase centre is represented by a mean constant offset from the physical point on a GPS antenna, known as the Antenna Reference Point (ARP), and an additional variable offset that is dependant on the transmitting satellite's elevation.

The properties of the electrical phase centre are different for every type of antenna. Importantly, the electrical phase centre can be modelled provided you know the antenna type.

Question 5.2 - What is the antenna height?

The antenna height is the vertical distance from the ground mark to the Antenna Reference Point (ARP). The ARP is the physical point on a GPS antenna that measurements are typically reduced to. The ARP varies between antenna types. As a WARNING, the ARP is rarely the top of the Antenna Ground Plane. The ARP height should NOT be confused with slant and other instrument height measurements commonly used in GPS processing.

Question 5.3 - What type of GPS antenna do I have?

AUSPOS uses the IGS antenna naming convention. The IGS - Naming Convention Document External site link provides more information.

Further information regarding the specifications of antennas can be found on the National Geodetic Survey (NGS) External site link antenna calibration web site.

Question 5.4 - What happens if I choose the DEFAULT(NONE) antenna?

If you choose the DEFAULT(NONE) antenna type; no antenna phase centre model or offset is applied.

If you set the antenna height to 0.0000 m and choose an antenna type, then the position of the ARP is computed.

Topic contact: geodesy@ga.gov.au Last updated: May 8, 2013