TRIUMPH-2 Antenna Calibration

TRIUMPH-2 shown with its slant height measurement point (SHMP). The green triangle is also the indication of the north orientation mark (NOM); the direction the antenna should be facing when surveying.

During its first year in existence, the TRIUMPH-2 had a special distinction made by NGS, specifically in regards to its antenna calibration data. During the year 2014, NGS had two different antenna models: one with the 25mm x 1/4” x 20 threaded adapter [10-590293-01] included and one without it. The net result related only to the Antenna Reference Point (ARP).

Beginning in January 2015, and in accordance with the standardized definition that the ARP is the lowest non-removable part of the antenna, NGS has removed the antenna type model that had included the 25 mm x 1/4” x 20 threaded adapter in its ARP. Accordingly, as of January 2015, NGS is listing only one model antenna type for the internal 360 antenna of the TRIUMPH-2; the JAVTRIUMPH_2A. This is the first distinction that users need to pay very close attention to; specifically, their HIs (ARPs) if they have recorded observations using the TRIUMPH-2 during the calendar year 2014 and then process those data after 2014.

PCOs and PCVs
Additionally, the second distinction that users need to be aware of is the antenna calibration data for the internal antenna has been updated. This separate distinction relates to both Phase Center Offset and Phase Center Variation values for the internal antenna of the TRIUMPH-2.

The original PCOs and PCVs that the NGS Antenna Calibration team had initially determined in March 2014 have been superseded by the highly precise values produced after recalibration on a Geo++ robot. These so-called nearfield calibrations included the use of the 25mm x 1/4” x 20 threaded adapter [10-590293-01] and is reflected by the suffix A attached at the end of the antenna model’s name: JAVTRIUMPH_2A. Finalization was coordinated through the International GNSS Service (IGS) in December 2014.

If survey work has been performed with the TRIUMPH-2 and processed using the superseded NGS values and which had critical elevation determinations, users are advised to reexamine those projects and to reprocess their data using the superior antenna model published in January 2015.

Differences in the elevation of surveyed points have been reported to be as much as 7 cm as improper Phase Center Variations will cause errors most notably in the vertical component in precise GPS surveys.

Measuring your HI
Beginning with the new standardized ARP definition, all antenna heights are to be measured to the lowest non-removable part of the antenna. This means that, for example, using a 2-meter fixed-height GPS pole, the correct HI will reflect the addition of the 25 mm adapter; i.e., 2.025 m. If the TRIUMPH-2 is setup on a standard tripod, measure the slant height from the mark to the green triangle on the side.

OPUS kindly reminds users of non-conforming antennas like the TRIUMPH-2 and the TRIUMPH-LS that the adapter must be added.

Please refer to the NGS Antenna Calibration webpage for additional information.