Subject: [SIR-Mail] No.1094: North reference point (NRP) definition added to antenna.gra From: Laura Sanchez This is a copy of [IGSMAIL-6987] North reference point (NRP) definition added to antenna.gra Dear IGS colleagues! In order to account for horizontal antenna phase center offsets (PCOs) and azimuthal phase center variations (PCVs), it is essential to know how receiver antennas have to be oriented with respect to the north direction. So far, this information was only provided by the antenna calibration facilities, whereas it was not contained in any of the IGS antenna files. At the IGS 2010 Workshop in Newcastle, the Antenna Working Group decided to follow the approach of a so-called ”north reference point” (NRP), in accordance with the well-established ”antenna reference point” (ARP) which provides the reference for measuring the antenna height above a certain marker. In contrast, the NRP designates the element of the antenna that has to be oriented toward the north direction. Following a recommendation of the IGS 2014 Workshop in Pasadena, the NRP definition could now be added to the IGS file antenna.gra that is available at ftp://ftp.igs.org/pub/station/general/antenna.gra There are four major features: MMI: man-machine interface NOM: north orientation mark (placed on antenna by manufacturer) RXC: receiver connector (connect antenna to external receiver) UNK: unknown Besides, there are twelve secondary features and connector designations that are only needed for specific antenna types. Generally, the north orientation mark (NOM) is chosen to be the NRP, in case it is present and clearly visible. If not, an alternative is needed. The NRP definition can be found in two places: 1) below the ARP definition within each antenna sketch (”???=NRP”), e.g.: > AOAD/M_T > > ----- > / > | | > +-------------------------------------------------+ <-- 0.1020 TCR > | | > | | > | | > | | > +-+-------------------------------------------------+-+ <-- 0.0380 > +-------------------+-------------+-------------------+ <-- 0.0350 BCR > | | > =| | > +------x------+ <-- 0.0000 BPA=ARP > RXC=NRP > <-- 0.3810 --> 2) besides the ARP definition within the machine-readable section at the end of the file, e.g.: > Machine-readable quick reference section begins here. ... > AOAD/M_T BPA RXC As regards the ”JAV_GRANT-G3T NONE” antenna, the NRP provided in antenna.gra (RXC=NRP) is not consistent with the robot calibration contained in igs08.atx so far. The latter referred to a north mark that was hardly visible. In consultation with the manufacturer, it was decided to harmonize the NRP for all JAV_GRANT/JAVGRANT antenna types. An updated robot calibration will be published with the next release of igs08.atx. IGS station operators are asked to consider the NRP definition provided in antenna.gra for future antenna installations, but NOT to touch current installations. Instead, a possible misalignment should be reported in the site log: > 4.x Antenna Type : (A20, from rcvr_ant.tab; see instructions) ... > Alignment from True N : (deg; + is clockwise/east) http://igscb.jpl.nasa.gov/igscb/station/general/blank.log Manufacturers are asked to provide NRP information together with the ARP definition when registering new antenna types for the IGS files. Ideally, each antenna type should be equipped with an easily visible north orientation mark. Help on identifying the NRP of outdated as well as uncalibrated equipment (all antenna types with UNK=NRP) is greatly appreciated. Please send a short note, ideally including a photo, to schmid@dgfi.badw.de! If you have further questions, please use the same e-mail address. Many thanks to everybody who helped to compile the long list of NRP definitions, especially to Geo++ and NGS! With best regards, Ralf Schmid on behalf of the IGS Antenna Working Group -- Laura Sanchez Deutsches Geodätisches Forschungsinstitut Alfons-Goppel-Str. 11, 80539 München phone: +49 89 23031-1295 fax: +49 89 23031-1240 mailto:sanchez@dgfi.badw.de http://www.dgfi.badw.de/