[IGSSTATION-5390] Pre-1995 antenna height of GOLD

[Jeff Freymueller]

From: Jeff Freymueller
email: jeff.freymueller at gi.alaska.edu

I am reprocessing some old data, and I think the current IGS log for GOLD may have the incorrect antenna height for the pre-1995 antenna. The relevant section of the current log is given below. The antenna height for the original antenna is given as -0.0709 m, which is listed as the measured height of the choke ring. Prior to a 2007 revision of the log, the height was given as zero.

I think the older log is correct and the revision is wrong, for two reasons. First, I see a roughly 7 cm step in the time series when I use the current log, which is consistent with an incorrect antenna height prior to November 1, 1995. Second, the entry 4.2 says that the reference surface is a mounting plate, with the new antenna mounted 2.54 cm above this. It is possible that the mounting plate was installed at the level of the top of the choke ring of the JPLD/M_R antenna, but it seems much more likely that the bottom of the JPLD/M_R antenna was on top of the mounting plate. As the ARP for the JPLD/M_R antenna was at the same level as the BCR, that would mean an antenna height of zero.

Actually, the older log also appears wrong in one respect. It gave an antenna height of 0.0 to the TCR of the antenna, and while this might be consistent with the solutions used for very old ITRF models, that reflects a different reference point from the current ITRF, which is based entirely on data after the change. So I think the correct entry for Antenna 4.1 should be a height of 0.0 to the ARP.

If anyone can confirm or refute my conclusions, or has solid evidence (like comparative photos) for how the old antenna was mounted, relative to current antenna, please contact me at jeff.freymueller at gi.alaska.edu. If there are several replies, I will summarize for the IGSSTATION mail.

Jeff

4.1  Antenna Type             : JPLD/M_R
     Serial Number            : 95
     Antenna Reference Point  : BCR
     Marker->ARP Up Ecc. (m)  : -0.0709
     Marker->ARP North Ecc(m) : 0.0000
     Marker->ARP East Ecc(m)  : 0.0000
     Alignment from True N    : 0
     Antenna Radome Type      : NONE
     Radome Serial Number     : 
     Antenna Cable Type       : (vendor & type number)
     Antenna Cable Length     : (m)
     Date Installed           : 1989-12-15
     Date Removed             : 1995-10-31
     Additional Information   : modified ARP from TCR to
                              : BCR, 2007-11-02
                              : (measured TCR-BCR of actual choke ring)

4.2  Antenna Type             : AOAD/M_T
     Serial Number            : 401-B
     Antenna Reference Point  : BPA
     Marker->ARP Up Ecc. (m)  : 0.0254
     Marker->ARP North Ecc(m) : 0.0000
     Marker->ARP East Ecc(m)  : 0.0000
     Alignment from True N    : 0
     Antenna Radome Type      : NONE
     Radome Serial Number     : 
     Antenna Cable Type       : (vendor & type number)
     Antenna Cable Length     : (m)
     Date Installed           : 1995-10-31
     Date Removed             : (CCYY-MM-DDThh:mmZ)
     Additional Information   : Low noise, wide band LNA
                              : Mounting plate is virtual marker surface,
                              : 1-inch spacer accounts for .0254 ARP Up