[IGSMAIL-204] Re

[Jeff]

From:     Jeff Freymueller
Subject:  Re: No 201: Proposal to standardize receiver and antenna names in
          RINEX
          -----------------------------------------------------------------



The name standardization proposal put forth by Ulf Lindqwister, Werner
Gurtner and Miranda Chin (in IGS Mail Message 201) is a good one, but
I have a few additional suggestions. This topic also brings a few other
ideas and questions to mind, which I will deal with after my comments
about the proposal.

For those who want to skim through this message, a quick summary is
 - Comments on proposed naming conventions
 - What are the monument inscriptions?
 - How were heights to Rogue and TurboRogue antennas measured?

In short, as a user of the IGS data (rather than a participant in IGS),
I think that we need to do a better job of site documentation
than has been done so far.


COMMENTS ON THE PROPOSED RECEIVER AND ANTENNA NAMING CONVENTIONS
> 
> The list below proposes a standardization of the receiver names and
> antenna names...
> 
> Trimble
> -------
> 
>         Receiver Type       Description
> 
>         TRIMBLE 4000S       4000SL and 4000SX (single frequency)
>         TRIMBLE 4000SD      4000SLD (dual freq. L2 squaring)
>         TRIMBLE 4000ST      4000SST (dual freq. L1 c/a, L2 squaring or p-code)
>         TRIMBLE 4000SE      4000SSE (dual freq. p-code on L1 and L2)

The RINEX format allows 20 characters for receiver name. I see no reason to
truncate Trimble's three letter typename to two letters. Fourteen characters
has no obvious advantages over fifteen!

More importantly, this list leaves out the Trimble 4000SDT, a receiver which
was used for some field campaigns in 1989 and early 1990. It was an
intermediate unit between the SLD and the SST. It was the last Trimble
receiver which could not sample on the integer GPS second.
> 
>         Antenna Type        Description
> 
>         GEODETIC L1         To use with Single frequency geodetic receiver 
>         GEODETIC L1/L2           "      Dual            "
>         KINEMATIC L1        antenna without a ground plane
>         KINEMATIC L1/L2                "

There have been at least three types of Trimble "Geodetic" antennas, called
the SXD, SLD and SST antennas. As far as I know, all three use the same
microstrip, but the dimensions of the ground planes and the preamp units
are different. Another antenna type is the built-in antenna that sat on
top of the receiver unit in some cases. Even though all but the SST are now
historical, our naming convention should not ignore them.

The mean phase centers for all these antenna types (and probably the
variation with azimuth and elevation) are different, due to the dimensions
of the package being different if nothing else.

The advantage of distinguishing between an L1 and L1/L2 antenna is not
clear. As far as I know, the L1 phase centers are identical for both types.
If that is true, then very little useful information is conveyed by
making the distinction. The only case I can think of where it might make
some difference is that if a dual frequency receiver was using a single
frequency antenna, knowing so would explain the lack of L2 data!
> 
> Ashtech
> ------
>         Receiver Type       Description
> 
>         MD-XII              Dual freq. L1 c/a and L2 squaring
>         P-XII               Dual freq. p-code on both L1 and L2

Don't forget the Ashtech L-XII receiver, which is similar to the MD-XII.
I don't remember what the differences are, except that the L-XII was the
earlier model..
> 
> 
>         Antenna Type        Description
> 
>         GEODETIC L1/L2      Dual freq. with a ground plane
>         MARINE/RANGE        Single freq. with a smaller ground plane
>         A-C L1              Single freq. without a ground plane for aircraft use
>         A-C L1/L2           Dual freq. without a ground plane for aircraft use
> 

There have also been at least two Ashtech "Geodetic" antennas. Again, the
microstrips are the same but the physical dimensions differ.


MARKER NAMES

It was decided early on in the IGS campaign that the "MARKER NAME" record
of the RINEX files should contain the four character site ID rather than
the actual marker name. In my opinion, this is not very useful since the
four character ID is also given in the file name. Furthermore, receivers
have been known to move to different monuments from time to time. I
maintain that in 5 years everyone will be hard pressed to remember what
"KOK2" was, or what happened at USUDA, or what distinguished the three
sites all named "CANB" (two moves in 1992, before the start of the IGS
Campaign). Marker inscriptions, on the other hand, do not change with
time and thus are a more useful permanent identification. I suggest that
there should be more discussion on this topic (perhaps by email between
interested parties). Even if it is necessary for some software to read
the four character site ID from the RINEX file, there is nothing to prevent
the actual marker inscription from being given in a "COMMENT" line in
the RINEX file.

On this topic, I have read through all the IGS mail messages except for a
few that I missed (and was unable to find), and I have yet to see a complete
listing of the marker inscriptions for all the IGS sites. Examples of sites
I have not seen inscriptions for are: CANB, FAIR, MATE, MCMU, METS,
NYAL, GOLD, PAMA, SANT, STJO, TAIW, USUD, YARG, DARW, and MASP. While
certainly some of these 15 are due to ignorance on my part, it is clear
that it is time (past time!) for a complete list to be compiled and
distributed through the IGS Mail.

I would like to say that the information given about the Pie Town and North
Liberty sites is exactly the way it ought to be done in the future. The
monument inscription, site ID, antenna type and antenna height were all
given at the time the receiver started tracking. I think it is important
for all future IGS sites to follow this example!

ANTENNA HEIGHTS

JPL has always distributed antenna heights measured to the TOP of the choke
rings. While not in accord with the RINEX standard, which would specify the
base of the antenna unit (where the screw mount is located), at least it
is a well-defined point. It is worth noting that the RINEX point, at least
on the TurboRogue antenna, is NOT the base of the rings themselves - but
rather the base of the ring unit (which is 3.4 cm below the base of the actual
rings. The 10.16 cm ring height includes this.

It is not clear how some of the other heights have been measured. If a height
is given as being to the base of the choke rings, does this mean the base
of the rings, or the base of entire unit?

TurboRogue antenna:
             ____
            /    \
       ----------------   <- TOP of choke rings
       |              |
       |              |
       ----------------   <- base of the actual rings - if a slant height
            |    |              was measured it would probably be to here.
            ------        <- RINEX point

Also, most of the JPL sites have antenna heights given as 16.30 cm to the
TOP of the choke rings. This height has been reported for sites with both
Rogue and TurboRogue antennas. Since the choke rings have different heights,
it is not clear how the same mounting system would give exactly the
same height to the top of the choke rings.

Jeff Freymueller  (jeff at pangea.stanford.edu)
Stanford University