What exactly is a CORS site?

[topflitejr1]

I went to AB5060 and AB5061 , and found EV3853 LIME, an Earthquake Research Station (LIME II) and a Gravity Station (PBB20). I could not find any BM's for AB5060 or AB5061, but did see a green fiberglass box and a GPS looking device about 8 feet tall. It was a small half-dome mounted on four fixed legs (quadropod?). The coords on my GPSr were within 6 feet of the given adjusted coords. Is this a CORS site or BM that I am looking for?

[DaveD]

CORS stands for Continuously Operating Reference Station, and what you found was the CORS. Each CORS consists of a dual-frequency GPS antenna and receiver mounted on a very stable platform. The receivers run 24/7/365 and in some cases have been operational for more than 14 years. At some, but certainly not all, there may be a classical passive bench mark nearby. The CORS form the foundation for contemporary positioning around the world. The positions of most CORS are accurate to +/- 1 cm in horizontal and 2-3 cm in ellipsoid height. If you go to the NGS home page www.ngs.noaa.gov, and select CORS/OPUS you will find a map of the network coordinated by NGS. Many of these sites have pictures of the antennas and receivers.

[+Klemmer]

Around here, many are inside various local city or county maintenance yards, and so are not very accessible. Personally, I rarely log them. Certainly no need to do so in the NGS database. Their position is well known!

 

On GC.com, I suppose if you lay eyes on them, or better yet get a picture, a log is appropriate if you want.

[topflitejr1]

Around here, many are inside various local city or county maintenance yards, and so are not very accessible. Personally, I rarely log them. Certainly no need to do so in the NGS database. Their position is well known!

 

On GC.com, I suppose if you lay eyes on them, or better yet get a picture, a log is appropriate if you want.

 

So I guess that I was looking for the CORS site and not an actual disc then. Funny that there are two different PID's for the same site. Thanks for your help again and to Dave.

[+Klemmer]

The details are often on the CORS website entry for the station, but the actual "mark" or "marks" are located in very specific locations on the system. For example, the base of the antenna, or the (theoretical) center of the phase loop of the antenna. That seems to be what the first two PIDs are in your original post. No discs for them, as you now realize.

[DaveD]

All CORS have two points that are positioned, the Antenna Reference Point (ARP) sometimes called the "monument," and the L1 Phase Center. An excellent description of the L1 Phase center comes from the paper of antenna calibrations by Dr. Gerry Mader of NGS, "the phase center of a GPS antenna is neither a physical point nor a stable point. For any given GPS antenna, the phase center will change with the changing direction of the signal from a satellite." The ARP is the physical point on which the GPS antenna is mounted. Surveyors can use either position in their GPS processing but are typically encouraged to use the ARP since the position of that point will seldom change, while the L1 phase center value would change if the antenna is changed for some reason. Note that the positional difference between these two points is almost exclusively in the ellipsoid height. In the case of the station at Pearblossom it's 6.4 cm. In extreme cases the offsets can be 8-12 cm. This can be a big problem for surveyors if they do not correctly identify exactly which type of antenna model they are using.

[Wintertime]

So I guess that I was looking for the CORS site and not an actual disc then.

Yeah, the terminology is confusing! You'd expect "Marker Type: NGS Benchmark" to mean a metal disk, wouldn't you? Not being very familiar with CORS stations myself, I did a double-take on that one, too. I guess if you want to look for traditional benchmarks, you'll need to look for the term "disk" in the data sheets (or in the "Type" column of Geocaching.com's benchmark listings).

 

Patty

[+Black Dog Trackers]

topflitejr1 -

 

Yeah those PIDs were a bit confusing as to what they were. Usually a CORS PID says it's a CORS. I think the NGS also doesn't need recovery reports CORS stations. In a way, they are being recovered constantly.

 

For logging them on this site, I think taking a picture of what looks like its satellite antenna is sufficient, or even saying you saw the gadget or some part of it without providing a picture would be a sufficient log. I haven't logged one of these myself, but I would do it from a distance if I did. They look sensitive and expensive so I wouldn't want to get very close even if I could.

[topflitejr1]

topflitejr1 -

 

Yeah those PIDs were a bit confusing as to what they were. Usually a CORS PID says it's a CORS. I think the NGS also doesn't need recovery reports CORS stations. In a way, they are being recovered constantly.

 

For logging them on this site, I think taking a picture of what looks like its satellite antenna is sufficient, or even saying you saw the gadget or some part of it without providing a picture would be a sufficient log. I haven't logged one of these myself, but I would do it from a distance if I did. They look sensitive and expensive so I wouldn't want to get very close even if I could.

 

Black Dog Trackers, Wintertime, Klemmer&TBM and DaveD, I give you all a "10" for informative responses. I now have a greater understanding on CORS sites. Reminds me of the time I had my wife look for a BM for me at the school she works ( she is a school nurse at Lake LA School about 12 miles away). She said that there were no disks, just a funny looking instrument with a fence around it. Knowing that she knows very little about BMing, I drove out to see for myself, and only saw the "funny looking instrument" and no BM's. When you look it up on the GEOCAC website, it says "No PID's listed..." So I gave up on it until I came across a "funny looking Instrument" again at AB5060/61. Turns out there are a few more here in the Antelope Valley, which should make for good "drive-bys" and to add to my count. I won't bother wasting Debs time by reporting them to her. Thanks again everyone-Ken

[DaveD]

Black Dog was right. The CORS collect GPS data are rates that vary from 1 to 30 seconds. The data for most stations is bundled and transmitted to NGS on the hour, so we have a pretty good idea when a station goes down.

[+GEO*Trailblazer 1]

CORS DISCUSSION

 

Here is a link and something we talked about on them before.

[Z15]

fYI

 

Here are some photos of a USCG CORS KEW1, up here on Lake Superior. If you look closely at the center of top image you can just make out the Lake. The bottom photo shows the NGS control point (a bunch surround this site, NOS, USCE, USLS, NGS)

 

 

This is not far from just of State Hwy M26 near McClain State Park out of Hancock

Edited March 26, 2008 by Z15