What Does Cors Mon. Mean?

[+Gonzo-YT]

Hi everyone,

 

First off, thanks to everyone for all the interest in my Alaska Highway benchmarks project. I'm hoping you can help me out. I have found NGS listings (no datasheets available) for three things in the same location:

 

WHITEHORSE CORS ARP

WHITEHORSE CORS L1 PHASE CENTER

WHITEHORSE CORS MON.

 

PIDs are DE6615 - 6617.

 

Based solely on the PIDs and descriptions, can anyone hazard a guess as to what this might be? It's located on top of a prominent hill near town, but a fair distance from the geodetic survey network along the highway.

 

Also, all the 1943 USC&GS discs I have been looking for have PIDS that start with TT. Does DE mean anything different? Could it have been placed at another time, or by another agency? I'm keen to go looking, but it's a 6km hike up that hill.

 

Regards,

Anthony

[+rogbarn]

This will be a simple reply. I'm sure others will be able to give more detail.

 

CORS is a Continuously Operating Reference Station (link is to NGS page on CORS).

They are new devices (compared to 1943). They are often (usually?) three PIDs, someone else will have to explain why they separate them. Don't disturb them. I've seen pictures, but I forget where.

 

As for the PID prefix, the general answer is that it doesn't mean a thing. The longer answer is that I often see newer PIDs with a DE prefix. I'm guessing that the area ran out of PID numbers for the assigned PID prefix and whoever assigns PIDs gave them a range in the DE prefix. I have also seen AA thru AF (or further perhaps) used for newer PIDs. Therefore, the longer answer shows that it is a newer PID.

 

try looking at these:

>JD2470 BLOOMFIELD 38 43 57.8/092 04 05.0 2 mo027.dat

>AI3678 BLOOMFIELD CORS ARP 36 52 47.1/089 58 21.0 A mo207.dat

>AI6543 BLOOMFIELD CORS L1 PHASE CENTE 36 52 47.1/089 58 21.0 A mo207.dat

 

In reviewing this group, I think your third entry is not part of the CORS, just a disk perhaps placed at the same time. The disk that I listed is some distance from the CORS station.

 

Anyway, that's a start, I'm sure some others will chime in.

 

EDIT:

Actually not usually three PIDs but usually two PIDs as both Gonzo-YT and my examples show.

Edited July 13, 2005 by rogbarn

[+PFF]

And not to be confused with the equally-important designation COORS, which gives the location where you can find a tall, cool beverage on a hot day.

 

-Paul-

 

______________________________________

Just outside Tryon, North Carolina, there

was a tavern called The Block House which

operated from the mid-1700's until the early

20th century. The state line divided the bar

room. It has been noted that all surveys of

this portion of the NC/SC border either started

or stopped at this tavern. Co-incidence? You

be the judge.

_____________________________________

[Z15]

Maybe you already found this but..

 

I tried to pull up the DS but all I get is;

 

** retrieval complete.

Elapsed Time = 00:00:00

Msg=FATAL_ERROR - No Marks found

 

Going down to bottom of the list the codes at teh far right tell me this.

 

N No geodetic control at this mark

O Outside NGS Publication Area

 

Is this mark in Canada? If so that would 'splain it.

 

Does DE mean anything different?

 

No, just entered into DB at different time and thus a different record number. Thats al the PID's are, a SYSBASE record number, like with any db program.

Edited July 13, 2005 by Z15

[+jwahl]

Each point will likely have the same lat long, but they represent different points vertically. The mon is the monument itself. Remember these have a GPS antenna permanently set on them, and there are a number of vertical values assigned from GPS antennas'.

 

A surveyor who is using a CORS station has collected GPS data using their own receiver at some point, then download the data from the CORS receiver and processes them to determine a position. To get an accurate vertical the post processing software must know how 'high' the CORS station GPS antenna is. To this end the "ARP" or antenna reference point is one method used. The surveyor must then look up the specs for the specific antenna and get the elevation difference between the ARP and the electrical center of the antenna. Another measure is called the L1 phase center, which is an average of the electrical center of the antenna for the L1 frequency used for static GPS survey work. There may also be an L2 phase center, and variations of these. The L1 value is commonly published.

 

So usually there will be the mark, above it somewhere the ARP and some small distance above that the L1 phase center.

 

There must be some good pics on the NGS cors web page to illustrate this, if anyone is curious I could hunt some down and post them. There are pics of many CORS stations out there.

 

- jlw

[Z15]

A surveyor who is using a CORS station has collected GPS data using their own receiver at some point, then download the data from the CORS receiver and processes them to determine a position.

 

To elborate on this, the data the surveyor or anyone for that matter with survey grade equipment downloads from the CORS site must be for the same date and time of his survey observations to come up with a solution. So if you have CORS stations in your area, your could set many point by sending your observations into the NGS OPUS processing site and get back solultions to your survey marks.

 

OPUS allows users to submit their GPS data files to NGS, where the data will be processed to determine a position using NGS computers and software.  Each data file that is submitted will be processed with respect to 3 CORS sites.  The sites selected may not be the nearest to your site but are selected by distance, # of obs, site stability, etc.  The position for your data will be reported back to you via email in both ITRF and NAD83 coordinates as well as UTM, USNG and State Plane Coordinates (SPC) northing and easting.

 

OPUS is completely automatic and requires only a minimal amount of information from the user:

 

        1. The email address where you want the results sent

        2. The data file that you want to process (which you may select using the browse feature)

        3. The antenna type used to collect this data file (selected from a list of calibrated GPS antennas)

        4. The height of the Antenna Reference Point (ARP) above the monument or mark that you are positioning

        5. As an option, you may also enter the state plane coordinate code if you want SPC northing and easting.

        6. As an option, you may select up to 3 base stations to be used in determining your solution.

 

 

Once this information is complete, you then click the Upload button to send your data to NGS.  Your results will be emailed to you, usually within a few minutes.  You may upload multiple data files in a zip archive if you wish.  However, be careful, the options that you choose will be applied to all of the data files in that archive (i.e. The same antenna type, ARP height will be used for all of the files in the zip file).

Edited July 14, 2005 by Z15

[+Gonzo-YT]

Thanks for the answers. Interesting question -- why would the NGS have established a CORS in Canada? It doesn't show up on their website, so I wonder if the site is still operating, sitting there derelict, or totally gone? I'm heading up there sometime for a geocache, so maybe I'll see what I can find.

[+bicknell]

They are new devices (compared to 1943). They are often (usually?) three PIDs, someone else will have to explain why they separate them. Don't disturb them. I've seen pictures, but I forget where.

A CORS location is actually a GPS Antanna / processing station. The reason there are three PIDs is that you need to know three things:

 

1) A MONument, eg the fixed location your monitoring. (Note, it appears some do not have a monument, but rather just the location of the antenna is surveyed, news to me.)

 

2) The Antenna Reference Point (ARP), which is the "center" of the receiving element of the antenna.

 

3) The L1 Phase Center, which for some reason is different from the ARP.

 

Anyway, the computer continously logs the data from the satellites. What it does, is it then reads the data and computes the differences from the known value of the monument to an extremely high degree of accuracy. It logs these differences over time, which you can download.

 

What are they used for? Well, a number of things. First, the WAAS corrections our GPS's receive come from some of the CORS stations (the ones run by the FAA, I believe). They compute the error, send it back out, and your GPS adjusts it's solution by the error detected by the CORS stations (basically).

 

Surveyors can download the data and post process observations in a similar, but more precise way to get higher accuracy survey data.

 

The NGS (and the DoD, who runs the satellites) can track the satellite error over time, to insure they don't drift.

 

It's a continuous reference for how fast the earth is moving (remember all those classes in middle school about contential drift and all that stuff).

 

And I'm sure there's 20 other applications.

 

I've not really tried to visit any, but the two I know of locally are on the roofs of government buildings and you're not going to be able to get anywhere close to them.

 

I'm sure some CORS expert would be horrifed by my oversimplification.

 

A picture, along with some data is at http://sal.uamont.edu/pages/cors/cors.htm

[Bill93]

The closest CORS station to me (that I know of) is North Liberty which is a university-operated radio astronomy station doing VLBI. Huge dish in a fenced area in woods overlooking the largest lake in our area.

 

I once was in a group that got a tour of the station, but either that was before CORS, or else it went right through my head because I didn't know what CORS was about at that time. I don't recall the GPS antenna.

 

Other than CORS data, their principal product was boxes of mag tape recordings that were processed together with observations from other stations. I recall the joke, "Never underestimate the bandwidth of a weekly station wagon full of mag tape." Maybe they have switched media since then but the adage still applies.

[Z15]

Coast Guard CORS near me. If you look closely you can just see Lake Superior between the 2 antenna's. There are 2 CORS at this site, one for backup. KEW1 and KEW2

 

The large antenna was the old system LORAN.

 

You can drive right up on the road by this but its all posted US Gov't Property and under electronic Survielence. Last time I was there, it appeared they were going to erect fencing. One think about trepassing on USCG property, they may not catch you at the moment but they have you on camera and WILL prosecute you, no exceptions. So think 2x before entering any of these sites, they will have you arrested and prosecuted in federal court.

 

The NGS control monument is back behind the building but there is a lot of vertical control in the vicinity and all on Coast Property.

 

 

Michigan CORS

Edited July 15, 2005 by Z15

[holograph]

Off topic comment: every time I see the header of this thread, I hear a deep Jamaican voice in my head asking "What does CORS mean, mon?"

 

Somewhat on topic reply to Bill93: a few years ago the company I worked for needed to exchange terabytes of data between Maryland and California. We determined that the highest bandwidth and most economic channel available was a FedEx cargo jet.