# Presentation: 448474

## National CORS: Products & Services  

- Richard Snay
- NOAA’s National Geodetic Survey
- Civil GPS Service Interface Committee
- San Juan, Puerto Rico
- May 23, 2006

## Continuously Operating Reference Stations (CORS)

## Current CORS Coverage in Puerto Rico

## CORS SITES

**CORS ANTENNAS**

## Mexican National Active Geodetic Network

## CORS OVERVIEW

- CORS Network contains 920+ sites
- CORS Network growing at rate of 15 sites per month
- More than 175 organizations participate in the CORS program
- Provides code range (C/A, P1, P2)
- and carrier phase observations (L1, L2)
- Expect to provide L2C code range in near future

## CORS APPLICATIONS

- Postmission Static Positioning (cm-level accuracy with a few hours of data, dm-level accuracy with one minute of data)
- Postmission Kinematic Positioning (dm-level accuracy for an aircraft, boat, or land vehicle)
- Geophysics / Crustal Motion
- Meteorology / Water Vapor in Atmosphere
- Space Weather / Free Electrons in Ionosphere

## Positioning Error vs. Duration of the Observing Session

- Dual-frequency GPS carrier-phase observations

- Positioning Accuracy with Code Data

- red = east-west
- blue = north-south

- Observation Time = 1 minute

- RMS error = 25 cm + 2 ppm

## Hourly Forecast of Precipitable Water 

## Three ways to download CORS Information

- Web-based User-Friendly CORS (UFCORS)
- Web-based “Standard” download
- FTP (File Transfer Protocol)

## OPUS

**OPUS**
**Online Positioning User Service **

- http://www.ngs.noaa.gov/OPUS/
- opus@ngs.noaa.gov

**Notes:**
Anybody that has done GPS data processing knows it is a pain. 
 I remember when NGS began the Space Geodesy Branch. 
 I went down there to learn GPS data processing with the OMNI software package.  
After two weeks I had processed a couple small projects
the results of which were just preliminary positions.  

It still had to be adjusted to the network by a different branch in NGS which would take another week or two.

Well now there’s OPUS

## HOW DOES OPUS WORK?

-   Collect at least 2 hours of GPS (dual frequency carrier phase) data
-  Submit your GPS data file(s) through NGS web page

-   Your data will be processed automatically, together with GPS data from 3 suitable CORS, using NGS computers and software

-   Receive computed positional coordinates via email (usually in minutes)

**Notes:**
4th Bullet
If everything is working as it should and nobody has hung up the system by submitting a bad RINEX file you can usually expect results in 5 minutes or so.

## HOW IS THE ANTENNA HEIGHT MEASURED?

**Notes:**
I promised we would talk more about antenna heights.

The height of the antenna is measure vertically from the from the mark, to the Antenna Reference Point which is almost always the center of the bottom-most, permanently attached piece o f the antenna.  

Some antennas have a short pipe or extension to them.  

If in doubt you can find photo’s and diagrams of each antenna (that we have calibrated) at the URL shown. 

So if you leave the antenna height as “0” this will be the height  OPUS returns.

## How Does OPUS Compute Position?

-  3 separate baselines computed
- 3 separate positions averaged

## P1

- P2

- P3

- P4

- P5

- P6

## B9999-1

- B9999-2

- P1

- P2

- P3

- P4

- P5

- P6

## OPUS-DB (OPUS-DataBase)

- Observation log

**OPUS-DB**** (OPUS-DataBase)**

- description form

- photo(s)

- NGS website:
- OPUS-DB

- NGS DATABASE

- NGS magic

**Notes:**
In contrast, OPUS-DB is very streamlined; all the work takes place on the NGS-side of the internet

Of course, that puts the burden of effort on NGS.

## ONGOING CORS RESEARCH

- 	* Developing OPUS-GIS which will process a few minutes of GPS code range data (for sub-meter accuracy).

## ONGOING CORS RESEARCH

- 	* Developing OPUS-RS (rapid static) that will enable users to obtain positional coordinates with cm-level accuracy using only 15 minutes of GPS carrier phase data.

## ONGOING CORS RESEARCH

- Exploring the use of NTRIP to stream GPS data from selected CORS via the Internet.
- Should NOAA use NTRIP to stream ionospheric and/or tropospheric models via the Internet?