# Presentation: 497766

## The National & Cooperative CORS Program

**Richard Snay**
**National Geodetic Survey**
**National Ocean Service, NOAA**
**CORS Users Forum**
**Portland, OR**
**September 9, 2003**

## Continuously Operating Reference Stations

## Regional CORS Coverage

## CORS SITES

**CORS SITES**

## CORS SITES

## CORS OVERVIEW

- Network contained 700+ sites as of August 2003
- Growing at rate of 8 sites per month
- More than 100 organizations participate in the CORS program
- Provides code range (C/A, P1, P2)
- and carrier phase observations (L1, L2)
- Provides meteorological data at some sites

## 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, a boat, or a land vehicle)
- Geophysics / Crustal Motion
- Meteorology / Water Vapor in Atmosphere
- Space Weather / Free Electrons in Ionosphere

## NATIONAL CORS NETWORK

- National CORS network contains 403 sites whose data are available directly from NOAA’s National Geodetic Survey in Silver Spring, MD
- GPS and “met” data stored in RINEX format
- Data made available to public via:
- World Wide Web
- File transfer protocol
- Currently 9 years of CORS data are online for immediate access
- Parallel CORS Data Site being established at NOAA’s National Geophysical Data Center in Boulder, CO

## COOPERATIVE CORS

- GPS base stations whose data are freely disseminated by cooperating organizations
- NGS provides link from its web site to that of each cooperating organization
- Site coordinates must be consistent with the National Spatial Reference System

## National CORS & Cooperative CORS

**National CORS & Cooperative CORS**

## CORS Networks

**National**
**CORS Network**

**Cooperative**
**CORS Network**

**Combo**
**CORS **
**Network**

## COMBO CORS

- The term “Combo CORS” designates a station whose GPS data is distributed both by NOAA and by a cooperating organization.
- Such accessibility to CORS data is highly desirable.
- Scripps Institution of Oceanography (LaJolla, CA) distributes data for 650+ sites in the CORS network.

## a

**CORS PARTNERS:  FEDERAL**

***Federal Highway Administration***
***Federal Railway Administration***
***Federal Aviation Administration***
***Forecast Systems Laboratory***
***National Geophysical Data Center***
***NASA***
***US Geological Survey***
***US Army Corps of Engineers***
***US Air Force***
***US Naval Observatory***

**Notes:**
To complement this framework for GPS coordinates, we manage a system of Continuously Operating Reference Stations or CORS....that process the GPS signals with correctors, thus enabling a 3 dimensional positioning with accuracies that approach a few centimeters, both horizontally and vertically.  We do this along with a number of partners including the Coast Guard, FAA and Highways in Transportation, USGS, Air Force and state and local agencies;

## CORS PARTNERS: STATES

- California Spatial
- Reference Center

- Louisiana Spatial
- Reference Center

## CORS PARTNERS:  SCIENTIFIC

- PANGA

- BARD

- SCIGN

- BARGN

- EBRY

- BAYONET

**International GPS Service (IGS)**
**University Navstar Consortium (UNAVCO)**
**Scripps Orbit & Permanent Array Center**

***Plate Boundary Observatory***
***SuomiNet***

## CORS PARTNERS:  INTERNATIONAL

- Guatemala
- El Salvador
- Honduras
- Nicaragua

- Mexico

- Jamaica

- Canada

***International Earth Rotation Service (IERS)***
***International GPS Service (IGS)***

- Bermuda

## CORS Partners: Private Industry

- “ If you want to see where GPS is going, then keep your eye on the GPS manufacturers.”
- 			Bill Strange
- 			Former Manager
- 			National CORS Program

- Many GPS companies have developed software that
- provides their customers with automatic access to
-  CORS data for postprocessing activities.

## LIDAR images of Manhattan before and after 11 SEP 2001

- CORS data used to position aircraft

- These images are computerized visualizations of elevation information of the World Trade Center from before (July 2000) and after (September 15, 2001) the attack.  These maps were produced using an airborne LIDAR (Light Detection and Ranging) system.  The LIDAR system creates detailed and highly accurate elevation information by the precise timing of thousands of laser pulses striking the ground surface.  These data can be manipulated in the digital environment to create an array of maps and views of the project site and to obtain precise measuresments of structures, debris fields, and other vital information.  These images were generated by EarthData (www.earthdata.com), and the aircraft was positioned using CORS data from the NJI2 site which is operated by the New Jersey Institute of Technology.

## Hourly Forecast of Precipitable Water 

## Earthquake effects on CORS coordinates

**http://www.ngs.noaa.gov/CORS/metadata1**

- Horizontal velocities relative to “stable” sites
**Points with more than 3 yrs of data**

- Vertical velocities relative to “stable” sites
**Stations with more than 3 yrs of data**

## WHAT IS OPUS?

- _ __O_n-line _P_ositioning                                            _U_ser _S_ervice

-  Provide GPS users faster & easier access to the National Spatial Reference System (NSRS)

## HOW DOES OPUS WORK?

-   Observe 2 or more hours of GPS data
-  Submit RINEX file through NGS web page

-   Processed automatically with  NGS 			computers & software

-   With respect to 3 suitable CORS

-   Obtain 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.

## OPUS USES 3 CORS SITES

**Notes:**
OPUS uses 3 CORS to compute a position.  

It tries to find the best CORS which may not necessarily be the closest.  

Number of obs and quality of data all go into the selection process.

That is no problem in the western portion of WA or OR.  

But getting out towards the eastern portion of those states and beyond is a different story.  

OPUS won’t have a many choices so it may have to settle.

## HOW DO I USE OPUS?

-  - Enter your email address

-  - Enter/Select RINEX file

-  - Select antenna type from menu

-  - Enter antenna height in meters (defaults to ARP)

-  - Upload File

- Check your email (usually only takes a few minutes)

- Go to OPUS web page   www.ngs.noaa.gov/OPUS

-  - Optional:State Plane Coordinates

-  - Select up to 3 base stations  (optional)

**Notes:**
I’ll go over this in detail shortly.  But the steps are

## OPUS Web Page

**Notes:**
This is what the opus page looks like.  It was designed to be simple and straight forward. 
 On the left hand side you have everything you ever wanted to know about the OPUS process.  
You can find answers to most of your questions about the process here.
To submit a project;     You’ll type in your email address.  
Then you will check what you typed because if you don’t get any results back it may be because you mis-typed.

You’ll enter your RINEX data file through the browse button. 
 It will list your directories and you’ll be able to navigate through it to click on your data file.

Then you WILL enter your antenna type from the drop-down menu. 
 This is really important, otherwise you could have significant height errors.  
We only use antennas that we have calibrated.

Enter your antenna height in meters. 
 If you leave it at the default OPUS will return the height of the ARP about which we will go into more detail.
You may request state plane coordinates.
You may select your favorite base stations which we’ll also talk more about or you can leave the driving to OPUS.and then you simply hit upload.

## HOW CAN I IMPROVE MY RESULTS?

-  The best way to get more accurate results is to observe longer sessions

-  Data sets of at least four hours have been shown to produce more reliable results

**Notes:**
The best way to improve your results  is to 

remember that time matters.  
Observe longer sessions

 Data sets of at least four hours have been shown to produce more reliable results

## RECENT OPUS UPGRADES

-  Users can submit compressed RINEX files
-  OPUS can process data that is less than a day old
-  Users can select one or more of the three CORS to be used as base stations by OPUS
-  Users can select one or more Cooperative CORS to be used as base stations by OPUS

- NGS is developing a version of OPUS that will process
- GPS data that has been observed simultaneously at
- several sites.

**Notes:**
The cooperative CORS will be added to the choice of reference stations in the very near future.

A coop CORS may be closer to your data site than a National CORS, so you may want to choose one of them.

There have been some problems with the RINEX-2 header records

And Gerry is even looking into the possibility of processing  single frequency CORS

## What are requirements for a more effective CORS program?

- Station spacing
- Data sampling rate
- Data latency
- Environmental setting of a CORS site
- Data quality

- Hardware capabilities
- Communication capabilities
- Data formats
- Metadata
- Education / documentation

## Front of room

- Reference station operation
- Weather/Ionosphere
- Cooperative CORS Network

- Coordinates/crustal motion
- Applications / outreach / technology transfer
- Data access – communications / formats/ utilities

## Hatanaka/Unix vs. gzip

- GPS data for CORS now stored as compressed RINEX files using the “gzip” compression utility
- NGS is proposing to compress such RINEX files using the “Hatanaka” algorithm followed by the Unix compression utility.
- Once implemented, NGS would support both formats for about 6 months, then delete all the “gzip” files.

## IMPACT OF USING Hatanaka/Unix

- Size of Hatanaka/Unix files equals 35% the size of equivalent gzip files (saving storage and enabling faster transmission of data)
- Hatanaka/Unix format is currently used by several other organizations that store and distribute GPS data (compatability)
- Will not affect users who obtain data via UFCORS utility
- Will affect users who obtain data via anonymous ftp (file transfer protocol)