National CORS: Products & Services

Richard SnayNOAA’s National Geodetic Survey

Civil GPS Service Interface CommitteeSan Juan, Puerto RicoMay 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

00.10.20.30.40.50.60.70.80.9

0 100 200 300 400

Baseline Length, km

RM

SE, m

eter

sPositioning Accuracy with Code Data

red = east-westblue = 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)

OPUSOPUS

Online Positioning Online Positioning User Service User Service

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

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)

HOW IS THE ANTENNA HEIGHT MEASURED?

ARP

MARK

The height is measured vertically (NOT the slant height) from the mark to the ARP of the antenna.The height is measured in meters.

The ARP is almost always the center of the bottom-most, permanently attached, surface of the antenna.

See GPS Antenna Calibration for photo’s and diagrams that show where the ARP is on most antennas:

http://www.ngs.noaa.gov/ANTCAL/

If the default height of 0.0000 is entered, OPUS will return the position of the ARP.

How Does OPUS Compute Position?

3 separate baselines computed

3 separate positions averaged

P1

P2

P3

P4

P5

P6

B9999-1 B9999-2

Place the Base Station over your first point and beginRTK survey ensuring that you are collecting Raw Datafor at least 2 hours (This data will be sent to OPUS).We will now refer to this as OPUS1.

Start Rover and begin setting and controlling your panels

B9999-1 B9999-2

P1

P2

P3

P4

P5

P6

Move the Base Station over your second point and begin RTKsurvey ensuring that you are collecting Raw Data for 2 hours.(This data will also be sent to OPUS).We will now refer to this as OPUS2.

Start Rover and begin controlling your panels from the second location.

GPS data Observation log

OPUS-DB (OPUS-DataBase)

description formphoto(s)

NGS website:

OPUS-DB

NGS DATABASE

NGS magic

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?