National CORS Products Services Richard Snay NOAAs National

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 ANTENNAS CORS SITES

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, P 1, P 2) – and carrier phase observations (L 1, L 2) – Expect to provide L 2 C 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 Observation Time = 1 minute red = east-west blue = north-south 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 Online Positioning 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 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. MARK

How Does OPUS Compute Position? 3 separate baselines computed 3 separate positions averaged

P 1 Place the Base Station over your first point and begin RTK survey ensuring that you are collecting Raw Data for at least 2 hours (This data will be sent to OPUS). We will now refer to this as OPUS 1. P 4 P 2 P 5 B 9999 -1 B 9999 -2 P 3 Start Rover and begin setting and controlling your panels P 6

P 1 Move the Base Station over your second point and begin RTK survey 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 OPUS 2. P 4 P 2 P 5 B 9999 -1 P 3 B 9999 -2 Start Rover and begin controlling your panels from the second location. P 6

OPUS-DB (OPUS-Data. Base) GPS data Observation log photo(s) NGS website: OPUS-DB NGS magic NGS DATABASE description form

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?