1	Towards Real Time National Geodetic Survey / NOS / NOAA Silver Spring, MD
2	Main Concepts Modify CORS sites for real time data transmission GNSS receiver data Transmission via the Internet Standardized protocols and formats Not a navigation service!
3	Framework for Real Time GNSS Networks Federal Network 200 CORS sites NDGPS, WAAS, NOAA, PBO sites Stream GNSS data, not correctors via NTRIP and tcp/ip protocol over the Internet, Regional and local Networks Use Federal network to calibrate and/or enhance local networks
4	CORS Site Modification Receiver modifications Firmware Multiple satellite systems Data interval Communications / Network modifications Routers Increased bandwidth Internet Software
5	Network Design Issues What format? What stations? What software? What distance? What data rate? What latency?
6	Data Distribution Formats RTCM-SC104 Versions – 2.0, 2.1, 2.2, 3.0 Type 1 Fixed GPS corrections (1 sec) Type 3 GPS reference station parameters (10) Type 16 GPS special message (30,60) Type 18 RTK uncorrected carrier phases (1) Type 19 RTK uncorrected pseudoranges (1) Type 22 Extended station parameters (15) Type 59 Proprietary messages (1)
7	Data Collection Formats Raw Topcon/Javad Compact (1) Ashtech MBEN (5) / PBEN (5) / SNAV Thales ASCII SP3 ASCII Trimble RT17, concise Leica LB2 RINEX BINEX
8	Communications Frame Relay – USCG, NDGPS CORS Internet (FTP, rcp) – State DOT’s, WAAS, university CORS. Satellite / Modem – Hawaii, PBO CORS NTRIP – RTK CORS
9	Software NTRIP - Networked Transport of RTCM via Internet Protocol (version 1.5) NTRIP is an RTCM standard Application-level protocol streaming Global Navigation Satellite System (GNSS) data over the Internet Based on hypertext transfer protocol (HTTP/1.1) Simultaneous connections from PC’s, laptops, receivers to a broadcast host Streams data to stationary and mobile users
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11	NTRIP PROS RTCM standard Open documentation Software components developed under GNU General Public License Communications through a HTTP port CONS Workload on server side Not supported by mobile IP provider
12	Processing Considerations for Real Time Centralized Processing - NGS Correction models Ionospheric – dynamic or recent data Tropospheric – dynamic or recent data Satellite clocks Multipath - from past data Ambiguity resolution of reference station observables Usually one communications channel Several processing locations Many reference stations lead to many corrector streams Several communications channels needed
13	Positioning Limitations from Real Time Networks DGPS L1 code corrections Range 200 – 400 km Meter level accuracy Time delay – varies up to a few seconds Continental coverage RTK – Single Base Station L1 code, L1 / L2 carrier corrections Range 10 to 15 km Centimeter level accuracy Time delay – typically less than a second Regional and local coverage
14	Post Processing Applications Post mission static positioning. cm-level accuracy with a few hours of data, dm-level accuracy with one minute of data. Solution delay - one hour. Post mission kinematic positioning. dm-level accuracy for an aircraft, boat, or terrestrial vehicle. Solution delay – more than one hour. Geophysics - crustal motion. Meteorology - water vapor in atmosphere. Space weather - free electrons in ionosphere.
15	Real Time Applications Structural monitoring GIS – Rapid Response, 911 Precision guidance – machines Meteorology - water vapor in atmosphere Space weather – ionosphere, troposphere Positioning – OPUS (rapid solution) Assist other real time applications - RTK
16	PROPOSED POLICY FOR STREAMING GPS DATA VIA THE INTERNET NOAA’s National Geodetic Survey is exploring the possibility of streaming GPS data (not correctors) from selected CORS via the Internet. These data will be publicly available and free of direct user fees. NGS is openly distributing these data to enable other organizations to provide location based services relative to the NSRS.
17	PROPOSED POLICY Monitor the distribution of free electrons in the atmosphere. Monitor the distribution of precipitable water vapor in the atmosphere. Record the passage of seismic waves. While these GPS data may be applied to track the path of a moving platform--such as an aircraft, water vessel, or land vehicle–these data will not possess sufficient “integrity” to support a robust navigation service.
18	NTRIP Installation at NGS NGS Broadcaster 140.90.112.133 2101 Converting NDGPS and other sites for NTRIP. RTK messages. NTRIP Server Modifications made to send receiver ID and password.
19	Conclusion Streaming GNSS data over the Internet is feasible No significant lack of performance compared to other transportation media Advantages for user / service providers Developments for various products Promising solution for GIS Faster data access
20	Questions / Comments