# Presentation: 004620

## Towards Real Time

- National Geodetic Survey / NOS / NOAA
- Silver Spring, MD

## 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!

## 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

## CORS Site Modification

- Receiver modifications
- Firmware
- Multiple satellite systems
- Data interval
- Communications / Network modifications
- Routers
- Increased bandwidth
- Internet
- Software

## Network Design Issues

- What format?
- What stations?
- What software?
- What distance?
- What data rate?
- What latency?

## 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)

## 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

## Communications

- Frame Relay – USCG, NDGPS CORS **
- Internet (FTP, rcp) – State DOT’s, WAAS, university CORS.
- Satellite / Modem – Hawaii, PBO CORS
- NTRIP – RTK CORS **

## 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

## Slide 10

## 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

## 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

## 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

## 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.

## 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

## 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.

## 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.

## 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.

## 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

## Questions / Comments