RTK Developments from NavCom Technology Inc. RTK GPS for Hydrographic Surveys and Seamless Vertical Datums Workshop NASA John C. Stennis Space Center 27 August 2002 Kevin Dixon NavCom Technology, Inc.

NavCom Technology Inc.  Founded 1992 by ex-Magnavox GPS Team  Principals include Jim Litton and Ron Hatch  100% Purchased by John Deere  OEM Products, Engineering Consulting and Development Services  Numerous Patents in GPS, Precise Positioning and Wireless Communications  Several thousand dual frequency GPS units in use worldwide

Seamless Datum Requirements  Global Horizontal and Vertical Reference Surfaces defined to an acceptable accuracy  Surveying Practices which realize the above  Standards and Implementation  Equipment which simplifies this realization

Reference Frames  Globally - Horizontal can be Vertical and vice versa Horizontal Here Vertical Here

Standards  International Hydrographic Organization Special Publication S-44  United Kingdom Offshore Operators Association (UKOOA)  NOAA Office of Coast Survey Specifications and Deliverables  IMCA

IHO S-44 Depth Accuracy

Local RTK Implementation  The NavCom developed RTK algorithm is a measurement space search around a code fixed starting point.  Wide lane integers are searched first followed by a step into L1 narrow lane integers and search.  An independent search is performed for each measurement epoch.  Up to 10 permutations which meet minimum quality requirements are scored and evaluated on a relative basis until a clear winner is declared. Often this occurs within a single epoch.

RTK Integer Search

RTK Positioning Results

The Hardware NCT2000D Quality Dual Frequency GPS SF2045L L-Band Demodulator

The Hardware SF-2050 GPS Sensor StarFire™ Enabled Modular System With RTK Correction Input Option

The Hardware 50Hz L1 Phase, L2 Phase, C/A, P1, P2 25Hz Position 10-30VDC 10 Watts Tri-band Antenna GPS L1/L2 and Inmarsat 70,000’ Certified

Realization SR7100 Shore Based Corrections via 2.4GHz Spread Spectrum Radio Seamless Transition from Global to Local RTK StarFire™ Global Corrections

StarFire™ Advantages  Truly global system – reference stations can be lost without adverse effects  Totally Automated - 24/7 Engineer standby  Dual hub system for redundancy  Correction data valid for up to 300 seconds  Automatic selection of Inmarsat satellite by user equipment  No need to select a reference station  IGS stations used as part of network to realize ITRF at the current epoch  Global monitor sites use end user equipment to constantly verify system performance

System Advantages  Single Manufacturer for  GPS Dual Frequency Board  L-Band Demodulator  Spread Spectrum Radio  StarFire™ Global Correction System  50Hz Raw Data for Post-Processing  Option to use existing GPS Choke Ring and L-Band Antenna  User Defined Position Cascade RTK  StarFire™  SBAS  Stand Alone

Developments  Improved vertical accuracy of StarFire™ - IHO S-44 Class I performance  Faster lock in times for StarFire™  900MHz and 5.8GHz Versions of SR7100