USM RTK Workshop Fugro Chance Inc. Starfix HP: High Performance GPS For Offshore Marine Survey, Navigation and Positioning Richard Barker, Dr. Dariusz apucha, Tony Wood FUGRO CHANCE INC. USM RTK Workshop Fugro Chance Inc.Introduction Differential GPS: DGPS: Meter level accuracy over wide area RTK: Centimeter level accuracy over small area Starfix High Performance (HP): Decimeter level accuracy over region using geostationary satellite broadcast Advance of Fugro Starfix Plus Iono free DGPS Service USM RTK Workshop Fugro Chance Inc. Starfix HP Characteristics High Precision Carrier Phase Measurements Evaluation of Error Sources Proprietary Method of DD Ambiguity Resolution Network Solution Long Baseline > 600 km Offshore Regional Service Target Accuracy 10 cm Horizontal 20 cm Vertical Baseline < 1000 km ITRF 00 Reference USM RTK Workshop Fugro Chance Inc. Fundamental HP Measurement 300 m (code)20 cm (phase) Measurement accuracy is 1% of wave length ==> Code < 3 m ==> Phase ~ 2 mm USM RTK Workshop Fugro Chance Inc. GPS Error Sources Satellite Orbit and Clock Satellite clock and broadcast ephemeris errors are from.52m. Orbits to 10m in rare instances Largely removed by DGPS and orbit correctors GPS Signal Multipath (reflections) and Receiver Noise Dependent on receiver type, antenna, and antenna placement.25 m Ionosphere Region of free electrons from 1001000 km Mitigated with models and measurements 545 m Troposphere The Atmosphere from sea level to 16 km Mitigated with models and measurements 220m USM RTK Workshop Fugro Chance Inc. The Ionosphere USM RTK Workshop Fugro Chance Inc. Ionospheric Errors The Ionosphere Is a Major Error Source for GPS Users Average daytime ionospheric zenith delay at L1 is 5-15 meters. Can be as much as 36m at equator during solar maximum At 5 degrees elevation, the total delay is about three times the zenith delay The Ionosphere Is a Dispersive Medium Scatters and distorts the GPS signal USM RTK Workshop Fugro Chance Inc. Current Solar Cycle USM RTK Workshop Fugro Chance Inc. Regions of Ionospheric Activity USM RTK Workshop Fugro Chance Inc. Single Frequency Baseline Rio de Janeiro - Recif 1860km 05/16/00 USM RTK Workshop Fugro Chance Inc. Dual Frequency Baseline Rio de Janeiro - Recif 1860km 05/16/00 USM RTK Workshop Fugro Chance Inc. Current Solar Cycle USM RTK Workshop Fugro Chance Inc. Current Kp USM RTK Workshop Fugro Chance Inc. The Troposphere USM RTK Workshop Fugro Chance Inc. The Troposphere Troposphere Is Another Major Error Source Tropospheric zenith delay is ~ 2.5 m. Tropospheric mapping functions have a value of about 10 at 5 elevation Troposphere Delay Can Be Separated Into Two Parts, Each With Its Own Mapping Function Hydrostatic (dry) term, f (P,T) Accounts for 80-90% of the total delay Can be predicted with high degree of accuracy Wet term, f (water vapor,T) Highly variable. Significant factor in GOM USM RTK Workshop Fugro Chance Inc. Starfix-HP Carrier Phase Positioning Based on dual frequency carrier phase Ionospheric elimination Tropospheric estimation Multiple reference stations Virtual base station corrections created on-the- fly Minimizing distance dependent errors Proprietary DD ambiguity resolution method Positioning rate independent on reference update rate High accuracy maintained during short (