GPS Services GroupC&C Technologies, Inc.,

www.cctechnol.com/cnav

 

C-Nav GcGPS System Background and Accuracy

Overview• What is C-Nav• Empirical accuracy measurements to

date.• Interesting issues• Hand off to Pete and John

– Interesting application to hydrography

– Latest developments in C-Nav

• Closing summary

The RTG Family

Why High Accuracy?

Stand alone GPS but…

• Ionosphere delay free

• Extended carrier smoothing

• Improved orbit and clock

correctors

• Troposphere delay modeling + estimation

This Week’s Schedule

Check Your Watch for Altitude!

Vertical Error (?) Vs Earth Tide

C-Nav AccuracyC-Nav GGA vs Zero Gravity Surveyed Position

95% Horizontal 95% Vertical

Static RTG 0.18 +/- 0.04 m 0.35 +/- 0.05 m

Static RTG Predicted tides

0.18 +/- 0.04 m 0.24 +/-0.04 m

Static RTG - Reference

0.18 +/- 0.04 m ~0.19 m

Dynamic RTG 0.13 +/- 0.7 m 0.25 +/- 0.05 m

Tidal Datums

• Chart datum is based upon historic water levels

• Chart datum is irregular wrt geoids and ellipsoids.

• You can determine chart datum at a point with a tide gauge.

• To projected it away from the tide gauge requires knowledge of tides.

Let the Experiment Begin!!

• Performed during NOAA hydrographic survey in Gulf of Mexico

• Used well surveyed cross-lines as ground truth

• Used verified tides to check ground truth• Collect C-Nav data on survey vessel and at

two monitoring stations• Analyze data

RTG Vertical re Chart Datum

Sea-Surface Height

Vessel Receiver Noisy Probably Antenna Location

Lafayette Houston Vessel

Mean 0.308 0.280 0.402

SD 0.065 0.043 0.173

RMS 0.315 0.283 0.438

146%

GST Vertical Error Estimate

Give it to Pete and John

• 0.2 m to 0.4 m vertical at 95% in preliminary test.

• ~0.3 meters vertical at 95% in tidal datum w/ blockage & 100nm baseline.

• Post processing required to deal with Earth tides.

• Squirrelly transformation into tidal datum.• Sensitivity to blockage and multipath