Carrier Phase GPS Navigation for Hydrographic Survey s, and Seamless Vertical Datums

1. Carrier Phase GPS Navigation for Hydrographic Surveys, and Seamless Vertical Datums University of Southern Mississippi GPS Tide Detection : Implementation of a full integrated solution for hydrographic surveys on the St-Lawrence from data collection to data processing. Louis Maltais Canadian Hydrographic Service Quebec Region

2. Introduction • Geographical situation • Chart Datum definition • Technique used for Hydrographic surveys on the River • New positionning capability • Seamless Datum definition and establishment • Accuracy • Data collection and processing • Opportunities • Summary

3. Geographical situation

4. Traditionnal Chart Datum • Chart datum should be so low that the water level will but seldom fall below it. • Not so low as to cause the charted depths to be unrealistically shallow. • Should vary only gradually from area to area and from chart to adjoining chart, to avoid significant discontinuities. • Represented on the shore by benchmarks.

5. Survey lines Tide readers talking with the survey vessel giving tide at each 5 minutes. Tide Staff or Stations Technique used now for Hydrographic Surveys in the Navigation Channel • Interpolation in space • Extrapolation in time • Hard to read a tide staff at the centimeter level • Need on human ressources on the field are high.

6. New positionning capabilities • Centimeter accuracy was possible in the past using post-processing methods. • Now with Real-Time Kinematic and On-the-Fly algorythms we can get accurate positionning in Real-Time. • Drawbacks • Limited range • Ionospheric effects

7. Why do we need a Seamless Datum ? Ellipsoid WGS84 GPS Height relative to WGS84 Separation beetween WGS84 and Chart Datum Antenna Height Tide Chart Datum Tide = GPS Height - GPS Antenna Height over water - Separation Value

8. Work that have been done on the St-Lawrence • 40 Primary Control points (Compensation by NRCAN) • 20 Secondary Control points (Validated with the RTK system) • Measurements have been made relative to WGS-84 Ellipsoid • Chart datum value at each control point. • Solution to get the seamless coverage : Krigging software to interpolate between stations. (Like doing a DTM but more rigourous, the surface has to pass throught each control point).

9. Accuracy of the Thales LRK GPS equipment

10. LRK Network – 2004 St-François – ID #1 431.1MHz Neuville – ID #2 430.1MHz Québec Montmagny Grondines – ID #3 431.1MHz Batiscan Ste-Croix Sainte-Marthe – ID #4 430.6MHz Pointe du Lac Sorel – ID #5 430.1MHz Lanoraie Silo du port Sorel Verchères – ID #6 431.1MHz Dredge Channel LRK Base stations Longueuil Montréal LRK base station repeators

11. Data Collection • All sensors on board logged as usual • Traditionnal DGPS replaced by RTK • Using NMEA quality indicator • GPS Tide values displayed (Not the full rigourous solution) • Only the raw position data is stored

12. What are we getting from RTK ? XYZ position of the antenna relative to WGS 84 What is included in that Z value ? • Antenna height • Heave • Pitch and Roll effects on antenna height • Static Draft of the vessel • Dynamic Draft of the vessel • Swell • Some of those values are already measured by others sensors, we have to make sure that we are not doing double correction.

13. Integration Choices : • 1- Single Beam without motion sensor • Reduce the antenna height to the water level using the HIPS VCF entries for the navigation antenna offset. • Result is ‘GPSTide’ water level with heave and dynamic draft still included. • 2- Single Beam with pitch and roll sensor • Remove vessel motion from recorded antenna height with the pitch and roll data. • Reduce the antenna height to the water level using the HIPS VCF entries for the navigation antenna offset. • Remove the dynamic draft (squat / lift) from the antenna height. • Result is ‘GPSTide’ water level with tide and heave included. • 3- Multibeam and Multitransducer with motion sensor • Remove vessel motion from recorded antenna height with the pitch and roll data. • Reduce the antenna height to the water level using the HIPS VCF entries for the navigation antenna offset. • Remove the heave from the antenna height by applying the recorded heave data. • Remove the dynamic draft (squat / lift) from the antenna height. • Result is ‘GPSTide’ water level with only the true tide effects remaining.

14. Channel survey vessels St. Lawrence River channel Quebec Grondines Montreal CCGS F.C.G Smith HYDROGRAPHIC SURVEY CATAMARAN 34.8m 33 Transducers - 6 MCS Navitronics Frequency 200kHz; Depth: 2 - 100 m Beamwidth 8 degrees Heave / Roll / Pitch compensated with TSS, Gyro and Speedlog

15. Channel survey vessels St. Lawrence River channel Quebec Grondines Montreal CCGS GC-03 HYDROGRAPHIC SURVEY CATAMARAN 18.5m 12 Transducers - 2 MCS Navitronics Frequency 200kHz; Depth: 2 - 100 m Beamwidth 8 degrees Heave / Roll / Pitch compensated with TSS 335B, Gyro and Speedlog

16. Channel survey vessels Quebec Grondines Montreal Morillon HYDROGRAPHIC SURVEY LAUNCH 6 Transducers - MCS2000/F6 Navitronics Frequency 200kHz; Depth: 2 - 100 m Beamwidth 4.5 degrees Honeywell HMR3000 Digital compass / Roll-Pitch St. Lawrence River channel

17. Heave Time Series Cleaning and Smoothing • Basic cleaning • Reject with interpolation • Reject without interpolation Pitch Roll • Smoothing capabilities • Fast Fourier Transform • Moving Average Tide GPSTide With this approch we can do a direct comparison between GPS Tide and traditionnal tide measurements or tide zones calculations. GPSHeight

18. Opportunities and future work • Bin format from NGS is used to store the values of the separation table (NRCAN has adopted the same format) • With that approch we have compatibility with any RTK receiver giving XYZ relative to the WGS-84 • Reference to any datum is possible (once you know the relation to WGS-84) • Squat measurement on large vessels • We want to test the integration in more dynamic conditions. • Carry the positionning quality flag the post-processing software.

19. Batiscan Tide Gauge SPINE 1.50 Finally, ajust the forecast at each node and interpolate in time and space at vessel time and position 1.60 New system to provide a water level via hydrodynamic model and automatic tide gauges. The goal is to provide the hydrographer with another water level to validate the GPS tide value. 1.40 -0.10 Observations are avalaible at 10:00:00 (3mins) Computation of ajustement at each tide gauge at 10:00:00 Hydrodynamic model nodes 1.30 1.23 Forecast at 10:00:00 1.24 0.95 -0.05 1.33 1.40 Forecast at 10:07:30 Bécancour Tide Gauge 1.25 1.18 Observations at 10:00:00 1.35 1.28 -0.07 -0.07 Ajustement at 10:00:00 Vessel Data UTC Time : 10:01:32 Latitude : 46.2568975 Longitude : 72.6589743 Interpolation of ajustement at each node 1.00 1.09 Forecast are available at each node of the hydrodynamic model (7.5 mins)

20. Summary • Centimeter accuracy in positionning in real-time is now possible. • GPS tide detection: Separation model between Ellipsoid an Chart Datum is needed. • Establishment of Seamless Datum is an issue. • Integration of GPS Tide implies additional computations • Limited range • Sun spot