GPS Tide Detection : Implementation of a full integrated solution for hydrographic surveys on the St-Lawrence from data collection to data processing

GPS Tide Detection : Implementation of a full integrated GPS Tide Detection : Implementation of a full integrated solution for hydrographic surveys on the St-Lawrence solution for hydrographic surveys on the St-Lawrence

from data collection to data processing.from data collection to data processing.

Louis MaltaisLouis MaltaisCanadian Hydrographic ServiceCanadian Hydrographic Service

Quebec RegionQuebec Region

Carrier Phase GPS Navigation for Hydrographic Carrier Phase GPS Navigation for Hydrographic SurveySurveys, and Seamless Vertical Datumss, and Seamless Vertical Datums

University of Southern MississippiUniversity of Southern Mississippi

IntroductionIntroduction

•Geographical situationGeographical situation

•Chart Datum definitionChart Datum definition

•Technique used for Hydrographic surveys on the RiverTechnique used for Hydrographic surveys on the River

•New positionning capabilityNew positionning capability

•Seamless Datum definition and establishmentSeamless Datum definition and establishment

•AccuracyAccuracy

•Data collection and processingData collection and processing

•OpportunitiesOpportunities

•SummarySummary

Geographical situationGeographical situation

Traditionnal Chart Datum Traditionnal Chart Datum

• Chart datum should be so low that the water level Chart datum should be so low that the water level

will but seldom fall below it.will but seldom fall below it.

• Not so low as to cause the charted depths to be Not so low as to cause the charted depths to be

unrealistically shallow.unrealistically shallow.

• Should vary only gradually from area to area and Should vary only gradually from area to area and

from chart to adjoining chart, to avoid significant from chart to adjoining chart, to avoid significant

discontinuities. discontinuities.

• Represented on the shore by benchmarks.Represented on the shore by benchmarks.

Technique used now for Hydrographic Surveys Technique used now for Hydrographic Surveys in the Navigation Channel in the Navigation Channel

Survey lines

Tide Staff or Stations

Tide readers talking with the survey vessel giving tide at each 5 minutes.

•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.

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

Why do we need a Seamless Datum ?Why do we need a Seamless Datum ?

Chart Datum

Ellipsoid WGS84

Tide

GPS Height relative to WGS84

Separation beetween WGS84 and Chart Datum

Tide = GPS Height - GPS Antenna Height over water - Separation Value

Antenna Height

Work that have been done on the St-LawrenceWork that have been done on the St-Lawrence

•40 Primary Control points (Compensation by NRCAN)40 Primary Control points (Compensation by NRCAN)

•20 Secondary Control points (Validated with the RTK system)20 Secondary Control points (Validated with the RTK system)

•Measurements have been made relative to WGS-84 EllipsoMeasurements have been made relative to WGS-84 Ellipsoiid d

•Chart datum value at each control point.Chart datum value at each control point.

•Solution to get the seamless coverage : Krigging software to Solution to get the seamless coverage : Krigging software to

interpolate between stations. (Like doing a DTM but more interpolate between stations. (Like doing a DTM but more

rigourous, the surface has to pass throught each control point).rigourous, the surface has to pass throught each control point).

Accuracy of the Thales LRK GPS equipment Accuracy of the Thales LRK GPS equipment

LRK Network – 2004LRK Network – 2004

Longueuil

Ste-Croix

St-François – ID #1431.1MHz

Montmagny

LRK base station repeators

LRK Base stations

Dredge Channel

Pointe du Lac

Sainte-Marthe – ID #4430.6MHz

Montréal

Québec

Batiscan

Sorel – ID #5430.1MHz

Grondines – ID #3431.1MHz

Neuville – ID #2430.1MHz

Verchères – ID #6431.1MHz

Lanoraie

Silo du port Sorel

Data CollectionData 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

What are we getting from RTK ? What are we getting from RTK ?

•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.

XYZ position of the antenna relative to WGS 84

What is included in that Z value ? What is included in that Z value ?

Integration Choices :Integration Choices :1- Single Beam without motion sensor1- 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 sensor2- Single Beam with pitch and roll sensor

• Remove vessel motion from recorded antenna height with the pitch and roll data.


• 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 3- Multibeam and Multitransducer with motion sensor

• Remove vessel motion from recorded antenna height with the pitch and roll data.


• 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.

St. Lawrence River channelSt. Lawrence River channel

MontrealMontreal

QuebecQuebec

GrondinesGrondines

Channel survey vesselsChannel survey vesselsChannel survey vesselsChannel survey vessels

CCGS F.C.G SmithCCGS F.C.G Smith

HYDROGRAPHIC SURVEY CATAMARAN 34.8mHYDROGRAPHIC SURVEY CATAMARAN 34.8m

33 Transducers - 6 MCS Navitronics 33 Transducers - 6 MCS Navitronics

Frequency 200kHz; Depth: 2 - 100 mFrequency 200kHz; Depth: 2 - 100 m

Beamwidth 8 degreesBeamwidth 8 degrees

Heave / Roll / Pitch compensated with TSS, Gyro Heave / Roll / Pitch compensated with TSS, Gyro and Speedlogand Speedlog


MontrealMontreal

QuebecQuebec

GrondinesGrondines


CCGS GC-03CCGS GC-03

HYDROGRAPHIC SURVEY CATAMARAN 18.5mHYDROGRAPHIC SURVEY CATAMARAN 18.5m

12 Transducers - 2 MCS Navitronics 12 Transducers - 2 MCS Navitronics


Beamwidth 8 degreesBeamwidth 8 degrees

Heave / Roll / Pitch compensated with TSS 335B, Heave / Roll / Pitch compensated with TSS 335B, Gyro and SpeedlogGyro and Speedlog

MontrealMontreal

QuebecQuebec

GrondinesGrondines



MorillonMorillon

HYDROGRAPHIC SURVEY LAUNCHHYDROGRAPHIC SURVEY LAUNCH

6 Transducers - MCS2000/F6 Navitronics 6 Transducers - MCS2000/F6 Navitronics


Beamwidth 4.5 degreesBeamwidth 4.5 degrees

Honeywell HMR3000 Digital compass / Roll-PitchHoneywell HMR3000 Digital compass / Roll-Pitch

Tide

GPS Tide

Roll

Pitch

Heave

GPS Height

Time Series Cleaning Time Series Cleaning and Smoothingand Smoothing

•Basic cleaning

•Reject with interpolation

•Reject without interpolation

•Smoothing capabilities

•Fast Fourier Transform

•Moving Average

With this approch we can do a direct comparison between GPS Tide and traditionnal tide measurements or tide zones calculations.

Opportunities and future workOpportunities 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.

SPINE

Bécancour

Tide Gauge

Batiscan

Tide Gauge

Hydrodynamic model nodes

Vessel Data

UTC Time : 10:01:32

Latitude : 46.2568975

Longitude : 72.6589743Forecast are available at each node of the hydrodynamic model (7.5 mins)

1.25

1.30

1.00

1.50

Forecast at 10:00:00

Forecast at 10:07:30

1.60

1.40

1.35

1.09

Observations are avalaible at 10:00:00 (3mins)

Observations at 10:00:00

1.40

0.95

Computation of ajustement at each tide gauge at 10:00:00

Ajustement at 10:00:00

-0.10

-0.05

Interpolation of ajustement at each node

-0.07 -0.07

Finally, ajust the forecast at each node and interpolate in time and space at vessel time and position

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.

1.18

1.28

1.23

1.331.24

SummarySummary

•Centimeter accuracy in positionning in Centimeter accuracy in positionning in real-time is now possible.real-time is now possible.

•GPS tide detection: Separation model GPS tide detection: Separation model between Ellipsoid an Chart Datum is between Ellipsoid an Chart Datum is needed.needed.

•Establishment of Seamless Datum is Establishment of Seamless Datum is an issue.an issue.

•Integration of GPS Tide implies Integration of GPS Tide implies additional computationsadditional computations

•Limited rangeLimited range•Sun spotSun spot

Documents

GPS Tide Detection : Implementation of a full integrated solution for hydrographic surveys on the St-Lawrence from data collection to data processing