United States Fleet Forces Ready Fleet … Global Reach Approved for public release; distribution is unlimited 11 Navigation Post-Processing for Ellipsoid-Referenced

United States Fleet ForcesUnited States Fleet Forces Ready Fleet … Global ReachReady Fleet … Global Reach

Approved for public release; distribution is unlimited

11

Navigation Post-Processing for Ellipsoid-Referenced Navigation Post-Processing for Ellipsoid-Referenced SurveysSurveys

Susan Sebastian

Naval Oceanographic Office

Navigation Department

28 April 2011

The inclusion of names of any specific commercial product, commodity or service in this presentation does not imply

endorsement by the U. S. Navy or NAVOCEANO.



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What is ERS?• Alternative to conventional water level Alternative to conventional water level corrections (tide+draft+squat+etc…)corrections (tide+draft+squat+etc…)• Vertical component of GPS (Vertical component of GPS (height from height from ellipsoidellipsoid) for water level all inclusive of ) for water level all inclusive of correctors.correctors.• Upgraded navigation equipment and software Upgraded navigation equipment and software allows use of GPS heights from ellipsoid for water allows use of GPS heights from ellipsoid for water level corrections. level corrections. • Termed Ellipsoidal Referenced Survey (ERS). Termed Ellipsoidal Referenced Survey (ERS).

Why ERS?Why ERS?1)1) Reduces the dependency on shore-based tide gauges.Reduces the dependency on shore-based tide gauges.2)2) Reduces dependency on difficult to measure Reduces dependency on difficult to measure

parameters, such as dynamic draft, settlement, squat.parameters, such as dynamic draft, settlement, squat.3)3) Provides a more seamless vertical datum than Provides a more seamless vertical datum than

conventional tidal zoning.conventional tidal zoning.



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ERS ComponentsERS Components

1)1) GPS measurement of the vertical height of the survey vessel GPS measurement of the vertical height of the survey vessel relative to the Ellipsoidrelative to the Ellipsoid

2)2) Two levels of GPS accuracy:Two levels of GPS accuracy:

a)a) NavCom NavCom RTGRTG data available data available real-time; real-time; meets Order 1 meets Order 1 minimallyminimally

b)b) PPPPPP (precise point positioning) can be generated after (precise point positioning) can be generated after 24 hours through 24 hours through post-processing; post-processing; will be required once will be required once process is in place. Requires re-merge of nav data prior process is in place. Requires re-merge of nav data prior to applying GPS water level correctors.to applying GPS water level correctors.

3)3) SEP (or separation) – distance from the Ellipsoid to chart SEP (or separation) – distance from the Ellipsoid to chart datumdatum

4)4) Water Level Correction – SEP minus GPS height @MRP Water Level Correction – SEP minus GPS height @MRP



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• h: Antenna height above ellipsoid

• RS: Raw sounding corrected for heave, re: master reference point (MRP)

• Za: Antenna Z offset on boat

• Zt: Transducer Z offset on boat

• T: Tide

• SEP: Chart datum to Ellipsoid separation

• CS: Corrected sounding, re: chart datum

• D: Draft (static, loading, and S&S)

ERS Corrected Sounding CalculationERS Corrected Sounding Calculation

From: RTK Tide Basics – Hydro International, December 2003, Pat Sanders

Conventional Water Level Reduction:CS = RS + D – T

ERS Water Level Reduction:CS = RS + SEP – h + Za

Reference Ellipsoid

Bottom

Chart Datum

RS

MRP

D

ZaWater

Surface

Heave Datum

heave

CS

Zt

T

h

SEP



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Data Types Needed for ERSData Types Needed for ERS

1) Raw GPS observables from a dual-frequency GPS receiver

a) NAVCOM raw GPS data @ 10Hz (primary GPS data source)

b) POSMV raw GPS data @5 Hz (backup GPS data source)

AND

c) Heave at 100Hz

2) GPS buoy and/or GPS observations at tidal benchmark



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GPS Observations at Tidal BenchmarkGPS Observations at Tidal Benchmark

SEP = X+Y+ZSEP = X+Y+Z X X obtained from 24-hour GPS observation over BMobtained from 24-hour GPS observation over BM YY obtained by level line obtained by level line ZZ obtained from 30 days of tide data obtained from 30 days of tide data

Provides SEP: Ellipsoid to Chart Datum SeparationProvides SEP: Ellipsoid to Chart Datum Separation

Ellipsoid

Geodetic BM

Tide Gauge

Chart Datum

Elev. BM to Gauge

Ell. HT

SEPSEP

Y

Z

X



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Data Collection RecommendationsData Collection Recommendations

1) Verify the NAVCOM output settings using a laptop and the Starfire utility program at the beginning and end of the survey.

2) Verify the POSMV output settings (frequency and telegram groups) at the beginning, middle, and end of the survey, using the POSMV controller program.



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Comparing GSP Tide vs. TidesComparing GSP Tide vs. Tides

To compare GPS WL correctors to conventional tide correctors, subtract WLZ from the GPS tide

Example:|GPS Tide Corr.| - WLZ = |Tide Corr.|

|-1.05| - 0.82 = |-0.23|, ~ |-0.22|



PR Tides vs. GPSz Correctors

A

BA

B

Residual Diff.

Bathy X-section, GPSz corrected



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Tide vs. GPSzTide vs. GPSz

Excellent vertical alignment desired for area- based editing.Excellent vertical alignment desired for area- based editing.

Predicted Tide Corrected

GPSz Corrected



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Tide vs. GPSzTide vs. GPSz

Excellent vertical alignment desired for area- based editing.Excellent vertical alignment desired for area- based editing.



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Area-Based Editing Tide vs. GPSzArea-Based Editing Tide vs. GPSz

Predicted TidesPredicted Tides GPSz, GPSz,

Smoother surface for automated processing.Smoother surface for automated processing.



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DATA PROCESSING FOR ERSDATA PROCESSING FOR ERS

1) Apply delayed heave

2) Apply GPS water level corrections

3) Review GPS water level correctors and ellipsoid heights in GSF file

4) Process and merge nav as needed

Note: Nomenclature for GPS water level corrections varies in the applications and documentation.

GPS water level corrections = GPS tides = GPSz



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Navigation Processing

Field processing navigation: Simple if no problems, complexity increases as degradations move upstream.

Final dataset, apply all final PPP.

Simple: RTG solution good

Complex; need PPP



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Apply GPS Tide correctors Apply GPS Tide correctors w/EGM2008 gravitationalw/EGM2008 gravitational model model

Need 2 files:

1. EGM2008 1-minute grid AND

2. Uncertainty for that surface

RTTIDE DTC

EGM Model and uncertainty



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Inspect GPS Tides and Ellipsoid Heights with Profile Viewer



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Use View Settings Menu to Configure Display

GSF

POSMVNAVCOM

Example: GSF E-HT bad, POSMV and NAVCOM OK

Note Ant. Height offset



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Exammb

Using the Cursor Information Menu on TSView, the time is shown to be around 08:18. This proves to be true as can be seen in the image below of exammb, showing that at 08:18:05, the ellipsoid heights jump from 28.68m to 3.49m.



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Processing Strategy

Note: GPS Tides must always be re-

applied after correcting the

ellipsoid heights

Increasing Complexity

A

B

C

D

E



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Profile Interpretation

A: GPS tides and ellipsoid heights in GSF file are good. No action needed.

B: GPS tide data is corrupted, and ellipsoid heights in GSF file are good. After re-applying GPS Tides, the ellipsoid heights were corrected.

Example A: All good.



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Example B: UNCORRECTED

Example B: CORRECTED by re-applying GPS Tides



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C: GPS tide data AND ellipsoid heights in GSF file corrupted

To correct this if POSMV ellipsoid heights OK, merge this data with the GSF file in SABER.



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D: GPS tide data AND ellipsoid heights in GSF file AND POSMV ellipsoid heights corrupted

To correct this if NAVCOM ellipsoid heights OK, merge this data with the GSF file in SABER. Remember NAVCOM needs the vessel file.

GSF

POSMV



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E: GPS tide data AND ellipsoid heights in GSF file AND POSMV ellipsoid heights AND NAVCOM ellipsoid heights corrupted

To correct this, post-process NAVCOM with GraphNav and merge PPP with the GSF file in SABER. Remember NAVCOM needs the vessel file.

NAVCOM Data



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• Example E corrected by merge with PPP



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MERGE NAV INTO MULTIBEAM

• NOTE:

– POSMV is lever-arm corrected; no vessel file needed

– NAVCOM is uncorrected; need a vessel file



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MERGENAV

• Process->Navigation->Merge Navigation.

• Select the GSF file or a list of files.

• Select the corresponding POSMV, NAVCOM, or PPP.

• NAVCOM data: select the vessel file.

• POSMV data: do not apply vessel offsets.



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Navigation Processing Log

• Fill out the Navigation Processing Log, a worksheet of the GSF Processing Log, Version 3.1.

• Use the orange section: RTG

• Blue Section: PPP



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Navigation Processing Log

Worksheet of the GSF Processing Log, Version 3.1



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• IHO Order 1 allowable vertical error from the tide component is IHO Order 1 allowable vertical error from the tide component is 30cm or better at 2 SD 30cm or better at 2 SD

• Data analysis to date has demonstrated that GPS PPP solution Data analysis to date has demonstrated that GPS PPP solution heights and a well defined SEP value give accuracies of 20 -25 cm heights and a well defined SEP value give accuracies of 20 -25 cm or betteror better

• GPS RTG solution heights accuracies with a well defined SEP are GPS RTG solution heights accuracies with a well defined SEP are generally 30-35cm accuracy; RTG solution heights are an generally 30-35cm accuracy; RTG solution heights are an acceptable field solution until automated procedures for field acceptable field solution until automated procedures for field processing of PPP data can be developedprocessing of PPP data can be developed

• A well defined SEP requires the use of a GPS buoy or GPS A well defined SEP requires the use of a GPS buoy or GPS observations over a tidal benchmarkobservations over a tidal benchmark

Accuracy RequirementsAccuracy Requirements



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More on SEPMore on SEP

Methods to define SEP:Methods to define SEP:

1) GPS observations over a tidal benchmark1) GPS observations over a tidal benchmark

2) GPS Buoy2) GPS Buoy

3) EGM 2008 Model – 1min x 1min model of geoid height 3) EGM 2008 Model – 1min x 1min model of geoid height relative to the WGS84 Ellipsoid; use of EGM 2008 will not relative to the WGS84 Ellipsoid; use of EGM 2008 will not meet IHO Order 1 accuracy requirements in shallow watermeet IHO Order 1 accuracy requirements in shallow water

Survey areas with large geoid undulations with Survey areas with large geoid undulations with respect to the Ellipsoid will require multiple SEP respect to the Ellipsoid will require multiple SEP measurements and might require conventional tide measurements and might require conventional tide data if IHO Order 1 is requireddata if IHO Order 1 is required



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Example Area of Large Geoid UndulationsExample Area of Large Geoid Undulations

Change in geoid-ellipse height of 2m across test areaChange in geoid-ellipse height of 2m across test area

ERS data accuracy (using EGM 2008) was 50 cm as ERS data accuracy (using EGM 2008) was 50 cm as compared to tide corrected datacompared to tide corrected data



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RTG v.s. PPP Uncertainty



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Precise Point Positioning SOPPrecise Point Positioning SOP

Resource intensive; SOP executed in-house. More resources needed to accomplish in the field.



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Nagging Offset in 2 Receivers

“intuition suggests that there is a systematic offset that weshould be able to correct, we need to keep the keep in mind that theobserved difference between the two height solutions is well within theexpected overall

uncertainty value” Shannon Byrne, SAIC



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SummarySummary

• Each ship SURVOP is collecting data needed for ERS, even if we’re not completely there yet.

• For ERS water level corrections, Navigation data must be inspected and sometimes processed.

• The issue in the field is to get the best vertical alignment for area-based editing purposes, which is GPS Tides in most cases.

• GPS Tides does increase the vertical alignment of the data so for building PFMs, it is advantageous, regardless of depth.

• Need dedicated Nav Lead to accomplish PPP in field and the last few days will always be done in-house.

Documents

United States Fleet Forces Ready Fleet … Global Reach Approved for public release; distribution is unlimited 11 Navigation Post-Processing for Ellipsoid-Referenced