GPS for NOAAHydrographic Surveying

CDR Gerd F. Glang & Jack L. Riley

National Ocean Service, NOAA

NOAA GNSS Workshop 2007

Introduction

• NOAA Charting

• NOAA Hydrographic Surveying

• GPS Positioning

• Vertical Datums

• Concluding Remarks

NOAA’s Charting Mission

• Safety of Navigation– Provide nautical charts and related hydrographic

information for safe navigation of maritime commerce

– Includes U.S. territorial waters and the U.S. Exclusive Economic Zone (EEZ)

– 3.4 million square nautical miles (snm) which extend 200 nautical miles offshore

• 500,000 snm Navigationally Significant Areas

• 43,000 snm Critical Areas (1994)

• High-quality charts depend on up-to-date, reliable hydrographic survey data

NHSP - Alaska

NOAA GNSS Workshop 2007

• NOAA Charting

• NOAA Hydrographic Surveying

• GPS Positioning

• Vertical Datums

• Concluding Remarks

Hydrographic Surveys

• Locate, Verify, Describe...– Features Below Mean High Water (MHW)

• Dangers-to-Navigation (DTONs)

– Aids to Navigation– MHW Shoreline

• Echosounder Bathymetry• Side Scan Sonar Imagery• Dive Investigations• Bottom Samples• Shoreline• Metadata

NOAA Survey Platforms

Equipment• GPS & Platform Attitude

– Applanix POS MV 320 v4

– Trimble DGPS, C-NAV WADGPS/PPP

• Multibeam Echosounders / Backscatter– Reson 8101, 8111, 8125, 8160, 7125

– Elac 1050 & 1180

– Simrad 1002, 3000

• Airborne laser (or lidar) bathymetry– Optech

– LADS

• Side Scan Sonar– Klein 3000 & 5000 Systems

• Phase Differencing (Interferometric) Sonars– Benthos C3D evaluation in AK during 2007

– Klein 5410

– Geoacoustics

• Autonomous Underwater Vehicle (AUV)– REMUS Hydroid w/ Kearfott T-16

• Vessel-based Laser Scanner for shoreline delineation– Experiment completed in VA during 2007

Measuring Bathymetry

Depth: uncertainty-weighted depth-most probable surface

Uncertainty: uncertainty-weighted uncertainty

Density: number of soundings that contributed to grid node

Standard Deviation: standard deviation of the soundings that contributed to grid node

Mean: “regular” average of the soundings that contributed to grid node

Shoal: shoalest of soundings contributing to grid node

Deep: deepest of soundings contributing to grid node

Gridded Bathymetry / Stats

Positioning Requirements

• Horizontal Accuracy (95%)– IHO S-44 Order 1: 5 meters + 5 percent of depth

• Vertical Accuracy (95%)– IHO S-44 Orders: ± [a2 + (b × depth)2]½

– Order 1: Depth ≤ 100 m a = 0.5 m, b = 1.3%– Order 2: Depth > 100 m a = 1.0 m, b = 2.3%– Special Order: a = 0.25 m, b = 0.75%

• Resolution– Complete Coverage – Detect Shoals:

• Depth ≤ 40 m 2-m x 2-m horizontal, 1-m vertical• Depth > 40 m 10% depth horizontal, 5% depth vertical

– Object Detection Coverage:• Depth ≤ 20 m 1 m3

• Depth > 20 m (5% depth)3

Vertical Components

seafloor

averagewater levelsea surface

tide

(( ))

static offset andvessel translation

& attitude

((

tide datum(zoned MLLW)

observed depth

charted depth

• Corrections from in-situ water level– High frequency (< 20s periods) via IMU heave– Medium frequency via dynamic draft model*– Low frequency via (> 3600s periods) zoned tides

Non-GPS Vertical Positioning

Tide Zoning

Chart Datum

tide datum(zoned MLLW)

seafloor

averagewater levelsea surface

charted depth

observed depth

tide

(( ))

static offset andvessel translation

& attitude

ITRF97 (1997.0)

NAD 83 (86)

NAVD 88

LMSL

geometrical relationship

GEOID99

spatialinterpolation of

tidal benchmarks tidal modeling ortidal benchmark

interpolation

((

ellipsoidal depth

antenna height

Surveying On The Ellipsoid

3-D position of vessel body related directly to a fixed coordinate system (ellipsoid datum)

No dynamic draft look-up table (biases)

Spectral combination of GPS height with inertial measurement unit (IMU) heave

Tidal zoning corrections replaced by vertical datum transformation

Real-time vs. post-processed solution

Surveying On The Ellipsoid

Survey Platform Ellipsoid Height

Time (sec) on J une 6

IMU

RP E

llipso

id H

eig

ht

(m)

Non-3D Positioning

50 cm pixels

3-D Positioning

50 cm pixels

Ad Hoc Datum Transform

Vertical Datum Transform

Ellipsoidal height MLLW depth is best achieved as a combination of stepwise transformations

ITRF97 (1997.0) NAD 83 (86)NAD 83 (86) NAVD 88

NAVD 88 LMSLLMSL MLLW

Each transformation step utilizes the best available theory and data

VDatum Transforms

NAD83 (NSRS)

NAVD 88 LMSL

MHHW

MHW

MTL

DTL

MLW

MLLW

WGS 84 (G873)

WGS 84 (G730)

WGS 84 (orig.)

ITRF97

ITRF94

ITRF96

ITRF93ITRF92ITRF91

ITRF90

ITRF89

ITRF88

SIO/MIT 92

NEOS 90

PNEOS 90

NGVD 29

GEOID99,GEOID03 TSS

(Topography of the Sea Surface)

ITRF2000 WGS 84 (G1150)

Datums Datums

3-D Datums Orthometric Tidal

Tidal Datum Fields

K2 Tide

2. Regional model computes elevation time series and tidal datums are computed based on analysis of these time series and adjusted to fit NOS tidal gauge datums

1. Global tide models provide boundary conditions to regional model

3. In bays TCARI is used to interpolate between differences in the regional model and the observed datums

VDatum Marine GridVDatum Marine GridModeled Tidal Datum Fields

Datum transformations also provided on regularly structured grids to VDatum:• Topography of the Sea Surface (NAVD88 – to – LMSL field): spatially

interpolated using benchmark data and a minimum curvature algorithm.

• VERTCON transformations between NAVD88 and NGVD29

• GEOID models

• NADCON horizontal datum transformations.

VDatum AvailableDec 2007Oct 2008

VDatum: West Coast

Puget Sound

North/CentralCalifornia

VDatum exists20072008

VDatum: Gulf Coast

VDatum AvailableOct 2007Oct 2008

Tampa Bay

Lake Charles

Port Fouchon

VDatum: East Coast

VDatum AvailableOct 2007Oct 2008Tidal Model Complete (waiting on geodetic ties)

North Carolina

New York BightDelaware Bay

VDatum: Great Lakes (Dec’07)

• Goal: All “surveying on the ellipsoid” by 2010• Implementation plan due 3rd QTR 2008

– PPK & PPK-aided inertial on the ship• Data acquisition & processing with QA• Vertical solution 100% availability within error budget• Maximize use of CORS

– VDatum to reduce soundings to MLLW (chart datum)– RTK? (need QA)– PPP when requirements allow (water depth)– GPS buoys to validate VDatum modeling– Augmentation & Hybrid GNSS?

Conclusion