GPS for NOAA Hydrographic 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: ± [a 2 + (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 m 3 Depth > 20 m  (5% depth) 3

Vertical Components

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

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

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  LMSL LMSL  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 ITRF93 ITRF92 ITRF91 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 K 2 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 Grid Modeled 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 Available Dec 2007 Oct 2008 VDatum: West Coast Puget Sound North/Central California

VDatum exists VDatum: Gulf Coast VDatum Available Oct 2007 Oct 2008 Tampa Bay Lake Charles Port Fouchon

VDatum: East Coast VDatum Available Oct 2007 Oct 2008 Tidal Model Complete (waiting on geodetic ties) North Carolina New York Bight Delaware Bay

VDatum: Great Lakes (Dec’07)

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