SEAMLESS VERTICAL DATUM A SEAMLESS VERTICAL-REFERENCE SURFACE FOR ACQUISITION, MANAGEMENT AND DISPLAY (ECDIS) OF HYDROGRAPHIC DATA A report prepared for the Canadian Hydrographic Service under Contract Number IIHS4-122 David Wells Alfred Kleusberg Petr Vanicek Department of Geodesy and Geomatics Engineering University of New Brunswick PO. Box 4400 Fredericton, New Brunswick Canada E3B 5A3 FINAL REPORT (DRAFT) November 22, 2004 Page 1 SEAMLESS VERTICAL DATUM Final Report 15 July 1995 FINAL REPORT (DRAFT) November 22, 2004 Page 2 SEAMLESS VERTICAL DATUM TABLE OF CONTENTS Table of contents...........................................................................................................................2 Executive summary.......................................................................................................................5 Acronyms used in this report ........................................................................................................6 1. Introduction...............................................................................................................................8 1.1 Problem statement.......................................................................................................8 1.2 The role of vertical-reference surfaces in navigation..................................................8 1.3 Vertical-reference surface accuracy issues..................................................................9 1.3.1 Depth measurement errors .........................................................................10 1.3.2 Water level measurement errors ................................................................10 1.3.3 Water level prediction errors......................................................................10 1.3.4 Vertical-reference surface accuracy...........................................................11 1.4 Opportunity provided by GPS...................................................................................12 1.4.1 What is OTF?.............................................................................................13 1.4.2 Status of OTF.............................................................................................13 1.5 The role of transformations.......................................................................................14 1.6 Restatement of the problem ......................................................................................16 1.7 Outline of the report..................................................................................................17 2. Vertical-reference surfaces......................................................................................................18 2.1 Tidal surfaces ............................................................................................................18 2.1.1 Present set of tidal surfaces........................................................................19 2.1.2 Other tidal surfaces ....................................................................................19 2.1.3 Representation of depths............................................................................19 2.1.4 Representation of heights...........................................................................20 2.1.5 Tidal analysis and prediction .....................................................................20 2.2 Hydrological surfaces................................................................................................20 2.2.1 Present vertical-reference surfaces in rivers ..............................................20 2.2.2 Other vertical-reference surfaces in rivers .................................................21 2.2.3 Present Vertical-reference surfaces in lakes ..............................................21 2.2.4 Other vertical-reference surfaces in lakes ..................................................21 2.3 Equipotential surfaces...............................................................................................22 2.3.1 Geoid..........................................................................................................22 2.3.2 Other equipotential-related surfaces ..........................................................23 2.4 Mathematical surfaces...............................................................................................23 2.4.1 REFERENCE ELLIPSOID........................................................................24 2.4.2 Other mathematical surfaces......................................................................24 2.5 Vertical-reference surfaces on land...........................................................................26 2.5.1 Land-based height control..........................................................................27 2.6 Reference surfaces for other purposes ......................................................................28 3. Transformation issues .............................................................................................................29 FINAL REPORT (DRAFT) November 22, 2004 Page 3 SEAMLESS VERTICAL DATUM 3.1 Vertical-reference system transformation concepts ..................................................29 3.2 Chart datum to a seamless datum..............................................................................30 3.3 Seamless surface to chart datum ...............................................................................30 3.4 Chart Datum to sea level...........................................................................................31 3.5 Seamless surface to sea level ....................................................................................31 3.5.1 Real time correction to instantaneous sea level .........................................32 3.6 Transformations between horizontal datums ............................................................32 3.7 Transformations of geodetic heights between horizontal datums.............................33 4. Practical issues involved.........................................................................................................35 4.1 Definition of CHS client groups ...............................................................................35 4.1.1 “Virtual corporation” collaborators ...........................................................35 4.1.2 Low complexity end users .........................................................................35 4.1.3 Medium complexity end users ...................................................................36 4.1.4 Critical end users........................................................................................36 4.2 Other users of vertical-reference surfaces.................................................................37 4.3 Stability versus quality..............................................................................................37 4.4 Digital database issues ..............................................................................................38 5. Selection of a seamless vertical-reference surface..................................................................40 5.1 Criteria for selection of a new reference surface.......................................................40 5.1.1 Navigation safety .......................................................................................40 5.1.2 Accuracy of final depth presentation to mariners ......................................40 5.1.3 Seamlessness..............................................................................................42 5.1.4 Consistency across land-sea boundary.......................................................42 5.1.5 Ease of realization and maintenance..........................................................42 5.2 Proposed strategy ......................................................................................................43 5.2.1 Selection of a seamless vertical-reference surface.....................................43 5.2.2 Other initiatives..........................................................................................46 6. Implementation of a seamless vertical-reference surface .......................................................48 6.1 Tools available for implementation ..........................................................................48 6.1.1 GPS ............................................................................................................48 6.1.2 TOPEX and other altimetric satellites .......................................................48 6.1.3 Appropriate mapping functions .................................................................49 6.2 Initial implementation steps......................................................................................50 6.2.1 Determine transformation at water level stations ......................................50 6.2.2 Chart datum boundaries and spatial extrapolation of chart datums...........51 6.2.3 Applying transformations ..........................................................................52 6.3 Proposed implementation strategy............................................................................52 6.3.1 Setting priorities.........................................................................................52 6.3.1 Specifications for GPS static baseline surveys ..........................................54 6.3.2 Meeting the GPS Specifications ................................................................55