P1252108595alFkQ

1
Geodetic and Tidal Vertical Datums
Reston, VA January 21, 2005
Dave Doyle NGS, Chief Geodetic Surveyor 301-713-31
78, dave.doyle_at_noaa.gov
Scott Duncan CO-OPS, Oceanographer 301-713-2890,
scott.duncan_at_noaa.gov
NOAA, NOS, CO-OPS NGS
2
Can You Answer These Questions?

• What is the current official vertical datum of
  the United States?
• Whats the difference between ellipsoid,
  orthometric and tidal heights?
• Why is a full metonic cycle used to compute
  primary tidal datums?
• The difference between NGVD 29 and NAVD 88 in
  most of Virginia is?
• Heights of obstructions to navigation on bays and
  rivers are referenced to which tidal daum?
• A point with a geoid height of -28.74 m means
  what?
• The tidal boundary for private lands in Virginia
  is?
• The long term sea level trend in Virginia is?
• What do you call an equipotential surface to
  which gravity is normal?
• Where is the point of origin for NAVD 88?

3
Outline of Presentation

• The National Spatial Reference System
• Metadata
• Datums and Coordinate Systems
• Horizontal NAD 27, NAD 83
• Global International Terrestrial Reference
  Frame
• Vertical MSL 29, NGVD 29, NAVD 88
• Tidal MSL, MLLW, MHHW etc.
• National Tidal Epoch Readjustment
• The Geoid
• What is it? How does it relate to other height
  surfaces?
• Geoid 99
• Geoid 03

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National Spatial Reference System

• The National Spatial Reference System (NSRS) is
  that
• component of the National Spatial Data
  Infrastructure (NSDI)
• which contains all geodetic control contained in
  the National
• Geodetic Survey (NGS) Data Base. This includes
  A, B, First,
• Second and Third-Order horizontal and vertical
  control, Geoid
• models such as GEOID 03, precise GPS orbits and
  Continuously
• Operating Reference Stations (CORS), and the
  National
• Shoreline as observed by NGS as well as data
  submitted by other
• Federal, State, and local agencies, Academic
  Institutions and the
• private sector

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National Spatial Reference System

• ACCURATE -- CM accuracy on a global scale
• MULTIPURPOSE -- Supports Geodesy, Geophysics,
  Land Surveying, Navigation, Mapping, Charting and
  GIS activities and derived products
• ACTIVE -- Accessible through Continuously
  Operating Reference Stations (CORS)
• INTEGRATED -- Related to International services
  and standards (e.g. International Earth Rotation
  and Reference System Service, International GPS
  Service etc.)

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National Spatial Reference System
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What is a Geodetic Datum?

• Geodetic Datum
• A set of constants specifying the coordinate
  system used for geodetic control, i.e., for
  calculating coordinates of points on the Earth
• above together with the coordinate system and
  the set of all points and lines whose
  coordinates, lengths, and directions have been
  determined by measurement or calculation.
• Definitions from the Geodetic Glossary,
  September 1986
• Characterized by
• A set of physical monuments and
• Published coordinates (horizontal and/or
  vertical) on
  the monuments

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Geodetic Datums

• Classical
• Horizontal 2 D (Latitude and Longitude, e.g.
  NAD 27)
• Vertical 1 D (Orthometric Height, e.g. NAVD 88)
• Contemporary
• Practical 3 D (Latitude, Longitude and
  Ellipsoid Height) Fixed and Stable Coordinates
  seldom change, e.g. NAD 83 (1991)
• Scientific 4 D (Latitude, Longitude,
  Ellipsoid Height, Velocities) Coordinates
  change with time, e.g. ITRF00

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Horizontal Control Datum?

• Horizontal Control Datum
• A Geodetic Datum specifying the coordinate
  system in which horizontal control points are
  located.
• Defined by 8 Constants
• 3 specify the location of the origin of the
  coordinate system.
• 3 specify the orientation of the coordinate
  system.
• 2 specify the dimensions of the reference
  ellipsoid.
• NAD 27, NAD 83
• Definition
  from the Geodetic Glossary, September 1986

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Vertical Control Datums

• A set of fundamental elevations to which other
  elevations are referred.
• Datum Types
• Assumed As the name implies
• Geodetic Either directly or loosely based on
  Mean Sea Level at one or more points at some
  epoch
• (NGVD 29, NAVD 88, IGLD85 etc.)
• Tidal Defined by observation of tidal
  variations over some period of time
• (MSL, MLLW, MLW, MHW, MHHW etc.)

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VERTICAL DATUMS OF THE UNITED STATES
First General Adjustment - 1899
Second General Adjustment - 1903
Third General Adjustment - 1907
Fourth General Adjustment - 1912
Mean Sea Level 1929 National Geodetic Vertical
Datum of 1929 (NGVD 29)
North American Vertical Datum of 1988 (NAVD 88)
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http//co-ops.nos.noaa.gov
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CO-OPS Data Retrieval Page
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New CO-OPS Web Page
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Data Retrieval
ZOOMABLE MAPS!
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Stainless steel rod driven to refusal
Poured in place concrete post
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Continuously Operating Reference Stations
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METADATAData About Data

• DATUMS
• NAD 27, NAD 83(1986), NAD83 (199X), NGVD29,
  NAVD88, MLLW, MSL, MHW etc.
• UNITS
• Meters, U.S. Survey Feet, International Feet,
  Chains, Rods, Poles, Links, Varas (CA or TX),
  Smokes, Smoots.
• ACCURACY
• A, B, 1st, 2nd, 3rd, 3cm, Scaled etc.

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METADATA??
Horizontal Vertical Datums??
Plane Coordinate System ??
Units of Measure ??
How Accurate ??
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METADATA??
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Reference Ellipsoids
a Semi major axis b Semi minor axis f
a-b Flattening a
N
b
a
S
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Ellipsoid, Geoid, and Orthometric Heights
H Orthometric Height (NAVD 88)
h Ellipsoidal Height (NAD 83)
H h - N
N Geoid Height (GEOID 03)

H
TOPOGRAPHIC SURFACE
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UNITED STATESELLIPSOID DEFINITIONS
BESSEL 1841 a 6,377,397.155 m 1/f
299.1528128
CLARKE 1866 a 6,378,206.4 m 1/f
294.97869821
GEODETIC REFERENCE SYSTEM 1980 - (GRS 80) a
6,378,137 m 1/f 298.257222101
WORLD GEODETIC SYSTEM 1984 - (WGS 84) a
6,378,137 m 1/f 298.257223563
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International Terrestrial Reference System (ITRF)

• GEOCENTRIC /- 3 to 4 CM
• MODELS FOR PLATE TECTONICS
• STATION VELOCITIES
• POSITIONAL STANDARD ERRORS
• REALIZED AS THE INTERNATIONAL TERRESTERIAL
  REFERENCE FRAME (ITRF)

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International Terrestrial Reference System (ITRF)

• The International Terrestrial Reference System
  (ITRS) constitutes a set of prescriptions and
  conventions together with the modeling required
  to define origin, scale, orientation and time
  evolution of a Conventional Terrestrial Reference
  System (CTRS). The ICRS is an ideal reference
  system, as defined by the International Union of
  Geodesy and Geophysics adopted in Vienna, 1991.
  The system is realized by the International
  Terrestrial Reference Frame (ITRF) based upon
  estimated coordinates and velocities of a set of
  stations observed by VLBI, GPS, LLR, SLR, and
  DORIS

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International Terrestrial Reference System (ITRF)
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GLOBAL POSITIONING SYSTEM

• GPS BLOCK IIF III
• Potential Future Developments
• 30 - 32 satellites
• Second (L2) and Third (L5)Civil Frequency
• (1227.60 MHZ 1176.45 MHZ)
• More Robust Signal Transmissions
• Real-Time Unaugmented 1 Meter (or better!)
  Accuracy
• Initial Launches 2005
• Complete Replacements 2015??

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GLOBAL NAVIGATION SATELLITE SYSTEMS(GNSS)

• POTENTIAL FUTURE DEVELOPMENTS
• (2005 2015??)
• GPS MODERNIZATION -- BLOCK IIR-M, IIF III
• GLONASS ENHANCEMENTS --M K
• EUROPEAN UNION -- GALILEO
• 70- 90 Satellites
• Second and Third Civil Frequency - GPS
• No Signal Encryption - GLONASS GALILEO

WGS 84
PZ 90
GTRF
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International Terrestrial Reference System
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Tectonic Motions
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Plate Tectonics A Dynamic Earth
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What is stable North America?
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PRELIMENARY Vertical Velocities CORS w/ lt2.5
yrs data
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PRELIMENARY North American Vertical Velocities
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PRELIMENARY Vertical velocities GPS vs Tide
Gauges
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NAD 83 and ITRF

NAD 83
ITRF
Earth Mass Center
2.2 m (3-D) dX,dY,dZ
GEOID
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Orthometric Heights

• Using Optical or Digital/Bar Code Leveling

B
Topography
A
C

• Adjusted to Vertical Datum using existing control
• Achieve 3-10 mm relative accuracy

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NGVD 29 TIDE CONTROL
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NGVD 29 and NAVD 88
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Orthometric HeightsComparison of Vertical Datum
Elements

• 
  NGVD 29 NAVD 88
• DATUM DEFINITION 26 TIDE GAUGES
  FATHERSPOINT/RIMOUSKI
• IN THE
  U.S. CANADA QUEBEC,
  CANADA
• BENCH MARKS
  100,000
  450,000
• LEVELING (Km)
  106,724
  1,001,500
• GEOID FITTING Distorted to Fit
  MSL Gauges Best Continental
  Model

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NAVD 88 Origin Point
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What is the GEOID?

• The equipotential surface of the Earths gravity
  field which best fits, in the least squares
  sense, mean sea level.
• Cant see the surface or measure it directly.
• Modeled from gravity data.
• Definition from the
  Geodetic Glossary, September 1986

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High Resolution Geoid ModelsGEOID03 (vs. Geoid99)

• Begin with USGG2003 model
• 14,185 NAD83 GPS heights on NAVD88 leveled
  benchmarks (vs 6169)
• Determine national bias and trend relative to
  GPS/BMs
• Create grid to model local (state-wide) remaining
  differences
• ITRF00/NAD83 transformation (vs. ITRF97)
• Compute and remove conversion surface from G99SSS

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High Resolution Geoid ModelsGEOID03 (vs. Geoid99)

• Relative to non-geocentric GRS-80 ellipsoid
• 2.7 cm RMS nationally when compared to BM data
  (vs. 4.6 cm)
• RMS ? 50 improvement over GEOID99 (Geoid96 to 99
  was 16)

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Composite Geoids

• Gravity Geoid systematic misfit with benchmarks
• Composite Geoid Warped to fit local benchmarks

Earths Surface
Ellipsoid
1.392 m in New Bern 2003 model
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Space-Based Gravity Observation Platforms
CHAMP
GRACE
GOCE
LAGEOS
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Gravity Recovery And Climate Experiment (GRACE)
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Gravity Recovery And Climate Experiment (GRACE)
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How to achieve accurate GPS heights

• 1) What types of heights are involved?
• Orthometric heights
• Ellipsoid heights
• Geoid heights
• 2) How are these heights defined and related?
• 3) How accurately can these heights be
  determined?

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Control Point Datasheets
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Sample Datasheet

• National Geodetic Survey, Retrieval Date
  JANUARY 7, 2005
• HU1583
  
• HU1583 CBN - This is a Cooperative
  Base Network Control Station.
• HU1583 TIDAL BM - This is a Tidal Bench
  Mark.
• HU1583 DESIGNATION - NORTH BEACH 2
• HU1583 PID - HU1583
• HU1583 STATE/COUNTY- MD/WORCESTER
• HU1583 USGS QUAD - TINGLES ISLAND (1972)
• HU1583
• HU1583 CURRENT SURVEY
  CONTROL
• HU1583 _________________________________________
  __________________________
• HU1583 NAD 83(1991)- 38 11 57.30665(N) 075
  09 21.86176(W) ADJUSTED
• HU1583 NAVD 88 - 1.460 (meters)
  4.79 (feet) ADJUSTED
• HU1583 _________________________________________
  __________________________
• HU1583 X - 1,285,739.500 (meters)
  COMP
• HU1583 Y - -4,851,265.771 (meters)
  COMP
• HU1583 Z - 3,922,826.915 (meters)
  COMP
• HU1583 LAPLACE CORR- 0.60 (seconds)
  DEFLEC99
• HU1583 ELLIP HEIGHT- -34.74 (meters)
  (02/12/02) GPS OBS

H h - N 1.46m - 34.74m - (- 36.17m) 1.46m ?
1.43m (0.03m/0.10 ft)
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Sample Datasheet

• HU1583 North East
  Units Scale Factor Converg.
• HU1583SPC MD - 60,750.798
  561,509.582 MT 1.00001905 1 09 26.3
• HU1583SPC MD - 199,313.24 1,842,219.35
  sFT 1.00001905 1 09 26.3
• HU1583UTM 18 - 4,227,934.312
  486,334.387 MT 0.99960230 -0 05 47.5
• HU1583
• HU1583! - Elev Factor x Scale
  Factor Combined Factor
• HU1583!SPC MD - 1.00000545 x
  1.00001905 1.00002450
• HU1583!UTM 18 - 1.00000545 x
  0.99960230 0.99960775
• HU1583
• HU1583 Primary Azimuth Mark
  Grid Az
• HU1583SPC MD - NORTH BEACH 2 AZ MK
  030 39 27.3
• HU1583UTM 18 - NORTH BEACH 2 AZ MK
  031 54 41.1
• HU1583
• HU1583------------------------------------------
  ---------------------------
• HU1583 PID Reference Object
  Distance Geod. Az
• HU1583
  dddmmss.s
• HU1583 DC8236 NORTH BEACH 2 AZ MK
  0314853.6
• HU1583 HU2581 NORTH BEACH 2 RM 3
  53.290 METERS 11507
• HU1583 DC8237 NORTH BEACH 2 RM 4
  77.588 METERS 23042

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VERTCON - Vertical Datum Transformations
Published 1.460 m Difference 0.011 m / 0.04 ft
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VERTCON - Vertical Datum Transformations
Published 3.089 m Difference 0.011 m / 0.04 ft
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Continuously Operating Reference Stations
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Continuously Operating Reference Stations
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Continuously Operating Reference Stations
VIRGINIA INSTITUT (VIMS),
VIRGINIA Retrieved from NGS DataBase on
10/29/02 at 154740. ___________________________
_________________________________________________

Antenna
Reference Point(ARP) VIRGINIA INSTITUT CORS ARP
-----------------------------
---------------------------
PID AI3289



ITRF00 POSITION
(EPOCH 1997.0)
Published by the IERS in Mar. 2001.
X
1250692.726 m latitude 37 36 30.07289
N Y -4902017.182 m
longitude 075 41 13.21387 W
Z 3871080.257 m ellipsoid height
-29.075 m

ITRF00 VELOCITY

Published by the IERS in Mar. 2001.
VX -0.0147
m/yr northward 0.0029 m/yr
VY -0.0011 m/yr eastward
-0.0145 m/yr VZ
0.0017 m/yr upward -0.0010 m/yr



NAD_83 POSITION
(EPOCH 2002.0)
Transformed from ITRF00 (epoch
1997.0) position in Mar. 2002.
X 1250693.276 m latitude 37 36
30.04548 N Y
-4902018.667 m longitude 075 41 13.20712
W Z 3871080.404 m
ellipsoid height -27.739 m

NAD_83 VELOCITY

Transformed from ITRF00 velocity in
Mar. 2002. VX
0.0012 m/yr northward -0.0010 m/yr
VY 0.0007 m/yr
eastward 0.0013 m/yr
VZ -0.0016 m/yr upward
-0.0013 m/yr
_______________________________________________
_____________________________
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Continuously Operating Reference Stations
GLOUCESTER POINT (GLPT),
VIRGINIA Retrieved from NGS DataBase on
10/29/02 at 154718. ___________________________
_________________________________________________

Antenna
Reference Point(ARP) GLOUCESTER POINT CORS ARP
-----------------------------
--------------------------
PID AI3283



ITRF00 POSITION
(EPOCH 1997.0)
Computed in Aug. 2001 using every
third day of data through 2000.
X 1186726.293 m latitude 37 14
54.74522 N Y
-4942863.964 m longitude 076 29 58.04117
W Z 3839372.516 m
ellipsoid height -22.030 m

ITRF00 VELOCITY

Computed in Aug. 2001 using every
third day of data through 2000.
VX -0.0150 m/yr northward 0.0024 m/yr
VY -0.0027 m/yr
eastward -0.0152 m/yr
VZ 0.0024 m/yr upward
0.0008 m/yr



NAD_83 POSITION (EPOCH 2002.0)
Transformed from
ITRF00 (epoch 1997.0) position in Mar. 2002.
X 1186726.840 m latitude
37 14 54.71815 N Y
-4942865.457 m longitude 076 29 58.03374
W Z 3839372.670 m
ellipsoid height -20.679 m

NAD_83 VELOCITY

Transformed from ITRF00 velocity in
Mar. 2002. VX
0.0008 m/yr northward -0.0012 m/yr
VY -0.0010 m/yr
eastward 0.0005 m/yr
VZ -0.0006 m/yr upward
0.0006 m/yr
_______________________________________________
_____________________________


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Continuously Operating Reference Stations
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OPUS WHAT IS IT?

• On-line Positioning User Service
• Provide GPS users faster easier access to the
  National Spatial Reference System (NSRS)

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OPUS HOW DOES IT WORK?

• Submit RINEX file through NGS web page
• Processed automatically with NGS computers
  software
• With respect to 3 suitable or user-selected
  National CORS
• Solution via email in minutes

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OPUS HOW DO I USE IT?

• Go to OPUS web page www.ngs.noaa.gov/OPUS
• Enter your email address
• Use browse feature to select RINEX file on your
  computer
• Select antenna type from menu
• Enter antenna height in meters
• Option to select State Plane Zone
• Click UPLOAD
• Check your email in a few minutes

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To enhance vertical accuracy use rapid orbits
available in 24 hours Broadcast Orbits 5 m
(real time) Ultrarapid Orbits 0.1 m (12
hours) Rapid Orbits 0.02 0.03 m (24
hours) Precise Orbits 0.01 0.02 m (two weeks)
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Upcoming OPUS Enhancements

• SPRING 2005
• On-Line Project Network Solutions
• Project User Profile
• Project Manager/Session Submission Passwords
• Virtually limitless GPS sessions
• OPUS submissions from remote sites
• Network Adjustment as required

• LATE 2005
• L1 only GPS observations
• Code phase solutions

• 2006 ????????
• OPUS database

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Whats Left?

• Leveling-Derived Orthometric Heights
• Modeled Geoid Heights
• GPS-Derived Ellipsoid Heights

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Available On-Line at the NGS Web
Site www.ngs.noaa.gov
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Components of NGS-58

• Basic Control Requirements
• Equipment Requirements
• Antenna Setup Requirements
• Data Collection Parameters

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Static GPS
Baseline or Vector (cm precision)
GPS gives us the relationship or vector between
two antennas
Position ultimately determined relative to known
points that must have high precision ellipsoid
heights
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Atmosphere-based Ionospheric Delay
Ionosphere
gt 10 km
lt 10 km
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Two Days/Same Time
-10.254 -10.251
gt -10.253
Difference 0.3 cm
Truth -10.276
Difference 2.3 cm
Two Days/ Different Times
-10.254
gt -10.275
-10.295
Difference 4.1 cm
Truth -10.276
Difference 0.1 cm
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Equipment Requirements

• Dual-frequency, full-wavelength GPS receivers
• Required for all observations greater than 10 km
• Preferred type for ALL observations regardless of
  length
• Geodetic quality antennas with ground planes
• Choke ring antennas highly recommended
• Successfully modeled L1/L2 offsets and phase
  patterns
• Use identical antenna types if possible
• Corrections must be utilized by processing
  software when mixing antenna types

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Antenna Setup

• Fixed-height tripods required for 2 cm standard
• Shade plumbing bubbles at least 3 min prior to
  plumbing
• Check perpendicularity of poles at beginning of
  project
• Fixed-height poles preferred for 5 cm standard
• Alternate tripod setups antenna heights MUST be
  measured carefully and accurately
• Check measuring system before project
• Check and adjust tribrachs at beginning of
  project
• Perform totally independent meter and feet
  measurements
• Have measurement computations checked by someone
  else

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Data Collection Parameters

• VDOP lt 6 for 90 or longer of 30 minute session
• Shorter session lengths stay lt 6 always
• Schedule travel during periods of higher VDOP
• Session lengths gt 30 minutes collect 15 second
  data
• Session lengths lt 30 minutes collect 5 second
  data
• Track satellites down to 10 elevation angle

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Tidal Datumsand TheirApplications
Scott Duncan, NOAA, NOS
Center for
Operational Oceanographic Products and Services
(CO-OPS)
81
http//co-ops.nos.noaa.gov
82
DATUM (VERTICAL)
CHART DATUM

• For marine applications
• a base elevation used as a reference from which
  to reckon heights or depths.
  
  
  
• TIDAL DATUM
• defined by a certain phase of the tide (ex. MHW)
  
• are local datums
• in order that they may be recovered when needed,
  such datums are referred to fixed points known
  as BENCH MARKS

• The tidal datum to which soundings on a nautical
  chart are referred.
• USA chart datum Mean Lower Low Water (MLLW)
• For non tidal waters (including Great Lakes)
  chart datum is Low Water Datum (LWD)

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Types of Tides
Semidiurnal Tide
Mixed Tide
Diurnal Tide
84
MHHW
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APPLICATIONS SUPPORTED BY THE NATIONAL WATER
LEVEL AND TIDAL CURRENT PROGRAMS
Function Application Navigation/Safety Real-Time
Navigation, Hydrographic Surveys, Airborne
Hydrography, HAZMAT Response ...etc. Environmen
tal Assessment/ Wetland Delineation,
Coastal Monitoring Zone Management
Enforcement, Insurance, Storm Surge, Tsunami
Warningetc. Basic Applied Research Modeling,
Wetland Studies, Global Warming Studies, Sea
Level Change, Estuarine/ Hydrodynamic
Studiesetc.
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Datums Boundary Applications
88
TIDES SUPPORT TO NAUTICAL CHARTING HYDROGRAPHY
APPLICATIONS
SOUNDINGS ARE REFERRED TO MLLW
HEIGHTS ARE REFERRED TO MHW
89
National Water Level Observation Network (NWLON)
175 Permanent Stations
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Next Generation Station with Backup Sensor
91
What Does an NWLON Station Look Like in Your Area?
92
NATIONAL TIDAL DATUM EPOCH

• A specific 19 year period that includes the
  longest periodic tidal variations caused by
  the astronomic tide-producing forces.
• Averages out long term seasonal meteorological,
  hydrologic, and oceanographic fluctuations.
• Provides a nationally consistent tidal datum
  network (bench marks) by accounting for seasonal
  and apparent environmental trends in sea level
  that affects the accuracy of tidal datums.
• The NWLON provides the data required to maintain
  the epoch
  
  
  and
  make primary and secondary determinations of
  tidal datums.

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IDEALIZED CHANGE OF TIDAL EPOCH
1983-01 EPOCH
95
RELATIVE SEA LEVEL CHANGE AT SEVERAL LOCATIONS
IN THE U.S.
96
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98
60-78 Epoch
83-01 Epoch
MSL1.747
MSL Linear Trend
MSL 1.643
Epoch Change
0..104 m
99
0.064m
0.076m
0.070m
0.073m
0.070m
0.057m
0.091m
0.104m
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National Water Level Observation Network (NWLON)
175 Permanent Stations
101
STATION HIERARCHY

• TERTIARY TIDE STATION
• more than 30 days but less than a year

• PRIMARY TIDE STATION
• minimum of 19 years
• allows statistical and datum control for short
  term stations

• SECONDARY TIDE STATION
• minimum of 1 yr but less than 19 yrs

102
MTL Money Pt.
MTL Sewells Pt.
1983-2001 MTL Sewells Pt.
103
GENERALIZED ACCURACY OF TIDAL DATUMS FOR SHORT
SERIES (BASED ON ONE STD DEV) Series
East Gulf West Length
Coast Coast Coast Mo
FT FT FT 1
0.13 0.18 0.13 3
0.10 0.15 0.11 6
0.07 0.12 0.08 12
0.05 0.09 0.06
104
Leveling and Datums
105
NOS BENCHMARK LEVELING
106
Relative to NAVD 88
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Summary

• Tidal datums are based on a phase of the tide
  (ex. MHW, MLLW).
• Station datums are based on a 19 year mean called
  an National Tidal Datum Epoch (NTDE).
• Tide stations are referenced to bench mark system
  for stability checks long term maintenance.
• Tidal datums are predominantly computed using the
  monthly mean simultaneous comparison method
  (MMSC).
• Datum applications PORTS, chart depths , marine
  boundaries, hydrographic surveys, dredging, storm
  surge, modeling, wetland restoration, etc.

109
QUESTIONS?
110
CO-OPS Tidal Geodetic Datums Overview
111
Web Access to Benchmark Data
http//www.co-ops.nos.noaa.gov
112
Published Benchmark Sheets
Also has links for non-US benchmarks as well as a
direct link to the National Geodetic Survey (NGS)
113
Published Benchmark Sheet Selections for CT
114
Benchmark Descriptions
NGS Data Sheet
115
Published Benchmark Sheet
NAVD 88
116
Visual Representation of Datums
Start at www.ngs.noaa.gov which is the NGS
home page.
117
The Easier Way
118
Datum Staff Representation
Geodetic Difference1.09 feet
119
How to Use CO-OPS Web Site to Determine Geodetic
Elevations Relative to Tidal Datums

• Start with the Published Benchmark Sheet area of
  the CO-OPS web site.

120
NGVD 29
Differences
The MATH
4.420 21.233 4.280 4.409 3.929
1.379 1.383 1.382 1.928 1.377
OMIT

1.380m
5.521
/4
NGVD 29
121
How can I relate these tidal datums to the
geodetic?
http//co-ops.nos.noaa.gov
122
CO-OPS Data Retrieval Page
123
What is station datum and why does it matter?
124
How can I relate these tidal datums to the
geodetic?
4.22 feet
125
Tidal and geodetic relationships revealed!
Relative to NAVD 88
2.749 1.418 1.285 0.000
-0.096 -0.106 -1.496 -1.601
-2.654
Relative to NAVD 88?
1.285
4.198
-1.601

126
TIDES SUPPORT TO NAUTICAL CHARTING HYDROGRAPHY
APPLICATIONS
SOUNDINGS ARE REFERRED TO MLLW
HEIGHTS ARE REFERRED TO MHW
127
Summary

• WWW.CO-OPS.NOS.NOAA.GOV
• Published benchmark sheets
• NGS/CO-OPS datum visual representations
• Find PIDs and their geodetic datums from NGS
  website
• Calculate geodetic datums on the fly
• Refer datums to NAVD 88

128
The End
Questions?