010912-02-geodeticverticaldatums-michalski -grayscale.pdf
TRANSCRIPT
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Michael Michalski, NOAA/National Ocean ServiceCenter for Operational Oceanographic Products and ServicesMonday, January 9 2012
Tidal Datums
Non-tidal Datum considerations
Datum Computations
Datums Relative to Benchmarks
Regional Variation in Tidal –Geodetic
Interpolation of Tidal – GeodeticRelationships
Application of VDatum
Tidal Theory
Station Configuration
Data Collection
Data Processing
Tidal Characteristics
NTDE (MTDE)
Relative Sea Level Trends
Caused by gravitational attraction between the Earth, Moon, & Sun
Periodic variation in the surface level of the oceansPeriodic variation in the surface level of the oceans
MeanSeaLevel
Tide : The alternating rise and fall of water levels withrespect to land
Tidal Current : Horizontal motion resulting from rise& fall of water levels
Tide Range : difference in height between highesthigh & lowest low
Tidal Period : Time between successive lows or highs(Average ~12.4hs)
Common TermsCommon Terms
Tidal Current
Tide curve
Time
Wa
ter
leve
lhe
igh
t
Cu
rren
tsp
eed
Time
Tidal Frequency : How often 1 tidal period occurs per day (Average ~1.9 cycles per day)
Mean Sea Level : Averageheight of sea surface
Astronomy - Tides are result of the
gravitational forces of the Earth, Moon & Sun
& the centrifugal forces of their rotations
Hydrodynamics - The range & timing of the tide& the speed, direction & timing of the tidalcurrent are also influenced by the configurationof the coastline, bottom topography & localwater depth
Astronomy & HydrodynamicsAstronomy & Hydrodynamics
Bay
Long WaveIn the Ocean
Both the moon & the sun affect the tides (sun’s effect is 0.46 times that of the Moon)
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Most important tide modulations result from phases of the Moon relative to SunMost important tide modulations result from phases of the Moon relative to Sun
- When moon & Sun align with earth – get larger more predominate tides = Spring Tides
- When moon & Sun at right angles – get smaller less predominate tides = Neap Tides
- These modulations occur once each lunar month - ~29 ½ days
Forces change with alignment- Strength of the gravitational force is strongest when Sun &Moon are aligned (Phase Inequality)
Tide producing force ofthe Moon is 2.5 times
that of the Sun
Force due to the moon isabout 2.5x greater thanthe force due to the sun
full moon
Spring tides, with higherhigh tides and lower lowtides
Gra
vita
tio
nal
pu
ll
Gravitational pullCentrifugal force
Gravitational pull Centrifugal force
Gra
vita
tio
nal
pu
llC
en
trif
uga
lfo
rce half moon
Neap tides – muted, withhigher lows and lowerhighs
new moon
Spring tides, with higherhigh tides and lower lowtides
Gravitational pull Centrifugal force
Spring and Neap tides
• Spring tide: sun and moonaligned
• Neap tide: sun and moon notaligned
Affects the amplitude of the tides (tidal range)Affects the amplitude of the tides (tidal range)
MoonPhases: NeapNeapNeapNeapSpringSpring SpringSpring
Less significant modulations result from the elliptical orbits of Earth & MoonLess significant modulations result from the elliptical orbits of Earth & Moon
Moon’s Orbit – Monthly modulation
Diurnal InequalityThe changing distance of the Moon aboveor below the equator causes a differencein amplitude of the two tides in the same
day & results in the various tide types(Semidiurnal, Mixed & Diurnal)
The two daily highs will be most similarwhen the declination is smallest
Forces change with angle - Strength of the gravitational force is strongest when angle is smallest(Declination Inequalities)
A longer period modulation results from the angled orbital paths of the Earth &A longer period modulation results from the angled orbital paths of the Earth &moon around the sunmoon around the sun
Ecliptic - Apparent path of Earth about the Sun, as seenfrom the Sun
Lunar Orbit - Apparent path of Moon about the Sun, asseen from the Sun
Nodes - Points where Moon’s path crosses the ecliptic.
Effects the amplitude of the Annual Mean Range(Difference in height between mean high & low)
Regression of the Moon’s Nodes – Variation in thepath of the Moon about the Sun, such that the angleof the moon’s orbital plane with the equatorial planevaries over 18.6 yrs
Forces change with angle - Strength of the gravitational force is strongest when angle is smallest(Regression of the Nodes)
Effects the amplitude of the annual mean rangeEffects the amplitude of the annual mean range
ANNUAL MEAN RANGE
MONTHLY MEAN RANGE
The time between peaks is the period of oscillation of the regression (~18.6yrs))
-- Basis for defining the National Tidal Datum Epoch (NTDE) as a 19yr periodBasis for defining the National Tidal Datum Epoch (NTDE) as a 19yr period
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National Water Level Observation Network (NWLON)National Water Level Observation Network (NWLON)
Remote Pacific Island Stations Not Shown
• Network of long-term and short-term water level stations
• 306 coastal stations recording 6-minute data
• Includes 53 stations in the Great lakes
• Includes 61 Short-term stations supportingprojects such as storm surge monitoring research,hydro / photo support, and habitat restoration
Control stationsControl stations are operated by NOS and disseminated over the internetare operated by NOS and disseminated over the internet
Primary Control Tide Station: Continuous observations over 19 yrs ormore & expected to continue- Data used for determining tidal datums
Secondary Control Tide Station: Subordinate station with continuousobservations over at least 1 yr, but less than 19 yrs, and has a planned finitelifetime- Data must be compared to a suitable control station for determining tidaldatums
Tertiary Control Tide Station: Subordinate station with continuousobservations over at least 30 days, but less than 1 yr, and has a plannedfinite lifetime- Data must be compared to a suitable control station for determining tidaldatums
Subordinate stations are usually installed by field teams prior to surveyoperations and removed after surveys are completed
Essential EquipmentEssential Equipment
• Automatic water level sensor
• Backup water level sensor
• Backup & Primary data
collection platform
• Protective well
• Shelter
• Solar Panel
• GOES satellite radios
• Telephone modem
• Ancillary geophysical instruments
• System of Bench Marks
• Data Collection Platform
• Acoustic or pressure sensor
• Solar Panel
• GOES Transmitter
Short term stations
Control Stations
• Water Level
• Wind Speed/Direction
• Barometric Pressure
• Air/Water Temp.
• Conductivity/Temp
• Chart Datum
• Tsunami/Storm Surge
Observations
Collected
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Water Level Measurement SystemsWater Level Measurement Systems
Primary Measurement System
Aquatrak® Air Acoustic water level sensor
• Self-calibrating measurement technique
• Directly Leveled to local benchmark network
Sutron Xpert data collection platform
• Multitasking Operating system
• 30 Days of Data Storage
• Satellite Data Telemetry
• Telephone Modem - Data retrieval andsoftware upgrades
Backup Measurement System
Pressure sensor based water level sensor
Sutron Data Collection Platform
• 60 Days of Data Storage
• Transfers data to Primary Measurement System
Vertical Datum ReferenceVertical Datum ReferenceVertical Datum Reference characteristics are:
• Water levels accurately known relative to the latest tidal datums on thelatest National Tidal Datum Epoch (NTDE)
• Water levels accurately known relative to the land and a local network ofrecoverable tidal bench marks
• Precise connections to the national geodetic datum (NAVD88) using levelconnections or GPS connections to the bench marks in the NationalSpatial Reference System(NSRS)
• NGS Accuracy Standards2nd Order, Class I for long-term stations3rd Order for short-term stations
• Annual leveling for NWLON
installation and removal
levels for short-term stations
• Emergency leveling
for storm events
Geodetic Benchmark(and its WGS84 value)
Relative to Tidal Datum
NO
AA
Tidal Bench mark4811 G 2004
Station Datum
Orifice0.7428m
Tidal Bench mark4811 G 2004
3.150 m
MHW2.736 m
MLLW1.220 m
Bench markwith geodetic control
(NAVD88, WGS84,etc.)
TideGauge
1.150 m(example)
Pier
GPS Receivers collecting simultaneousdata over existing bench marks allowfor datum transformation.
2.000 m
GPSReceiver
NAVD88
Sent from stations via satelliteSent from stations via satellite
NESDISNational Environmental Satellite,
Data and Information Services
PORTS®® ServerNWLON Server
Data Analyst
CO-OPS Web Page
GOESSatellite
Continuous Operational RealContinuous Operational Real--Time Monitoring System (CORMS)Time Monitoring System (CORMS)
Real-Time 24x7 QA/QC•Human Analysis•Data Quality Flags (e.g. Rate of Change)•Corrective Action
Post-Processing•Error in Data (e.g. spikes, missing data)•Data Quality Flags: shifts, bias, changes•Tabulation & Product Generation•Backup Gain and Offset•Verification & Acceptance
Initial Automated ProcessingInitial Automated Processing
Data Processing & Analysis Subsystem (DPAS)
• NOS Database Management System
• Receives water level data from stations– Calls NESDIS to download new water level data every hour
• Performs automated QC checks
• Generates QC Reports
Monthly Product Generator (MPG)•Software system that activates on the first day of each month to process the rawsensor data for all active stations
– check to insure that no product data exists for the month
– fill data gaps using a hierarchy of techniques
– develop quality control metrics - tabulate highs and lows - calculate monthly means
– insert the generated product into the database.
Works well with semidiurnal/mixed tidal dataof significant range, or data without breaks
Doesn’t work well with diurnal, lowrange or noisy data
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Initial Automated ProcessingInitial Automated Processing
• When MPG doesn’t work well you will see:
Not designed toreplace analysts
• Double or missing tides• Overlapping time series
• Data spikes• Bad break fills
Data Processing ProceduresData Processing Procedures
1. Preliminary Analysis
• Check station parameters
• Examine data inventories
• Initialize Working Water Level data
– Move data from sensor areas into working WLTable
• Review 6-minute Data plots
– Data Gaps
– Large standard deviations indicate a problem
Check station parameters
Review data plots
Data Processing ProceduresData Processing Procedures
1. Preliminary Analysis (Cont’d)
• Fill Breaks
– Fill-six program or QC Spreadsheet
– Use Backup WL data, compatible nearby stationdata, predictions, or curve fit for small breaks
• Perform Offline QC Checks
• Check and correct erroneous data using theQC Spreadsheet, nearby station checks
Fill with backup (B1) or nearby station
Curve fit
Backup Fill
Fill with predicted (PR)data
Fill Breaks
Perform Offline QC Checks Programmed into the computer algorithms.Programmed into the computer algorithms.
1. Two-hour rule: Adjacent high and low waters must be different by 2 hours or more intime in order to be counted as a tide.
2. One-tenth of a foot rule (same as 0.03 m rule): Adjacent high and low waters must bedifferent in elevation be one tenth of a foot (or 0.03 m) or more in order to be counted as atide for tabulation.
Criteria for determining a TideCriteria for determining a Tide
Difference inelevation
Difference in time
2. Tabulation
• Tabulate High and Low waters
– Select DIUR or EXHL
– Tide Check Report – summary & error messages
• Use QC Spreadsheet to edit Hourly Heights and Hi/Lo waters
• Plot WL w/ HI/LO picks and corrections
• Run Hi/Lo check option
Data Processing ProceduresData Processing Procedures
Hi-Low Water
Hourly Heights
Hi-Low Picks
Tide Check Report
2. Tabulation (Cont’d)
• Compute Monthly Means
• Mark data Complete
• Make output reports
• Final Time Series Check
4.Verification
• Check by a senior analyst
5.Compute Datums
Data Processing ProceduresData Processing Procedures
Monthly Means
Verified HI / LO
Verified WATERLEVEL HOURLY
ACCEPTED Datums
VerifiedMonthlyMeans
VerifiedSIX-MINUTE
WATER LEVEL
RAW SIX-MINUTEWATER LEVEL
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• 6 minute data values
• Hourly Heights
• Highs and Lows
• Monthly means
Final Water Level ProductsFinal Water Level Products
- Because we know which frequencies will have tidal energy,• we can predict the tide or tidal current• without really knowing anything about the hydrodynamics• Though, we can do a better job of prediction, if we do understand the hydrodynamics
- As long as we have a long enough data time series at a location,• we can analyze that data,• extracting amplitude and phase information for each tidal frequency,• and make reasonably good tidal predictions
* for (only) that specific location for anytime in the future or past
Tide Analysis & PredictionTide Analysis & Prediction
Portland, ME
Harmonic ConstituentsHarmonic Constituents
Principal components that make up tide signal, & are used to make tide predictionsPrincipal components that make up tide signal, & are used to make tide predictions
M2 - Principal lunar
S2 - Principal solar
N2 - Larger lunar elliptic
K1 - Luni-solar diurnal
O1 - Principal lunar diurnal
P1 - Principal solar diurnal
More than 1 component fromsun & moon
• due to their orbits beingelliptical
• and at angles to the plane
• both changing over time
Analysis & Prediction
• Observed tides areanalyzed for theirconstituents
• Constituents are then usedto create predicted tides
Need observations over asuitable period of time
• 1 – 10yrs depending onconstituent to analyze
COMPARISON OF TIDAL VS. NONCOMPARISON OF TIDAL VS. NON--TIDAL EFFECTSTIDAL EFFECTSREDUCTION OF VARIANCE STATISTICSREDUCTION OF VARIANCE STATISTICS
(FROM ONE(FROM ONE--YEAR HARMONIC ANALYSIS)YEAR HARMONIC ANALYSIS)
STATION TIDAL NON-TIDAL
BOSTON, MA 98.2% 1.8%
BALTIMORE, MD 44.8% 55.2%
CHARLESTON, SC 91.2% 8.8%
KEY WEST, FL 74.5% 25.5%
PENSACOLA, FL 45.4% 54.6%
GALVESTON, TX 39.5% 60.5%
SAN FRANCISCO, CA 98.6% 1.4%
SEATTLE, WA 98.8% 1.2%
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two daily highs & lows~ similar height
Most common
two daily highs & lows~ not similar height
one daily high & low
US Tide Types by RegionUS Tide Types by Region
East CoastPrimarily SemidiurnalSemidiurnal
West Coast & AlaskaPrimarily MixedMixed
Gulf CoastPrimarily DiurnalDiurnal
Ocean City, MD
San Francisco, CA
Panama City, FL
Tide Type Varies by Region due to Local HydrodynamicsTide Type Varies by Region due to Local Hydrodynamics Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Eastport, MEEastport, MEEstablished in 1929Established in 1929
Mean Range = 5.59mMean High Water = 5.729m (MLLW)
Mean Low Water = 0.136m (MLLW)
(K1 + O1) / (M2 + S2) = 0.09(Semidiurnal = 0.0 - 0.24)
Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Examples for East CoastExamples for East Coast
Primarily Semidiurnal
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Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Effects the amplitude of the annual mean rangeEffects the amplitude of the annual mean range
ANNUAL MEAN RANGE
MONTHLY MEAN RANGE
The time between peaks is the period of oscillation of the regression (~18.6yrs))
-- Basis for defining the National Tidal Datum Epoch (NTDE) as a 19yr periodBasis for defining the National Tidal Datum Epoch (NTDE) as a 19yr period
Examples for East CoastExamples for East Coast
Primarily Semidiurnal
Galveston Pleasure Pier, TXGalveston Pleasure Pier, TXEstablished in 1957Established in 1957
Mean Range = 1.46ftMean High Water = 1.85ft (MLLW)
Mean Low Water = 0.39ft (MLLW)
(K1 + O1) / (M2 + S2) = 1.92(Mixed – Diurnal = 1.5-2.99)
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
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Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
Examples for Gulf CoastExamples for Gulf Coast
Primarily Diurnal
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Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
North Spit, CANorth Spit, CAEstablished in 1977Established in 1977
Mean Range = 4.89ftMean High Water = 6.15ftMean Low Water = 1.26ft
(K1 + O1) / (M2 + S2) = 0.74(Mixed – Semidiurnal = 0.25-1.49)
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
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Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Examples for West Coast & AlaskaExamples for West Coast & Alaska
Primarily Mixed
Alaska
Bering Sea Tidal Characteristics
feet
feet
feet
feet
Examples for Great LakesExamples for Great LakesLake Superior
Examples for Great LakesExamples for Great Lakes
Seiche (pronounced “saysh”)• Standing wave in an enclosed body of water
Oscillation and storm surge on Lake Erie 17-22 September 2003
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A specific 19 year period that includes the longest periodic tidalvariations caused by the astronomic tide-producing forces.
Averages out long term seasonal meteorological, hydrologic, andoceanographic fluctuations.
Provides a nationally consistent tidal datum network (bench marks) byaccounting for seasonal and apparent environmental trends in sealevel that affects the accuracy of tidal datums.
The NWLON provides the data required to maintain the epoch andmake primary and secondary determinations of tidal datums.
A common time period to which tidal datums are referencedA common time period to which tidal datums are referenced
National Tidal Datum Epoch (NTDE)National Tidal Datum Epoch (NTDE)
• Official time period of tidal observations that are used for primary datum calculations
– Time it takes the Earth, Moon, & Sun to complete an epoch tidal cycle
– 19 year time period (Present NTDE is 1983-2001)
– Considered for revision every ~20-25yrs
– Includes the longest period tidal variations (18.6 year node cycle)
– Averages out seasonal fluctuations
– Provides a nationally consistent tidal datum network by accounting for seasonal andapparent environmental trends in sea level that affect the accuracy of tidal datums
1983-2001 EPOCH
Mean Sea Level TrendsMean Sea Level Trends Mean Sea Level TrendsMean Sea Level Trends
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Mean Sea Level TrendsMean Sea Level Trends
There are areas of Louisiana, Texas, SE Alaska and SW Alaska wherethere are anomalous sea level trends compared to most othergeographic regions of the United States.
“New Procedures” have been developed to address these regions sothat published tidal and geodetic relationships are representative ofcurrent conditions
COMPUTING TIDAL DATUMS IN AREAS OF ANOMALOUS SEA LEVEL TRENDS
Tidal Datums
Base reference elevation from whichBase reference elevation from which locallocal water levels are measuredwater levels are measured
Vertical Datum: Base elevation used as a reference from which to reckon heightsor depths
Tidal Datum : Local standard elevation defined by a certain phase of the tide fromobserved data (i.e. MLW, MHW, MSL)
- Derived from continuous observations over time at specific tide stations
- Are referenced to fixed and stable points on land (Bench Marks)
- Are local references and should not be extended into areas with differentoceanographic characteristics
- Are also used as a basis for establishing legal boundaries and regulations
Chart Datum : Water level datum to which nautical chart soundings are referred
- USA chart datum is Mean Lower Low Water (MLLW) for tidal areas,
or a Low Water Datum (LWD) for non-tidal areas
Definitions of some commonly used DatumsDefinitions of some commonly used Datums
Station Datum: Unique to each water level station- Established at a lower elevation than the water is ever expected to reach.- Referenced to the primary bench mark at the station- Held constant regardless of changes to the water level gauge or tide staff
MHHW: Mean Higher High WaterThe average height of the higher high water of each tidal day observed over the NTDE
MHW: Mean High WaterThe average of all the high water heights observed over the NTDE
DTL: Diurnal Tide LevelThe arithmetic mean of mean higher high water and mean lower low water
MTL: Mean Tide LevelThe arithmetic mean of mean high water and mean low water
MSL: Mean Sea Level or LMSL: Local Mean Sea LevelThe arithmetic mean of hourly heights observed over the NTDE
MLW: Mean Low WaterThe average of all the low water heights observed over the NTDE
MLLW: Mean Lower Low WaterThe average of the lower low water height of each tidal day observed over the NTDE
Definitions of some commonly used Datums (cont’d)Definitions of some commonly used Datums (cont’d)
GT: Great Diurnal RangeThe difference in height between mean higher high water and mean lower low water
MN: Mean Range of TideThe difference in height between mean high water and mean low water
DHQ: Mean Diurnal High Water InequalityThe difference in height of the two high waters of each tidal day for a mixed or semidiurnal tide
DLQ: Mean Diurnal Low Water InequalityThe difference in height of the two low waters of each tidal day for a mixed or semidiurnal tide
HWI: Greenwich High Water Interval (Lunitidal Interval)The average interval (in hours) between the moon's transit over the Greenwich meridian andthe following high water at a location
LWI: Greenwich Low Water Interval (Lunitidal Interval)The average interval (in hours) between the moon's transit over the Greenwich meridian andthe following low water at a location
TcHHWI: Tropic higher high water intervalThe lunitidal interval pertaining to the higher high waters
TcLLWI: Tropic lower low water intervalThe lunitidal interval pertaining to the lower low waters
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Principal tidal datums related to a beach profilePrincipal tidal datums related to a beach profileThe intersection of tidal datums with land define marine boundariesThe intersection of tidal datums with land define marine boundaries
Chart Datum
The chart datum is the level of water that charted depths displayed on nauticalcharts are measured from. The chart datum is generally a tidal datum; that is, adatum derived from some phase of the tide. Common chart datums are lowestastronomical tide and mean lower low water.
Mean Lower Low Water
The United States' National Oceanic and Atmospheric Administration uses meanlower low water (MLLW), which is the average of the lowest tide recorded at a tidestation each day during the recording period. MLLW is generally located above LATand therefore some tidal states may have negative heights. The advantage of usingMean Lower Low Water is avoiding the costs and confusion that moving to LATwould involve.
Lowest Astronomical Tide
Many national charting agencies, including the United Kingdom Hydrographic Officeand other hydrographic services, such as those of Canada and Australia, thatoriginated with the British Admiralty use the Lowest astronomical tide (LAT), theheight of the water at the lowest possible theoretical tide, as chart datum. Theadvantage of using LAT is that all tidal heights must then be positive (or zero)avoiding possible ambiguity and the need to explicitly state sign. Calculation of theLAT only allows for gravitational effects so lower tides may occur in practice due toother factors (e.g. meteorological effects such as high pressure systems).
Tidal Datums from time series dataTidal Datums from time series data
LMSL (Local Mean Sea Level) = avg. of hourly levels (over 19yr Epoch)MTL (Mean Tide Level) = avg. of MHW and MLW (over 19yr Epoch)DTL (Diurnal Tide Level)= avg. of MHHW and MLLW (over 19yr Epoch)
Day 1 Day 2
Higher HighHigher High Higher HighHigher High
MHHWMHHW
MHWMHW
LowLow
Lower LowLower Low LowLow
Lower LowLower LowMLLWMLLW
MLWMLW
ObservedWater Level
HighHigh
Special DatumsSpecial Datums
(Non(Non--Tidal Regions)Tidal Regions)
Non-Tidal = GT < 0.3’
Special DatumsSpecial Datums
(Non(Non--Tidal Regions)Tidal Regions)
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West Bank 1, Bayou Gauche, LA
Special DatumsSpecial Datums
(Non(Non--Tidal Regions)Tidal Regions)
87624828762482
Columbia River, OR & WA
Special DatumsSpecial Datums
(Non(Non--Tidal Regions)Tidal Regions)
Great Lakes and IGLD
Datum ComputationDatum Computation
1. Make observations (NWLON Stations)2. Tabulate the tides (Data Processing)
3.3. Compute tidal datumsCompute tidal datums
A.A. Control StationsControl Stations -- Stations with over 19 years data
Primary determination (NTDE Tidal Datums)
Method: First Reduction or Arithmetic mean
= Average of observations over a 19-year National Tidal Datum Epoch (NTDE)
B.B. Subordinate StationsSubordinate Stations -- Stations with less than 19 years data
Secondary determination (NTDE Equivalent Tidal Datums)
Method: Simultaneous comparison - Subordinate Station with Control Station3 Methods for Simultaneous Comparison: (Depending on tide type)
Standard Method Modified-Range Ratio Method Direct Method
VerifiedMonthlyMeans
ACCEPTED Datums
Datum ComputationDatum Computation
A.A. Control StationsControl Stations –– Primary determination using First Reduction
• Average of observations over a 19-year NationalTidal Datum Epoch (NTDE)
• Mean of all tidal heights for a particular phase (ieHW or LW) over the epoch time period
• Accepted NTDE datum values for that station
• Available online at CO-OPS Tides & CurrentsWebsite
• Used as a reference for converting elevations takenin that area to a common datum(i.e. hydro survey depths to MLLW for charting)
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B.B. Subordinate StationsSubordinate Stations -- Secondary determination using Simultaneous Comparison
Method of Comparison of Simultaneous Observations is a twoMethod of Comparison of Simultaneous Observations is a two--step process:step process:
1. Compute the differences and/or ratiosCompute the differences and/or ratios in the tidal parameters and differences inmean values between short-term and control stations over the period ofsimultaneous comparison.
2. Apply the differences and ratiosApply the differences and ratios computed above to the NTDE Accepted Values atthe control station. This provides equivalent NTDE values for the short-term station.
Datum ComputationDatum Computation Methods for Subordinate StationsMethods for Subordinate Stations
Simultaneous Comparison – compare monthly means between control & subordinate station1. Choose an appropriate control station to compare with2. Choose an appropriate computation method for the tide type3. Compare values to the control stations to correct to NTDE equivalent
Standard Method: (mixed tide types) West Coast & Pacific Islands
Modified-Range Ratio Method: (semidiurnal & diurnal) East Coast, Gulf Coast, & Caribbean
Direct Method: Generally used when a full range of tidal values are not availableDatums determined by direct comparison with appropriate control station
The Bodnar Report
Bodnar (1981), drawing upon Swanson (1974) applied regressionequations estimating the accuracy of computed datums
Bodnar developed formulas forMean Low Water (MLW) and Mean High Water (MHW).
The 3 Month equation for Mean Low Water is presented below.
Error = 0.0043 ADLWI + 0.0036 SRGDIST + 0.0255 MNR + 0.029
ESTIMATING ACCURACIES OF TIDAL DATUMSFROM SHORT TERM OBSERVATIONS
ADLWI : average difference between low water intervalsSRGDIST: square root of the distance between stationsMNR: mean range of the tide signal
ADLWI : average difference between low water intervalsSRGDIST: square root of the distance between stationsMNR: mean range of the tide signal
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1. Make ObservationsWL Data collected at 6-minute intervals, downloaded toDMS, CORMS & Auto QC
2. Preliminary AnalysisCheck station parameters, initialize data into workingtable, fill gaps, QC
3. TabulationTabulate Highs & Lows, QC & edit Hourly Heights & Hi/Lopicks, Compute Monthly Means
4. Compute Datums - Subordinate Station with <19ys of dataMake secondary determinations using simultaneous comparison of Monthly Means
• Choose appropriate control station
Charleston, SCCharleston, SC
• Choose appropriate method(east coast=Semidiurnal)
ModifiedModified--Range Ratio MethodRange Ratio Method
East Coast Example 1East Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
East Coast Example 1East Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
Modified-Range Ratio MethodNeed corrected MTL, DTL, Mn, & GT from comparison to appropriate controlstation
MLW = MTL - (0.5*Mn) MHHW = MLLW + GTMHW = MLW + Mn DHQ = MHHW - MHWMLLW = DTL - (0.5*GT) DLQ = MLW - MLLW
East Coast Example 1East Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
• Calculate mean monthly difference between control and subordinate valuesfor each MTL, DTL, Mn, & GT over the length of the data set
• Then correct MTL, DTL, Mn, & GT for the subordinate station using the meandifference & accepted 19yr datum from the control station
Accepted 19yr Tidal Datums - control station (Charleston)(Charleston)
Accepted MTL 19yr datumfrom control station
Accepted19yr datumfrom control
station
Computedmean
monthlydifference
I.e. Corrected MTLMTL = MTL + MTL
= 1.622 + 0.497 = 2.1192.119
ComputedMTL meanmonthly
difference
MTL mean monthly difference(Sub. - control station)
Worksheet
East Coast Example 1East Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
Modified-Range Ratio Method
Ft. Pulaski NTDE Equivalent datumsMLW = 2.119 - (0.5*2.146) = 1.046 MHHW = 0.974 + 2.325 = 3.299MHW = 1.046 + 2.146 = 3.192 DHQ = 3.299 - 3.192 = 0.107MLLW = 2.137 - (0.5*2.325) = 0.974 DLQ = 1.046 - 0.974 = 0.072
B. Apply corrected MTL, DTL, Mn, & GT to formulas for Modified-Range RatioMethod to calculate remaining NTDE equivalent datums for the subordinate
1. Make ObservationsWL Data collected at 6-minute intervals, downloaded toDMS, CORMS & Auto QC
2. Preliminary AnalysisCheck station parameters, initialize data into workingtable, fill gaps, QC
3. TabulationTabulate Highs & Lows, QC & edit Hourly Heights & Hi/Lopicks, Compute Monthly Means
4. Compute Datums - Subordinate Station with <19ys of dataMake secondary determinations using simultaneous comparison of Monthly Means
• Choose appropriate control station
San Francisco, CASan Francisco, CA
• Choose appropriate method(west coast=Mixed)
Standard MethodStandard Method
West Coast Example 1West Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Alameda, CAAlameda, CA –– Subordinate StationSubordinate Station
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West Coast Example 1West Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Alameda, CAAlameda, CA –– Subordinate StationSubordinate Station
• Calculate mean monthly difference between control and subordinate valuesfor each MTL, Mn, DHQ, & DLQ over the length of the data set
• Then correct MTL, Mn, DHQ, & DLQ for the subordinate station using themean difference & accepted 19yr datum from the control station
Accepted 19yr Tidal Datums - control station (San Francisco)(San Francisco)
Accepted MTL 19yr datumfrom control station
Accepted19yr datumfrom control
station
Computedmean
monthlydifference
I.e. Corrected MTLMTL = MTL + MTL
= 2.728 + -0.685 = 2.0432.043
ComputedMTL meanmonthly
difference
MTL mean monthly difference(Sub. - control station)
Worksheet
West Coast Example 1West Coast Example 1 –– Comparison of Monthly MeansComparison of Monthly Means
Alameda, CAAlameda, CA –– Subordinate StationSubordinate Station
B. Apply corrected MTL, Mn, DHQ, & DLQ to formulas for Standard Method tocalculate remaining NTDE equivalent datums for the subordinate
Standard Method:Need corrected MTL, Mn, DHQ, & DLQ from comparison with appropriate control station
MLW = MTL - (0.5*Mn) MHHW = MHW + DHQMHW = MLW + Mn DTL = 0.5*(MHHW + MLLW)MLLW = MLW - DLQ GT = MHHW - MLLW
Alameda NTDE Equivalent datumsMLW = 2.043 - (0.5*1.479) = 1.304 MHHW = 2.783 + 0.188 = 2.971MHW = 1.304 + 1.479 = 2.783 DTL = 0.5*(2.971 + 0.965) = 1.968MLLW = 1.304 – 0.339 = 0.965 GT = 2.971 - 0.965 = 2.006
1. Make ObservationsWL Data collected at 6-minute intervals, downloaded toDMS, CORMS & Auto QC
2. Preliminary AnalysisCheck station parameters, initialize data into workingtable, fill gaps, QC
3. TabulationTabulate Highs & Lows, QC & edit Hourly Heights & Hi/Lopicks, Compute Monthly Means
*** This example*** This example -- Data series too short to compute monthly means, or data starts & ends in middleData series too short to compute monthly means, or data starts & ends in middleof monthsof months
4. Compute Datums - Subordinate Station with <1 month<1 month of dataMake secondary determinations using simultaneous comparison of High & Low waters
• Choose appropriate control stationCharleston, SCCharleston, SC
• Choose appropriate method(east coast=Semidiurnal)
ModifiedModified--Range Ratio MethodRange Ratio Method
East Coast Example 2East Coast Example 2 –– Tide by Tide ComparisonTide by Tide Comparison
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
East Coast Example 2East Coast Example 2 –– Tide by Tide ComparisonTide by Tide Comparison
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
A. Compare highs & lows between Subordinate & Control to calculate corrected MTL,DTL, Mn, & GT for subordinate that will be used to calculate remaining datums(MLW, MHW, MLLW, MHHW, DHQ, DLQ)
1. Plot highs and lows to ensure that designations agree– If they do not, a type conversion is done for the subordinate
(ie. If sub. value is designated as LL, where control is L, then sub. is changed from LLto L so that the pair remains matched in designation)
East Coast Example 2East Coast Example 2 –– Tide by Tide ComparisonTide by Tide Comparison
Fort Pulaski, GAFort Pulaski, GA –– Subordinate StationSubordinate Station
3. Using the above values calculated in step 2, and the accepted means from thecontrol station, calculate the corrected MTL, DTL, Mn, & GT for the subordinateto use in Modified-Range Ratio calculations
Accepted 19yr Tidal Datums - control station (Charleston)(Charleston)
Accepted19yr datumfrom control
station
Corrected MTLMTL = MTL + ∆MTL = 1.622 + 0.484 = 2.1062.106
AcceptedCorrected DTLDTL = DTL + ∆DTL = 1.643 + 0.482 = 2.1252.125
AcceptedCorrected MnMn = Mn * Mn ratio = 1.606 * 1.369 = 2.1982.198
AcceptedCorrected GTGT = Gt * Gt ratio = 1.768 * 1.339 = 2.3672.367
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Example 3Example 3 (West Coast)(West Coast) –– Direct MethodDirect Method
Hamilton AFB, CAHamilton AFB, CA –– Subordinate StationSubordinate Station
Compute Datums - Subordinate Station where full range of tidal values are not available(i.e. Upper reaches of a Marsh – low tides are cut off)
Make secondary determinations using simultaneous comparison of available data
• Choose appropriate control stationRichmond, CARichmond, CA
• Choose appropriate method(west coast=Mixed – full range of tidal values not available)
Direct MethodDirect Method
Types of HeightsTypes of Heights
Orthometric (H) - i.e. Leveling
• The distance between the geoid and apoint on the Earths surface measuredalong the plumb line
Ellipsoid (h) - i.e. GPS
• The distance along a perpendicular fromthe ellipsoid to a point on the Earth’ssurface
H
H = Orthometric Height (NAVD 88)
H = h - Nh = Ellipsoidal Height (NAD 83)
N = Geoid Height (Geoid03)
h
Ellipsoid
N
GeoidGEOID 03(Hi Res Model)
TOPOGRAPHICSURFACE
GPS-Derived Orthometric Heights
Tidal Datum : Local standard elevation defined by a certain phase of the tide from observed data (i.e. MLW,MHW, MSL)
- Derived from continuous observations over time at specific tide stations
- Are referenced to fixed and stable points on land (Bench Marks)
- Are local references and should not be extended into areas with different
oceanographic characteristics
- Are also used as a basis for establishing legal boundaries and regulations
GPS Connections Between BenchmarksGPS Connections Between Benchmarks
NO
AA
Tidal Bench mark4811 G 2004
Station Datum
Orifice
0.7428 m
Tidal Bench mark4811 G 2004
3.150 m
MHW2.736 m
MLLW1.220 m
Bench markwith geodetic control
(NAVD88, WGS84,etc.)
TideGauge
1.150 m(example)
Pier
Geodetic Benchmark(and its WGS84 value)
Relative to Tidal Datum
GPS Receivers collecting simultaneousdata over existing bench marks allow fordatum transformation.
2.000 m
GPSReceiver
Ellipsoid
NAVD88
• GPS-derived orthometric heights can be used for datum transfers (H = h – N)
• Not as limited as line of sight leveling for making benchmark connections
• Allows for connections over greater distances
Web Access to Benchmark DataWeb Access to Benchmark Datahttp://www.tidesandcurrents.noaa.govhttp://www.tidesandcurrents.noaa.gov
Data Available through OPenDAP andWeb Services
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Getting IDB datasheets from NGS websiteStart at: www.ngs.noaa.gov which is the NGS home page.
Getting OPUS datasheets from NGS websiteStart at: www.ngs.noaa.gov which is the NGS home page.
Online GPS Processing
Rapid Return on Ellipsoidal Solution
Lower accuracy than traditional leveling ~ cm
Currently ~ 1000 records in OPUS Database
CO-OPS Published benchmarksheet Elevations of individual
BM relative to tidaldatums.
Can identify the relativeelevation differencesbetween individual BM
Note the elevations arebased on a series (2 ormore) of levels.
BM identified as unstablebased on elevationsrelationships determinedby leveling will not beincluded.
Individual CO-OPS tidalbenchmarks with NGS IDBPID will be hyperlinked tothe data sheets.
Geodetic comps sheet CO-OPS Accepted Datumspage Published NAVD88 are
based on a minimum of2 published NGS IDBvalues.
Values are within in 9mmrelative to one anotherwhen set to local stationdatum.
Value are static Future alterations
Currently working onexpanding to includeOPUS-DB values
Publishing a singleNAVD88 value.
Including Ellipsoidalvalues.
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DatumDatumInformation onInformation onthe BM Sheetthe BM Sheet
Epoch, Series &Control Station
Tidal DatumsRelative to
MLLW
BenchmarksRelative toMLLW and
MHWThe NAVD 88 and the NGVD 29 elevations related to MLLW were computed from Bench Mark,941 1340 TIDAL 1, at the station. Displayed tidal datums are Mean Higher High Water(MHHW),Mean High Water (MHW), Mean Tide Level(MTL), Mean Sea Level (MSL), Mean Low Water(MLW),and Mean Lower Low Water(MLLW) referenced on 1983-2001 Epoch.
Get Orthometric heightsfrom NGS data sheets
(Links on CO-OPSBenchmark Sheet)
Seattle, WASeattle, WA
Unknown ?
NAVD 88 FromNGS Data Sheets
5.869m = 0.713m4.896m = 0.714m5.695m = 0.713m6.519m = 0.712m
= 0.713m
Calculate NAVDusing heights fromNGS data sheets
and MLLW datumfrom CO-OPSDatums Page
Seattle, WASeattle, WA
Unknown ?
NAVD88 FromNGS Data Sheets
3.996m = -0.024m5.029m = -0.016m
= -0.020m
Calculate NAVDusing heights fromNGS data sheets
and MLLW datumfrom CO-OPSDatums Page
San Francisco, CASan Francisco, CA
Connection Between Tide Datums & Geodetic DatumsConnection Between Tide Datums & Geodetic Datums
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The Georgia Anomaly???
???
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
CA
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88 Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
AK
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Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
OR
WA
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88 Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
FL
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
0.071
-0.090
-0.013
-0.108
0.109
-0.009
-0.102
0.034
-0.157
-0.009
-0.135
-0.278
-0.134
-0.240
-0.3000
-0.2500
-0.2000
-0.1500
-0.1000
-0.0500
0.0000
0.0500
0.1000
0.1500
MLL
WR
ela
tive
toN
AV
D8
82
00
6.8
1(m
)
NOAA Water Level Stations (East to West)
NAVD88 2006.81
Tidal Datums Relative to Geodetic Datum NAVD88Tidal Datums Relative to Geodetic Datum NAVD88
0.220
0.035
0.0700.055
0.161
0.066
0.041
0.107
0.059
0.320
0.137
0.1060.092
0.128
0.0000
0.0500
0.1000
0.1500
0.2000
0.2500
0.3000
0.3500
LMSL
Re
lati
veto
NA
VD
88
2006
.81
(m)
NOAA Water Level Stations (East to West)
NAVD88 2006.81NAVD88 2006.81NAVD88 2006.81NAVD88 2006.81
LMSL Relative to NAVD88 2006.81 (m)
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KNOWN(Charleston) MTL – NAVD88 = 1.253 – 0.152 = 1.101 m
(North Bend) MTL – NAVD88 = 1.387 – 0.295 = 1.092 m
AVE. MTL – NAVD88 = 1.101 + 1.092/ 2 = 1.097
UNKNOWNSitka Dock (9432879) MTL – X = AVE. MTL – NAVD88
NAVD88 = 1.270 (MTL) – 1.097 (MTL – NAVD88)Therefore NAVD88 @ Sitka Dock ~ 0.173 m
Sitka Dock ~ 0.173 m using interpolation, compare to published…..
Available Data / Differing DatumsAvailable Data / Differing Datums
BUT there are a many different vertical datums inuse around the nation
Ellipsoid Datums
Orthometric Datums
Tidal Datums
MHHW, MHW,MTL, DTL,LMSL,MLW, MLLW
NAVD 88,NGVD 29
WGS 84,NAD 83(NSRS), 17others
GeodeticDatums
For elevation data sets to be blendedtogether they must be referenced to samevertical datum.
All elevation data is referenced to a vertical datum.
7 TidalDatums
18 3-DDatums
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GEODETIC DATUMS
Geoid---the shape the ocean surface would haveif it were not in motion and only influenced bygravity.
● It is an equipotential surface of gravity.● Is the zero surface as defined by the Earth’s
surface.● May be approximated by MSL● Orthometric height ( dynamic height in
academia)
What is the Geoid?
Equipotential
Surface
of Gravity
GRACE Gravity Model 01- Released July 2003
Why do we need an ellipsoid?
This image depicts the earth’sshape without water and clouds.
Calculation of geographicposition on this irregular surfaceis very complex. A simplermodel is needed.
This simplified mathematical
surface is the ellipsoid.
GPS - Derived Ellipsoid Heights
Z Axis
X Axis
Y Axis
(X,Y,Z) = P (,,h)
h
Earth’sSurface
ZeroMeridian
Mean Equatorial Plane
Reference Ellipsoid
P
Ellipsoidal Height (NAD 83)
An ellipsoidal height (h) is the distance from a point on the Earth’s surface measured along aline perpendicular to a mathematically-defined reference ellipsoid.
(Reference) ellipsoidal surface: a mathematical (geometric) model which approximates theirregular shape of geoid.
H
H = Orthometric Height (NAVD 88)
H = h - N
TOPOGRAPHIC SURFACE
h = Ellipsoidal Height (NAD 83)
N = Geoid Height (GEOID 03)
h
Ellipsoid(NAD 83)
N
Geoid(NAVD 88)
Geoid Height(GEOID03)
Ellipsoid, Geoid,Ellipsoid, Geoid, and Orthometric Heights
AB
Orthometric Height (NAVD 88)
An orthometric height (H) is the distance from a point on the Earth’s surface measured along aline perpendicular to a geoid.
Tri office responsibilities Assessment:
• Existing Stations on 83-01 Epoch:• Connections to other datums• Ellipsoidal (NAD83)• Orthometric (NAVD88)
• Land usages:• Identify land types. (wetlands,developed areas, tidal flats).• Topographic heights
• Tidal and Geodetic Dynamics:• Tidal range change of 0.2 ft / mi orgreater• Datum relationships: Identifyorthometric (NAVD88) or ellipsoidal(NAD83) dynamic regions
• Marine analysis:• Bathy depths• Identify bottom types.• Identify dredged areas.• Identify commercial transit routes.
• Hydrodynamic model:• Infer tidal dynamics and currentdynamics.
CO-OPS Responsibilities:
Results:
• New geodetic survey onbenchmark that is connected toexisting stations with 83-01 epochdata to establish tidal geodeticconnection.
• Installations of a new CO-OPSwater level station.
• Reoccupation of historical CO-OPS water level station.
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Report:
Documentation of existing 83-01datums.
Definition of stations requiringsurveys or installations.
Survey work lists
Graphic:
Present data
Recommendations
Datum errors
Datum relationships
NWLON gaps
National VDatumNational VDatum
Vertical Datum Transformation Tool
• software tool to allow a seamless transform of elevations between approximately 27vertical datums of three categories: tidal (MSL), orthometric (NAVD88) and ellipsoidal(NAD83) vertical datums
• Data from many different resources can be be referenced to a common vertical datum
Bathy/Bathy/TopoTopoDigital Elevation ModelDigital Elevation Model
NOAANOAABathymetryBathymetry
USGSUSGSTopographyTopography
EllipsoidModel
TidalModel
GeoidModel
National VDatum( Vertical Datum Transform Tool )
Bathy/TopoDigital Elevation Model
Bathymetry
TopographyVDatum
VDatum and Creation of Digital Elevation Models
• Inundation modeling from storm surge,tsunamis, and sea level rise.
• Erosion, accretion, renourishment
• Analyzing storm impacts
• Determining setback lines
• Determining local, state, and nationalboundaries
• Navigation Products andServices
• Habitat restoration
• Shoreline Change Analysis
• Analyzing environmental andnatural resources
• Permitting
Applications for Seamless Bathy/Topo Datasets: NAD83 (NSRS) NAVD 88 LMSL
MHHW
MHW
MTL
DTL
MLW
MLLW
NGVD 29
GEOID99,GEOID03 TSS
(Topography ofthe Sea Surface)
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
WGS 84 (G1150)
ITRF2000
3D Datums Tidal DatumsOrthometric
Datums
VERTCON
Tide Models
Calibrated HelmertTransformations
Vertical Datum Transformation “Roadmap”
Choose a horizontal datum
Choose a geoid model
Choose input andoutput vertical
datums:
Run as single point, batch, or insert into programming
Uncertainty has been calculated for transformationsacross the full process…
Ellipsoid Orthometric Tidal
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Current VDatum Availability
VDatum.noaa.gov
162
Questions?
12/20/2011
28
Michael Michalski, NOAA/National Ocean ServiceCenter for Operational Oceanographic Products and ServicesMonday, January 9 2012