AKA Replacing NAVD 88 Dru Smith NSRS Modernization Manager NOAAs National Geodetic Survey 20180507 1 Modernizing the Geopotential Datum Creating 20180507 2 Modernizing the Geopotential Datum ID: 700092
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Slide1
Modernizing theGeopotential Datum AKA “Replacing NAVD 88”Dru SmithNSRS Modernization ManagerNOAA’s National Geodetic Survey
2018-05-07
1
Modernizing the Geopotential Datum
CreatingSlide2
2018-05-072Modernizing the Geopotential DatumSlide3
NSRS Modernization
The Old:
NAVD 88
PRVD 02
VIVD09ASVD02NMVD03
GUVD04
IGLD
85
IGSN71
GEOID12B
DEFLEC12B
The New:
The North American-Pacific Geopotential Datum of 2022 (NAPGD2022)Primary component is a global harmonic model of geopotential which includes all GRAV-D data:GM2022 Related regional gridded products:GEOID2022DEFLEC2022GRAV2022
August 1, 2017
SaGES, Oregon State University
OrthometricHeights
NormalOrthometricHeights
Dynamic
Heights
Gravity
GeoidUndulations
Deflections of
t
he VerticalSlide4
Expected changes to orthometric heights2018-05-07Modernizing the Geopotential Datum4Slide5
Expected changes to orthometric heights2018-05-07Modernizing the Geopotential Datum5Slide6
NAPGD2022“North American-Pacific…”Because the gridded components (geoid, DoV, gravity, DEM) will cover all major USA populated territories, and these happen to fall in the general regions of “North America” and “The Pacific Ocean”However, the foundation of the gridded components will be a global geopotential model2018-05-07Modernizing the Geopotential Datum6Slide7
The three gridded regions2018-05-07Modernizing the Geopotential Datum7“North American region”¼ of the Earth“Guam/CNMI region”“American Samoa region”Slide8
NAPGD2022“…Geopotential…”Because it isn’t just about heights, but rather about all geodetic coordinates related to Earth’s geopotential field (geoid, deflections, etc)2018-05-07Modernizing the Geopotential Datum8Slide9
NAPGD2022“…Datum…”Because a “geopotential reference frame” was, frankly, an unwieldy term that had no precedence in geodetic literature. “Reference Frame” only carries a geometric connotation in geodesyIt is replacing, and expanding upon, the idea of a “vertical datum”2018-05-07Modernizing the Geopotential Datum9Slide10
NAPGD2022“…2022”Because that is our target release date2018-05-07Modernizing the Geopotential Datum10Slide11
Static and Dynamic ComponentsProductAreaFormatStaticDynamicGM2022GlobalGeopotential CoefficientsSGM2022DGM2022
GEOID2022Regional (3)
GridSGEOID2022
DGEOID2022
DEFLEC2022Regional (3)Grid
S
DEFLEC2022
D
DEFLEC2022
GRAV2022
Regional
(3)GridSGRAV2022DGRAV2022*DEM2022Regional (3)
GridSDEM2022DDEM2022*2018-05-0711Modernizing the Geopotential Datum* Not scheduled for release by 2022 Slide12
Static ComponentsWill model reality circa 2020.00SGEOID2022 is NGS’s best attempt to model the geoid as it truly is on date 2020.00, etc2018-05-07Modernizing the Geopotential Datum12Slide13
Dynamic ComponentsWill model reality relative to 2020.00DGEOID2022 is NGS’s best attempt to model the geoid changes since 2020.00Both forward and backward in time, with limitsMay be in a variety of formatsDGEOID2022 might includeRegional grid of dN/dt valuesLocal grids of event-based changes (massive earthquakes)2018-05-07Modernizing the Geopotential Datum13Slide14
The next few slides are found in Blueprint for 2022, Part 2Represent a flow-chart for:Begin with a GNSS receiverEnd with NAPGD2022 valuesOrthometric heights, Gravity, Etc…2018-05-07Modernizing the Geopotential Datum14Slide15
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SummaryNAPGD2022 is a self-consistent set of values connected to Earth’s geopotential fieldReplaces all vertical datums of the NSRSTime dependentGNSS/CORS/OPUS is the way to access all of these valuesPassive control as well, but as a secondary source2018-05-07Modernizing the Geopotential Datum18Slide19
Thank you2018-05-07Modernizing the Geopotential Datum19Slide20
Questions2018-05-07Modernizing the Geopotential Datum20Slide21
Extra Slides2018-05-07Modernizing the Geopotential Datum21Slide22
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Time Dependency2018-05-07Modernizing the Geopotential Datum24Slide25
Time and MassMass quantity in the Earth system is effectively constantMass distributions in the Earth system are time dependent and some are large enough to be measurableSecularShape change to every equipotential surface (like the geoid)Size change to global mean sea levelEpisodicPeriodic2018-05-07Modernizing the Geopotential Datum25Slide26
Secular Mass MovementMass is flowing in the mantleto coalesce under HudsonBay, pushing the crust up.GPS on the crust sees this as one effect:An increase in ellipsoid heightA gravimeter on the crustsees two effects:(small) decrease in gravity as thegravimeter location getsfarther from the geocenter(larger) increase in gravity as theamount of mass below thegravimeter pulls harder
This gravity change causes thegeoid to “swell” in the area
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Episodic Mass Movement272018-05-07
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Ramillien G et al. Geophys. J. Int. 2004;158:813-826
© 2004 RAS
Periodic
Mass Movement
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Geoid Monitoring Service (GeMS)Goal: Track all changes to the geoid which would prevent 1 cm accuracyAspects included:Shape, Secular: e.g. Hudson BayShape, Episodic: e.g. Massive EarthquakesW0, Secular: Global Sea Level Change (see next slides)Examples of things excluded:Size, Secular: Mass quantity of Earth is effectively staticShape, Periodic: Seasonal glacier cycle2018-05-07Modernizing the Geopotential Datum29Slide30
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Sea Level and The GeoidSlide31
Secular Sea Level ChangeSpecial geoid-definition problem…Consider only the mechanics of sea-level change:Mass is moving about (geopotential change)Land ice melts and joins the ocean, re-distributing mass around the globeGlobal mean sea level is rising (geometric change)By long standing tradition, the geoid is the one equipotential surface that fits global mean sea level2018-05-07Modernizing the Geopotential Datum31Slide32
Time Passes
Sea Level Rises
Scenario 1: Geoid Definition remains tied to GMSL
H
1
H
2
As Global Mean Sea Level rises, orthometric height gets smaller
Geoid
GMSL
Geoid
GMSL
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Time Passes
Sea Level Rises
Scenario 2: Geoid Definition decoupled from GMSL
H
1
H
2
As Global Mean Sea Level rises, orthometric height remains constant
Geoid
GMSL
Geoid
GMSL
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Choosing a new geoid as GMSL changes2018-05-07Modernizing the Geopotential Datum34Slide35
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NAPGD2022Slide36
Definitional Relationship2018-05-07Modernizing the Geopotential Datum36
Time-dependencies of
ellipsoid heights
come from OPUS, where time-dependent
CORS coordinates serve as control for
your time-dependent GNSS
survey.
Time-dependencies of
geoid undulations
are captured in the dynamic component
of GEOID2022 (“DGEOID2022”), whichwill come from the geoid monitoringservice, or GeMS.Slide37
High resolution products2018-05-07Modernizing the Geopotential Datum37All will be 1 x 1 arcminute gridsAll will cover three finite regions of the globeAll will have a static and dynamic componentDynamic surface gravity not expected to be ready by 2022GEOID2022Official converter of *TRF2022 ellipsoid heights into NAPGD2022 orthometric heightsDEFLEC2022Surface deflections of the vertical in N/S and E/WGRAV2022Surface acceleration of gravity Slide38
The three gridded regions2018-05-07Modernizing the Geopotential Datum38“North American region”¼ of the Earth“Guam/CNMI region”“American Samoa region”Slide39
2018-05-07Modernizing the Geopotential Datum39
Leveling? Yes!Slide40
Leveling? Yes!Leveling yields differential heightsIf you want absolute heights, you need one or more known heightsPreviously this was about finding a benchmark with a published NAVD 88 heightDoes published mean “known”? Does it mean “trusted”?Does it mean “current”?2018-05-07Modernizing the Geopotential Datum40Slide41
When was this point last leveled?2018-05-07Modernizing the Geopotential Datum41Has an “adjusted” NAVD 88 height to a millimeter…
It’s in Louisiana whereaccurate heights are
very important…
It was monumented in
1968 (ignore the glitch),
and was last known to be
in good condition in 2002…
It’s a trick question.
You can’t figure it out
from anything on here.
But the answer is:
Just once: 1968.Savvy datasheet snoopersmay recognize this text as
meaning “it was adjustedas part of the original roll-out of NAVD 88…Slide42
When was this point leveled?2018-05-07Modernizing the Geopotential Datum42You wouldn’t know it, but it wasleveled in:1917, 1942, 1942 (again), 1945,1951, 1981The 1981 data went into the NAVD 88 heightQ: But what about 64 years and 6 occupations?A: You get a “warning” about vertical movement, but no estimate of the rate.Less than ¼ mile away is AH1055, leveled once in 1981, with NO warnings.Slide43
Leveling - ControlIn NAPGD2022, “known” heights for a leveling survey:Primary: Perform your own GPS surveyYields starting orthometric heights using GEOID2022RTK may be perfectly acceptable!Secondary: Find a “not stale” passive mark“Staleness” depends on the markTertiary: Use VERTCON 3 on an NAVD 88 heightPlease don’t do this2018-05-07Modernizing the Geopotential Datum43Slide44
Updates and ReplacementsNAPGD2022 will come with a version numberUpdates will change the versionBug fixes, new data, new theories, minor improvementsReplacements will change the nameWhen GMSL has changed by some threshold (20 cm)About 50-70 years2018-05-07Modernizing the Geopotential Datum44Slide45
Content: Geoid Modeling HistoryProvides context as to why “sea level” has been a perpetual human choice for “surface of zero height”Attempts to model the sea level go back to the 1800sKnowledge of currents and global sea level change have complicated the matter in the last 30 years or so“Height above sea level” is too vague. Which “sea level” and on what date?2018-05-0745Modernizing the Geopotential DatumSlide46
2018-05-07Modernizing the Geopotential Datum46
Surface of equal gravity potential energy
(W=62,630,000 m^2 / s^2)
Surface of equal gravity potential energy
(W=62,620,000 m^2 / s^2)
Surface of equal gravity potential energy
(W=62,610,000 m^2 / s^2)
Surface of equal gravity potential energy
(W=62,640,000 m^2 / s^2)
Surface of equal gravity potential energy
(W=62,650,000 m^2 / s^2)
Surface of equal gravity potential energy
(W=62,660,000 m^2 / s^2)
Earth’s Geopotential Field
Surface of equal gravity potential energy
(W=62,636,856 m^2 / s^2 = W )
The “Holy Grail”…
“THE” geoid…
0Slide47
Geopotential Field2018-05-07Modernizing the Geopotential Datum47GravityPotentialEnergy……as a function of geocentric co-latitude, geocentric longituderadial distance from the center of the Earth…
…can become…
Geoid Undulations…
Acceleration of Gravity…
Deflection of the Vertical…
Etc., ad
nauseum
.