Progress toward the Geopotential Reference Frame Dru Smith Dan Roman Vicki Childers 45 minutes April 13, Geospatial Summit1

Outline Background Terminology What does “done” look like? – Spoiler alert: there are 5 components… Getting to “done” – Spoiler alert: we need 12 “things” to exist… Progress toward completion What comes after “done”? April 13, Geospatial Summit2

Background What’s being replaced: HorizontalVertical – NAD 83(2011) – NAD 83(PA11) – NAD 83(MA11) April 13, Geospatial Summit3 – NAVD 88 – PRVD 02 – VIVD09 – ASVD02 – NMVD03 – GUVD04 – IGLD 85 Latitude Longitude Ellipsoid Height State Plane Coordinates Heights

Terminology Horizontal Datum – Geometric Reference Frame Geocentric X, Y, Z Latitude, Longitude, Ellipsoid Height Vertical Datum – Geopotential Reference Frame Geoid undulation Orthometric height Gravity Deflection of the Vertical April 13, Geospatial Summit4

What does “done” look like? 1 of 5 April 13, Geospatial Summit5 New Geometric Reference survey epoch  =38° 42’ ” =073° 17’ ” h= m New Geopotential Reference survey epoch H= m H= m Dyn 1: This version of OPUS exists

What does “done” look like? 2 of 5 April 13, Geospatial Summit6  =38° 42’ ” =073° 17’ ” h= m NAD 83(2011)* epoch New Geometric Reference Frame epoch : This new transformation tool exists  =38° 42’ ” =073° 17’ ” h= m * Or NAD 83(PA11) or NAD 83(MA11)

What does “done” look like? 3 of 5 April 13, Geospatial Summit7 NAVD 88, and etc* New Geopotential Reference Frame, epoch : This new transformation tool exists H= m * Helmert Orthometric Heights in NAVD 88. Normal Orthometric Heights in PRVD02, ASVD02, NMVD03, GUVD04, VIVD09 All, “as published in ”. H= m

What does “done” look like? 4 of 5 April 13, Geospatial Summit8 IGLD 85 New Geopotential Reference Frame, epoch : This new transformation tool exists H= m Dyn H= m Dyn

What does “done” look like? 5 of 5 April 13, Geospatial Summit9 5: The FGCS has voted to approve the new frames

“Done” : Summary A.OPUS: All basic coordinates in new frames B.Tool: Lat/Lon/Eht to new geometric C.Tool: Ortho heights to new geopotential D.Tool: Dynamic heights to new geopotential E.FGCS approval April 13, Geospatial Summit10

Getting to “done” April 13, Geospatial Summit11 A.K.A. What must exist to get to “done”?

Getting to “done” 1: IGSxx = The most recent IGS reference frame prior to 2022 April 13, Geospatial Summit12

Getting to “done” 2: A complete, self-consistent airborne-based gravity* data set over the USA and territories, at epoch , in IGSxx. * “gravity” will mean “vertical acceleration of gravity” unless stated otherwise April 13, Geospatial Summit13 g

Getting to “done” 3: A terrestrial gravity data set over the USA and territories, consistent with #2, at epoch April 13, Geospatial Summit14

Getting to “done” 4: A DEM of ellipsoid heights in IGSxx/GRS-80 at 30 meter resolution, for epoch , over the USA and territories April 13, Geospatial Summit15

Getting to “done” 5: Three final geoid models (North America, Guam/CNMI and American Samoa), consistent with #2, #3 and #4, each centered at the center of IGSxx April 13, Geospatial Summit16

Getting to “done” 6: Three geoid secular velocity models, as companions to #5 April 13, Geospatial Summit17 cm / yr

Getting to “done” 7: GNSS positioning in all OPUS products in IGSxx at the epoch of the survey April 13, Geospatial Summit18 survey epoch  =38° 42’ ” =073° 17’ ” h= m

Getting to “done” 8: Software to interpolate geoid undulations April 13, Geospatial Summit19

Getting to “done” 9: Software to compute dynamic heights from ellipsoid heights, geoid undulations and surface gravity April 13, Geospatial Summit20 Dyn hNghNg H

Getting to “done” 10: GNSS survey on NAD 83 marks April 13, Geospatial Summit21 ,,h in NAD 83(2011)* ~”thousands” * Or NAD 83(PA11) or NAD 83(MA11) Thankfully the CORS are the first 2000 such points with both “recent GNSS data” and “published NAD 83 coordinates”

Getting to “done” 11: GNSS survey on NAVD 88 marks April 13, Geospatial Summit22 H in NAVD 88* ~”thousands” * Or PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Getting to “done” 12: GNSS survey on IGLD 85 marks April 13, Geospatial Summit23 H in IGLD 85 ~”hundreds” Dyn

Getting to “done”: Summary 1)IGSxx 2)Airborne Gravity 3)Surface Gravity 4)DEM 5)3 Geoid models 6)3 Geoid change models April 13, Geospatial Summit24 7)OPUS in ITRFxx 8)Interp. software 9)Dyn. Ht software 10)GPS on 83 marks 11)GPS on 88 marks 12)GPS on 85 marks

Progress toward completion April 13, Geospatial Summit25

Progress toward completion: Warning NGS has lost significant expertise in the last few years and has struggled to gain new expertise. Many tasks listed next are in RED, indicating they are are likely to cause failure at 2022 if not corrected quickly. April 13, Geospatial Summit26

Progress toward completion: #1) IGSxx 1)The creation of each iteration of IGSxx is done under the auspices of the IGS (part of the IERS) 2)NGS participates in and contributes to this process but does not control it 3)In the absence of any future IGSxx’s, NGS will use IGS08 April 13, Geospatial Summit27

Progress toward completion: #2) Airborne Gravity 1)GRAV-D is on track for a 2021 completion 42% done as of today 2)Re-processing into new IGSxx’s is time consuming. May require substantial contract work immediately prior to )Decision about how to move old surveys into epoch is being hotly debated in NGS April 13, Geospatial Summit28 g

Progress toward completion: #3) Surface Gravity 1)NGS has over 2 million surface gravity points at epochs spanning a century 2)No comprehensive effort is currently underway to adjust these data to be consistent with airborne gravity. April 13, Geospatial Summit29

Progress toward completion: #4) DEM 1)A DEM exists from SRTM data covering all needed areas at the correct resolution 2)The DEM epoch is )Other DEMs (TerraSar-X, etc) may need to be adopted to achieve a DEM nearer to the epoch 4)Transformation of the final DEM will still need to occur to be in IGSxx April 13, Geospatial Summit30

Progress toward completion: #5) Geoid Models 1)Experimental geoid models have been created with airborne gravity since 2011, and regularly since )Geoid Slope Validation Surveys have begun (2011) to prove the accuracy of a gravimetric geoid model – 2011: 1 cm proven! – 2014: Being analyzed – 2016: Line Investigation begins next month 3)An agreement with Canada on W0 exists. April 13, Geospatial Summit31

Progress toward completion: #5) Geoid Models 4)NGS does not yet have internal agreement about the proper and final method of combining all gravimetric data sources into a geoid model. 5)The plan to ensure Canada and Mexico are in agreement upon final data sets and final computational methods to arrive at a mutually acceptable North American geoid model in 2022 is not yet complete. April 13, Geospatial Summit32

Progress toward completion: #6) Geoid Velocity Models 1)Satellite missions, especially GRACE, currently provide a secular view of geoid shape change through time 2)NGS has decided that episodic geoid shape changes, such as Earthquakes, will be re-surveyed at a to-be- determined threshold. 3)NGS has decided that periodic geoid change (annual melt/thaw cycles of glaciers) will not be tracked as part of the geoid. April 13, Geospatial Summit33

Progress toward completion: #6) Geoid Velocity Models 4)The geoid’s size (i.e. its relationship to rising sea level) is being hotly debated at NGS. 5)No plan exists at NGS for how we will monitor secular geoid change in the absence of satellite missions. April 13, Geospatial Summit34

Progress toward completion: #7) OPUS in IGSxx This has been covered in the “Progress toward a new Geometric Reference Frame” talk. April 13, Geospatial Summit35  h

Progress toward completion: #8) Interpolation Software 1)NGS has many products and services that require interpolation from either random points or off of a grid. 2)Many of the historic interpolators presumed computers had little RAM which meant loading less of the grid. This meant ease of use but “step function” errors could occur. Small RAM is less of an issue today and entire geoid grids could easily be loaded in most modern personal computers. 3)NGS must decide which interpolator to install in all products and services April 13, Geospatial Summit36

Progress toward completion: #9) Dynamic Height Software 1)Dynamic heights in IGLD85 came from geopotential numbers which, in turn, came from surface gravity and field leveling. 2)In the new geopotential reference frame, GNSS based ellipsoid heights, will be converted (via a geoid) into orthometric heights which will then be converted to geopotential numbers using surface gravity which will then, finally, be converted into dynamic heights. No leveling. 3)No resources have yet been allocated to study the accuracies achievable from GNSS-derived dynamic heights, nor to convert that research into a functioning piece of software for customer use. April 13, Geospatial Summit37 Dyn hNghNg H

Progress toward completion: #10) GPS on NAD 83 points 1)To properly support a transformation tool, any new GNSS on NAD 83 points must occur near enough to 2022 that the IGSxx velocities remain linear (no accelerations or earthquakes) 2)NGS supports a “GPS on BM” campaign annually, which often collect data on joint NAD 83/NAVD 88 points. 3)In order to support the greatest nationwide accuracy, a national GNSS campaign should occur between about 2018 and 2021 April 13, Geospatial Summit38

Progress toward completion: #11) GPS on NAVD 88 points 1)Similar to #10 2)Thankfully, most “GPS on BM” data are on joint NAD 83/NAVD 88 points. April 13, Geospatial Summit39

Progress toward completion: #12) GPS on IGLD85 points 1)Similar to #10 and #11, but research mentioned in #9 must occur 2)A joint USA/Canada campaign to survey GPS on as many IGLD85 points as possible should occur near 2021 April 13, Geospatial Summit40

Progress toward completion: Summary 1)NGS is in critical shortage of geodesists to accomplish all of the tasks needed to have the geopotential reference frame complete by )Numerous “nice, but not necessary” tasks have been reduced in priority to make success more likely (like having a gravity or DOV interpolator built into OPUS). April 13, Geospatial Summit41

What comes after “done”? April 13, Geospatial Summit42

What comes after “done”? 1)What you’ve seen is the bare minimum for NGS to successfully define, maintain and provide access to a new geopotential reference frame. 2)Other significant tasks remain. With additional resources, they could be accomplished before Without them, they will not be started until after April 13, Geospatial Summit43

Thank You! April 13, Geospatial Summit44

1)Coordinates in the new frames will evolve over time, but the transformation tool will only take you to epoch )Nothing was said about passive control being published in the new reference frames. 3)OPUS doesn’t yield up other values of interest, like deflections of the vertical, geopotential or acceleration of gravity. April 13, Geospatial Summit45 “Done” : What you probably noticed was missing

4)Nothing was mentioned about whether latitude and longitude would be plate fixed 5)Nothing was said about NGS accepting GNSS or leveling or gravity or DOV or traverse surveys in the new geopotential reference frame April 13, Geospatial Summit46