Benefits of the New Reference Frames Dru Smith Joe Evjen 60 minutes April 13, Geospatial Summit1

Outline Needed repairs Benefits of new frames: – Repairs – Improvements April 13, Geospatial Summit2

What is a repair? A fix to something in the current system that is currently causing NGS to: – Fail to provide heights, or – Provide inaccurate heights, or – Put undue burden on users, or – Waste resources April 13, Geospatial Summit3

What is an improvement? A change to something in the current system that by itself is not causing significant problems, but whose cost/benefit ratio is worthwhile and which helps NGS to provide: – Better service and/or – Better accuracy and/or – Better sustainability and/or – Better efficiency April 13, Geospatial Summit4

Needed Repairs April 13, Geospatial Summit5

Needed Repairs: NAVD 88 Inherent weaknesses of passive marks – Fragility, convenience, movement – Cost-prohibitive maintenance Adjustment issues – Minimally constrained, Helmert approximation, inconsistent surface gravity surveys Sparseness Bias and Tilt – WRT GRACE/GOCE geoid models April 13, Geospatial Summit 6

Needed Repairs: NAD 83 NAD83 frame ≠ GPS navigation frame NAD83 frame ≠ WAAS navigation frame NAD83 frame ≠ satellite orbits frame NAD83 frame ≠ satellite product frame NAD83 frame ≠ international geodetic frame – International flights take off & land on different datums – Many geodetic tools assume ITRF as default April 13, Geospatial Summit7

map how you navigate? meters Your GNSS frame, ITRF Your map datum, NAD 83 * As GNSS un-augmented user range error improves over time …

NAD 83(2011) to IGS08 at epoch

NAD 83(PA11) to IGS08 at epoch

Needed Repairs: Island datums (PRVD02, ASVD02, NMVD03, GUVD04, VIVD09) April 13, Geospatial Summit15 Many of the same issues as NAVD 88 – Fragility, convenience, movement, MCA, sparseness, bias, tilt Normal orthometric heights

Needed Repairs: Hawaii April 13, Geospatial Summit16 No vertical datum exists!

Needed Repairs: IGLD 85 Many of the same issues as NAVD 88 – They were co-defined from the same leveling and gravity data Thirty years of GIA have changed the levels of the lakes April 13, Geospatial Summit17

Repairs that come with the new reference frames April 13, Geospatial Summit18

Repairing NAVD 88 April 13, Geospatial Summit19

Repairing NAVD 88* Problem: Fragility of bench marks Repair: In the new geopotential reference frame, orthometric heights are available to GNSS receivers without need for any bench marks April 13, Geospatial Summit20 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAVD 88* Problem: Inconvenient bench mark locations Repair: In the new geopotential reference frame, orthometric heights are equally available to GNSS receivers everywhere in the USA April 13, Geospatial Summit21 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAVD 88* Problem: Unchecked movement of bench marks Repair: In the new geopotential reference frame, orthometric heights at the epoch of the survey, are available to GNSS receivers because of time- dependent geoid models and time-dependent CORS positions April 13, Geospatial Summit22 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAVD 88* Problem: Minimally Constrained Adjustment (absolute accuracy of heights is dependent on distance from origin) Repair: In the new geopotential reference frame, the absolute accuracy of orthometric heights will have greater consistency throughout the country. April 13, Geospatial Summit23 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAVD 88 Problem: Helmert Approximation (heights rely on a first-order approximation which doesn’t propagate into accuracy statistics) Repair: In the new geopotential reference frame, approximations are being quantified and bounded and will be reflected in accuracy statistics. April 13, Geospatial Summit24

Repairing NAVD 88 Problem: Inconsistent surface gravity surveys (heights rely 2 million surface gravity measurements which span decades and reflect no time dependency) Repair: In the new geopotential reference frame, the gravity field will be consistent, and epoch dependent, directly influencing the time dependent geoid and time dependent orthometric heights April 13, Geospatial Summit25

Repairing NAVD 88* Problem: Sparseness (bench mark spatial distribution tends to cluster around population clusters) Repair: In the new geopotential reference frame, orthometric heights are equally available to GNSS receivers everywhere in the USA April 13, Geospatial Summit26 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Benefits of repairs: NAVD 88* Problem: Bias and Tilt (“zero height surface” of datum is not the geoid) Repair: In the new geopotential reference frame, the geoid will be the zero height surface, and will be built upon global satellite models April 13, Geospatial Summit27 * and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAD 83 April 13, Geospatial Summit28

Repairing NAD 83 1)Align US frame with ITRF, GPS, WAAS 2)Remove non-geocentricity 3)Move beyond cascade of NAD83 realizations 4)Better agreement across USA – Mexico border 5)Velocities everywhere, so we use similar techniques everywhere April 13, Geospatial Summit29

Repairing Island datums (PRVD02, ASVD02, NMVD03, GUVD04, VIVD09) April 13, Geospatial Summit30

Repairing Island datums (PRVD02, ASVD02, NMVD03, GUVD04, VIVD09) Problem: Normal Orthometric Heights (heights do not rely on actual gravity measurements) Repair: In the new geopotential reference frame, orthometric heights will be available to GNSS receivers, not normal orthometric heights April 13, Geospatial Summit31

Repairing Hawaii April 13, Geospatial Summit32

Repairing Hawaii Problem: No Vertical Datum (NGS has never officially defined a vertical datum for Hawaii) Repair: In the new geopotential reference frame, orthometric heights will be available to GNSS receivers in Hawaii, consistent with heights across the North American continent April 13, Geospatial Summit33

Repairing IGLD 85 April 13, Geospatial Summit34

Repairing IGLD 85 Problem: GIA changes aren’t reflected in IGLD 85 Repair: In the new geopotential reference frame, dynamic heights at the epoch of the survey, are available to GNSS receivers because of time- dependent geoid models, time-dependent CORS positions and time dependent gravity field models April 13, Geospatial Summit35

Improvements that come with the new reference frames April 13, Geospatial Summit36

Improving Heights Continental consistency In the new geopotential reference frame, heights will be consistent from pole to equator and Aleutians to Greenland. April 13, Geospatial Summit37

Extent of 2022 geoid model used for new geopotential reference frame April 13, Geospatial Summit38

Hawaii Many US Pacific Territories (not Guam, CNMI nor American Samoa) April 13, Geospatial Summit39

April 13, Geospatial Summit40 Canada Alaska, including entire Aleutian Island Chain CONUS (USA)

Mexico All Central American Countries All Caribbean Countries Bermuda April 13, Geospatial Summit41

Improving Heights Time-dependent heights on passive control In the new geopotential reference frame, heights on passive control will eventually be stored at and distributed by NGS, and changes over time will be reflected as actual changes April 13, Geospatial Summit42

H time Assume “H” was determined four different times: 1990: : : : 2.180

H time In standard NGS procedure, a height is held fixed until replaced. So plotting the height as seen on a datasheet over time would look like this: Height unknown before first survey

H time This will change in the future. First, error bars will be shown. Shown here are the same values of “H”, but with error bars representing their standard deviations. 1990: / (3.75 cm) 1994: / (2.50 cm) 2002: / (2.00 cm) 2009: / (2.50 cm)

H time Using least squares, we could fit a line, using appropriate weights to fit to the data

H time Using a simple H = mt+b fitting, we get: m = m/y (+5.05 cm uplift per year) b(1970) = m H = ( )(t-1970)

H time Now, we can find H at various time intervals.

H time And propagating the actual measurement error forward and backward in time, we see that there is a strong dependence on higher accuracy height estimates occurring near the actual surveys.

H time Compare this with current NGS procedures… Height unknown before first survey

H time Compare this with current NGS procedures… The only place current NGS procedures match the predicted heights 5 cm 10 cm* (*and growing)

Improving Dynamic Heights In the new geopotential reference frame, dynamic heights will be available from GNSS surveys, rather than just leveling surveys April 13, Geospatial Summit52

Improving Clarity “All coordinates are referenced to the North American Datum of 1983 (NAD 83) which is equivalent to the World Geodetic System 1984 (WGS 84)” - U.S. Supreme Court, Dec 15, 2014 In the new geopotential reference frame, the name “NAD 83” will be gone, and issues such as this will hopefully be left behind as well. April 13, Geospatial Summit53

Thank You! April 13, Geospatial Summit54

Extra Slides April 13, Geospatial Summit55

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Needed Repairs: IGSN 71 Most NGS surface gravity is in IGSN 71, an international network, not under NGS control Based on pre-microGal absolute meters No maintenance April 13, Geospatial Summit58