Need for a New 3D North American Datum. A Simple Truth. Modernizing the NSRS: The NGS 10 year plan

Transcription

1 Need for New 3D North Americn Dtum Dvid Zenk NGS Advisor MN Society of Professionl Surveyors 2011 Annul Conference St. Cloud, MN 1 A Simple Truth Some Users Will Not Worry About A Dtum Chnge Until It Is Officilly Published, then They Will Ask You Why You Didn t Inform Them Erlier About The Chnge Let s not go down tht rod! 2 Modernizing the NSRS: The NGS 10 yer pln Comments by Dru Smith, NGS Chief Geodesist NOAA s s Ntionl Geodetic Survey My 10-11, 11, 2010 Silver Spring, MD 3

2 NGS nd dtums Outline Accurcy vs. constncy The NGS 10 yer pln Trnsitioning 4 NGS s role nd uthority vis--vis dtums (1 of 6) Cost nd Geodetic Survey Act (Public Lw ) gives the Deprtment of Commerce the right to (mongst numerous other things): conduct geodetic control surveys 5 NGS s role nd uthority vis--vis dtums (2 of 6) OMB Circulr A-16 (revised): Nmes DOC nd NOAA s led gency for Geodetic Control, nd sys: All NSDI frmework dt nd users' pplictions dt require geodetic control to ccurtely register sptil dt. The Ntionl Sptil Reference System is the fundmentl geodetic control for the United Sttes. 6

3 NGS s role nd uthority vis--vis dtums (3 of 6) OMB Circulr A-16 (revised): Becuse NGS is the only gency inside DOC or NOAA tht sets geodetic control, the NSRS responsibility flls to NGS. The NGS mission reflects this OMB-grnted responsibility: NGS Mission: To define, mintin, nd provide ccess to the Ntionl Sptil Reference System to meet our ntion s economic, socil, nd environmentl needs 7 NGS s role nd uthority vis--vis dtums (4 of 6) FGCC Federl Register Notice (Vol. 54, No. 113, 1989) Affirms NAD 83 s the officil civilin horizontl dtum for U.S. surveying nd mpping ctivities performed or finnced by the Federl Government. Furthermore, to the extent prcticble, leglly llowble nd fesible, ll Federl gencies using or producing coordinte informtion should provide for n orderly trnsition from NAD 27 to NAD NGS s role nd uthority vis--vis dtums (5 of 6) FGCS Federl Register Notice (Vol. 58, No. 120, 1993) Affirms NAVD 88 s the officil civilin verticl dtum for surveying nd mpping ctivities in the United Sttes performed or finnced by the Federl Government. To the extent prcticble, leglly llowble, nd fesible, require tht ll Federl gencies using or producing verticl height informtion undertke n orderly trnsition to NAVD

4 NGS s role nd uthority vis--vis dtums (6 of 6) Summry: OMB A-16 estblishes DOC/NOAA (implying NGS) s led gency for NSDI geodetic control (the NSRS) NGS hs defined the horizontl/verticl dtum portions of the NSRS s NAD 83/NAVD 88 FGCC/S grees tht ll civilin federl surveying nd mpping be in NAD 83/NAVD 88 These regultions do not pply to DoD nor to stte nd locl surveying, but these groups often do dopt the NSRS. 10 NGS 10 yer pln Drfting nd vetting to the public took 18 months Officil NGS policy s of Jn 2008 By 2018, without relince on pssive geodetic mrks: Replce NAVD 88 with GNSS/geoid dtum Replce NAD 83 with geocentric GNSS bsed dtum 11 Accurcy vs. Constncy NGS is n gency bsed in science, nd lwys seeking ccurcy nd truth in positioning The Erth is dynmic / coordintes chnge NGS is n gency with lrge user bse tht relies on ner constncy of coordintes Some dynmics cn be modeled nd removed for nerconstncy (N.A. plte rottion : lt / lon) Some dynmics should be trcked nd regulrly ccounted for (subsidence in the Gulf cost : ht) 12

5 Accurcy vs. Constncy Sttic dtum: Coordintes do not chnge. Dynmic dtum: All coordintes chnge (ITRF) Semi-dynmic dtum: Chnges re trcked t NGS, but not necessrily prt of the dtum unless they exceed some criticl level 13 Trnsition Exmple: Digitl TV Rdio Frequency Spectrum is like rel estte. Only so much to go round. Somebody thought: If we use multiplexing, nd brodcst digitl signls, we cn get 5 times s mny brodcsts in the sme rdio frequency spectrum! 14 Trnsition Exmple: Digitl TV 1996 Congress: Trnsition coming in 2006! 2005: Anlog TVs still being mss produced Congress: Um, how does Februry 2009 sound? 2006: Anlog TVs still being mss produced Congress: Hey, we re serious 2009 is coming 2008: FCC finlly cretes DTV website Feb 2009: Too few people hve converters Congress: How does June 2009 sound? 15

6 Trnsition Exmple: Digitl TV At its core, this trnsition went poorly for mny resons, but one in prticulr: There wsn't perceived need to convert to digitl. TV isn't necessity. (Though Emergency Rediness?) Nonetheless, vilble spectrum ws running out with ll the new technologies nd mking efficient use of existing spectrum mde lot of sense to those who understood nd cred A clssic exmple of solution to problem tht people didn t know existed. 16 A problem tht does exist The White Pper (Improving the NSRS.pdf) should explin the problems nd rise wreness of them The burning question is no longer why but how Moving forwrd must be done with contempltion, cution nd commitment 17 Modernizing the Geometric Reference System: Replcing NAD 83 Comments by Richrd Sny, NOAA (retired) NOAA s s Ntionl Geodetic Survey My 10-11, 11, 2010 Silver Spring, MD 18

7 Defining ECEF Reference System * ECEF = Erth centered, Erth fixed * Z-xis = Erth s pole of rottion * X-xis = Intersection of equtor nd prime meridin * Y-xis = Forms right-hnded system with X- nd Z-xes * Scle = meter or distnce tht light trvels in vcuum during 1/299,792,458 seconds * Ellipsoid = needed to define ltitude nd ellipsoidl height * Complictions rise from Erth s dynmics (Polr motion, plte tectonics, erthqukes, subsidence, etc.) 19 Zero Meridin X Axis 3-D ECEF Coordintes Z Axis λ φ h P(X,Y,Z) = P (φ,λ,h) Erth s Surfce Men Equtoril Plne Reference Ellipsoid Y Axis 20 North Americn Dtum of 1983 (NAD 83) * Legl reference system in the United Sttes * Ntionl Geodetic Survey is responsible gency in U.S. * First relized in 1986, revised for HARN, revised gin for CORS * Originlly, NAD 83 ws mostly horizontl reference system * Evolved to 3-dimensionl reference system, thnks to GPS 21

8 NAD 83 (continued) * Origin is locted bout 2 meters from Erth s center Redefined to be mthemticlly equivlent to ITRF96 in the lte 1990 s. Tht is, the U.S. nd Cnd jointly dopted 14-prmeter trnsformtion from ITRF96 to NAD 83 such tht if person knows the ITRF96 coordintes of point, then he/she cn compute the corresponding NAD 83 coordintes nd vice vers. Points locted in stble North Americ should experience no significnt horizontl motion reltive to NAD IMPROVING POSITIONAL ACCURACY REFERENCE TIME ABSOLUTE RELATIVE FRAME SPAN ACCURACY ACCURACY NAD Meters First-Order (1 prt in 0.1 million) NAD Meter First-Order (1 prt in 0.1 million) HARN Meter B-Order (1 prt in 1 million) A-Order (1 prt in 10 million) CORS Meter - Horizontl 0.04 Meter - Ellipsoid Height 23 HIGH ACCURACY REFERENCE NETWORKS (HARN) 24

9 Continuously Operting Reference Sttions (CORS) 25 NAD 83 NAMING CONVENTIONS NAD 83 (UVWXYZ) the prt within prentheses is clled the Dtum Tg Originl reliztion clled NAD 83 (1986), becuse the djustment ws completed in This reliztion of NAD 83 ws bsed minly on tringultion, triltertion nd doppler dt. 26 NAD 83 NAMING CONVENTIONS The HARN reliztions re nmed NAD 83 (1987), NAD 83 (1988),, NAD 83 (2004) where the number in prentheses usully identifies the yer when the GPS observtions were performed. The CORS reliztion is clled NAD 83 (CORS96) where 96 identifies tht this reliztion ws defined in terms of trnsformtion from ITRF96. NAD 83 (NSRS2007) ws creted for pssive reference sttions. It is designed to be consistent with NAD 83 (CORS96). 27

10 NAD 83 READJUSTMENT of 2007 RESULTING REFERENCE FRAME CALLED NAD 83 (NSRS 2007) 28 Brief HARN History FIRST SURVEYS OF HARN COMPLETED BETWEEN 1987 AND GPS HEIGHT MODERNIZATION SURVEYS OF HARN COMPLETED BETWEEN 1997 AND D ADJUSTMENT OF ALL HARN SURVEYS AND OTHER SELECTED GPS SURVEYS COMPLETED IN ADJUSTMENT USED CORS COORDINATES REFERRED TO NAD 83 (CORS96) FOR CONTROL TO REMOVE SMALL REGIONAL DISTORTIONS (3-6 CM) Definitions A Geometric Reference System is set of rules for ssigning positionl coordintes (nd velocities) to points on or ner the Erth. A Geometric Reference Frme is reliztion of Geometric Reference System tht is obtined by ssigning specific positionl coordintes (nd velocities) to set of identifible points. NAD 83 is geometric reference system. NAD 83 (xxxx) is geometric reference frme. 30

11 World Geodetic System of 1984 (WGS 84) * GPS brodcst orbits give stellite positions in WGS 84 * Deprtment of Defense is the responsible gency * System originlly greed with NAD 83 * Revised to gree with Interntionl Terrestril Reference Frme (ITRF) in erly 1990 s 31 GPS Trcking Network Defining WGS 84 Alsk Schriever AFB Vndenberg AFB Cpe Cnverl USNO Wsh, DC Englnd Bhrin South Kore Hwii Ecudor Ascension Diego Grci Kwjlein Thiti Argentin South Afric Austrli New Zelnd Mster Control Sttion (MCS) Alternte MCS Ground Antenns Air Force Monitoring Sttions NGA Monitoring Sttions Future NGA Monitoring Sttions 32 WGS 84 Nming Conventions WGS 84 (trnsit) this is the originl reliztion of WGS 84 which is bsed on trnsit doppler stellite dt WGS 84(G730), WGS 84(G873), WGS 84(G1150) these reliztions re bsed on GPS dt, the number in prentheses identifies the GPS week tht the militry dopted the version. WGS 84 is reference system. WGS 84 (xxxx) is reference frme. 33

12 Interntionl Terrestril Reference System (ITRS) * Supports ccurte 3-dimensionl positioning * Interntionl Erth Rottion nd Reference Frme Service is responsible orgniztion * Defines interntionl stndrd for origin, orienttion, nd scle * Provides positions nd velocities for severl hundred sites worldwide 34 Interntionl Terrestril Reference System (ITRS) * Positions nd velocities revised every few yers, producing the following Interntionl Terrestril Reference Frmes: ITRF88, ITRF89,, ITRF2000, ITRF2005, ITRF2008 * Integrtes results from vrious observing techniques: - Globl Positioning System (GPS) - Very Long Bseline Interferometry (VLBI) - Stellite Lse Rnging (SLR) - Doppler Orbitogrphy & Rdiopositioning Integrted by Stellite = (DORIS) * Combintion of severl solutions, ech performed independently by n nlysis center 35 36

13 37 7-Prmeter Helmert Similrity Trnsformtion (preserves shpe) The following equtions represent n pproximtion bsed on the ssumption tht the rottion ngles re smll. x NAD = T x + (1+S) x ITRF + R z y ITRF -R y z ITRF y NAD = T y -R z x ITRF + (1 + S) y ITRF + R x z ITRF z NAD = T z + R y x ITRF -R x y ITRF + (1 + S) z ITRF 3 trnsltions (T X, T Y, T Z ) 3 rottions (R X, R Y, R Z ) One differentil scle (S) 38 Effect of trnsltion on ellipsoid height 2.2 meters ITRF 97 Origin h 83 h 97 Erth s Surfce (Identiclly shped ellipsoids NAD 83 = 6,378, meters Origin 1/f = ) 39

14 Effect of rottion bout the Y-xis 40 Trnsformtion Prmeters ITRF96 --> NAD_83(CORS96) Trnsltions: T x = meters T y = meters T z = meters Rottions: R x = [ (t )] k rdins R y = [ (t )] k rdins R z = [ (t )] k rdins Scle chnge: S = 0.0 (unitless) Where: t = dte in yers (eg., = 23 APR 1999) nd k = (10**-9) 41 Trnsitive Property (A D) = (A B) + (B C) + (C D) So: (ITRF2000 NAD83) = (ITRF2000 ITRF96) + (ITRF96 NAD83) Reflective Property (B A) = - (A B) Agin, these properties re bsed on smll ngle ssumption. 42

15 Horizontl Time-Dependent Positioning (HTDP) HTDP llows users to trnsform positionl coordintes cross time nd between different ECEF reference frmes. HTDP incorportes dopted 14- prmeter trnsformtions. 43 Replcing NAD 83 Wnt the new reference system to be more geocentric Option 1: Adopt ITRF20xx Option 2: Adopt reference frme tht grees with ITRF20xx t some instnt of time, but does not move reltive to stble North Americ. 44 Option 1: Adopting ITRF20xx Advntge: Idelly there would be just one reference frme for everyone in the world. (Note: The current WGS84 reliztion is essentilly equivlent to ITRF2000 nd its next reliztion will be essentilly equivlent to ITRF2008.) Disdvntge: All points in North Americ would hve significnt horizontl velocities In centrl & estern CONUS, between 1 nd 2 cm/yr In Cliforni, western Oregon, western Wshington, Alsk nd Cnd, more thn 2 cm/yr 45

16 Option 2: Frme fixed to North Americn plte Advntge: Points in stble North Americ would experience no significnt horizontl motion. Disdvntge: Ech tectonic plte would need its own reference frme. Hwii is locted on the Pcific plte, Puerto Rico on the Cribben plte, nd Gum on the Mrin plte. Also, points locted ner plte boundries would still be moving significntly (eg., Cliforni, Oregon, Wshington, southern Alsk) Horizontl velocities in the western U.S. reltive to the North Americn Dtum of 1983 s derived from geodetic observtions. 48

17 Anlogy with time systems The world hs dopted essentilly two time systems: Universl Coordinted Time (UTC) for globl pplictions Locl time for pplictions within single time zone The conversion between the two time systems is simply mtter of dding or subtrcting n integrl number of hours. 49 Cn the geosptil community del with two geometric reference systems? ITRF20xx for inter-plte pplictions Plte-specific reference frmes for intr-plte pplictions A conversion between two given frmes would simply involve pplying set of 3 rottion rtes. 50 EPOCH DATE dte for which published positionl coordintes re vlid. Antenn Reference Point(ARP): GRAND MARAIS CORS ARP PID = DE6003 ITRF00 POSITION (EPOCH ) Computed in Jul., 2002 using 19 dys of dt X = m ltitude = N Y = m longitude = W Z = m ellipsoid height = m ITRF00 VELOCITY Predicted with HTDP_2.6 June VX = m/yr northwrd = m/yr VY = m/yr estwrd = m/yr VZ = m/yr upwrd = m/yr NAD_83 POSITION (EPOCH ) Trnsformed from ITRF00 (epoch ) position in Jul., X = m ltitude = N Y = m longitude = W Z = m ellipsoid height = m NAD_83 VELOCITY Trnsformed from ITRF00 velocity in Jul., VX = m/yr northwrd = m/yr VY = m/yr estwrd = m/yr VZ = m/yr upwrd = m/yr 51

18 IGS Renlysis Severl IGS Anlysis Centers (including NGS) hve ech reprocessed ll IGS dt observed since NGS hs lso reprocessed ll CORS dt observed since This nlysis included new clibrtion results for both GPS stellite trnsmission ntenns nd GPS receiver ntenns. NGS will use results from this renlysis to produce ITRF2008-comptible positions nd velocities for sttions in the CORS network. 52 NAD 83 (CORS96) NGS will use new ITRF2008 coordintes nd velocities for CORS to produce new reliztion of NAD 83 to be clled NAD 83 (CORS96) NAD 83 (CORS96) will be defined so tht the 14- prmeter trnsformtion between it nd NAD 83 (CORS96) will be the identity function. Hence, NAD 83 (CORS96) coordintes should be consistent with NAD 83 (NSRS2007) coordintes nd with the use of GEOID09 to convert NAD 83 (CORS96) ellipsoid heights to NAVD 88 orthometric heights. 53 NAD 83 (CORS96) - continued NAD 83 (CORS96) coordintes will, nevertheless, differ from NAD 83 (CORS96) coordintes becuse they re being derived using More GPS dt More rigorous computtionl procedures More ccurte models for systemtic errors NAD 83 (CORS96) should become vilble in the fll of CORS coordintes were lst revised, in wholesle mnner, in Hence, current CORS coordintes re less ccurte thn desired. 54

19 Wht bout verticl velocities? 55 Modernizing the Geopotentil Dtum: Replcing NAVD 88 Comments by Dniel R. Romn, Ph.D. NOAA s s Ntionl Geodetic Survey My 10-11, 11, 2010 Silver Spring, MD 56 Outline Wht is verticl dtum? Why isn t NAVD 88 good enough nymore? Possible wys to fix NAVD 88 How will I ccess the new verticl dtum? Additionl Informtion 57

20 Wht is verticl dtum? Mny vritions of the definition exist Strictly speking, verticl dtum is: A surfce representing zero elevtion Trditionlly, verticl dtum hs been thought of in more brod sense: A system for the determintion of heights bove zero elevtion surfce 58 Wht is verticl dtum? A verticl dtum lwys hs two components: Its definition Prmeters nd other descriptors Its reliztion Its physicl method of ccessibility 59 Wht is verticl dtum? Exmple: North Americn Verticl Dtum of 1988 (NAVD 88) Definition: The surfce of equl grvity potentil to which orthometric heights shll refer in North Americ*, nd which is meters (long the plumb line) below the geodetic mrk t Fther Point/Rimouski (NGSIDB PID TY5255). Reliztion: Over 500,000 geodetic mrks cross North Americ with published Helmert orthometric heights, most of which were originlly computed from minimlly constrined djustment of leveling nd grvity dt, holding the geopotentil vlue t Fther Point/Rimouski fixed. 60

21 Verticl Control Network NAVD ,000 BM s over 1,001,500 km 61 Why isn t NAVD 88 good enough nymore? NAVD 88 suffers from use of bench mrks tht: Are lmost never re-checked for movement Dispper by the thousnds every yer Are not funded for replcement Are not necessrily in convenient plces Don t exist in most of Alsk Weren t dopted in Cnd Were determined by leveling from single point, llowing cross-country error build up 62 Why isn t NAVD 88 good enough nymore? NAVD 88 suffers from: A zero height surfce tht: Hs been proven to be ~50 cm bised from the ltest, best geoid models (GRACE stellite) Hs been proven to be ~ 1 meter tilted cross CONUS (gin, bsed on the independently computed geoid from the GRACE stellite) 63

22 Why isn t NAVD 88 good enough nymore? Erth s Surfce H (NAVD 88) H NAVD 88 reference level The Geoid Errors in NAVD 88 : ~50 cm verge, 100 cm CONUS tilt, 1-2 meters verge in Alsk NO trcking 64 Why isn t NAVD 88 good enough nymore? Approximte level of geoid mismtch known to exist in the NAVD 88 zero surfce: 65 Possible wys to fix NAVD 88 Short term fixes: Provide fst methods of expnding NAVD 88 in res where it is needed Long term fixes: Re-level some / ll of NAVD 88 Replce NAVD 88 bench mrks 66

23 Possible wys to fix NAVD 88 Short term fix: Height Moderniztion GPS surveys Hve provided fst wy to disseminte NAVD 88 bench mrk heights to new mrks through the use GPS nd constrined lest squres djustment NOAA TM NOS NGS 58 nd 59 guidelines Keeps NAVD 88 useful nd ccessible, but does not ddress the mjority of problems of NAVD 88 itself 67 GPSBM2009 (GEOID09 Control Dt) totl, less 1003 rejected, leves 18,867 (CONUS) plus 576 (Cnd) 68 Possible wys to fix NAVD 88 Long term fix: Re-level some/ll of NAVD 88 Re-leveling NAVD 88 would cost between $200 Million nd $2 Billion This wouldn t fix ll of the problems ssocited with the use of bench mrks though 69

24 Possible wys to fix NAVD 88 Long term fix: Replce NAVD 88 Find method of defining verticl dtum tht seeks to fix ll of the known issues with NAVD 88 Best option: Define the dtum s given geoid model nd relize it through GNSS technology GRAV-D 70 Possible wys to fix NAVD 88 Long term fix: Replce NAVD 88 (continued) GRAV-D Trde-offs: Dtum is only relizble to 2 cm t best t ny given point (GNSS error + geoid error) However, this is n improvement over NAVD 88 reliztion error The dtum could then be disseminted loclly through very precise geodetic leveling 71 Reltionship between Grvity nd Heights g 1 = grvity on geoid t sttion 1 g 1 = verge grvity from g 1 to g* 1 g* 1 = surfce grvity t sttion 1 g 2 = verge grvity from g 2 to g* 2 g 2 = grvity on geoid t sttion 2 g* 2 = surfce grvity t sttion 2 H 1 = orthometric height to sttion 1 H 2 = orthometric height to sttion 2 Sttion 2 g* 2 Sttion 1 H 2 g* 1 C 5 H 1 C 4 C 3 C 2 C 1 C 0 geoid g g 1 1 > g 2 H1 = C5/g 1 g g* 2 1 > g* 2 H2 = C5/g 2 g 1 > g 2 H 1 < H 2 Note tht surfce loction of sttion 1 is closer to the geoid thn sttion 2. A steep grdient of geops indictes higher grvity less steep indictes lower grvity. The geops being frther prt beneth sttion 2 to reflect lower locl mss nd grvity. Hence, H1 should be less thn H2 even though both hve the sme geopotentil. 72

25 Geoid Power nd Dt Sources Work with mny groups to obtin other dt sets s well s wht we observe Vrince (m 2 ) 1.E+04 1.E+02 1.E+00 1.E-02 1.E-04 1.E-06 1.E stellite models (GRACE/GOCE) irborne nd surfce grvity terrin nd density models Degree (n) km Spectrlly merge the dt sources to obtin semless grvity field Work with neighbors to incorporte regionl dt (North Americn Geoid/IAG CP 2.2) Use rigorous geodetic theory nd/or forwrd modeling to mke geoid height model 73 Possible wys to fix NAVD 88 Long term fix: Replce NAVD 88 (continued) GRAV-D Interntionl Issues Cnd hs greed to move to geoid bsed verticl dtum Negotitions with USA underwy Mexico hs discussed this with USA, but hve not chosen to move to geoid bsed dtum yet Centrl Americn, Cribben: No policy to switch, but the dtum will be freely vilble to them 74 How will I ccess the new verticl dtum? Primry ccess (NGS mission) Users with geodetic qulity GNSS receivers will continue to use OPUS suite of tools Ellipsoid heights computed, nd then grvimetric geoid removed to provide orthometric heights in the new dtum No pssive mrks needed But, could be used to position pssive mrk 75

26 Reltionship between ellipsoid, geoid nd orthometric heights. Men Se Level Ellipsoid DoV h N + H GEOID HEIGHT OR UNDULATION P Erth s Surfce Plumb Line h Q N Geoid P O Ocen h (Ellipsoid Height) = Distnce long ellipsoid norml (Q to P) N (Geoid Height) = Distnce long ellipsoid norml (Q to P O ) H (Orthometric Height) = Distnce long plumb line (P O to P) 76 How will I ccess the new verticl dtum? Secondry ccess (Use t your own risk) Pssive mrks tht hve been tied to the new verticl dtum NGS will provide dt shring service for these points, but their ccurcy (due to either the qulity of the survey or the ge of the dt) will not be responsibility of NGS 77 How will I ccess the new verticl dtum? NAVD 88 conversion to new dtum A conversion will be provided between NAVD 88 nd the new dtum Only where recent GNSS ellipsoid heights exist to provide modern heights in the new dtum 78

27 Note tht the ITRF00-NAD83 trnsformtion is not included here This ws neglected to highlight the significnt systemtic fetures 79 How will I ccess the new verticl dtum? Exmple 1: Flood insurnce survey House 1954: Leveling Performed to bench mrk : Subsidence BM 1991: Originl 1954 leveling dt is used to compute the NAVD 88 height which is then published for this BM NAVD 88 zero height surfce H 88 (true) H 88 (published) Obviously the true height reltive to the NAVD 88 zero surfce is not the published NAVD 88 height 80 How will I ccess the new verticl dtum? Exmple 1: Flood insurnce survey House BM Using Existing Techniques: Find bench mrk (if you cn) Get published NAVD 88 height Level off of bench mrk No ccount for subsidence! House BM NAVD 88 zero height surfce H 88 (true) H 88 (published) 81

28 How will I ccess the new verticl dtum? Exmple 1: Flood insurnce survey House House BM BM Using Future Techniques: Find bench mrk if you wish, or set new one of your choosing Use GNSS/OPUS to get n orthometric height in the new dtum Level off of bench mrk s needed Subsidence is ccounted for by CORS nd geoid tht re monitored constntly! NAVD 2018(?) zero height surfce = geoid H(2018?) from GNSS/geoid 82 How will I ccess the new verticl dtum? Exmple 2: Bringing in the dtum Point where I need n orthometric height Nerest level lines re bout 25 km nd 50 km wy respectively. Bench mrks my or my not exist, 83 How will I ccess the new verticl dtum? Exmple 2: Bringing in the dtum Choice 1: Leveling Will we live with spur or mybe check in with nother level line? Leveling for 25 km Leveling for 50 km Lucky dy, we find 6 undisturbed Bench mrks! Luckily we find 1 undisturbed bench mrk! Now it s time to bluebook the dt, submit to NGS, wit for the bcklog to cler. And ll this ssumes the published 84 heights re correct to begin with

29 How will I ccess the new verticl dtum? Exmple 2: Bringing in the dtum Choice 2: Height Mod survey Crete pssive mrks round re of interest Using progressive GNSS surveys (NGS 59 Guidelines), trnsfer orthometric heights to Primry, Secondry nd Locl mrks Now it s time to bluebook the dt, submit to NGS, wit for it to be loded into the IDB. And ll this ssumes the published 85 heights re correct to begin with How will I ccess the new verticl dtum? Exmple 2: Bringing in the dtum Choice 3: Once GRAV-D is complete Set up GNSS receiver over mrk Submit dt to OPUS nd receive orthometric height Feeling generous? Shre your results with others using the NGS online dtbse (no bluebooking involved). If not, tke your height nd wlk wy. 86 Additionl Informtion The NGS 10 yer pln ( ) The GRAV-D Project Socio-Economic Benefits of CORS nd GRAV-D 87

30 Questions? 88