Height Mod Focus Group - U.S. National Geodetic Survey

Height Mod Focus Group - U.S. National Geodetic Survey

GPS Derived Heights: A Height Modernization Primer Marquette, Michigan.January 24, 2006 Flint, Michigan..January 26, 2006 Renee Shields National Geodetic Survey National Oceanic and Atmospheric Administration Height Modernization is the ability to compute the establishment of accurate, reliable heights using GPS technology in conjunction with accurate orthometric (sea level) heights traditional leveling, gravity, using GPS technology and modern

remote sensing information. How to achieve accurate GPS heights 1) What types of heights are involved? Orthometric heights Ellipsoid heights Geoid heights 2) How are these heights defined and related? 3) How accurately can these heights be determined? What is a GEODETIC DATUM? Geodetic Datum A set of constants specifying the coordinate system used for geodetic control, i.e., for calculating coordinates of points on the Earth* [above] together with the coordinate system and the set of all points and lines whose coordinates, lengths, and directions have been determined by measurement or calculation.* *Definitions from the Geodetic Glossary, September 1986 Not To Be Confused With: Ellipsoid A closed surface, whose planar sections are either ellipsoids or circles.*

Mathematical figure which helps define a Reference Frame Clarke 1866, GRS80 Reference Frame A coordinate system associated with a physical system.* NSRS, ITRF *Definitions from the Geodetic Glossary, September 1986 Horizontal Control Datum? Horizontal Control Datum A Geodetic Datum specifying the coordinate system in which horizontal control points are located. Defined by 8 Constants 3 specify the location of the origin of the coordinate system. 3 specify the orientation of the coordinate system. 2 specify the dimensions of the reference ellipsoid. NAD 27, NAD 83 *Definition from the Geodetic Glossary, September 1986 Comparison of Horizontal Datum Elements NAD 27 ELLIPSOID DATUM POINT

ADJUSTMENT BEST FITTING CLARKE 1866 a = 6,378,206.4 m 1/f = 294.9786982 Triangulation Station MEADES RANCH, KANSAS 25k STATIONS Several Hundred Base Lines Several Hundred Astro Azimuths North America NAD 83 GRS80 a = 6,378,137. M 1/f = 298.257222101 NONE EARTH MASS CENTER 250k STATIONS Appox. 30k EDMI Base Lines 5k Astro Azimuths Doppler Point Positions VLBI Vectors World-Wide

NAD 27 and NAD 83 Vertical Control Datum? Vertical Control Datum A Geodetic Datum specifying the system in which vertical control points are located. * A set of fundamental elevations to which other elevations are referred NGVD 29, NAVD 88 Orthometric, Sea Level Others Cairo, Local Tidal *Definitions from the Geodetic Glossary, September 1986 Orthometric Heights Comparison of Vertical Datum Elements NGVD 29 DATUM DEFINITION NAVD 88 26 TIDE GAUGES IN THE U.S. & CANADA FATHERS POINT/RIMOUSKI QUEBEC, CANADA BENCH MARKS 100,000

450,000 LEVELING (Km) 102,724 1,001,500 GEOID FITTING Distorted to Fit MSL Gauges Best Continental Model NGVD 29 and NAVD 88 Conventional Leveling ROD 1 ROD 2 ROD 1 Backsight 5 BM 100 Foresight

Backsight 105 HI 6 Foresight 96 4.5 7.5 INSTR 99 INSTR BM Ellipsoid, Geoid, and Orthometric Heights H = Orthometric Height (NAVD 88) h = Ellipsoidal Height (NAD 83) N = Geoid Height (GEOID 03) H =h-N

h A Ellipsoid GRS80 Geoid H TOPOGRAPHIC SURFACE N GEOID03 B Gravity measurements help answer two big questions Earths Surface Geoid How high above sea level am I? (FEMA,

USACE, Surveying and Mapping) How large are near-shore hydrodynamic processes? (Coast Survey, CSC, CZM) Orthometric Ht From Leveling Coast Ocean Surface Ellipsoid Ellipsoid Ht From GPS Geoid Height From Gravity From Satellite Altimetry What is the GEOID? The equipotential surface of the Earths gravity

field which best fits, in the least squares sense, mean sea level.* Cant see the surface or measure it directly. Can be modeled from gravity data. *Definition from the Geodetic Glossary, September 1986 In Search of the Geoid Courtesy of Natural Resources Canada www.geod.nrcan.gc.ca/index_e/geodesy_e/geoid03_e.html High Resolution Geoid Models G99SSS (Scientific Model) Earth Gravity Model of 1996 (EGM96) Long Wavelength - global 2.6 million terrestrial, ship-borne, and altimetric gravity measurements Medium Wavelength - regional 30 arc second Digital Elevation Data Short Wavelength - local

3 arc second DEM for the Northwest USA Decimated from 1 arc second NGSDEM99 Computed on 1 x 1 arc minute grid spacing GRS-80 ellipsoid centered at ITRF97 origin High Resolution Geoid Models USGG2003 (Scientific Model) 2.6 million terrestrial, ship, and altimetric gravity measurements offshore altimetry from GSFC.001 instead of KMS98 30 arc second Digital Elevation Data 3 arc second DEM for the Northwest USA Decimated from 1 arc second NGSDEM99 Earth Gravity Model of 1996 (EGM96) Computed on 1 x 1 arc minute grid spacing GRS-80 ellipsoid centered at ITRF00 origin Gravity Coverage for GEOID03 High Resolution Geoid Models GEOID03 (vs. Geoid99) Begin with USGG2003 model 14,185 NAD83 GPS heights on NAVD88 leveled benchmarks

(vs. 6169) Determine national bias and trend relative to GPS/BMs Create grid to model local (state-wide) remaining differences ITRF00/NAD83 transformation (vs. ITRF97) Compute and remove conversion surface from USGG2003 High Resolution Geoid Models GEOID03 (vs. Geoid99) Relative to non-geocentric GRS-80 ellipsoid 2.7 cm RMS nationally when compared to BM data

(vs. 4.6 cm) RMS 50% improvement over GEOID99 (Geoid96 to 99 was 16%) GPS on Bench Marks in Michigan Composite Geoids Earths Surface h h h h H Ellipsoid H H N N N

h H H N N Composite Geoid 0.308 M in 0.271 Traverse City 1999 model 2003 Gravity Geoid Gravity Geoid systematic misfit with benchmarks Composite Geoid biased to fit local benchmarks Feb 13, 2020 Sample Datasheet

National Geodetic Survey, Retrieval Date = DECEMBER 28, 2005 PL0314 *********************************************************************** PL0314 DESIGNATION - V 27 PL0314 PID - PL0314 PL0314 STATE/COUNTY- MI/GRAND TRAVERSE PL0314 USGS QUAD PL0314

PL0314 *CURRENT SURVEY CONTROL PL0314 ___________________________________________________________________ PL0314* NAD 83(1994)- 44 39 02.41202(N) 085 46 04.27942(W) ADJUSTED PL0314* NAVD 88 257.838 (meters) 845.92 (feet) ADJUSTED PL0314 ___________________________________________________________________ PL0314 X 335,419.145 (meters) COMP PL0314 Y - -4,532,722.532 (meters) COMP PL0314 Z 4,459,971.520 (meters) COMP PL0314 LAPLACE CORR5.18 (seconds) DEFLEC99 PL0314 ELLIP HEIGHT223.17 (meters) (07/17/02) GPS OBS PL0314 GEOID HEIGHT-34.68 (meters) GEOID03 PL0314 DYNAMIC HT 257.812 (meters) 845.84 (feet) COMP

PL0314 MODELED GRAV980,508.8 (mgal) NAVD 88 PL0314 H h N Sample Datasheet

PL0314 PL0314 HORZ ORDER - FIRST PL0314 VERT ORDER - FIRST CLASS II PL0314 ELLP ORDER - FOURTH CLASS I PL0314 PL0314.The horizontal coordinates were established by GPS observations PL0314.and adjusted by the National Geodetic Survey in February 1997. PL0314 PL0314.The orthometric height was determined by differential leveling PL0314.and adjusted by the National Geodetic Survey in June 1991. PL0314 PL0314.The X, Y, and Z were computed from the position and the ellipsoidal ht. PL0314 PL0314.The Laplace correction was computed from DEFLEC99 derived deflections. PL0314 PL0314.The ellipsoidal height was determined by GPS observations

PL0314.and is referenced to NAD 83. PL0314 PL0314.The geoid height was determined by GEOID03. PL0314 PL0314.The dynamic height is computed by dividing the NAVD 88 PL0314.geopotential number by the normal gravity value computed on the PL0314.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 PL0314.degrees latitude (g = 980.6199 gals.). PL0314 PL0314.The modeled gravity was interpolated from observed gravity values. PL0314 Sample Datasheet

PL0314 PL0314.The modeled gravity was interpolated from observed gravity values. PL0314 PL0314; North East Units Scale Factor Converg. PL0314;SPC MI C 149,194.606 5,888,865.237 MT 0.99992569 -0 59 23.3 PL0314;SPC MI C 489,483.62 19,320,424.01 iFT 0.99992569 -0 59 23.3 PL0314;UTM 16 - 4,944,883.803 597,700.224 MT 0.99971738

+0 51 57.6 PL0314 PL0314! - Elev Factor x Scale Factor = Combined Factor PL0314!SPC MI C 0.99996501 x 0.99992569 = 0.99989070 PL0314!UTM 16 0.99996501 x 0.99971738 = 0.99968240 PL0314 PL0314 SUPERSEDED SURVEY CONTROL PL0314 PL0314 ELLIP H (02/03/97) 223.19 (m) GP( ) 4 1 PL0314 NAD 83(1986)- 44 39 02.41257(N) 085 46 04.28315(W) AD( ) 1 PL0314 NAD 83(1986)- 44 39 02.38347(N) 085 46 04.27988(W) AD( ) 3 PL0314 NAVD 88 (09/30/91) 257.84

(m) 845.9 (f) LEVELING 3 PL0314 NGVD 29 (??/??/92) 257.915 (m) 846.18 (f) ADJ UNCH 1 2 PL0314 PL0314 Superseded values are not recommended for survey control. PL0314.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums. PL0314 Sample Datasheet

PL0314_U.S. NATIONAL GRID SPATIAL ADDRESS: 16TEQ9770044884(NAD 83) PL0314_MARKER: DB = BENCH MARK DISK PL0314_SETTING: 7 = SET IN TOP OF CONCRETE MONUMENT PL0314_SP_SET: CONCRETE POST PL0314_STAMPING: V 27 1930 846.176 PL0314_MARK LOGO: CGS PL0314_MAGNETIC: N = NO MAGNETIC MATERIAL PL0314_STABILITY: B = PROBABLY HOLD POSITION/ELEVATION WELL PL0314_SATELLITE: THE SITE LOCATION WAS REPORTED AS SUITABLE FOR PL0314+SATELLITE: SATELLITE OBSERVATIONS - October 24, 1992 PL0314 PL0314 HISTORY - Date

Condition Report By PL0314 HISTORY - 1930 MONUMENTED CGS PL0314 HISTORY - 1951 GOOD NGS PL0314 HISTORY - 1984 GOOD NGS PL0314 HISTORY - 19890428 GOOD NGS PL0314 HISTORY - 1990 GOOD USPSQD PL0314 HISTORY - 19910701 GOOD NGS PL0314 HISTORY - 19920824 GOOD MIDT PL0314 HISTORY

- 19921024 GOOD MIDT PL0314 HISTORY - 19971029 GOOD USPSQD PL0314 PL0314 STATION DESCRIPTION PL0314 PL0314'DESCRIBED BY NATIONAL GEODETIC SURVEY 1951 PL0314'IN INTERLOCHEN. PL0314'AT INTERLOCHEN, 131 FEET EAST OF THE JUNCTION OF THE ABANDONED PL0314'BRANCH OF THE MANISTEE AND NORTHEASTERN RAILROAD AND THE C AND Sample Datasheet

National Geodetic Survey, Retrieval Date = DECEMBER 28, 2005 PL0314 *********************************************************************** PL0314 DESIGNATION - V 27 PL0314 PID - PL0314 PL0314 STATE/COUNTY- MI/GRAND TRAVERSE PL0314 USGS QUAD PL0314 PL0314 *CURRENT SURVEY CONTROL PL0314 ___________________________________________________________________ PL0314* NAD 83(1994)- 44 39 02.41202(N) 085 46 04.27942(W) ADJUSTED PL0314* NAVD 88 257.838 (meters) 845.92

(feet) ADJUSTED PL0314 ___________________________________________________________________ PL0314 X 335,419.145 (meters) COMP PL0314 Y - -4,532,722.532 (meters) COMP PL0314 Z 4,459,971.520 (meters) COMP PL0314 LAPLACE CORR5.18 (seconds) DEFLEC99 PL0314 ELLIP HEIGHT223.17 (meters) (07/17/02) GPS OBS PL0314 GEOID HEIGHT-34.68 (meters) GEOID03 PL0314 DYNAMIC HT 257.812 (meters) 845.84 (feet) COMP PL0314 MODELED GRAV980,508.8 (mgal) NAVD 88 PL0314 NAVD88 Ellip Ht + Geoid Ht = 257.838 223.17 34.953 = -0.285 USGG2003 257.838 223.17 34.68 = -0.012 GEOID03

H h N Whats Left? Leveling-Derived Orthometric Heights Modeled Geoid Heights GPS-Derived Ellipsoid Heights Guidelines N O A A T e c h n ic a l M e m o r a n d u m N O S N G S - 5 8 G U ID E L I N E S F O R E S T A B L I S H I N G G P S - D E R I V E D E L L IP S O I D H E IG H T S (S T A N D A R D S : 2 C M A N D 5 C M ) V E R S IO N 4 .3 D a v id B . Z ilk o s k i J o s e p h D . D 'O n o f r i o S te p h e n J . F ra k e s S i lv e r S p r i n g , M D Novem ber 1997 U .S . D E P A R T M E N T O F COMMERCE

N a t i o n a l O c e a n ic a n d A t m o s p h e r i c A d m i n i s t r a ti o n N a t io n a l O c e a n S e r v ic e N a t io n a l G e o d e t i c S u rv e y Available On-Line at the NGS Web Site: www.ngs.noaa.gov GPS Error Sources Orbit and clock error Broadcast v.s. Predicted Precise v.s. Post-processed Clock error corrections Atmospheric Effects Ionosphere, Troposphere Multipath Height of phase center above mark Atmosphere-based Ionospheric Delay Ionosp

< 10 km here > 10 km Multipath h Figure 1 Multipath Description August 1987 -Ionospheric refraction and Multipath Effects in GPS Carrier Phase Observations Yola Georgiadou and Alfred Kleusberg IUGG XIX General Assembly Meeting, Vancouver, Canada Components of NGS-58 Equipment requirements Field Procedures/Data Collection Parameters Basic Control Requirements Processing/Analysis Procedures

Equipment Requirements Dual-frequency, full-wavelength GPS receiver Required - observations > 10 km Preferred - ALL observations regardless of length Geodetic quality antennas with ground planes Choke ring antennas; highly recommended Successfully modeled L1/L2 offsets and phase patterns Use identical antenna types if possible Corrections must be utilized by processing software when mixing antenna types Equipment Requirements Fixed Height Tripod Fixed-height tripods required for 2 cm standard Fixed-height poles preferred for 5 cm standard Data Collection Parameters

VDOP < 6 for 90% or longer of 30 minute session Shorter session lengths stay < 6 always Schedule travel during periods of higher VDOP Session lengths > 30 minutes collect 15 second data Session lengths < 30 minutes collect 5 second data Track satellites down to 10 elevation angle Repeat Baselines Different days Different times of day Detect, remove, reduce effects due to multipath and having almost the same satellite geometry Gg REPEAT BASELINE DIFFERENCES BY DISTANCE 172 BASELINES - 3% Above 3 cm Gg REPEAT DIFFERENCES (CM) 6 5 gg

0113-H83A 4 3.1 1933-0121 3.1 6669-6666 4.9 6669-0092 4.7 0092-1933 3.1 3 2 1 0 0 5000 10000

15000 20000 25000 30000 35000 40000 BASELINE LENGTH (M) Station pairs with large residuals, i.e., greater than 2.5 cm, also have large repeat base line differences. NGS guidelines for estimating GPS-derived ellipsoid heights require user to re-observe these base lines. Following NGS guidelines provides enough redundancy for adjustment process to detect outliers and apply residual on appropriate observation, i.e., the bad vector. FREE ELLIPSOID HEIGHT RESIDUAL BY BASELINE LENGTH 455 BASE LINES - 2.6% ABOVE 3 cm 7 6 0092-0039

5.1 0113-H83A 3.1 5 0092-0039 3.8 4 3 0114-0913 2.6 RESIDUAL (CM) 6666-6669 -4.9 1933--0121 3.1 2 1 0 -1 -2 -3

6666-6669 -4.9 1933-0092 -3.1 -4 -5 0038-0913 -3.7 -6 6669-0092 -6.5 0127-6294 --3.5 -7 0.0 5.0 10.0 15.0

20.0 1933-0092 -6.5 25.0 30.0 35.0 BASE LINE LENGTH (KM) After performing minimum constraint adjustment, plot ellipsoid height residuals (or dU residuals) and investigate all residuals greater than 2 cm. 40.0 Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE (30 Minute solutions computed on the hour and the half hour) -10.254 > -10.253 -10.251 MOLA to RV22 10.8 Km dh (m)

Hours Diff. Day 265 27hrs 17:00-17:30 27hrs 17:30-18:00 27hrs 18:00-18:30 27hrs 18:30-19:00 27hrs 19:00-19:30 27hrs

19:30-20:00 27hrs 20:00-20:30 27hrs 20:30-21:00 21hrs 15:00-15:30 21hrs 15:30-16:00 21hrs 16:00-16:30 21hrs 16:30-17:00 18hrs

14:00-14:30 20:30-21:00 -10.281 -10.278 -10.281 -10.291 -10.274 -10.287 -10.279 -10.270 -10.277 -10.271 -10.277 -10.271 -10.259 -10.254 18hrs 14:00-21:00 -10.275 Day 264 14:00-14:30

14:30-15:00 15:00-15:30 15:30-16:00 16:00-16:30 16:30-17:00 17:00-17:30 17:30-18:00 18:00-18:30 18:30-19:00 19:00-19:30 19:30-20:00 20:00-20:30 Two Days/Same Time dh (m) Day 264 * minus diff Mean dh Day 265 >2 (m) (cm) cm 14:30-15:00 -10.279 -10.270

-10.278 -10.274 -10.274 -10.276 -10.261 -10.251 -10.270 -10.276 -10.278 -10.286 -10.278 -10.295 -0.2 -0.8 -0.3 -1.7 0.0 -1.1 -1.8 -1.9 -0.7 0.5 0.1 1.5 1.9 4.1

14:00-21:00 -10.276 0.1 * -10.280 -10.274 -10.280 -10.283 -10.274 -10.282 -10.270 -10.261 -10.274 -10.274 -10.278 -10.279 -10.269 -10.275 "Truth" -10.276 Mean dh * minus diff "Truth" >2

(cm) cm -0.5 0.2 -0.4 -0.7 0.2 -0.6 0.6 1.5 0.2 0.2 -0.2 -0.3 0.7 0.1 Difference = 0.3 cm Truth = -10.276 Difference = 2.3 cm Two Days/ Different Times -10.254 -10.295 > -10.275 Difference = 4.1 cm Truth = -10.276 Difference = 0.1 cm Four Basic Control Requirements

Occupy stations with known NAVD 88 orthometric heights Stations should be evenly distributed throughout project Project areas < 20 km on a side, surround project with NAVD 88 bench marks i.e., minimum number of stations is four; one in each corner of project Project areas > 20 km on a side, keep distances between GPSoccupied NAVD 88 bench marks to less than 20 km Projects located in mountainous regions, occupy bench marks at base and summit of mountains, even if distance is less than 20 km Sample Project Area: East San Francisco Bay Project Latitude 37 50 N to 38 10 N Longitude 121 45 W to 122 25 W Receivers Available: 5 Standards: 2 cm GPS-Derived Heights Primary Base Stations 3820N CORS HARN NAVD88 BM

New Station D191 19.0km 10CC km 29.6km 31 .6k m .7 38 m 7k 28. m 25.7k LATITUDE Primary Base Station

MART 38 .3k m 25.8km LAKE MOLA 3750N 12235W LONGITUDE 12140W GPS-Usable Stations CORS HARN NAVD88 BM New Station Spacing Station Primary Base Station

8.2km Observation Sessions 3816N Session F CORS HARN NAVD88 BM New Station Spacing Station Session E Session D LATITUDE Primary Base Station Session G Session A 3755N 12220W Session B

LONGITUDE Session C 12140W Independent Base Lines 3816N F CORS HARN NAVD88 BM New Station Spacing Station F E F E G Primary Base Station D E

LATITUDE F E D D G D G A G C B A A B C B

A 8.2km C B C 3755N 12220W LONGITUDE 12140W Processing: Five Basic Procedures Perform 3-D minimally constrained (free) adjustment Analyze adjustment results Compute differences between GPS-derived orthometric heights from free adjustment and published NAVD88 BMs Evaluate differences to determine which BMs have valid NAVD88 height values Perform constrained adjustment with results

from previous step Appendix B: GPS Ellipsoid Height Hierarchy HARN/Control Stations (75 km) 5.5 hr 3 days different times Primary Base (40 km) 5.5 hr 3 days different times Secondary Base (15 km) 0.5 hr 2 days different times Local Network Stations (7 to 10 km) 0.5 hr 2 days different times Start with CORS Harbor Beach Mt. Pleasant Bayer at Saginaw Next Level - Michigan HARN

Have good NAVD88 Control L26235, phases 1 & 2, courtesy of students at Ferris State University Height Modernization Project HARN - Average 50km, max 75km Primary 20-25km, max 40km = = = = HARN Primary Base Network Secondary Base Network Local Base Network Secondary - Average 12-15km, max 15km Local Average 6-8 km, max 10km = Existing NGS Level line = New HMP Level line Basic Concept of Guidelines

Stations in local 3-dimensional network connected to NSRS to at least 5 cm uncertainty Stations within a local 3-dimensional network connected to each other to at least 2 cm uncertainty Stations established following guidelines are published to centimeters by NGS Network / Local Accuracy Sample Datasheet Leveling

1 National Geodetic Survey, Retrieval Date = NOVEMBER 25, 2003 *********************************************************************** DESIGNATION - 2K76 PID - AI6151 STATE/COUNTY- WI/WASHINGTON USGS QUAD - ALLENTON (1971) AI6151 AI6151 AI6151 AI6151 AI6151 AI6151 AI6151 AI6151 AI6151* AI6151* AI6151 AI6151 AI6151

AI6151 AI6151 *CURRENT SURVEY CONTROL ___________________________________________________________________ NAD 83(1997)- 43 25 39.39446(N) 088 18 24.15369(W) ADJUSTED NAVD 88 343.002 (meters) 1125.33 (feet) ADJUSTED ___________________________________________________________________ X 137,097.884 (meters) COMP Y - -4,637,622.691 (meters) COMP Z 4,362,336.158 (meters) COMP AI6151 . . . AI6151 The orthometric height was determined by differential leveling AI6151 and adjusted by the National Geodetic Survey in October 2000. AI6151

Sample Datasheet - GPS 1 National Geodetic Survey, Retrieval Date = JUNE 7, 2004 HL0673 *********************************************************************** HL0673 DESIGNATION - FAA 5CO0 B HL0673 PID - HL0673 HL0673 STATE/COUNTY- CO/LA PLATA HL0673 USGS QUAD

- LOMA LINDA (1968) HL0673 HL0673 *CURRENT SURVEY CONTROL HL0673 ___________________________________________________________________ HL0673* NAD 83(1992)- 37 12 34.23430(N) 107 51 59.34354(W) ADJUSTED HL0673* NAVD 88 2038.7 (meters) 6689. (feet) GPS OBS HL0673 ___________________________________________________________________ HL0673 X - -1,560,867.458 (meters) COMP HL0673 Y - -4,842,221.299 (meters) COMP HL0673 Z 3,837,158.007 (meters) COMP HL0673. . . HL0673 The orthometric height was determined by GPS observations and a HL0673 high-resolution geoid model. HL0673

Sample Datasheet GPS Using NGS58 OM1256 OM1256 OM1256 OM1256 OM1256 OM1256 OM1256 OM1256 OM1256* OM1256*

OM1256 OM1256 OM1256 OM1256 CBN DESIGNATION PID STATE/COUNTYUSGS QUAD - This is a Cooperative Base Network Control Station. CAMBRIA GPS OM1256 WI/COLUMBIA RANDOLPH (1980) *CURRENT SURVEY CONTROL ___________________________________________________________________ NAD 83(1997)- 43 34 10.47581(N) 089 06 09.35995(W) ADJUSTED NAVD 88 303.84 (meters) 996.8 (feet) GPS OBS ___________________________________________________________________ X

72,495.418 (meters) COMP Y - -4,628,194.515 (meters) COMP Z 4,373,750.772 (meters) COMP OM1256 . . . OM1256.The orthometric height was determined by GPS observations and a OM1256.high-resolution geoid model using precise GPS observation and OM1256.processing techniques. Goal Achieved? With the means to get more accurate ellipsoid heights, we can now use these ellipsoid heights on benchmarks to further improve the geoid model. With the improved geoid model we can use GPS to compute accurate orthometric heights. Questions? http://www.ngs.noaa.gov/heightmod/ MichiganMarquetteAgenda.pdf http://www.ngs.noaa.gov/heightmod/

MichiganFlintAgenda.pdf Renee Shields Grants Manager N/NGS1, SSMC3 1315 East-West Highway Silver Spring, MD 20910 301-713-3231, x116 www.ngs.noaa.gov [email protected]

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