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Edit Comment Close Premium member Presentation Transcript The NGS Gravity Program and Geoid ModelingProfessional Land Surveyors of Colorado2006 Fall Technical Program and Annual Meeting: The NGS Gravity Program and Geoid Modeling Professional Land Surveyors of Colorado 2006 Fall Technical Program and Annual Meeting Daniel R. Roman National Geodetic Survey National Oceanic and Atmospheric AdministrationOUTLINE OF TALK: OUTLINE OF TALK Introduction Overview of current gravimetric geoid models Overview of current hybrid geoids Heights and the datasheet Plans for Geoid Modeling at NGS Ongoing research areas Of local interest ConclusionsGEOIDS versus GEOID HEIGHTS: GEOIDS versus GEOID HEIGHTS “The equipotential surface of the Earth’s gravity field which best fits, in the least squares sense, (global) mean sea level.”* Can’t see the surface or measure it directly. Can be modeled from gravity data as they are mathematically related. Note that the geoid is a vertical datum surface. A geoid height is the ellipsoidal height from an ellipsoidal datum to a geoid. Hence, geoid height models are directly tied to the geoid and ellipsoid that define them (i.e., geoid height models are not interchangeable). *Definition from the Geodetic Glossary, September 1986In Search of the Geoid…: In Search of the Geoid… Courtesy of Natural Resources Canada www.geod.nrcan.gc.ca/index_e/geodesy_e/geoid03_e.htmlHigh Resolution Geoid ModelsG99SSS (Scientific Model): Earth Gravity Model of 1996 (EGM96) 2.6 million terrestrial, ship-borne, and altimetric gravity measurements 30 arc second Digital Elevation Data 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 G99SSS (Scientific Model)High Resolution Geoid ModelsUSGG2003 (Scientific Model): 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 originSlide7: Gravity Coverage for GEOID03Ellipsoid, Geoid, and Orthometric Heights: H H = Orthometric Height (NAVD 88) H = h - N TOPOGRAPHIC SURFACE h = Ellipsoidal Height (NAD 83) N = Geoid Height (GEOID 03) Ellipsoid, Geoid, and Orthometric Heights A BComposite Geoids: Composite Geoids Gravity Geoid systematic misfit with benchmarks Composite Geoid biased to fit local benchmarks e = h – H - N Earth’s Surface Ellipsoid Hybrid or Composite Geoid =~ NAVD 88 Gravity Geoid 0.055 M in Lakewood, CO – 1999 model 0.015 M in Lakewood, CO – 2003 modelHigh Resolution Geoid ModelsGEOID03 (vs. Geoid99): 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 USGG2003High Resolution Geoid ModelsGEOID03 (vs. Geoid99): High Resolution Geoid Models GEOID03 (vs. Geoid99) Relative to non-geocentric GRS-80 ellipsoid 2.4 cm RMS nationally when compared to BM data (vs. 4.6 cm) RMS 50% improvement over GEOID99 (Geoid96 to 99 was 16%)GEOID03 Conversion Surface: GEOID03 Conversion SurfaceSlide15: GEOID99 Conversion SurfaceSample 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 CORR- 5.18 (seconds) DEFLEC99 PL0314 ELLIP HEIGHT- 223.17 (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 GRAV- 980,508.8 (mgal) NAVD 88 PL0314 Sample Datasheet N H h 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 DatasheetSample 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 FT 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 DatasheetSample 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 DatasheetSample 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 CORR- 5.18 (seconds) DEFLEC99 PL0314 ELLIP HEIGHT- 223.17 (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 GRAV- 980,508.8 (mgal) NAVD 88 PL0314 Sample Datasheet N H h NAVD88 – Ellip Ht + Geoid Ht = … 257.838 – 223.17 – 34.953 = -0.285 USGG2003 257.838 – 223.17 – 34.68 = -0.012 GEOID03Plans for Geoid Modeling at NGS: Plans for Geoid Modeling at NGS Near term plans are to define gravimetric geoids and hybrid geoids for all U.S. territories (USGG2006 & GEOID06). Gravimetric geoids would all have a common Wo value (geoid datum) and be based on GRACE-based global gravity models such as the forthcoming EGM06 from NGA Gravimetric geoids will be tested against tide gauges and lidar-observed sea surface heights to confirm choice of Wo. Hybrid geoids would be tied to NAD 83 & local vertical datums NAVD 88 for Alaska and CONUS PRVD02 for Puerto Rico Etc. The quality of VDatum will be improved as the ties between the oceanic and terrestrial datums are better understood. Likewise, it would be very useful in providing decimeter or better accurate heights to estimate flooding potential.Slide22: Long term goals are to define a cm-level accurate geoid height model valid for all of North America Work is ongoing with the Canadians Other nations joining in (Mexico/INEGI, etc.) We likely will also adopt a vertical datum based on a refined geoid height model – the ultimate in Height Mod! Conversion surface will provide means of transforming between this new datum and NAVD 88 – much as VERTCON does now between NGVD 29 and NAVD 88. This maintains compatibility with archival data. To do this, several major areas need work: Gravity database cleansing/analysis/standardization Acquisition of additional data sets Refinement of geoid theory Plans for Geoid Modeling at NGS (cont.)Slide23: We must have a consistent and seamless gravity field at least along the shorelines if not across all the U.S. Use GRACE data to test long wavelength accuracy. Use aerogravity to locate and possibly clean systematic problems in terrestrial or shipborne surveys (biases, etc.). Determine and remove any detected temporal trends in the nearly 60 years of gravity data held by NGS. Ensure consistency of datums, corrections and tide systems. This solves problems of current remove-compute-restore approach, which honors terrestrial data over EGM’s. Exploration of utility of coastal/littoral aerogravity Need a consistent gravity field from onshore to offshore. Aids in database cleansing; also fills in coastal gaps. Ties to altimetric anomalies in deeper water. In conjunction with tide gauges & dynamic ocean topography models, this will aid in determining the optimal geopotential surface for the U.S. (Wo). Ongoing research areasSlide24: Must acquire data and models for outlying regions. Definitely need surface gravity (terrestrial and shipborne) and terrain models for Guam, CNMI, American Somoa. Desire to get such for nearest neighbors including Mexico, Caribbean nations, Central American nations, etc. Also need to get any available forward geophysical models for all regions (such as ICE-5G for modeling the Glacial Isostatic Adjustment). GPS/INS evaluation of the gravity field. GPS & IMU information were also collected on flights. This data can be used to derive gravity disturbances and to estimate gravity anomalies. It may be useful in benign areas for determining the gravity field. Possibly cheaper and more cost-effective than aerogravity (run with other missions?). Ongoing research areas (cont.)Slide25: Geodetic theory improvements. Downward continuation of high altitude gravity observations. Merging of gravity field components. Current approach is remove-compute-restore. Spectral merging of EGM, gravity and terrain data. Would honor long wavelength (GRACE). Retain character of the terrain and observed data. Determination of geoid height using ellipsoidal coordinates instead of the spherical approximation. Resolution of inner and outer zone effects from terrain on gravity observations. Ongoing research areas (cont.)Slide26: Geoid Ellipsoid Earth’s Surface Coast Ellipsoid Ht From GPS How “high above sea level” am I? (FEMA, USACE, Surveying and Mapping) Ocean Surface From Satellite Altimetry How large are near-shore hydrodynamic processes? (Coast Survey, CSC, CZM) Gravity measurements help answer two big questions… Geoid Height From Gravity Orthometric Ht From Leveling Extent of Gravity and Data Collection Flights: Extent of Gravity and Data Collection FlightsImplied Geoid Changes: Implied Geoid ChangesGPS/INS-Derived Aerogravity vs. Surface Point Gravity in CA: GPS/INS-Derived Aerogravity vs. Surface Point Gravity in CAGEOID03 Conversion Surface: GEOID03 Conversion SurfaceSlide31: A Consistent vertical datum between all U.S. states and territories as well as our neighbors in the region. Reduce confusion between neighboring jurisdictions. Local accuracy but national consistency. This provides a consistent datum for disaster management. Storm surge, tsunamis, & coastal storms. Disasters aren’t bound by political borders. Heights that can be directly related to oceanic and hydrologic models (coastal and inland flooding problems). The resulting improvements to flood maps will better enable decision making for who does & doesn’t need flood insurance. Updates to the model can be made more easily, if needed, to reflect any temporal changes in the geoid/gravity. Finally, offshore models of ocean topography will be improved and validated. These models will provide better determination of offshore water flow (useful for evaluating the movement of an oil slick). Expected ResultsQUESTIONS?: QUESTIONS? Geoid Research Team: Dr. Daniel R. Roman, research geodesist firstname.lastname@example.org Dr. Yan Ming Wang, research geodesist email@example.com Jarir Saleh, ERT contractor, gravity database analysis William Waickman, programming & database access Website: http://www.ngs.noaa.gov/GEOID/ Phone: 301-713-3202 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.