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45 th Annual Alaska Surveying & Mapping Conference February 21-25, 2011 Hilton Anchorage Hotel Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska Part III: Geoid Modeling. Daniel R. Roman and Vicki A. Childers. Outline. Introduction Crossovers - PowerPoint PPT Presentation
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45th Annual Alaska Surveying & Mapping ConferenceFebruary 21-25, 2011 Hilton Anchorage Hotel
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Part III: Geoid Modeling
Daniel R. Roman and Vicki A. Childers
Outline
• Introduction• Crossovers• Gridded Residual Gravity• Equivalent Geopotential• Residual Terrain Modeling• Future Geoid Models• Outlook
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12002
Introduction
• Airborne gravity = Aerogravity• Relative gravity observations (i.e., need a base)• Collected on a fast-moving platform (400-500 kmh)• Kinematic GPS fixes positions• Also helps to determine gravity (a/c accelerations)• Very complicated process to “observe” aerogravity• Product is a function of observations and processing• Lastly, it is observed at very high altitudes (20 kft)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12003
Purpose of GRAV-D
• Aerogravity are for a geoid – not a gravity grid• A pattern of observation poor for gravity
might be sufficient for geoid determination• The longest wavelengths affect the geoid• Gravity data highlight shorter wavelengths• Random gravity observation errors are “short”• Transformation into geoid effectively removes• Systematic errors are the cause of geoid errors45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12004
Creating a Gravimetric Geoid
• Satellites provide global consistency & accuracy• GRACE has been up a long time – likely follow-on• GOCE supplements coverage of GRACE• Combined satellite model would cover 200 km >• Significant errors exist below 200 km• GRAV-D aerogravity will help to resolve these• Terrain modeling captures the smallest features• Melding all these together remains the challenge45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12005
Crossover Plots for AK08
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12006
AK08 Residual Gravity Profiles
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12007
AK08 Residual Geopotential (N=1440)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12008
AK08 Residual Geopotential (Min=175, Max=1440)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12009
Crossover Plots for AK09
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120010
AK09 Gridded Residual Gravity
AK09 Residual Geopotential (N=1440)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120012
AK09 Residual Geopotential (Min=175, Max=1440)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120013
Statewide Geoid Modeling• Each month-long survey covers 400x500 km• All surveys collected in a consistent manner• All constrained to a GRACE/GOCE model• GRACE/GOCE will account for long wavelengths• Aerogravity will bridge the gap to surface data• Shortest wavelengths will come from DEM’s• Must properly account for all these signals• “Short” wavelength gravity can have big effects45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120014
Residual Terrain Modeling
• Terrain creates the smallest gravity signal• Density contrast between rock and air• EGM2008 accounted for signal to 5’ (10 km)• Remaining signal between 5’ and 3” (90 m)• This neglected signal has a systematic effect• Examples are given for CONUS and Alaska
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120015
Point Gravity Minus EGM2008
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120016
RTM Gravity Signal from 3” to 5’
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120017
Point Gravity Less EGM2008 and RTM
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120018
Filtered Residual Gravity
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120019
Equivalent Residual Geoid
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120020
Alaska RTM• For CONUS, SRTM was available for uniformity• In Alaska, several models were melded into one– SRTM below 60 N Latitude– NED was used for Alaska– CDED was used in Canada– GTOPO30 was used in Russia– Dr. Xiaopeng Li used GPSBM’s to unify them all– Final grid is improved, but probably not consistent
• ASTER was looked at but didn’t perform as well45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120021
Combined Terrain Models
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120022
Alaska DEM (USGG2009)
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120023
Point Gravity Minus EGM2008
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120024
RTM Gravity Signal from 3” to 5’
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120025
Point Gravity Less EGM2008 and RTM
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120026
RTM Summary
• RTM signal 3”-5’ significantly helped• Residual gravity much reduced• DEM for CONUS is from SRTM 3” – uniformity• DEM for Alaska built from many sources• In CONUS, long wavelength residuals– Small signal but yields big geoid residual– No equivalent signal for Alaska – too many gaps
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120027
Future Geoid Models
• By the end 2012, plan is to be about 80% done• Comparison to Canadian data in overlap regions• Potentially, in next national gravimetric geoid– (e.g. USGG20xx)
• GRACE/GOCE - long wavelengths (200 km >)• Aerogravity – mid-wavelengths (20 - 400 km)• RTM – short wavelengths (0.1 – 20 km)• Terrestrial gravity – all wavelengths – just too few45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120028
Outlook• Aerogravity is improving local gravity field• Significant improvements being implemented• Aim is for 2 mgal crossovers or better• Random errors have minimal impact• Systematic errors create geoid errors• Aerogravity will bridge satellite and terrestrial • DEM’s provide shortest wavelengths• Satellite, airborne, terrestrial, & terrain all merged• Removing errors in each yields an accurate geoid
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120029
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-12003030
Questions?GEOID Team• Daniel R. Roman, Ph.D.• Yan Ming Wang, Ph.D.• Xiaopeng Li, Ph.D. (ERT)• Simon Holmes, Ph.D. (SGT)
Websites• http://www.ngs.noaa.gov/GEOID/• http://www.ngs.noaa.gov/GRAV-D/
Aerogravity Team• Vicki A. Childers, Ph.D.• Theresa Diehl, Ph.D.• Sandra A. Preaux (DST)
Processing Support• William Waickman • Xu Yang (SGT)
Why we didn’t use Aster
45th Annual Alaska Surveying & Mapping Conference February 21-25, 2011
Impact of Airborne Gravity Surveys on Geoid Modeling in Alaska
Thursday, 0800-120031