1 / 16

Advances and Best Practices in Airborne Gravimetry from the U.S. GRAV-D Project

Advances and Best Practices in Airborne Gravimetry from the U.S. GRAV-D Project. Theresa M. Damiani 1 , Vicki Childers 1 , Sandra Preaux 2 , Simon Holmes 3 , and Carly Weil 2 U.S. National Geodetic Survey Data Solutions and Technology Earth Resources Technology. What is GRAV-D?.

lecea
Download Presentation

Advances and Best Practices in Airborne Gravimetry from the U.S. GRAV-D Project

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Advances and Best Practices in Airborne Gravimetry from the U.S. GRAV-D Project Theresa M. Damiani1, Vicki Childers1, Sandra Preaux2, Simon Holmes3, and Carly Weil2 U.S. National Geodetic Survey Data Solutions and Technology Earth Resources Technology

  2. What is GRAV-D? • Program critical to U.S. National Geodetic Survey’s (NGS’) mission to define, maintain, and provide access to the U.S. National Spatial Reference System • Gravity for the Redefinition of the American Vertical Datum • Official NGS policy as of Nov 14, 2007 • Re-define the Vertical Datum of the USA as a gravimetric geoid by 2022 (at current funding levels) • Airborne Gravity Snapshot • Absolute Gravity Tracking • Target: 2 cm accuracy orthometricheights EGU Conference

  3. Requirements • To achieve the target 1-2 cm accuracy of the geoid will require: • GRACE and GOCE • Highly accurate (1 mGal) airborne gravity data across the nation • Improved terrestrial gravity data • Accurate residual terrain modeling • Geoid theory and spectral data blending • Re-evaluate sources of error in airborne gravity methods: collection (3 slides) and processing (3 slides). • After five years and > 27% of the country surveyed, significant improvements have been made: Case Study: 2008 Alaska Survey (6 slides).

  4. Data Collection Best Practices • Remove Gravity Tie Bias Uncertainty • Measurements at Aircraft Parking Spot: • Absolute Gravity (Micro-g LaCoste A-10) • Vertical Gravity Gradient (G-meter and “G-pod”) G-meter w/ Aliod Parking spot ID A-10 “G-pod”

  5. Data Collection Best Practices • Gravimeter very close to center of gravity of aircraft • Navigation Grade IMU, mounted on top of TAGS • Multiple High-rate GNSS receivers on aircraft (GPS/GLONASS) • Lever Arm between instruments with surveying equipment Micro-g LaCoste TAGS Gravimeter NovAtel SPAN-SE w/ Honeywell µIRS IMU

  6. Data Collection Quality Control • >5 years, 14 operators, and 7 aircraft: Requires standardized checklists, worksheets, instructions, logbooks; Test Flights • Quality Control Guidelines: Troubleshooting Guides, Operating Specifications, and Visualization Tools

  7. Gravity Processing Advances • Past (1960s through 1980s): • Low & slow flights (low altitude, low velocity) • Less computation power resulted in use of small angle approximations and dropped terms in gravity correction equations • Desired < 10 mGal error, biases ok • GRAV-D: • High altitude, high velocity, desire as close to 1 mGal as possible • Recognition of OfflevelCorrection Limitations • Better Filtering • Discrete Derivatives • GPS and IMU research for positioning, aircraft heading/attitude calculations, and inputs to gravity corrections • Still Ongoing!

  8. Gravity Processing Advances Example: Eotvos Correction • Acceleration of a moving object in a rotating reference system Centrifugal Variation in rotation rate Coriolis Relative acceleration • Harlan 1968 • - defines r and ω in terms of latitude, longitude and ellipsoidal height • - 1st order approximation drops all terms <1 mgal to get an overall error <10 mgal Vertical Acceleration Eötvös Correction

  9. U.S. Latitudes: 30 to 50 degrees N; Europe Latitudes: 35 to 55 degrees N High & Fast Low & Fast Low & Slow

  10. Case Study: Alaska 2008 http://www.ngs.noaa.gov/GRAV-D/data_products.shtml • Crossover differences of same 202 points for all versions • Airborne gravity compared with EGM2008 at altitude

  11. Crossover Difference Maps Newton (IMU) AeroGrav Newton (no IMU)

  12. Crossover Statistics • From 2008 to 2012: • 65.0% Decrease in Range • Mean about the same (within error range) • 61.5% Decrease in Standard Deviation • Increased Internal Consistency of Airborne Data, solely due to data processing advances

  13. Difference with respect to EGM2008 NGS Terrestrial Gravity Newton (no IMU) AeroGrav Newton (IMU)

  14. High-frequency Spectral Analysis • Create three GRAV-D airborne gravity ellipsoidal harmonic models (with EGM2008 outside the area) out to n=2159. • Inside the survey area, compare airborne models with increasing n from 360 to 2159 with EGM2008 (always n=2159) • This modeling is for evaluation purposes only. Model 1: AeroGrav n=2159 Model 2: Newton (no IMU) EGM2008 N=2159 GRAV-D n=361 GRAV-D n=362 GRAV-D n=360 GRAV-D n=2159 Model 3: Newton (IMU) EGM2008

  15. 2008 to 2012 Improvement Childers et al., 1999 Estimated Resolution n≈1450 13.8 km n≈1700 11.75 km 55 km 27 km 18.5 km 14 km 11 km 9 km

  16. Thank You • Airborne Gravity Data Products Portal: • http://www.ngs.noaa.gov/GRAV-D/data_products.shtml • More information: • http://www.ngs.noaa.gov/GRAV-D • Contacts: • Dr. Theresa Damianitheresa.damiani@noaa.gov • GRAV-D Program Manager, Dr. Vicki Childersvicki.childers@noaa.gov Green = Blocks Available for Download

More Related