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motivation: much of the deep ocean floor is uncharted by ships

Towards 1 MilliGal Global Marine Gravity from CryoSat , Envisat , and Jason- 1* David Sandwell Emmanuel Garcia Khalid Soofi Paul Wessel Walter H. F. Smith. motivation: much of the deep ocean floor is uncharted by ships

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motivation: much of the deep ocean floor is uncharted by ships

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  1. Towards1 MilliGal Global Marine GravityfromCryoSat, Envisat, and Jason-1*David Sandwell Emmanuel GarciaKhalid SoofiPaul WesselWalter H. F. Smith • motivation: • much of the deep ocean floor is uncharted by ships • high spatial resolution gravity can reveal tectonic fabric, uncharted seamounts, and seafloor roughness • objectives: • spatial resolution < 6 km (1/2 wavelength) • accuracy < 2 mGal • (* published in: The Leading Edge, August, 2013)

  2. Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1 • higher accuracy = improved range precision + improved coverage • why retracking is essential for optimal gravity accuracy • retracking improves range precision by 1.5 times and reduces “spectral hump” • current gravity accuracy (V22.1 grid) • some tectonic examples

  3. Geosat – descending (18 mo. old)

  4. ERS-1 – descending (12 mo. old)

  5. Envisat – descending (new)

  6. CryoSat-2 – descending (34 mo. new)

  7. Jason-1 – ascending (14 mo. new)

  8. Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1 • higher accuracy = improved range precision + improved coverage • why retracking is essential for optimal gravity accuracy • retracking improves range precision by 1.5 times and reduces “spectral hump” • current gravity accuracy (V22.1 grid) • some tectonic examples

  9. 1 Hz data has inadequate spatial resolution

  10. 2-pass retracking to improve range precision • retrack waveforms with standard 3-parameter model • smooth wave height and amplitude over 40-km • retrack waveforms with 2-parameter model • Note: this assumes wave height varies smoothly along track. [Sandwell and Smith, GJI, 2005]

  11. jason w.r.t. V22 - 3par

  12. jason w.r.t. V22 - 2par

  13. 20 Hz range precision of all altimeters 3-parameter 2-parameter

  14. 2-pass retracking reduces “spectral hump”

  15. Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1 • higher accuracy = improved range precision + improved coverage • why retracking is essential for optimal gravity accuracy • retracking improves range precision by 1.5 times and reduces “spectral hump” • current gravity accuracy (V22.1 grid) • some tectonic examples

  16. Global Gravity Anomaly V22.1

  17. Gravity Anomaly V22.1 (10 mGal contours)

  18. comparisons in the Gulf of Mexico satellite gravity with CryoSat LRM, Envisat and Jason-1 ship gravity source: EDCON 5 mGal contour interval

  19. GPS Navigated Gravity survey of Alaminos Canyon (Alan Herring, personal communication, Dec. 2011.)

  20. spatial comparisons in the Gulf of Mexico V22 CryoSat-2 Jason-1 Envisat Geosat ERS-1 V18 Geosat ERS-1 Noise contribution from the EDCON data is 0.51 mGal.

  21. spectral comparisons in the Gulf of Mexico

  22. along track slope difference in microradian (0.98 mGal)

  23. current gravity accuracy accuracy ~1.6 mGal latitudes < 66˚ accuracy ~3.5 mGal in Arctic

  24. Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1 • higher accuracy = improved range precision + improved coverage • why retracking is essential for optimal gravity accuracy • retracking improves range precision by 1.5 times and reduces “spectral hump” • current gravity accuracy (V22.1 grid) • some tectonic examples

  25. vertical gravity gradient

  26. vertical gravity gradient old V18

  27. vertical gravity gradient new V22

  28. vertical gravity gradient new V22

  29. Conclusions • “newer” altimeters have 1.4 times better range precision and 2 times better coverage. • 2-pass waveform retracking provides 1.5 times range precision for all altimeters and reduces “spectral hump”. • Marine gravity accuracy is currently 1.6 – 3.5 mGal with most improvement in the 13 – 40 km wavelength band. • Most academic fleet ship gravity is less accurate than altimeter gravity. • The new V22 gravity has less filtering but lower noise so subtle tectonic features are now apparent. • We have not performed any long-wavelength corrections to the data so some corrections may improve areas of high mesoscale variability.

  30. actual gravity improvement V22 – CryoSat-2, Jason-1, Envisat, ERS-1, Geosat V18 – ERS-1, Geosat total improvement What is the contribution from each altimeter? Do we still need ERS-1 and Geosat?

  31. CryoSat-2 provides significant noise reduction over all latitude bands. improvement Jason-1 mainly improves east component between +/- 66. improvement

  32. Envisat provides greatest noise reduction in Arctic and Antarctic. improvement Geosat improves east component at low latitudes and east component in 66-72 latitude band improvement

  33. First attempt at comparing all academic fleet ship gravity (1500 cruises) with V21.1 satellite gravity courtesy of Paul Wessel. • The median absolute deviation between academic fleet gravity and satellite gravity is 2.75 mGal. • Most academic fleet cruises are less accurate than the satellite gravity.

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