motivation: much of the deep ocean floor is uncharted by ships high spatial resolution gravity can...
TRANSCRIPT
•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)
Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1*
David Sandwell Emmanuel GarciaKhalid SoofiPaul Wessel
Walter H. F. Smith
•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
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
Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1
2-pass retracking to improve range precision
1) retrack waveforms with standard 3-parameter model
2) smooth wave height and amplitude over 40-km
3) retrack waveforms with 2-parameter model
Note: this assumes wave height varies smoothly along track.
[Sandwell and Smith, GJI, 2005]
•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
Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1
comparisons in the Gulf of Mexico
ship gravitysatellite gravitywith CryoSat LRM, Envisat and Jason-1
5 mGal contour interval
source: EDCON
spatial comparisons in the Gulf of Mexico
Noise contribution from the EDCON data is 0.51 mGal.
V18Geosat ERS-1
V22CryoSat-2Jason-1EnvisatGeosat ERS-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
Towards 1 MilliGal Global Marine Gravity from CryoSat, Envisat, and Jason-1
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.
V22 – CryoSat-2, Jason-1, Envisat, ERS-1, GeosatV18 – ERS-1, Geosat
What is the contribution from each altimeter?Do we still need ERS-1 and Geosat?
actual gravity improvement
total improvement
CryoSat-2 providessignificant noise reduction over all latitude bands.
Jason-1 mainly improves east component between +/- 66.
improvement
improvement
Envisat provides greatest noise reduction in Arctic and Antarctic.
Geosat improves east component at low latitudes and east component in 66-72 latitude band
improvement
improvement