bathymetry from satellite altimetry - hydro conferences - …€¦ · · 2017-12-11bathymetry...
TRANSCRIPT
Bathymetry from satellite altimetryPau Gallés
Research and services provider enterprise in the Earth Observation Field
INDEX
HYDRO 2016 – 9th November – BASE platform 2
1. Introduction
• Approach
• The Principle
2. Method
• Sea surface height
• Gravity anomalies
• Bathymetry
3. Results
4. Ongoing tasks
Bathymetry from altimeter
• Our approach
– Open ocean bathymetry
– Optimized local calculations
– New SAR mode
• Geological features
– Plate tectonics
– Mid-ocean ridges
– Volcanic chains
– Submarine landslides
– Submarine canyons
– …
@USGS
@NASA
@NOAA
HYDRO 2016 – 9th November – BASE platform 3
The Principle
• Seafloor topography creates gravity anomalies tilting the ocean surface (measurable by radar)
– Ocean surface tilts can be interpreted as an anomaly in direction of gravity (deflection of the vertical)
– Measured deflections converted to gravimetric anomalies through Laplace’sEquation
– Bathymetric maps obtained exploiting correlation of bathymetry with gravity (inverse transfer function)
@Smith & Sandwell, 2004
HYDRO 2016 – 9th November – BASE platform 4
Method - Sea Surface Height
• 2 modes: LRM, SAR
• Delay Doppler
– LRM resolution cells are rings.
– SAR mode also has along track divisions generating greater amount of resolution cells.
• Retracking
– Analytical models for the waveform fitting
HYDRO 2016 – 9th November – BASE platform 5
http
://ww
w.altim
etry.info
/
L2 Sea Surface Height
• Data pattern
– Cryosat2 > N-S
– Jason1 > E-W
– Multi satellite > slopes
• Geophysical corrections
• Permanent effects
– Average data
– Filter long wavelengths
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x
y
α
HYDRO 2016 – 9th November – BASE platform 6
Gravity Spectrum
EGM2008 SSH Up.Con.
~180 km ~10km
Spherical harmonicsDegree and order > 2000
inten
sity
HYDRO 2016 – 9th November – BASE platform 7
[Pavlis et al., 2008].
High Resolution Gravity
• Remove – Restore
• DOV
• Planar approach
Sandwell & Smith (1997)
>10km from shore
> 2km depth
• The approximation is good when local undulations are small compared with a constant regional depth
• The lack of land data effects about 10 km from shore
HYDRO 2016 – 9th November – BASE platform 8
Bathymetry
• Isostatic compensation (high-pass filter)
• Upward continuation (low-pass filter)
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ρ_mantle < ρ_crust → Buoyancy
CrustUpper mantle
Δg ≈ 0
inten
sityHYDRO 2016 – 9th November – BASE platform 9
Density
• Unknown Density
HYDRO 2016 – 9th November – BASE platform 10
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Mauritian Islands – LRM mode by ESA
[m]
isardSAT GEBCO DTU
isardSAT
DTUGEBCO
222 224
222
RMS [meters]
[km] [km][km]
HYDRO 2016 – 9th November – BASE platform 11
SAR mode processed by isardSAT
• Central Pacific
• RMSE against its fitted version
HYDRO 2016 – 9th November – BASE platform 12
Delay Doppler and Retracking
MERGE
algorithms
LRM mode algorithm
SAR
Delay Doppler and Retracking
SAR modebathymetry
HYDRO 2016 – 9th November – BASE platform 13
THANK YOU!
HYDRO 2016 – 9th November – BASE platform