Increasing the accuracy of Arctic gravity field modelling using Cryosat-2 SAR altimetry.
Ole B. Andersen, L. Stenseng and J. Maulik
EGU Vienna, April 20122 DTU Space, Technical University of Denmark
Outline
• What Cryosat offers
• Cryosat Problems:”Mode jumps”
• The Baffin Bay test.
• Retracking of Cryosat-2 SAR
• Towards DTU12
EGU Vienna, April 20123 DTU Space, Technical University of Denmark
Cryosat
Offers a factor of two in SSH accuracy
369 Day repeat (similar to ERS-GM)
SAR in Arctic+Coastal -> Alongtrack res improved
Important for shallow water (upward continuation)
Should improve gravity substantially
EGU Vienna, April 20124 DTU Space, Technical University of Denmark
The (mean) Sea surface height mimicks the geoid
Gravity from MDT corrected MSS (= Geoid) Laplace
)2(1
2)(r
N
r
N
r
T
r
TTLg g
1 mGal -> Alongtrack heights differences over 10 km need to be accurate to <1 cm
02
2
2
2
2
2
r
Satellite orbit
Altitude (H)Range (R)
Reference ellipsoid
GeoidSea surface
RHhsurface
errortidesIBDTgeoidssh hhhhhh
EGU Vienna, April 20125 DTU Space, Technical University of Denmark
Mode – jumps Cryosat ESA L2 GDR SAR+LRM in the Arctic
South North
Large ”jumps” at mode shift
Different between processors
LRM SAR SAR-In
EGU Vienna, April 20126 DTU Space, Technical University of Denmark
Baffin Bay • Interesting because its partly icecovered. • This enables comparison C2 SAR and LRM
EGU Vienna, April 20127 DTU Space, Technical University of Denmark
Cryosat SAR + LRMEntire 2011
LRM mode (summer)
SAR mode (winter)
EGU Vienna, April 20128 DTU Space, Technical University of Denmark
Retracking of Cryosat-2 SAR
Experimenting with 5 retrackers on 1 year Level 1b SAR waveform (black)
Entire waveform: OCOG + 5 parameter beta retracker with exp tail (blue)
and threshold retracking.
Leading Edge: OCOG and threshold retracking (50% for SAR)
(Se Poster XY348 by M. Jain today)
50% Th-
reshold
OCOG
LE OCOG
Range bin
EGU Vienna, April 20129 DTU Space, Technical University of Denmark
Retracking 1 Year 20 Hz SAR dataonly SSH data in leads used
Highpass to 100 km
Std (ESA L2 GDR) = 17.5 cm
Std (Leading Edge OCOG) = 11.1 cm
Std (Leading Edge Treshold) = 10.8 cm
Leads defined by ERS-L2 data.
EGU Vienna, April 201210 DTU Space, Technical University of Denmark
ERS GM ENVISAT+GFO ERM
ICESAT GEOSAT GM
CESAT
EGU Vienna, April 201211 DTU Space, Technical University of Denmark
Gravity comparison Identical parameter set to DTU10 for gravity comparison.
6696 obs Max Std
EGM2008 54 5.51
DTU10 47 4.89
ESA L2 SAR 44 4.66
NOAA LRM (2 month) 45 4.68
Entire WF retrack OCOG Beta 5 param Treshold
464241
4.744.194.12
Lead Edge retrack
OCOG
Treshold
39
39
4.01
3.96
OCOG SAR & SAR-in 38 3.96
Getting a 30% improvement
EGU Vienna, April 201212 DTU Space, Technical University of Denmark
Coastal regions heavily improvedDTU 2012 Beta
Including CRYOSAT LRM data
(ESA L2 vs NOAA)
Including CRYOSAT SAR data
Currently testing Cryosat SAR-IN
Working on adjust ”mode jumps”
Updating all existing GM data.
Standards DNSC08/DTU10 DTU12 Beta
Dry troposphere ECMWF ECMWFWet troposphere ECMWF RadiometerIonosphere Altimeter AltimeterDynamic Atmosphere IB (1013 mbar) MOG-2D_IBOcean tides GOT 00.2 GOT4.7Sea State Bias BM4 Non-PARAM
Aim to release DTU12 at ”20 years of progress” in september 2012
EGU Vienna, April 201213 DTU Space, Technical University of Denmark
Coastal regions heavily improved
All > 10.000 obs DTU12 DTU10 SAND 18 EGM2008
Purple (0-20 m DEPTH) 3.01 3.30 3.69 3.20
Dark Blue (20-50 m) 2.79 2.79 3.42 2.80
Light Blue (50-200 m) 3.22 3.27 3.52 3.23
Green (200-500 m) 3.53 3.49 3.79 3.51
Yellow (500-1000 m) 4.33 4.30 4.35 4.35
Red/Pink (>1000 m) 4.83 4.82 4.69 4.85
All 321.000 3.72 3.81 4.09 3.83
DTU 2012 Beta
Preliminary North Atlantic
field including 1.6 years of
NOAA C2 LRM Data
(30% data increase)
Getting a 4-10% improvement
EGU Vienna, April 201214 DTU Space, Technical University of Denmark
Summary
CRYOSAT-2 Succesful retracking of SAR data.
SAR-In: Currently working on retracking
LRM: we can currently not compare with ERS-L2 GDR.
Dramatic improvement in the Arctic Ocean (factor of 1.3)
Problems with mode jumps – ESA but also our own retracker.
In global ocean we only se marginal improvement, but more improvement to come once we ”have gained experience”
The new Jason EOL Geodetic Mission will complement Cryosat. Will be fantastic for the future.
Acknowledgement:
Support/data and coorporation with the NGA (US)