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Global altimetric marine gravity field mapping
The impact of Cryosat-2
Ole B. Andersen and L. Stenseng
Acknowledging support/data and coorporation with the NGA (US)And retracked ERS from P. Berry (UK)
EGU Vienna, April 20122 DTU Space, Technical University of Denmark
Outline
• Satellite altimetry – State of the art gravity
• Cryosat-2 (what it offers) – ”new geodetic mission”.
• Noise estimation (20 Hz vs 1 Hz) for Gravity • DTU12 Beta.
EGU Vienna, April 20123 DTU Space, Technical University of Denmark
The (mean) Sea surface height mimicks the geoid
Gravity from MDT corrected MSS (= Geoid) Laplace
sea mount
Gravity fieldGravity field
Gravity field
)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
EGU Vienna, April 20124 DTU Space, Technical University of Denmark
321.400 obs Mean Std Dev. Max Dev Note
KMS02 0.44 5.15 49.38
DNSC08DTU10
0.390.39
3.913.82
36.9136.89
Double Retrack
SS V12.1 0.62 5.79 82.20
GSFC 00.1 0.68 6.14 89.91
NTU01 0.79 6.10 92.10
SS V16.1SS V18.1
0.590.41
4.883.96
45.2936.99
Retracked ERS1+GSA
State of the Art:
EGU Vienna, April 20125 DTU Space, Technical University of Denmark
C2 will improve
Shortwavelength scale signal
Bathymetry -> oceanography
Long wavelength signal still in error.
EGU Vienna, April 20126 DTU Space, Technical University of Denmark
Cryosat ”promises”
Factor of 2 on ssh accuracy over conventional altimetry
Accuracy independent of Sea state:
Jason-1: 1 Hz (altim noise = 1.5 cm): 20 Hz = 6.4 cm
C2 DD: 1 Hz (altim noise = 0.75 cm): 20 Hz LRM = 3.2 cm (sqrt averaging)
Conventional
DD Cryosat
EGU Vienna, April 20127 DTU Space, Technical University of Denmark
ESA Level 2 GDRProducts.(20 Hz data)
Identical profile2011 / 2012All corr applied
NOAA 1 Hz LRM dataAll corr applied
SAR-In
SAR
LRM
Hawaii
EGU Vienna, April 20128 DTU Space, Technical University of Denmark
18 Hz Cryosat
”Noise” (Standard Dev) LRM SAR SAR-In
2011 Proc 2.1 (20Hz) 6.9 cm 13.46 cm 27.1 cm
2012 Proc 2.4 (20 Hz) 10.1 cm 9.9 cm 14.3 cm
SOUTH North
Large ”jumps” at mode shift
LRM SAR SAR-In
2011
V 2.1
2012
V 2.4
>100 mGal
EGU Vienna, April 20129 DTU Space, Technical University of Denmark
1 Hz ”Noise” Entire profile North part (42->)
L2 – Proc 2.1 2011 3.5 cm 2.4 cm (no jumps)
L2 – Proc 2.4 2012 2.8 cm 3.1 cm
RADS 2012 2.8 cm 2.8 cm
EGU Vienna, April 201210 DTU Space, Technical University of Denmark
ERS-1 GEOSAT ERM CRYO-2
Number 8936 13698 3783 12430
Std All / Alongtrk 8.9 (5.7) 7.2 (4.8)* 5.2 (2.4) 7.5 (5.7)
EGU Vienna, April 201211 DTU Space, Technical University of Denmark
Coastal regions heavily improvedDTU 2012 Beta
Including CRYOSAT LRM data - 30% more data.
Currently investigating ESA L2 LRM vs NOAA LRM data.
Including Retracked L1 CRYOSAT SAR and SAR-In data
Has to solve for ”mode jumps first”
Updating all existing GM data.
Ocean tide correction updated to GOT 4.7
SSB correction updated (N/A for Cryosat-2)
Dynamic Atmosphere updated from IB alone
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
EGU Vienna, April 201212 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 testing using 1.6 years of NOAA C2 LRM Data
EGU Vienna, April 201213 DTU Space, Technical University of Denmark
Retracking of Cryosat-2 SAR
• Level 1b SAR waveform (black) with fitted five parameter beta retracker with exponential tail (blue) and surface estimate (red).
Level 1b SAR waveform (black) with fitted five parameter beta retracker with exponential tail (blue) and surface estimate (red). Green is cut off for leading edge Center of Gravity
COG – Center of Gravity
EGU Vienna, April 201214 DTU Space, Technical University of Denmark
Summary
ESA L2 LRM are very good for marine gravity
Processor upg (2.1-2.4) removes spikes and is better for SAR-In
But increases noise for LRM
Jumps between modes are clear and needs to be handled
Current Cryosat 2 data are comparable to retracked GM altimetry
Aims at releasing DTU12 at “20 years progress of altimetry”
Jason-1 EOL Geodetic Mission ?
Acknowledgement:
Support/data and coorporation with the NGA (US)