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
• Brief about satellite altimetry• On Retracking
• Cryosat.
The Baffin Bay test.
EGU Vienna, April 20123 DTU Space, Technical University of Denmark
The Sea surface height mimicks the geoidMSS = Geoid + Mean Dynamic Topography (MDT)
Gravity from MDT corrected MSS (=Geoid)
sea mount
Gravity fieldGravity field
Gravity field
)2(1
2)(r
N
r
N
r
T
r
TTLg g
EGU Vienna, April 20124 DTU Space, Technical University of Denmark
Cryosat
EGU Vienna, April 20125 DTU Space, Technical University of Denmark
Cryosat SAR+LRM L2 in the Arctic
EGU Vienna, April 20126 DTU Space, Technical University of Denmark
SAR-In
SAR
LRM
Hawaii
EGU Vienna, April 20127 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
Different between processors
LRM SAR SAR-In
2011
V 2.1
2012
V 2.4
EGU Vienna, April 20128 DTU Space, Technical University of Denmark
Baffin Bay • Interesting because its partly icecovered. • This enables comparison C2 SAR and LRM
EGU Vienna, April 20129 DTU Space, Technical University of Denmark
Cryosat SAR + LRMEntire 2011
LRM mode (summer)
SAR mode (winter)
EGU Vienna, April 201210 DTU Space, Technical University of Denmark
Retracking of Cryosat-2
Experimenting with 5 retrackers on Level 1b SAR waveform (black)
Entire waveform: OCOG + 5 parameter beta retracker with exponential tail (blue)
and threshold retracking.
Leading Edge retracking - OCOG and threshold retracking (50% for SAR, 75% for SarIn)
(Se Poster XY348 by M. Jain today)
50% Th-
reshold
OCOG
LE OCOG
EGU Vienna, April 201211 DTU Space, Technical University of Denmark
Retracking 20 Hz SAR dataonly SSH data in leads used.
Std (ESA) = 36 cm
Std (Leading Edge OCOG) = 22 cm
EGU Vienna, April 201212 DTU Space, Technical University of Denmark
Existing GM data (ERS-1)
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ERM ENVISAT/TP/GFO
GEOSAT
ICESAT
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Marine Gravity.
6696 datapoints used
Within
67N to 75N
55W to 65 W
EGU Vienna, April 201215 DTU Space, Technical University of Denmark
Gravity comparison
Identical parameter set to DTU10 for gravity comparison. No finetuning yet.
6696 obs std
EGM2008 5.51
DTU10 4.89
DTU (EIGEN 6C) 5.87
CRYOSAT
ESA L2 SAR 4.66
Lead Edge OCOG - SAR 4.01
Leading Edge Treshold 3.96
LE OCOG (SAR & SAR-in) 3.96
NOAA LRM (2 month) 4.68
EGU Vienna, April 201216 DTU Space, Technical University of Denmark
Coastal regions heavily improvedDTU 2012 Beta
Including CRYOSAT LRM data (1.8 year from NOAA).
Including CRYOSAT SAR data
Currently testing Cryosat SAR-IN
Updating all data.
Particularly Ocean tide correction to GOT 4.7
Also SSB correction updated (na for Cryosat-2).
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 201217 DTU Space, Technical University of Denmark
Summary
Employes a Ph.d on retracking.
Succesful retracking of SAR data. Trying SAR-IN now.
This is certainly work in progress and we are really on the way
Current Cryosat 2 data are comparable to existing GM altimetry
Need to await new Cryosat 2 and the back processing. Will take time
Rumours that Jason-1 will be changed to Geodetic Mission, but this will only improve up to 66N (no Arctic here).