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)