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

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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

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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

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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

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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).