Global altimetric marine gravity field mapping

The impact of Cryosat-2

Ole B. Andersen and L. Stenseng

EGU Vienna, April 20122 DTU Space, Technical University of Denmark

Outline

• Satellite altimetry – State of the art gravity

• Cryosat-2 (what it offers).

• Noise estimation (20 Hz vs 1 Hz) for Gravity • DTU12 Beta.

EGU Vienna, April 20123 DTU Space, Technical University of Denmark

Satellite orbit

Altitude (H)Range (R)

Reference ellipsoid

GeoidSea surface

Altimetry – basic principles

RHhsurface

errortidesIBDTgeoidssh hhhhhh

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

sea mount

Gravity fieldGravity field

Gravity field

)2(1

2)(r

N

r

N

r

T

r

TTLg g

1 mGal -> Alongtrack heights differences need to be accurate to <1 cm

Rule of Thumb: 1 cm Height difference over 10 km equals 1 mGal.

02

2

2

2

2

2

r

EGU Vienna, April 20125 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 20126 DTU Space, Technical University of Denmark

Cryosat ”promises”

Factor of 2 on 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

C2 will improve

Shortwavelength scale signal

Bathymetry -> oceanography

Long wavelength signal still in error.

EGU Vienna, April 20128 DTU Space, Technical University of Denmark

ESA Level 2Products. (20 Hz data)

Identical profile2011 / 2012

SAR-In

SAR

LRM

Hawaii

EGU Vienna, April 20129 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 201210 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 201211 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 201212 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 201213 DTU Space, Technical University of Denmark

Retracking of Cryosat-2

• 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

DTU12? Gravity

EGU Vienna, April 201215 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 201216 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 ? . Will still be a fantastic asset for marine gravity up to the 66 parallel (no Arctic here).