The DTU10 Global Gravity field and mean sea surface ...

The DTU10 Global Gravity field and mean sea surface – improvements in the Arctic

Ole B. Andersen

Acknowledge

NGA (Kenyon et al.)

De Montford (P. A. M Berry)

IGFS-2, Fairbanks, Alaska, Sept 2010 2 DTU Space, Technical University of Denmark

Outline

From DNSC 08 -> DTU 10

• Intro – setting the scene outline the problems

• Retracking

• Data Editing (ERS-1 and ENVISAT) Existing ERM data

• Ice-retreat

• Corrections (which to apply – difference)

• Accuracy

IGFS-2, Fairbanks, Alaska, Sept 2010 3 DTU Space, Technical University of Denmark

The Sea surface height mimicks the geoidMSS = Geoid + Mean Dynamic Topography (MDT)

Gravity from MDT corrected MSS (=Geoid)

)2(12)(rN

rN

rT

rTTLg g +

∂∂

−≈−∂∂

−==∆ ∆ γ

sea mount

Gravity field Gravity fieldGravity field

Invert and map of the distribution of mass within the earth: density changes and bathymetry -> Bathymetry prediction.

IGFS-2, Fairbanks, Alaska, Sept 2010 4 DTU Space, Technical University of Denmark

Problems / Editing ENVISAT and ERS2

Height rel to PGM04 : ERS-2 (ALL) ENVISAT (ALL)

IGFS-2, Fairbanks, Alaska, Sept 2010 5 DTU Space, Technical University of Denmark

Data – Quality (Edited)

Retracking Needed

Number of Envisat points (out of 90 repeats)

82

81

79

77

75180W Canada Greenland Nova Zemlya 180E

IGFS-2, Fairbanks, Alaska, Sept 2010 6 DTU Space, Technical University of Denmark

Different Surfaces – Retracking Revisited

1 5 9

13 17 21 25 29 33 37 41 45 49 53 57 61

S1

S11

0

200

400

600

800

1000

1200

1400

1600

Pow

er (c

ount

s)

Bin number

ERS-2 Ocean Waveforms

1 6

11 16 21 26 31 36 41 46 51 56 61

S1

S13S250

500

1000

1500

2000

2500

3000

3500

counts

Rsampled bins

NO.

Topex C Sahara 15N000E

1 5 9

13 17 21 25 29 33 37 41 45 49 53 57 61

S1

S12

0

5000

10000

15000

20000

25000

Powe

r (co

unts

)

Bin number

Inland Water Waveforms

Ocean Echoes

Desert – Australia Inland Water (River – lake - ice)

R, P. Berry, J. Freeman

IGFS-2, Fairbanks, Alaska, Sept 2010 7 DTU Space, Technical University of Denmark

Waveform distributionPolar regions

Others

Patch

Ocean

Sea Ice-Like

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 5

6 10

11 1516

2021

2526

3031

3536

4041

4546

5051

5556

6061

6566

7071

7576

8081

8586

9091

95

96 100

101 10

5

106 11

0

111 11

5

116 12

0

121 12

5

126 13

0

131 13

5

136 14

0

141 14

5

146 15

0

Number of waveforms from coast

Abnormally wide leading edge

‘Real’ ocean waveforms

Ocean-like with quasi-specular component

0

200

400

600

800

1000

1200

1400

1600

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63Waveform Bin Number

0

200

400

600

800

1000

1200

1400

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63Waveform Bin Number

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63Waveform Bin Number

”Famous” GM example

14 Different waveforms

Analysed using EAPRS

IGFS-2, Fairbanks, Alaska, Sept 2010 8 DTU Space, Technical University of Denmark

Retracking ERS-2 Melting Ice example

- First test

TRACK EX

NOT THIS

TRK USED

IGFS-2, Fairbanks, Alaska, Sept 2010 9 DTU Space, Technical University of Denmark

MSS + Gravity Improvent:

Succesfully retracked the ERS-1 GM mission. The ERS-2 GM + ENVISAT GM is ongoing (MSS + Climate + Sea level Change)DTU12MSS, DTU12GRAV

Until then: DTU10MSS, DTU10GRAVImproved editingTake advantage of Climate Change (Ice-retreat)

Improving: Range and geophysical Corrections (ocean tide etc)Implementing Annual correction for better mean (seasonal data)

IGFS-2, Fairbanks, Alaska, Sept 2010 10 DTU Space, Technical University of Denmark

Total sea ice retreat

Decrease in total sea ice extent:

September: 11.1 % per decadeMarch: 2.8 % per decade

Richter-Menge et al, 2008

March

September

Fortunately ENVISAT survived 2007. Will investigate

IGFS-2, Fairbanks, Alaska, Sept 2010 11 DTU Space, Technical University of Denmark

Data – Quality (Edited)

Editing problems??

IGFS-2, Fairbanks, Alaska, Sept 2010 12 DTU Space, Technical University of Denmark

Replace Mask editing with MSS editing

IGFS-2, Fairbanks, Alaska, Sept 2010 13 DTU Space, Technical University of Denmark

Range + Geophys Corrections

Standards CLS01 DNSC08MSS DTU 10

Reference period 1993-1999 1993-2004 1993-2009Orbit ORB_POE_N GGM02/ITRF2000 EIGEN-GL04CDry troposphere ECMWF ECMWF ECMWFWet troposphere Radiometer ECMWF RadiometerIonosphere Altimeter Altimeter AltimeterDynamic Atmosphere IB (1011 mbar) IB (1013 mbar) MOG-2D_IBOcean tides GOT 99 GOT 00.2 GOT4.7Sea State Bias BM4 BM4 Non-PARAM

These will affect the MSS determination, but not so much Gravity.

IGFS-2, Fairbanks, Alaska, Sept 2010 14 DTU Space, Technical University of Denmark

Extending MSS to 17 years

cm

DTU10MSS – DNSC08MSS (3 cm average difference)

IGFS-2, Fairbanks, Alaska, Sept 2010 15 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

Gravity – DTU10

RefiningFiltering (lower)

IGFS-2, Fairbanks, Alaska, Sept 2010 16 DTU Space, Technical University of Denmark

900 points Std (mGal) Max (mGal)KMS02Laxon and McAdoo (97)ArcGP (01-06)SS 16.1 / 18.1DSNC08DTU10

9.47.25.8

8.2 / 5.94.14.0

51.246.234.4

44.9 / 37.424.024.0

Correlation length remains

The same.

IGFS-2, Fairbanks, Alaska, Sept 2010 17 DTU Space, Technical University of Denmark

Summary

DTU10MSS + DTU10GRAV is an improvement over DNSC08.

Currently improving:

Retracking the entire ERS-2 + ENVISAT

Exact Repeat Mission (17 years)

CRYOSAT-2 First results are

VERY INTERESTING………..

New 2011/2012 fields in preparation DTU10 removed striation caused

By HarmSynth and visible in EGM08

1 minute field.