Philip Moore

Jiasong Wang

School of Civil Engineering and Geosciences

University of Newcastle upon Tyne

Newcastle upon Tyne

NE1 7RU

philip.moore@ncl.ac.uk

jiasong.wang@ncl.ac.uk

ENVISAT Orbit & RA2 CCVT in Newcastle University

ENVISAT Precise Orbit Determination

Force ModelGravity model

3-body perturbation

Earth tides

Ocean tides

Atmospheric density

SRP + Albedo + Infrared

Relativity

Param (Dynamic)

Param (Reduced Dyn)

GRIM5-C1(120×120)

DEC403 JPL Eph

IERS96

GOT99

MSIS86

Macro/ESA; SRP factor = 1

Schwarzschild

6-hour drag+daily 1cpr along/cross track

6-hour drag+hourly 1cpr along/cross track

Sigma=5.E-9m/s/s

Correl. Time = 3 hours

Altimeter Range model adopted

Model Source ENVISAT / ERS2

Total geocentric

ocean tide (1) + pole tide

Solid earth tide

Dry troposphere

Wet troposphere

Ionosphere

Inverse Barometer

Sea state bias

Orbit

GOT99: ENVISAT from GDR; model for ERS2

Model (from GDR): both satellites

Model (from GDR): both satellites

Model (from GDR): both satellites

GIM + scale from IRI95: both satellites

ENVISAT from GDR; inferred for ERS2

Model (from GDR): both satellites

From GDR or NCL POD

0

1

2

3

4

5

6

7

c10-1

c10-2

c10-3A

c10-3B

c10-4

c10-5

c11-1A

c11-1B

c11-2

c11-3

c11-4A

c11-4B

c11-5

SLR(redu) DORI S(redu) SLR(dyn) DORI S(dyn)

RMS of SLR (cm) and DORIS RMS (0.1mm/s)

residuals in NCL POD

0

0. 5

1

1. 5

2

2. 5

3

3. 5

c10-1

c10-2

c10-3A

c10-3B

c10-4

c10-5

c11-1A

c11-1B

c11-2

c11-3

c11-4A

c11-4B

c11-5

NCL-DEOS CNES-DEOS NCL-DEOS

RMS radial orbit difference (cm) for

ENVISAT cycles 10 and 11

0

1

2

3

4

5

6

7

8

c10-1

c10-2

c10-3A

c10-3B

c10-4

c10-5

c11-1A

c11-1B

c11-2

c11-3

c11-4A

c11-4B

c11-5

NCL-DEOS CNES-DEOS NCL-CNES

RMS cross-track orbit difference (cm) for ENVISAT cycles 10 and 11

Radial orbit difference between reduced dynamic and dynamic POD: RMS values over 4º long. by 2º lat. bins

Radial orbit difference between DEOS and NCL (cyc10)

RMS values 4º long. by 2º lat. bins

Radial orbit difference between DEOS and NCL (cyc11):

RMS values over 4º long. by 2º lat. bins

Altimeter statistics

Flag Rejected

Cyc 10

Rejected

Cyc 11

1. Land 673042 667684

2. Shallow water

(reject if > -1000m)

311764 260787

3. SWH = 0 90339 78204

4. Tide (reject if > 20m) 936 1016

5. Peakiness (reject if

<1.5 or > 1.8)

75382 69038

Total rejected 1151463 1076729

Accepted 933856 945734

RMS of crossover residuals cycles 10-11:

CNES v NCL reduced SLR+DORIS orbit

6

6. 5

7

7. 5

8

8. 5

c10-1

c10-2

c10-3A

c10-3B

c10-4

c10-5

c11-1A

c11-1B

c11-2

c11-3

c11-4A

c11-4B

c11-5

CNESReduDyn

Sea State bias and altimeter time tag estimation from single crossovers

orbit 1 = CNES; orbit 2 = NCL (Reduced dynamic);

• Max time diff=5day, rejection criterion 20cm

Orbit Used/rejected RMS change t(ms) SSB: %SWH

1/Cyc 10

2/Cyc 10

6003/319

6030/292

9.46—7.25cm

9.23—6.94cm

0.01 ±0. 36

-0.01 ±0. 36

4.85 ± 1.03

4.83 ± 1.02

1/Cyc 11

2/Cyc 11

4791/582

5132/241

9.26—7.29cm

8.81—6.80cm

-0.17 ± 0.40

-0.20 ± 0.39

4.29 ± 1.08

4.16 ± 1.03

Note: SSB given as % of SWHConclusion: Results independent of orbit

Sea State bias and altimeter time tag estimation from single crossover

Max time diff = 5day, NCL orbit applied, for Cyc 10 +11

Reject

level

Used/rejected RMS change t(ms) SSB: %SWH

60cm 11347/348 9.81—7.71cm -0.10 ± 0.26 4.62 ± 0.71

20cm 11154/540 9.03—6.87cm -0.09 ± 0.26 4.53 ± 0.73

Conclusion: Rejection level unimportant

ENVISAT - ERS2 SSH: Ascending passes

Corrections applied: sea state bias and USO drift (ERS2) only

ENVISAT - ERS2 SSH: Descending passesCorrections applied: sea state bias and USO drift (ERS2) only

ENVISAT - ERS2 SSH: All passesAll Corrections applied:

Note: All corrections applied:

descending pass mean = 118.1cm ;

ascending pass mean = 115.0cm

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78) solid Earth tide corrections: Note mean = -1.1cm

Differences between ENVISAT (cyc 11) and ERS2 (cyc 79) solid Earth tide corrections: Note mean = -0.8cm

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78) total tidal corrections. Note mean = 1.4cm. Noise from total geocentric ocean tides, see next slide

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78) inverse barometer corrections: Note mean = -3.0cm

Differences between ENVISAT (cyc 11) and ERS2 (cyc 79) inverse barometer corrections: Note mean = -2.8cm

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78)iono+wet+dry+inverse bar. corrections: Note mean = -3.1cm

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78) wet trop. Correction: Note mean = -0.4cm

Differences between ENVISAT (cyc 10) and ERS2 (cyc 78)iono (GIM) corrections: Note mean = 0.14cm

ENVISAT (cyc 10): mean = 1.237m

ENVISAT (cyc 11): mean = 1.237m again!!

Conclusions

• Orbits – agree to near 2cm RMS radially between analysis

centres– Reduced dynamic is better than dynamic OD

• Sea-state bias– Zero values (for very low wave heights??)– Assuming wave heights correct first look SSB

4.6% SWH – Non-parametric approximation not yet applied

Conclusions

• Altimetry correction (Cyc10, 11)– inverse barometer correction has a bias of -3.0cm with

ERS2

– tide effect is different from ERS2 with mean=-1.4cm

• Crossover residuals – RMS about 7cm; shows benefit of DORIS tracking and

to a lesser extent dual frequency altimeter.

Great results c.f. 6.0cm for TOPEX/Poseidon

•Sea surface height (SSH) difference with ERS2 (Cyc10, 11)

–With only SSB correction applied, bias=112cm

–With all corrections for both satellite , bias=117cm

–For Ascending pass and descending pass , 3cm difference for this relative bias calculation. Within error bars?

•SSH compared with mean sea surface (CLS01) (Cyc10)

– Bias=123.7cm (ENVISAT Cyc 10)

– Bias=5.4cm (ERS2 Cyc 078)

– relative bias = 118.3cm between two satellites

Conclusions