philip moore jiasong wang school of civil engineering and geosciences university of newcastle upon...
TRANSCRIPT
Philip Moore
Jiasong Wang
School of Civil Engineering and Geosciences
University of Newcastle upon Tyne
Newcastle upon Tyne
NE1 7RU
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
