RA-2/MWR Cross-Calibration and Products Validation Orbit Validation Objectives, Approach, Results and Recommendations Summary J. Benveniste, M. P. Milagro, B. Greco, P. Féménias et al. P. Vincent, B. Duesmann (OVT) ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 1
Presentation Overview * * RA-2 * Cross-Calibration and Validation Objectives Approach Activity so far and results • • • MWR DORIS • * * * Algorithm Verification Product Validation Cross-calibration on ERS-2 RA/MWR calibration and Validation results Orbit Validation Team results Conclusion Recommendations ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 2
Objectives of the ENVISAT Validation Workshop * * * Recall of the In-flight calibration of the instruments Recall of the Verification of level 1 b data processing (engineering parameters) -- Review the evolution Review the verification of the Level 2 product algorithms (geophysical parameters) Review the consistency of the level 2 data products Provide an error estimate of the Level 2 products Formulate conclusions and recommendations to be delivered at the final plenary session. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 3
In One Slide. . . From the RA-2/MWR Cross-Calibration and Validation Team ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 4
Sea Level Anomaly in Oct 2002 ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 5
Objectives of the Cross-Calibration and Validation * Cross-calibrated data products: • • * Determine relative biases between ENVISAT RA-2 and ERS 2 RA, at the mm level for the range, or/and other altimeters (T-P, GFO, Jason). Rationale: to ensure ERS-2/ENVISAT data products consistency and unify the two mission-long time series with high precision. Validated data products: • • Geophysical validation of the processing models and the data products. Rationale: to authorize distribution of validated data products to all users. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 6
Cross-Calibration and Validation Approach (1) (i) Cross-calibration of the RA-2 main geophysical parameters against ERS-2 (and/or TP, GFO, Jason): • • Global comparison at cross-overs and along the collinear tracks of millions of globally distributed data (significant error reduction) Global statistical comparison against ERS-2, Models, In-situ data (ii) Preparation of long-term drifts detection: • Global tide gauge network for RA-2 range monitoring ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 7
Cross-Calibration and Validation Approach (2) (iii) Product validation • • • Verify with real data the consistency of the product package (document, media, format and actual dataset) Quantify the inherent validity and accuracy of the range and altitude wave height, wind speed measurements and the geophysical corrections. Estimation of pseudo-time tag errors by minimization of crossover height differences over ocean. The data products are used by the whole CCVTeam for the cross -calibration activities: This will enhance the quality and thoroughness of the validation. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 8
Cross-calibration objectives for RA-2 & MWR data ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 9
RA-2/MWR CCVT Activity So Far * * * * Quick look data inspection at Switch-on (night of 12 March) In house verification of reference processors versus NRT processor (IPF) Level 2 Algorithm Verification w/ ESLs • Verification and tuning for IPF and F-PAC Support to Instrument and Level 1 B verification • Pseudo-time tag bias, range bias and sigma 0 bias investigations MWR Instrument and Level 1 B verification Met offices validation of NRT data circulation. Preliminary cross-calibration with one cycle of data ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 10
Algorithm Verification * Level 1 b/2 data from the IPF verified through comparison with real data Test Data Sets from the ref. processors: • • * 3 IPF algorithm updates since launch Only very minor discrepancies present in current IPF Level 2 algorithms verification and products validation activities performed by the ESLs: • • Ocean retracker and geophysical corrections validated, ice 2 retracker verification preliminary, more ongoing OCOG/sea-ice retrackers and LIP algorithms verified ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 11
IPF status • IPF version (4. 53) operative at Kiruna since 27 Nov. – previous v. 4. 52 operative since mid August • Remaining discrepancies: – Very minor differences in few output values from reference ocean retracking » default ocean ranges when ref. value was non-default » negative SWH values over non-ocean surfaces » No impact on product quality as there are no ocean waves on land! ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 12
CMA status * * Version of CMA used for the cycle of data provided to the CCVT members (4 Oct- 16 Nov. ): V 5. 4 New version (V 5. 5) to be operative in CMA by mid December. This new version solves some known (minor) bugs in v. 5. 4 ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 13
Range Noise Estimation Range noise estimate is: à à 8 cm rms at 18 Hz 1. 8 cm rms at 1 Hz for SWH < 2 m ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 14
Range Standard Deviation Ku peak at 8 cm (1. 8 cm) S peak at 27 cm (5. 2 cm) Ku This confirms that RA-2 is indeed a low noise instrument S ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 15
ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 16
Range Standard Deviation * Estimated on the ocean at cross-over of tracks • • CLS: Pseudo Time Tag Bias : -0. 3 ms DEOS: ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 17
Pseudo-Time Tag Bias * Estimated on the ocean at cross-over of tracks • • DEOS: CLS: MSSL: NCL U -0. 5 ms -0. 3 ms -0. 4 ms +/- 0. 5 ms ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 18
Cross-Over Analysis * Estimated sea surface height RMS on the ocean at cross-over of tracks • • • CLS: 8. 98 cm NCL U: 9. 5 cm MSSL : 8. 5 cm with orbit error correction: 6. 25 cm --> Confirms low noise from Envisat Altimetry (on top of ocean natural variability) ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 19
Ionospheric Correction * Impact of the ionospheric correction on the estimated sea surface height RMS on the ocean at cross-over of tracks GDR T < 10 days (1372 X points) Bent iono. correction 8. 98 DORIS iono. correction 8. 68 RA-2 altimeter correction 8. 53 Filtered (300 km) Altimeter correction 8. 49 Confirms RA-2 doing better! ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 20
Estimated Relative Range Bias • • DEOS: CLS: OSU: -40. 4 cm -40. 7 cm -43. 1 cm -39. 95 cm / ERS-2 / CLS 01 MSS / OSU 95 MSS / Great-Lakes Tide gauges ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 21
Significant Wave Height * * The special design of RA-2 with two additional digital filters located on the waveform leading edge to improve its slope estimation is giving excellent results in picking up the smaller waves. The SWH algorithm has been further improved to estimate smaller waves ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 22
Significant Wave Height ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 23
ENVISAT Performance Coming Off Land • Envisat RA 2 gives good values for SWH and U 10 < 2 s when leaving land close to 90°. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 24
SWH Regression Against Buoys • 20 NDBC buoys (< 30 mins , < 50 km) • N = 30 • ODR Correction: “True” Hs = 1. 0579 Env. Hs - 0. 1438 • 95% conf. Intervals: Gradient 0. 9701 - 1. 1456 Intercept -0. 3513 - 0. 0636 • SWH (Ku) not significantly different from buoy “truth”. • 1 months data: error margins ± 9%, ± 20 cm ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 25
SWH in Near Real Time * Ready to be used by met offices ! ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 26
Rain Is Under Control ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 27
Rain Flag Performance ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 28
Passive Sigma 0 Calibration * * * Calibration experiment methodology validated on small data sample Improved method to complement the sigma 0 absolute calibration transponder experiment by providing the inter-frequency bias Need more data to reach final results ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 29
Altitude in FDGDR/FDMAR * 30 meter Orbit error * 4 cy/rev * Jumps Use DORIS Navigator instead (30 cm)! ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 30
NRT Sea Surface Height dominated by orbit error US NAVY Inclusion of the full rate DORIS Navigator on FDMAR product is fundamental to real time oceanography ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 31
Conclusion (1/2) * * * Ref. processors fully verified and optimised • Only “ice 2” verification is preliminary, more ongoing IPF verified, since last update (27 Nov) F-PAC data processing verification • • * perfect match for the outputs from ice 1/ice 2/sea-ice retrackers between F-PAC and IPF Very minor differences existing wrt NRT data (ocean retracker over non-ocean surfaces, flags, . . ) No show-stopper for the Cross-Cal activities ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 32
Conclusion (2/2) * The preliminary 1 performance estimation of RA-2/MWR yields very good results • • Low Range noise estimated over low waveheight area of the ocean: at 1 Hz: 1. 8 cm for Ku-band, 5. 2 cm at 1 Hz for S-band SWH compares well with ERS-2 and Models: 30 cm rms – RA-2 measures low waveheights much better than ERS (a feature!) – Algorithm has been further improved • Wind speed rms only 1. 4 m/s – Sigma 0 cross-cal w/ERS-2 on more data • Range preliminary cross-calibration on ERS-2 : bias = - 40 cm 1 The RA-2/MWR Cross-Calibration and Validation Team has worked with four months of FDMAR and (only) one cycle of IGDRs, SGDRs data (need three). ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 33
Next Steps * Future upgrade of L 2 Auxiliary files • Sigma 0 cross-calibrated on ERS-2 – The next step will be to introduce the Absolute calibrated sigma 0 and upgrade geophysical models using sigma 0 (wind, sea state bias, MWR tropospheric correction) * Future upgrade of CMA • * * to account for latest algorithms modifications on L 2 ref. processors and IPF| Finalise Validation activity on 3 cycles of data Perform Cross-calibration on 3 cycles of data ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 34
MWR Calibration and Validation Conclusions • • The MWR Brightness Temperatures are well calibrated for the two channel, as expected The Level 2 Wet Tropospheric correction is in very good agreement with the ERS-2 MWR one. Dh bias < 5 mm. Envisat MWR already appears to be in better agreement with the radiosoundings, when compared to ERS-2 MWR 36 Ghz channel may require anyway some stabilization due to aging and thermal cycling of the components – Current drift from the BOM of 0. 25 counts/K – No specific on-board problem has been identified. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 35
MWR Recommendations (1/2) • Implementation of the new MWR Side Lobes corrections within Level 1 B (Improvement > 1 cm in specific zones) – Algorithm validation on-going, to be completed by mid-February 2003. – Specifications ready by the end the 2002 • • Priority for the MWR level 2 algorithm to have a RA-2 Sigma 0 in line with ERS-2, in a first step. ‘MWR’ Sigma 0 meant to be higher by 1 d. B w. r. t. to RA-2. This will be in injected in the recommended Level 2 Neural Network algorithm upgrade. – Specifications ready by January 2003. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 36
MWR Recommendations (2/2) • • • Continuous monitoring of the 36 GHz channel gain drift and LO CH 2 behavior is recommended, to assess possible stabilization. Execute some further testing, the redundant LO at 36. 5 GHz could be used for an observation period. Nevertheless this is not recommended at this stage. Linear correction factors on the MWR Brightness Temperatures and RA-2 Sigma 0 to be implemented in the Level 1 B processing to correct for potential drifts ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 37
Orbit Validation Team Results ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 38
ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 39
Orbit Validation Team Conclusion * Results based on tracking residuals and on orbit comparisons are very encouraging: • * Further evaluation through external tests is required: • • * the 3 cm goal of accuracy for the radial component is realistic use of altimeter data OVT plan: use the first 3 consecutive 35 -day cycles made available by the F-PAC Important recommendation: • • The ultimate goal being to get optimal error estimation both in terms of RMS and importantly in terms of geographical distribution, Then, the global DORIS tracking data acquired onboard are required for the on ground orbit processing ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 40
RA-2/MWR CCVTeam Recommendation 1/4 * Supply 100% DORIS Doppler to SSALTO in less than 2 days as a highest priority. • A gap in DORIS data deteriorates the Altimetry and this propagates for several orbits into the Altimetry product ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 41
RA-2/MWR CCVTeam Recommendation 2/4 * Include the DORIS Navigator data in the fast delivery Products (FDGDR, FDMAR). • Reported efforts done in this direction since the Cal Review but need to sustain the effort for this implementation US NAVY ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 42
RA-2/MWR CCVTeam Recommendation 3/4 * Publish individual echoes processing algorithm. ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 43
RA-2/MWR CCVTeam Recommendation 4/4 * ERS-2 / ENVISAT tandem mission configuration • • * after the three cycles data up-take, the CCVTeam can release the constraint on the 30 minutes separation Making same measurement 30 mn later is not useful any longer after the Cross-Calibration data is acquired. Recommendation: Move one satellite for a more optimal space-time sampling of the Earth • Options discussed in terms of mission objectives – Oceanography – Marine Geodesy ENVISAT Validation Workshop - ESRIN - 9– 13 Dec 2002 - Altimetry Session Summary Page 44
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