Sentinel-3 Cal/Val plan

Sentinel-3 Cal/Val Plan E1 & E2 

H. Rebhan, P. Goryl, H. Bonekamp, P. 

Femenias, C Donlon, A. O’Carroll, E. 

Kwiatkowska 

ESA/EUMETSAT 

Sentinel-3 Cal/Val Workshop 2012 

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• Programmatic aspects 

• The ESA/EUM Cal/Val Plan Concept 

• Outline of Cal/Val tasks definitions 

• Conclusion 

Presentation outline 


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Cal/Val: Organisation and Responsibility 

• Satellite project team (ESTEC) 

• conducted and organised pre-launch calibration activities 

• lead phase E1 (Commissioning Phase) 

• Establish E1 Cal/Val Teams 

• Ensure Level 1 product Cal/Val 

• Payload Data Ground Segment (PDGS) teams at ESRIN/EUMETSAT 

• Ensure Level 2 product validation 

• Support to Commissioning Phase for Product Cal/Val activities. 

• In parallel conduct the PDGS commissioning (i.e. ensure product availability, 

timeliness) 

The phase E2 Cal/Val activities are under the responsibility of Mission 

Management. 


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Cal/Val Schedule 

• Data availability and data quality will follow a progressive ramp-up 

scenario starting at launch. 

• Cal/Val activities are continuous task during the mission life time. 


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Generic Cal/Val workflow and data streams 


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The Sentinel-3 Cal/Val Plan Document 

• Draft prepared by ESA/EUMETSAT 

– Based on technical input from industry partners 

– Considers heritage and “lessons learned” from 

Envisat/ERS 

• Draft Document has not been published before WS 

– Need to consolidate programmatic aspects 

– Need for external advise to balance technical content and 

priorities 

• -> To be published after your input has been properly 

considered 


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Cal/Val Document Concept 

• Concept of Traceability: 

– All Cal/Val activities shall be linked to Mission Requirements 

– Mission Requirements defined in MRD and MRTD 

– MRTD: numbered and classified MRD requirements 

• Each MRTD requirement can be linked to a product 

• For each product major error terms are identified 

– ( e.g., SST accurate to < 0.3K) 

• An Error tree/budget can be established for each product at the top level 

– (level of detail depends on resources available) 

• Based on Product Errors, a hierarchy of Cal/ValTasks is defined. All task 

are described in standardized format. 

• Tasks conclude with results that categorise compliance to MRTD 

Requirements 


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Traceable Cal/Val Requirements 


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Traceable Cal/Val Requirements (2) 

• A coherent All Cal/Val Tasks description format is the basis of the Cal/Val 

plan (i.e. what needs to be done) 

• Tasks define: 

– Which parameters shall be used in the calval activity 

– The necessary input data required to perform the activity 

– Tools required to perform the activity 

– A description of the activity method 

– Details on how the results shall be communicated 

– Specification of when the activity must start and end 

• A dynamic part of the Cal/Val plan documents how the Validation tasks 

will actually be implemented, by whom and when. 

• Similar tasks can then be grouped together under specific activities 

dedicated to multiple aspects of Cal/Val 

• e.g a ship cruise, aircraft campaign, on-orbit spectral cal etc. 


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Instrument 

Errors (I) 

Product Error sources 

Total error in Sentinel-3 Product 

Satelliteinstrument 

coupling Errors (C) 

Satellite 

Errors (S) 


Processing 

Errors (P) 

• Product Errors can be classified in generic source components: 

• This allows us to link and classify various cal/val activities with products 

• Care is required to ensure that we have all of the errors identified for a 

comprehensive validation 

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Derive Cal/Val Tasks: Example SST 

• MRTD Req: S3-MR-400 “Sentinel-3 shall provide SST measurement capability to 

at least the quality of AATSR on ENVISAT: SST shall be accurate to < 0.3 K @ 1 

km spatial resolution and with improved swath coverage. “ 

• The example error budget for the Sea Surface Temperature product contains 

the following error contributions leading directly to Cal/Val tasks: 

• Measurement accuracy of TIR radiance data (I) 

– assign to Cal/Val task SLSTR-L1B-CV-200) 

• Uncertainty of on-board calibration sub-system (I) 

– assign to Cal/Val task SLSTR-L1B-CV245 

• Satellite position and attitude (S) (P) 

– assign to Cal/Val task SLSTR-L1B-CV400 

• SST retrieval algorithm and cloud flagging etc (P) 

– assign to Cal/Val task SLSTR-SST-CV-100 

• … 


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• OLCI Level 1 

• SLSTR Level 1 

• OLCI Level 2 

– Ocean colour 

– Land product 

• SLSTR Level 2 

– SST 

– LST 

• SYN Level 1 

Cal/Val Tasks – optical instruments 

• SYN Level 2 

– Surface reflectance and aerosol 

– VGT continuity 


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Example: OLCI Level 1 


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OLCI CalVal Tasks 


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Cal/Val Tasks – OLCI Level 1 

• Similar to MERIS approach – more in Ludovic Bourg / Steven Delwart 

presentation 

• OLCI on board calibration: 

– two radiometric diffusers – every 2 weeks / 3 months degradation monitoring 

– one spectral diffusers – every 3 months (or 6 months) 

• Spectral model derived from the on board Erbium diffuser 

– complemented by spectral campaign O2 and Fraunhoffer absorption (yearly?) 

• Vicarious calibration techniques. 

– Rayleigh, glint, desert/snow/ice/cloud 

– SNO, Reference BRF model, temporal angular matching… 

• Geometric calibration: 

– Calibration (mainly during commissioning phase): instrument mode 

– Orbit and attitude 

– Validation and verification (reference image, matching correlation, coast line…) 


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Validation Generic Approach 

• Validation against precise in-situ measurement (few points but precise) 

• Validation against in-situ measurements (more points less precise) 

• Validation against others sources (satellite comparison) 

• Validation against Models (data assimilation rejection statistics, integrated 

model analyses…) 

• Validation using Level 3 data and stable source: Statistical comparison 

between various L-3 from various sensors constitutes an extremely useful 

tool (mean, median, sd, bias, RMS…. for selected zones, transects, 

latitudinal bands, seasonal trends… ) for a cross-validation of the products 

• Validation using monitoring tools (statistic, trend, QC..Etc.) 


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OLCI Marine Product Validation 

• OLCI marine validation performed in “different steps” : 

– Vicarious adjustment: NIR adjustment, Visible adjustment 

– Validation mooring buoys 

– Validation Aeronet Ocean Colour Network 

– Validation ad-hoc campaign (international effort) 

– Comparison (sensors comparison, statistic, monitoring…etc…) 

• Tools 

– Validation Match-up database (MERMAID like) 

– Level 3 generation 

– Statistic analysis, stability analysis, intercomparison 

– Processing and validation environment (ODESA like or Calvalus like 

• Protocols 

– Protocols NASA (Ref TBD) / MERMAID 


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OLCI Validation Marine ex: matchup DB 

• Total number of ≈1300 

radiometric matchups in 

MERMAID with less than 50% 

pixels cloud, ice_haze or 

high_glint (transects not 

considered here) 

• This is only a global view. In situ 

data are by nature 

heterogeneous 

• users are free to select their 

matchups according to the 

protocol document and other 

choices (flags…) for their own 

validation activity 


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• OGVI - FAPAR 

– Comparing OGVI values to 

similar products generated by 

other independent sensors colocated 

and quasi 

simultaneously acquired data. 

• Comparing against groundestimates 

of FAPAR. 

• OCTI – Chlorophyl Terrestrial 

Index 

– Use of Ground data of 

chlorophyll 

– Airborne Campaigns with 

Spectral Imager/ Radiometer. 

More information in N.Gobron – J. 

Dash Presentation 

Validation OLCI Land 


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SLSTR CalVal Tasks 


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Cal/Val Tasks – SLSTR Level 1 

SLSTR is a self-calibrating instrument with on-board 

calibration system with: 

– Two specially designed and highly stable blackbody 

– Observed at each scan 

– Reflecting target (VISCAL) that is illuminated once per orbit 

(for the VIS-SWIR channels) at the pole. 

•Vicarious calibration 

– Stable sites (Desert, snow) 

– used to characterize / correct 

the drift. 

•Similar to AATSR approach – more in Dave Smith 

presentation 


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Validation SLSTR SST 

More information on the Gary Corlett presentation 

•Drifting buoys: 

– The global array on in situ drifting buoys providing 

SST measurements at depth of 0.25-0.5 m as a 

reference data set 

•“Transistion” radiometry: AATSR -> SLSTR 

– IR radiometers mounted on ships, also to validate L2 

products in specific regions. 

•measurement protocols for SST validation are 

available 

– heritage from the ENVISAT AATSR 

– Extensive inter-comparison with other infrared and 

visible satellite systems 


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Validation SLSTR LST 

More information on the Gary Corlett presentation 

•Specific validation campaigns, and the collection of ground-based 

measurements. 

•Sites under investigation: 

– LSA-SAF sites: Evora, Portugal; Gobabeb, Namibia; Dahra, Senegal 

– ARM sites: SGP, Oklahoma, USA; Niamey, Niger. 

– Others: Valencia, Spain – University of Valencia; Cardington, UK – UK Met 

Office, Australian sites. 

•Level 3 analysis: 

– Times series of average LST and ‘monthly’ maps produced 

•Sensor comparisons (modis, Severi…etc…) 

•Auxiliary data QC: 

– Biomes classification, Fraction vegetation, WV, cloud masking …. 


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Cal/Val Tasks – Synergy Product 


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Inter-channel co-registration analysis 

(SYN-L1C-CV-200) 

• Task description 

– For the synergy product the co-registration uncertainty needs to be analysed 

and compared with the requirements 

• Methodology 

– This analysis uses a database of ground control points (GCP) to monitor coregistration 

at certain reference sub-images (“imagettes”) of OLCI and 

SLSTR bands…. 

– The database contains precise geographic coordinates for a ground point 

together with a small high-resolution reference image of the surrounding 

area…. 

• Input/Output Data need 

– Database of GCP 

• Tools 

– …. 


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Validation Synergy Product 


More on Peter North’s presentation 

- Validation using AERONET 

-Ad-Hoc ground based campaign 

- Sensor comparison 

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Vegetation Product Validation 

(SYN-VGT-CV100) 

• Task Aim and Objectives 

– The objective of this task is to assess the quality to the product derived from the 

SYNERGY branch simulating the SPOT VGT products. 

• Parameters for analysis 

– The parameters that will be validated are the Top Of Atmosphere radiance and 

the bottom of atmosphere reflectance provided as the continuity of SPOT VGT. . 


– Assuming availability of the previously mentioned missions at the time of the S-3 

operations, direct comparisons over fixed terrestrial sites of S-3 VGT like TOA 

radiances versus the VEGETATION and Proba-V . 

– Vicarious calibration tool and methodologies can be used for further assessment 

of the radiometric capacity after the SYN VGT L2 processing. 

– Subtasks aiming at the verification of the spectral interpolation, binning process 

and atmospheric correction process will conducted. 

• More on Eric Gontier’s presentation 


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• SRAL Level 2 

• MWR Correction Parameter 

• Precise Orbit Determination 

• GNSS 

• DORIS 

Cal/Val Tasks –Topography Payload 


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• Range 

Topography Mission – Performance 

– SWH, Sigma0 & WindSpeed 


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SRAL CalVal Plan Activities (1) 


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SRAL internal calibration characterisation 

(SRAL-L1B-CV-110) 

• In-flight characterization and cross-comparison with ground measurement 

• Ground processing tuning 

• Long term monitoring 

• Calibration Planning definition (vs data acquisition) 

1.1 

1.05 

1 

0.95 

0.9 

0.85 

1 

11 

21 

31 

41 

51 

61 

71 

81 

91 

101 

111 

121 


IF mask On-ground 

IF mask 3 

IF mask 2 

IF mask 1 

IF mask operational 

e.g. CAL2 Receiver Transfer Function (IF 

Mask) 

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SRAL Range and Simga-0 Calibration 

(SRAL-L2MA-CV-130) 


– Monitoring of Altimeter range calibration over a dedicated 

site (bias and drift estimation) 

– Regional Cal/Val method also enables to increase the 

number of bias estimations and consequently reinforces 

the bias statistical reliability. 

Need for a dedicated reference Cal/Val 

site to be assessed. 

-> Do we need a S-3 Venice Tower? 


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SRAL CalVal Plan Activities (2) 


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Microwave Radiometer - Cal/Val Tasks 

• MWR calibration characterization 

• MWR cross-calibration vs Envisat 

• Calibration versus simulated Brightness Temperatures (from 

ECMWF meteorological fields) 

• MWR validation & Long term monitoring 

• L1B: Vicarious calibration: 

– Statistical selection of coldest ocean TB, geographical selection 

of hot TB over rain forests 

– Comparison to models 

• L2: Radiosondes, Comparison to models 

multi-sensor 

comparison 


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Topography Mission – Additional Information 

• Envisat Altimetry mission alignment to S-3 STM mission shall be done as 

much as possible prior to S-3 launch to facilitate cross-calibration 

• Needs for algorithm upgrade, sensor calibration, ADF updates, Cal/Val 

activities, format change, etc, shall be considered 


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Tools and Resources for Cal/Val 

• 1.) Optical Payload 

– Extraction tools 

– Systematic extraction over area of interest 

– Static and dynamic areas (drifting buoys) 

– Post processing for vicarious calibration – METRIC type 

– Matchup data Base 

– OC DB (ex: MERMAID) 

– Existing DB for SST,LST and Land Products 

• 2.) Topographic Payload 

– BRAT Tool-box 

– Orbit-CFI (ESTEC Orbit Calc Library) 

• For all instruments 

– Monitoring tools, analysis tool, comparison tool 

– Selected parameters systematically extracted and monitored 

– Level 3 QC tools 


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Radiometric vicarious calibration in the CEOS 

/ IVOS context 

• Use “CEOS agreed fixed sites” 

– Desert 

– Snow 

– Rayleigh 

– Instrumented sites (Landnet) 

• Use “CEOS agreed methodologies” 

– Share the resources / results in the CEOS community 

– Cal/Val portal for communication / exchanges 

– CEOS insitu intercomparison exercise (MIAMI3, Tuzgulu, OC AAOT 

workshop) 

• Vicarious calibration used for monitoring, characterization, uncertainty 

estimation, comparison with other sensors (GMES, CCI) and potential intercalibration. 

– need to be an international and coordinated effort (GEOSS) 


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CONCLUSION 

• Active Preparation for S3 Calibration & Validation has started 

• Concrete steps like the definition and scope of a “Mission Performance 

Center” framework are under preparation 

• Any input and suggestions from you is appreciated! 


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Backup Slides 


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SRAL cross-comparision with in-situ data 

Use independent data (as Tide Gauges or Temperature/Salinity profilers) to 

estimate global altimeter mean sea level drift and also sea-level consistency 

between in-situ and altimetry data. 

Comparison of tide gauge and 

altimetry Sea Surface Height (SSH) 


Comparison of T/S and altimetry 

Sea Surface Height (SSH) 

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SRAL Range Calibration 

- Monitoring of Altimeter range calibration over a 

dedicated site (bias and drift estimation) 

- Regional Cal/Val method also enables to increase the 

number of bias estimations and consequently reinforces 

the bias statistical reliability. 

Corsica Calibration site 

Need for a dedicated reference Cal/Val 

site to be assessed. Do we need a S-3 

Venice Tower? 


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SRAL Absolute Calibration 

• Range Absolute Calibration via Transponder 

• Sigma0 Absolute Calibration 

Keyword: Absolute calibration and long term monitoring (bias and 

drift estimation) 

Over the Envisat Phase E2, the TPD calibration showed a fairly 

stable gain, exhibiting drifts with maximum deviation of 0.2 dB 

1.80 

1.60 

1.40 

1.20 

1.00 

0.80 

0.60 

0.40 

13-feb-04 

12-giu-04 

10-ott-04 

suspected overestimated 

attenuation 

7-feb-05 

tpd failure 

very dew: suspected 

underestimated attenuation 

7-giu-05 

5-ott-05 

2-feb-06 

2-giu-06 

Bias Temporal Trend 

corrected MWR corr no tropo corr raw low res 

30-set-06 

Att.Sett. unstable 

1st permanent site 

acquisition in Low Res. 

TPD positioning 

problem 

28-gen-07 

8-mag-07 

25-set-07 

23-gen-08 

2-mag-08 

19-set-08 

17-gen-09 

7-mag-09 

14-set-09 

12-gen-10 

2-mag-10 

9-set-10 


RA-2 sigma0 transponder installed on 

permanent site (Rome) since October 

2005 

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Sentinel-3 Cal/Val plan

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