cp4o progress meeting 1 - frascati - 21-23 november 2012 - 1 - wp 5000 – impact assessment s....

CP4O Progress meeting 1 - Frascati - 21-23 November 2012

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WP 5000 – Impact Assessment

S. Labroue, T. Moreau, P. Thibaut (CLS) N. Picot, F. Boy (CNES)


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• Round Robin exercise– Collaborative context :

• In the consortium : iteration loops and review processes will be set up• Outside the consortium : open to other data set evaluation

(contributions from NOAA, TAS, ENSEEIHT, UCL, …)

– CLS should define the metrics and the methodology for the quality assessment• With the retracking experts (special sensitivity in SAR processing which are not present in LRM

processing) • Taking into account the WP2000 conclusions/recommendations

=> Metrics and methodology has to be approved by the consortium

– Comparison of one retracking taking another one as reference• Importance to all agree on the reference• Comparison focused on SLA and sea state (SWH and sigma0 when available in RDSAR)• Detection of differences between the algorithms• Work on metrics able to quantify the relative advantages/drawbacks of each of them. • Feedbacks to the WP4000 retracking experts • Possibly recommend one algorithm?

KOM

WP5000: Impact Assessment - Methodology


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• Objectives of this assessment for open ocean1. Detect correlated errors for scales beyond 150 km

2. Confirm that the SAR processing allows retrieving smallest spatial scales (20-70 km) thanks to 20 Hz noise reduction in the along track direction

• The objective of WP5000 is to compare the algorithms on metrics agreed by everyone.

• The metrics are not able to detect everything => some subtle processing differences might not be detectable by the proposed metrics (impact of a few mm difficult to separate from the oceanic signal)

• The multiplication of different metrics is important


KOM


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• Each processing has been validated individually by each responsible of WP4000 task

• The objective of the WP5000 is to go further in the geophysical validation of these algorithms for each sub-team with a focus on retracking methods (assessment of the geophysical correction is not foreseen)

• Product Validation Reports are provided for each algorithm in WP4000• Data sets are produced by WP4000 contributors on agreed areas and

periods• Analysis performed at 1 Hz and at 20 Hz depending on the objective

=> Data sets with 20 Hz sampling would be preferred (compression at 1 Hz can be performed by the WP5000)


KOM


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WP5000Impact AssessmentRound Robin exercise

Overall impact assessment report

WP5000: Impact Assessment – Work Plan

• WP4400 data set• Data set user manual• WP4000 Product validation

report• WP4000 ATBDs

• CNES/CLS database(other EO satellite data and

geophysical corrections)

• CNES/CLS database(L2 CPP SAR/RDSAR)

I N P U T S

• WP2000 recommandationsWP4000 contributors

are consulted to check and agree the outputs


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WP5000: Impact Assessment - Work Plan• We propose the CPP/CNES retracking as a reference for the LRM because we

have a large data set (since January 2011) available and already validated

• We recommend the use of L1 CPP data over SAR mode areas as inputs of SAR and RDSAR retrackings

1. to perform direct differences between collocated SAR and RDSAR measurements

2. because SAR waveforms are consistent in time with unchanged IPF data processing (no over-sampling in range and truncation, and no azimuth Hamming weighting implemented)

• RDSAR retrackings should be validated compared to the CPP LRM retracking

• SAR retrackings should be validated compared to RDSAR retracking to be chosen (in the most intelligent manner to evidence the best of each algorithm)

• No SSB corrections applied to SAR and LRM mode. This could potentially explain some observed discrepancies between SAR and LRM SLA


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• How to validate SAR processing?– Difficult because limited areas and not a global coverage compared to LRM mode– No overlap between LRM and SAR zones

• We propose a 2 steps approach– SAR validated versus Reduced SAR = Relative Validation

• The easiest one since the reference is collocated• Analysis of Cryosat-2 data alone

– Reduced SAR validated versus LRM = Absolute Validation (3 means)• Analysis of Cryosat-2 data• Cross calibration with J2• Analysis of the LRM/RDSAR transition


KOM

Absolute validation Relative validation

LRMRDSAR

SARRDSAR-LRM transition

SAR-LRM transition

SAR-RDSAR

• This 2 steps approach could be completed by absolute validation between SAR and LRM (without using the RDSAR comparison)


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• Analysis of Cryosat-2 data– Maps of rejected data– Spectral analysis of SLA, SWH– Analysis of the parameters related to the retracking (histograms, maps)– Analysis of the parameters related to the 20Hz =>1 Hz compression– Detection of dependencies

• Focus on scales greater than 150 km• Sensitivity to radial velocity, SWH, mispointing, etc…

– Performance at cross-overs and SLA– Exploit the change of geographical mask that provides a few crossovers

between LRM and SAR mode (before and after the 7th May 2012)– Analysis of parameters wrt to coastal distance – Sea floor mapping over the Pacific ocean region operating in SAR mode:

• To find new structures (using data where we have never got any ones)• To evaluate the quality of the data (Cryosat SAR noise level and its qualities at different wavelengths)

by comparing SAR retracked data to mss or mean profiles.

KOM

WP5000: Impact Assessment – Absolute Validation


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• Cross calibration with J2– Qualitative by comparing 2 along track profiles

by selecting parallel tracks– Quantitative with statistics at crossovers

• Analysis of the LRM/RDSAR transition– Important to insure RDSAR validation– Histograms of parameters in LRM mode at the transition location– Histograms of parameters in SAR mode at the transition location– Analysis of the difference RDSAR-LRM at the transition location

WP5000: Impact Assessment – Absolute Validation

KOM


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• Analysis of differences between 2 retrackings

• Some of the metrics should certainly be analysed by the WP4000 validation reports – Maps of gained or rejected data compared to the reference based on our

experience in data editing– Spectral analysis of differences of SLA, SWH (cancels out the physical

signal)– Analysis of the parameters differences (histograms, maps)– Detection of dependencies in the difference

• Focus on scales greater than 150 km• Sensitivity to radial velocity, SWH, mispointing, etc…

WP5000: Impact Assessment – Relative Validation

KOM


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WP5000: Impact Assessment - Metrics

• Problem of multi-degrees of freedom:

– Data analyses will focus on the dependencies wrt radial velocity and off-nadir mispointing angle of the satellite (that may impact the estimates)

– Need to separate ascending and descending tracks that are related to different radial velocity and off-nadir angle values at the same point location.

– We might have to consider all SAR mode areas to cover the largest range of values as possible for allowing robust statistical analyses and efficient assessment of the impact of each new products


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May 2012

May 2012


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August 2012

August 2012


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• Equatorial Pacific – Acquisition since 7 May 2012 (and reduced

area since 01/10)– Brown-like zone (few rain/blooms, SWH close

to 2 m, low oceanic variability stable in time)

• Med Sea– Well known region– But with calm seas (bloom events)– Coastal region

• North Atlantic– Seasonal variation (with bloom events in

summer time) – High waves in winter time

• Agulhas Current– Zone studied in PISTACH => J2 high resolution

data sets available (20Hz) with optimised processing

– High waves

WP5000: Impact Assessment – Zones & Period

August 2012

April 2012


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August 2012

February 2012


• What is the recommended geographical coverage: Global– to separate the errors linked to radial velocity, mispointing, SWH– to cover most of the range of radial velocity, mispointing, SWH values


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• What is the recommended time :– At least 2 months time series (1 cycle in summer and 1 cycle in winter) to

provide significant variation of SWH and mispointing


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WP5000: Impact Assessment - Zones & Period• To assess the quality of the sea level spectrum at all spatial scales, the

spectral analysis should be able:– To detect noise level @ high frequency– To identify correlated errors for scales between 10 and 80km– To check consistency of the oceanic signal @ high wavelength

1 cycle over SAR Pacific

zone

1 day over SAR Pacific zone

3 cycles over SAR Pacific zone

SAR CPP CS2

LRM J2

RDSAR CPP CS2

First valuable result


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• The different metrics listed will help to answer to the 4 sub themes

Themes Metrics

Open OceanCoastal Ocean

Sea Floor MappingPolar Ocean

AllDistance to coast

SLA from multi-tracks tightly spacedAll

WP5000: Impact Assessment - Synthesis

KOM


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• Inputs– WP1000 user requirements synthesis– WP2000 synthesis – WP4000 validation reports

• Deliverables– Validation report for each algorithm– Synthesis report

• Risks– Not enough data to assess each algorithm (open ocean)– No clear conclusion coming out from this assessment

WP5000: Impact Assessment - Synthesis

KOM


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WP5000: Impact Assessment – Tools

• Comparisons will be performed in terms of:

– Cartographies (to visualize geographyically correlated mean error)– Histograms– Spectral analysis (allowing to identify the energy/error levels at different spatial

wavelengths)– Time series analysis– Depedencies analysis (correlations between parameters)


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cp4o progress meeting 1 - frascati - 21-23 november 2012 - 1 - wp 5000 – impact assessment s....

Documents

wp5000 wp5000

impact assessment work

quality assessment

kom wp5000

objective of wp5000

cp4o progress meeting

proposed metrics impact

retracking methods assessment