CP4O: State of the Art Analysis June 2013

1. CP4O: State of the Art Analysis June 2013 Marc Naeije1 + support from CP4O/WP2000 partners 1Astrodynamics & Space missions, TUDelft

2. Contents • Overview of work package WP2000: state of the art analysis • WP2000 work breakdown in 5 sub packages • Summary and conclusions D2.1 Preliminary Analysis Report • Summary and conclusions D2.2 Development and Validation Plan

3. Overview of work package WP2000:state of the art analysis • Timing: positioned between WP1000 and WP3000 • Involved: NOC, CLS, DTU-Space, STARLAB, isardSAT, Noveltis,U Porto, SatOC, and TUDelft (WP leader) • Objective: review all existing CryoSat-2 products and availability, review all suitable models for re-tracking and data integration approaches, and survey auxiliary data sources to help the development and validation of CryoSat+ ocean products, survey upcoming activities that could support CryoSat-2, and choose suitable test areas for validation purposes. • Deliverables: Preliminary Analysis Report (PAR) and the Development Validation Plan (DVP) • Quality control: draft review by CP4O team and steering group

4. WP2000 workbreakdownand partners

5. WP2100 – Review existing CryoSat-2 products and availability • Review CryoSat-2 LRM products over the ocean, among which L1B, L2, FDM, RADS, CNES RDSAR and LRM CPP products (TUDelft) • Review CryoSat-2 SAR products over water: L1B and L2 (NOC) • Review CryoSat-2 SAR products at high latitude and over sea ice: L1B and L2 (DTU) • Review CryoSat-2 altimeter corrections over open, coastal and polar ocean, including orbits, ionosphere, wet troposphere, tides, SSB and DAC (Uporto, Noveltis, TUDelft)

6. WP2200 – Review suitable models and data integration • Review SAR re-tracking open ocean, coastal ocean and sea-floor mapping: e.g. SAMOSA2 and SAMOSA3 re-tracking algorithms, numerical SAR waveform models (NOC, DTU) • Review SAR re-tracking over open ocean (CLS) • Review SAR re-tracking over sea ice: e.g. threshold, leading edge, double ramp, beta and OCOG re-trackers for polar regions (DTU) • Review RDSAR methodologies: SAR FBR processing to pseudo- 
LRM (Starlab, CLS, RADS)

7. WP2200 cont’d • Review improved/dedicated corrections for • LRM over open ocean: e.g. SSB (TUDelft) • SAR over coastal ocean: e.g. GNSS-derived wet trop (U. Porto, 
CLS), regional tidal models, ionosphere correction models and 
DAC corrections (Noveltis, CLS) • SAR over polar ocean: better ionosphere (Noveltis) and tides (DTU) • Review sigma0 retrieval in LRM and SAR mode: identification 
of needed algorithms and auxiliary data sources (NOC, TUDelft) • Review data integration methods: optimized methods to integrate 
data from multiple satellite altimeters targeted to develop higher resolution products (DTU, TUDelft)

8. WP2300 – Survey auxiliary data for development and validation • Survey of satellite altimeters over the oceans through RADS (TUDelft) • Survey of satellite data over polar regions: like SAR, ICESAT and Envisat (DTU) • Survey of airborne data, particularly CRYOVEX (DTU) • Survey of in situ data: tide gauges, wave measurements, including wave period and direction, datasets available through Globwave (NOC, SatOC, Noveltis)

9. WP2400 – Survey other (upcoming) CryoSat-2 initiatives • Survey of RADS (NOAA/Altimetrics/TUDelft) • Survey of eSurge (NOC) • Survey of REAPER (CLS, isardSAT, Altimetrics and TUDelft) • Survey of SAMOSA (SatOC) • Survey of COASTALT (NOC) • Survey of PISTACH (CLS) • Survey of LOTUS (DTU) • Survey of CNES CPP SAR re-tracking for Sentinel-3: CryoSat-2 experiments (CLS) • Survey other initiatives like CCI sea level ECV

10. WP2500 – Selection test areas for validation activities • Selection of open ocean LRM areas for global comparison with other altimeters (TUDelft) • Selection of open ocean SAR areas: sites with in situ data, especially directional wave buoy data, if possible collocated with tide gauges (Starlab, NOC, CLS, SatOC) • Selection of open ocean SAR areas for sea-floor mapping: sites with high-resolution marine gravity information (DTU)

11. WP2500 cont’d • Selection of coastal ocean SAR areas: sites with wet tropo, iono and regional tidal corrections and in situ data, especially directional wave buoy data, preferably collocated with tide gauges e.g. English Channel, Gulf of Lion, Gulf of Cadiz, German Bight, and North Western Mediterranean Sea (Tuscany/Corsica) (NOC, Noveltis, SatOC) • Selection of coastal ocean SARIn areas (isardSAT) • Selection of polar ocean SAR areas: SSH validation data in the Arctic region, tide gauges and mean sea surfaces

12. WP2000 and themes Open Ocean – meso-scale and sub mesoscale • Low Rate Mode (LRM) and SAR Mode • Assess accuracy /continuity with respect to previous and concurrent missions • RDSAR processing - Generate LRM like products from SAR mode • New SAR re-tracking schemes Coastal Zone – fine scale – coastal processing • SAR and SARIN • SAR retracking - approaches to minimise land contamination • SARIN – investigate potential to mitigate contamination from off-nadir land targets

13. Themes cont’d Polar Ocean – Polar ocean circulation, improved tide models • LRM, SAR and RDSAR • Develop and evaluate processing schemes applicable to sea-ice affected regions Sea-Floor Mapping – High resolution sea floor topography • SAR Mode • Critically depends on > 1 year continuous data over suitable region Geophysical corrections • Ionosphere, wet troposphere, regional tide models

14. SAR innovations • Dedicated SAR altimetry (Delay-Doppler) processing, not only for CryoSat-2 but also to prepare for Sentinel-3 and Jason-CS missions (SAR waveform is very different from LRM waveform): • (semi-) analytical approach (Halimi et al., 2012). 5 parameters model (including mispointing angles) has been developed • Analytical SAMOSA-3 model, accounts for mispointing • Numerical re-tracking as done by CNES CPP, accounts for mispointing • Different methods need further comparison and validation • Sigma0 retrieval in SAR mode needs further development • Ability to observe smaller scales than 100km (where LRM sees geographically coherent SLA error)

15. Innovations cont’d • Reduced SAR techniques (RDSAR), also referred to as pseudo LRM (PLRM): processing FBR data into LRM waveform data, and apply re-tracking dealing with the LRM/SAR differences in PRF • SAMOSA approach processes subsets of waveforms, remaining issues subset optimization and time tag bias • CNES RDSAR from the Cryosat Processing Prototype (CPP) based on averaging all pulses from 4 SAR bursts (256 FBR echoes), CPP_LRM and CPP_RDSAR are routinely ingested in CNES/SALP products • NOAA/Altimetrics RDSAR as used in RADS based on stacking and averaging all individual SAR echoes CP4O compares and validates all three techniques

16. State of the art • Provides a review of the current state of the art of delay Doppler altimetry – baseline for product development and validation in CP4O • Known issues with ESA Cryosat-2 products (Baseline A and B) • Need to resolve mispointing, time tag, tracking point issues • Effect of truncation of waveform trailing edge in Baseline B • Does it change sensitivity of retrieved SSH to mispointing? • impact on coastal applications (mitigate land signals) ? • Some issues have already been addressed in new FD Marine products

17. s.o.t.a. cont’d • Other issues to address: • Is there an effect of long waves, wave direction on SAR SSH and SWH ? • Spreading of the SAR leading edge (in baseline B) impacts C2 SAR retrieval accuracy • Sea State Bias model for SAR waveform re-tracking

18. PreliminaryAnalysisReport • Available through CP4O web and ftp site • 168 pages • Currently under review by ESA

19. PAR summary per theme:open ocean • general aim is to contribute to mesoscale and sub-mesoscale oceanography, and the ability to map fine scale features • We used both LRM and SAR mode data, assessed accuracy and sought continuity with respect to previous and concurrent missions • We also have investigated LRM-like products from SAR mode (RDSAR) to ensure continuity from coastal zone to open ocean, and continuity from LRM to SAR mode • New SAR retracking schemes have been proposed, developed and investigated with a focus on mapping fine scale features in the sea surface height

20. PAR summary per theme:coastal zone • In the coastal zone even finer scales are wanted • we explored dedicated SAR retracking with the purpose of minimizing the effect of land contamination in the radar echo • and investigated SARIN mode data also with a focus on mitigating contamination from off-nadir land targets

21. PAR summary per theme:polar ocean • The polar ocean is not much different from the open ocean • Challenges in the form of sea ice and the fact that no altimeter satellite has gone beyond 81.5° latitude before • We looked at (to be improved) LRM, SAR and RDSAR products • We developed and evaluated processing schemes specifically applicable to sea-ice affected regions • All targeted to improving mean sea surface models, mean dynamic topography models, polar ocean circulation, and polar ocean tide models

22. PAR summary per theme:sea floor mapping • We investigated the ability to resolve short-wavelength sea surface signals caused by marine gravity and sea-floor topography • Investigated the ability to map uncharted seamounts and trenches • exploited the CryoSat-2 SAR mode data to enable the highest along-track sampling resolution • To achieve highest cross-track sampling resolution we need to wait for at least 1 year of continuous data over a suitable region: SAR area (according to latest mode mask) in the North Pacific

23. PAR summary: altimeter corrections • A lot of effort also went into the assessment of the necessary geophysical corrections, and updates are proposed for the ionosphere, wet troposphere, and ocean tide corrections.

24. SAR advantages overconventional LRM • more independent looks (multi-look) leads to improved retrieval precision, thought the theoretical factor 2 is not yet practically achieved (closer to factor 1.5) • Finer spatial resolution along-track (about 300 metres) • Higher SNR (about 10 dB more) • Better performance close to land, especially tracks that incident land at about 90° (perpendicular to coastline) • Less sensitive to sea state

25. Outlook • In 2014 the 1st Sentinel-3 surface topography satellite will provide LRM over open ocean and SAR globally over all coastal areas and over sea ice, later followed by the 2nd Sentinel-3 • The efforts in the CP4O project not only benefit exploitation of CryoSat-2 data but also pave the way for proper exploitation of Sentinel-3 SAR data and later from Jason-CS (≈2017). • Core of CP4O is the development and validation of algorithms and processing schemes for new CryoSat-2 ocean products • From the state-of-the-art analysis we propose the creation of 7 new experimental altimeter data sets, and 4 data sets with new geophysical corrections

26. CP4O product development overview

27. Development &ValidationPlan • Available through CP4O web and ftp site • 47 pages • Currently under review by ESA

28. Development and Validation Phases • Analyse, develop and validate the methods and algorithms needed to derive CryoSat-2 products fit for scientific exploitation in the Open Ocean, Coastal Ocean, Sea Floor Mapping and Polar Ocean sub-themes. • Validate the methods and algorithms against independent data sources and report the error analysis and cross-comparisons in the Product Validation Reports (PVRs). • Document the selected methods and algorithms for each sub-theme in the form of Algorithm Theoretical Basis Documents (ATBDs). • Produce Cryosat-2 products for the Experimental Data Set needed in WP5000 for the public round-robin exercise

29. Planned dates for provision of draft deliverables for each sub-theme