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Envisat Wideswath SLC Products: Processing & Exploitation Potential

Envisat Wideswath SLC Products: Processing & Exploitation Potential. Ralph Cordey, Tim Pearson, Yves-Louis Desnos, Betlem Rosich. 44°. 16°. ~ 0.2s. Envisat ASAR Wideswath Mode. Operates over 5 sub-swaths giving 406km total swath width Bursts of 50 to 71 pulses per subswath

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Envisat Wideswath SLC Products: Processing & Exploitation Potential

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  1. Envisat Wideswath SLC Products: Processing & Exploitation Potential Ralph Cordey, Tim Pearson, Yves-Louis Desnos, Betlem Rosich

  2. 44° 16° ~ 0.2s Envisat ASAR Wideswath Mode • Operates over 5 sub-swaths giving 406km total swath width • Bursts of 50 to 71 pulses per subswath • Giving typically two glimpses of a target • 0.19 seconds between glimpses

  3. ASAR WS Products • ESA currently offers only a multi-look detected (and under-sampled) level 1B product: ASA_WSM_1P • No complex product is offered ASA_WSS_1P doesn’t yet exist

  4. This Limits Potential Applications… So far we have highlighted: • Contiguous ocean wave field retrievals • especially in coastal environments for which global wave models are likely to be inadequate • Mesoscale ocean current mapping • based on retrieval of residual Doppler information • WS-WS or WS-IM INSAR • e.g. strategies for rapid acquisition of a base member of an INSAR pair • Increased area characterisation of atmospheric water vapour

  5. What is ESA Doing To Put this Right? • Has sponsored POLIMI & POLIBA to develop a prototype WS-SLC processor • Has let a contract for its implementation into the operational PF-ASAR processor • To complete August 2004 • Aimed to be operational for users December 2004 • Initiated an ad-hoc working group…

  6. WS-SLC Ad-Hoc Working Group • Aims to: • Identify applications potential of a wide-swath SLC product • Influence its operational implementation • Encourage the flow of information to science users & applications developers

  7. WS-SLC Ad-Hoc Working Group Current membership: Andrea Monti-Guarnieri POLIMI Bertrand Chapron IFREMER Johannes Schulz-Stellenfleth DLR Alberto Moreira DLR Ramon Hanssen T.U. Delft Johnny Johannessen NERSC Harald Johnsen NORUT Membership is not closed. We do require that future members sign “Category-1” terms.

  8. Specimen Products • Generated using the POLIMI / POLIBA prototype processor • Intended to provide basis for • Example applications demonstrations • Discussion of processing parameters and tradeoffs • Discussion of data selection strategies

  9. Scene 1: Galicia, NW Spain, orbit 3741, 17 Nov 2002, VV, Descending ASA_WS__0PNPDE20021117_104431_000000402011_00180_03741_0131.N1

  10. ASA_WSM_1P as output from POLIMI processor

  11. ASA_WSS_1P processed using POLIMI processor 5 sub-swaths arranged side by side

  12. Swath SS5 Swath SS4 406 km Swath SS3 Swath SS2 Swath SS1 0.19 s

  13. full sub-swath width one burst multiple imaging of all points sub swath 4

  14. Scene 2: Cape Hatteras, USA, orbit 4903, 6 Feb 2003, VV, Descending ASA_WS__0PNPDK20030206_150206_000000602013_00340_04903_1720.N1

  15. ASA_WSS_1P processed using POLIMI processor 5 sub-swaths arranged side by side

  16. Scene 3: Central Spain, orbit 6754, 15 Jun 2003, VV, Ascending ASA_WS__0CNPDE20030615_220129_000000602017_00187_06754_1454.N1

  17. First results…

  18. Contiguous Wave Field

  19. Contiguous Wave Field Retrieval • Timing issues: • Time lag between two consecutive bursts of 0.19s is a good separation time to allow enough phase change for unambiguous wave direction retrieval while keeping some correlation at the scale of dominant wave field components. • Algorithms: • Using similar algorithm to ASAR level 2 wave mode, we could obtain for the sample product over Galicia 71% of successful ambiguity removal • This ensures overall ambiguity removal for the whole scene using continuity considerations.

  20. WS-WS Interferogram

  21. Issues for WS-SLC Processor • Non-correction of residual Doppler shifts • To support ocean current estimation • Beam pattern correction • To support intensity methods in wind-field retrieval • Product size limited to 2 GByte • Tradeoff between over-sampling to track residual Doppler and product coverage • Distribution medium • DVD not exabyte!

  22. Selection of WS-WS INSAR Pairs • More critical than IM-IM INSAR or IM-WS INSAR • In addition to conventional baseline selection, also have a burst timing issue • Distributed targets need to share overlap in Doppler spectra to co-operate • At present that is entirely hit and miss! For Spain we failed, for NL we succeeded. • Currently examining the information available with ASAR datasets to see if a data selection tool can be constructed

  23. Conclusions & Contacts • ESA are implementing a WS-SLC processor for the end of 2004 • An ad-hoc working group has been set up to understand & promote applications of WS-SLC • Membership not closed • Anticipate significant applications demand for the product • This could have future implications for the HLOP ?

  24. ASAR Wide-Swath SLC Working Group Site… http://earth.esa.int/wsswg/

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