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The aim of the CAWA project is to develop novel retrieval techniques, the objectives are:

  1. Extension of the Envisat/MERIS Cloud-Top Pressure (CTP) algorithm for land and oceans areas, application of this CTP-O2 A-band algorithm to the Envisat/MERIS data set, and preparation of the algorithm for the Sentinel-3/OLCI channels and observation geometry
  2. Extension of a simultaneous aerosol optical depth and surface properties retrieval land and oceans areas, application of the extended GRASP algorithm to ESA Envisat/MERIS measurements, and preparation of the algorithm for the Sentinel-3/OLCI channels and observation geometry
  3. Extension of the DUE GlobVapour Envisat/MERIS total column water vapour (TCWV) algorithm over land and ocean, application of this TCWV algorithm to the Envisat/MERIS data set, preparation of the TCWV algorithm for the Sentinel-3/OLCI channels and observation geometry
  4. Production of homogeneous, well-characterised (i.e. provision of an end-to-end uncertainty estimation), geophysically validated and documented datasets of Envisat/MERIS and EOS-Aqua/MODIS and Sentinel-3/OLCI type cloud-top pressure (CTP), aerosol optical depth (AOD), and total column water vapour (TCWV)
  5. Performing a sensitivity analysis using the newly generated Envisat/MERIS atmospheric datasets on the atmospheric correction for land and ocean products for Envisat/MERIS
  6. Contributing to the exploitation of dataset beyond the existing user community by participating in international activities such as GEWEX-GVaP, GEWEX-ISCCP, AEROSAT, ICAP, and IRC


CAWA is structured into seven major tasks, which are shortly summarised:

  • Task 1: Scientific Review and Requirements Consolidation
  • Task 2: Algorithm Development/Improvement
  • Task 3: Product Generation
  • Task 4: Algorithm Evaluation and Validation
  • Task 5: Sensitivity Analysis of Atmospheric Correction
  • Task 6: Sentinel-3 OLCI
  • Task 7: Project Outreach

After a scientific review and a consolidation of the appropriate requirements, the algorithms are developed so that a diagnostic dataset can be produced. This dataset allows a first evaluation and validation and hence a feedback to the algorithm improvement. The improved and evaluated algorithms are then used for the production of the full MERIS instrument datasets. This data will be analysed, validated and compared to standard algorithms. The outcomes will be distributed to the scientific community, i.e. to support the GEWEX Water Vapor Assessment (G-VAP). Furthermore, the achieved uncertainties can be used to estimate their impact on an improved atmospheric correction.

After the launch of Sentinel-3, six months of OLCI data will be processed with the new CAWA algorithms and validated.


The CAWA project started July 2014, for a duration of 24 months.

The Requirements Baseline Document (RB) and the Algorithm Theoretical Baseline Documents for all CAWA products have been written, however, updates of all documents will be performed at the end of the project to address the progress of the algorithm development.

The product validation and evolution of the algorithm are currently being performed.

After the 12 months of algorithm development and validation, the complete MERIS dataset will be processed and the results will be analysed.