HydroCoastal: coastal ocean and inland water altimetry

HYDROCOASTAL was a project aimed at maximising the exploitation of SAR and SARIn altimeter measurements in the coastal zone and inland waters, by evaluating and implementing new approaches to process data from CryoSat-2 and Sentinel-3. Optical data from Sentinel-2 MSI and Sentinel-3 OLCI instruments will also be used in generating River Discharge products.

New SAR and SARIn processing algorithms for the coastal zone and inland waters were developed, implemented and evaluated through an initial Test Data Set for selected regions. From the results of this evaluation a processing scheme was implemented to generate global coastal zone and river discharge data sets. Case studies assessed these products in terms of their scientific impacts. All the produced data sets are available on request to external researchers, and full descriptions of the processing algorithms will be provided.

What are the specific science and technical focuses?

The scientific objectives of HYDROCOASTAL were to enhance our understanding of interactions between inland water and coastal zone, between coastal zone and open ocean, and small-scale processes that govern these interactions. Also the project aimed to improve our capability to characterize the variation at different time scales of inland water storage, exchanges with the ocean and the impact on regional sea level changes.

The technical objectives were to develop and evaluate new SAR and SARIn altimetry processing techniques in support of the scientific objectives, including stack processing, filtering and retracking. Also an improved Wet Troposphere Correction was developed and evaluated.

Associated user needs, applications, and issues

The potential benefits of global data sets were investigated through a series of impact assessment case studies in the second year of the project. Case studies considered different estuaries and coastal regions including the Bristol Channel (UK), the German Bight and South-Western Baltic Sea, the Northern Adriatic, and the Ebro River and Delta. They each exhibit specific features, but common across the locations are flooding and erosion, sedimentation, the importance of accurate high resolution local modelling, the vulnerability of coastal habitats, the connection between river discharge and coastal sea levels. Inland Water Case Studies considered selected river systems in China to investigate the potential to develop operational hydrological forecasting, lakes and rivers in Ireland to investigate the impacts of lake size and riverbank configuration on the accuracy of water level retrievals, the river Po in Italy to validate water level time series and discharge estimates, and also the River Rhine and Lake Constance to validate water level time series.

Who are the End Users that have been or will be engaged?

The project team includes key experts in the use of satellite data in coastal zone and inland water studies. External end-users are encouraged to access the data products to evaluate and implement them in their own applications.

Solutions, outputs and products Publicly available outputs and products include:

• Detailed technical descriptions of the algorithms and processing schemes applied.
• Initial validation coastal zone and inland water Test Data Sets for selected regions,
• An improved Wet Troposphere Correction for the coastal zone and inland waters
• A final global coastal zone product, and a river discharge product for large and medium sized rivers.
• An impacts assessment report on the applications and benefits of these global products
• Educational and outreach material

A final scientific roadmap provides recommendations for further development of processing algorithms, for further SAR and SARin altimeter missions, and priorities for further scientific research in the coastal zone and inland waters.

Dependencies

As well as altimeter data from Sentinel-3A and -3B, and from CryoSat, HYDROCOASTAL has used data from Sentinel-1 (river mask, coastline), Sentinel-2 (MSI) and Sentinel-3 (OLCI, SLSTR).

What and where are the gaps in existing capability?

Previous projects and initiatives, most recently the ESA SCOOP (http://www.satoc.eu/projects/SCOOP) and SHAPE projects (http://projects.alongtrack.com/shape) have worked separately to develop and implement improved processing schemes for inland water and coastal domains, but HYDROCOASTAL is the first project aiming to consider them together in synergy. The junction between the Coastal Zone and Inland Water provides a challenge to researchers as it represents a boundary between different science domains (hydrology and oceanography), and different satellite measurement regimes. It is also a region of high variability in small spatial and temporal scales, pushing to the limit the ability of satellite data in terms of sampling and providing accurate measurements.

Tools, Services, Software, or Portals needed

Websites and tools that will be used by HYDROCOASTAL include:

Data and satellite information resources

• ESA Sentinels online: http://sentinel.esa.int
• Copernicus: http://www.copernicus.eu
• Cryosat Missions and Products: https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/cryosat

Inland Water data and information sites

• ESA River and Lake website: http://earth.esa.int/riverandlake/
• HYDROWEB: http://www.legos.obs-mip.fr/fr/soa/hydrologie/hydroweb/
• USDA Lake DB web site: http://www.pecad.fas.usda.gov/cropexplorer/global_reservoir/
• TUM Database for Hydrological Time Series of Inland Waters (DAHITI): http://dahiti.dgfi.tum.de/en/

Related Project Websites

• SAMOSA: http://www.satoc.eu/projects/samosa/
• CP4O: http://www.satoc.eu/projects/CP4O/
• SCOOP: http://www.satoc.eu/projects/SCOOP/
• CRUCIAL: http://research.ncl.ac.uk/crucial/
• SHAPE: http://projects.alongtrack.com/shape/
• RIDESAT: http://hydrology.irpi.cnr.it/projects/ridesat/

Other resources:

• ESA online SAR and SARIn altimetry Processing (registration needed): https://gpod.eo.esa.int
• Coastal Altimetry web site (for papers and presentations): http://www.coastalaltimetry.org
• OSTST web site (for papers and presentations): https://meetings.aviso.altimetry.fr

What specific technical Tasks need to be done?

There are four tasks to the project:-

• Scientific Review and Requirements Consolidation: Review the current state of the art in SAR and SARin altimeter data processing as applied to the coastal zone and to inland waters.
• Implementation and Validation: New processing algorithms were designed and implemented to generate Test Data Sets, which were then validated against models, in situ data and other satellite data sets. Selected algorithms were then used to generate global coastal zone and river discharge data sets.
• Impacts Assessment: The impact of these global products was assessed in a series of Case Studies.
• Outreach and Roadmap: Outreach material have been prepared and distributed to engage with the wider scientific community and provide recommendations for development of future missions and future research.

Data sets Three data sets are available:

• HYDROCOASTAL Final Product:
  • L2 along-track re-tracked product
  • L3 inland water level time series
  • L4 river discharge time series.
• HYDROCOASTAL Test Data Set: L2
  along-track re-tracked product.
• HYDROCOASTAL CCN2 isardSAT coastal
  product.

A readme file provides a more detailed description of these products, and a Product Specification Document describes the product contents and format