ESA-DLR-NASA collaboration around a harmonised Sentinel-1 NRB ARD product

Abstract

The current family of SAR products from Sentinel-1 primarily contains Level-1 Single Look Complex and Ground Range Detected data types, which inherit their definition from the European Synthetic Aperture Radar (SAR) satellite missions ERS-1/2 and ENVISAT. These products have proven to be reliable, high-quality data sources over the years. In particular, users largely benefit from the open and free data policy of the Copernicus programme (European Space Agency, European Commission). This has led to Sentinel-1 products being routinely used in several operational applications and to a substantial growth of the user base of SAR data in general. However, the rapid increase of data volume is presenting a challenge to many users who still want to exploit this wealth of information but lack the processing resources needed to convert these Level-1 products into interoperable geoinformation. Cloud solutions offer opportunities for accelerated data exploitation but require new strategies of data management and provision. As a consequence, the term Analysis Ready Data (ARD) was coined and several activities have indicated the potential of extending the Earth Observation product family by such ARD products. With the aim to standardize different categories of ARD, the Committee on Earth Observation Satellites (CEOS) has set up the CEOS Analysis Ready Data (CEOS ARD4) initiative. Within this context, Analysis Ready Data were defined as: « satellite data that have been processed to a minimum set of requirements and organized into a form that allows immediate analysis with a minimum of additional user effort and interoperability both through time and with other datasets. » Different SAR product specifications are currently being defined to provide guidelines on how to best process and organize data to serve as many use cases as possible with the respective products. In this context, ESA, DLR, NASA-JPL, and NASA-ASF have decided to collaborate with the goal to define a joint-Sentinel-1 ARD Normalised Radar Backscatter product. This product should be terrain-corrected, denoised, projected and geolocated in order to allow immediate analysis by the users. The same gridding / tiling system (MGRS) as Sentinel-2 and Landsat ARD products shall be used in order to allow for interoperability with these missions. The use of Cloud-Optimised GeoTIFF (COG) or similar raster files, VRT files, as well as XML and STAC metadata will enable an efficient exploitation of these datasets in cloud-computing environments. Finally, using open-source code and libraries to generate these new products will represent a considerable step towards Open Science. The status of the development of this Sentinel-1 ARD product jointly developed by ESA, DLR, JPL, and NASA ASF will be presented, together with the plans for its generation for the whole Sentinel-1 archive.