A fundamental element of Copernicus, the EU's Earth Observation and monitoring programme, is the development and operation of an independent, dedicated and sustained space-based observation infrastructure. Six series of so-called Sentinel satellites ensure continuity until 2026-2028 (First Generation). The “CSC Expansion” programme includes the new missions that have been identified by the European Commission (EC) as priorities for implementation in the coming years.
Among the new missions presently under preliminary design phase, the Copernicus L-band SAR will support key European policy objectives through the filling of observation gaps in the current Copernicus satellite constellation and will provide enhanced continuity for diverse operational services, supporting the down-stream commercial and institutional users.
The mission is presently named “Radar Observing System for Europe L” (ROSE-L), to indicate its capability to work in synergy with other Copernicus SAR-based space elements operating at a different frequency (particularly Sentinel-1 operating at C-band) as an element of a System of Systems (SoS). In the frame of the work carried out to preliminarily design the system, the ESA Mission Advisory Group (MAG) helps to advice on the mission requirements. The requirements are mainly inspired by the Copernicus service needs, that are being collected by the MAG looking at previous studies, at the EC Copernicus Service evolution document, as well as at the outcome of specialised workshops in diverse application fields.
Due to the longer wavelength and enhanced penetration capabilities, L-Band SAR observations from space provide additional information that cannot be gathered by other means, for instance on volumetric targets (vegetation, forest, ice, etc…) or on moisture content. ROSE-L is capable to address important measurement gaps from space, leveraging unique information on land, disasters and geohazards and the cryosphere. This includes the collection of ground motion and high-resolution soil moisture information on vegetated areas, the provision of vegetation biomass data, improved land cover. The quantification of the vegetation scattering contribution is another key factor to ensure a better coherence of the signal for interferometric applications. The unique interaction mechanisms of L-band longer wavelength will also bring additional information when exploiting multifrequency datasets, e.g., for sea ice observations. Being an element of a complex mission system, ROSE-L will support the overall continuity of the Copernicus observations, e.g., improving their accuracy, the products quality, the temporal and spatial resolution of collected data.
A summary of what ROSE-L will be able to provide to the user community will be given during the conference, discussing what unique information can be gathered at L-band and which mission performance parameters (resolution and coverage) are considered necessary to fulfill the user needs.
Usually dedicated to ground imaging, Spot SAR processing can also be applied to moving targets, when proper autofocusing is used. In this case, the simultaneous motions of carrier and target both have an impact on the azimuth resolution. That is why these motions have to be estimated and their effects corrected. The process is then a joint SAR-Inverse SAR (ISAR) imaging. For ship targets, the typical roll, pitch and yaw motions (usually unknown for real, non co-operative targets) produce some residual uncorrected migrations of scatterers. The consequence of these migrations is a blurring of SAR/ISAR range-Doppler maps of the target.
A "snapshot" technique, based on a short imaging time, allows some robustness to these residual migrations during imaging time, but it has two main disadvantages. First, it makes it difficult to achieve high azimuth resolution. Second, it produces a series of range-Doppler maps, which include both useful and unsuitable images for extracting the outline of the ship target. The interest of a particular image depends on the moment in the unknown rotation of the target.
We developed a criterion enabling us to choose suitable snapshots in a series, and also a segmentation technique adapted to the typical shapes of ship targets. This criterion can be adapted to range undersampled data and the presumed Doppler spread of the target return. Its complexity and accuracy may therefore be adapted to the context. The criterion and the segmentation technique have both been tested on synthetic and real in-flight data. A highly effective way of producing easy recognizable height profiles of ship targets at sea has been achieved.