The paper provides a summary on the context and on the updated status of the ROSE-L mission, which carries an L-Band SAR instrument and represents one of the six ESA Copernicus Sentinel Expansion missions. The overview will include the description of the SAR imaging modes and performance, as expected at the current mission phase (start of phase C), and of the synergic illumination design with Sentinel-1.

The present paper provides an overview of the ROSE-L instrument architecture and functionality, with emphasis on internal calibration, mode design, and overall SAR performance. In particular, all the SAR modes have been described and relevant (simulated) performance has been presented.Moreover, a sequential internal calibration concept is also proposed and discussed.

The Copernicus Programme is a joint European initiative developed by the European Commission (EC) and the European Space Agency (ESA) to provide accurate, up-to-date, and comprehensive Earth observation data for environmental monitoring, climate change analysis, disaster management, and security. The Copernicus program comprises a series of dedicated satellite missions i.e., the Sentinels spanning a wide range of the electromagnetic spectrum with different sensing techniques.Sentinel-1 [1] is the radar imaging component of Copernicus. It is a two-satellites constellation placed in the same orbit and spaced 180º apart. The Sentinels are providing systematically data to the Copernicus service component and scientific users.The Copernicus operational services are covering key operational applications tailored to support the definition and monitoring of European policies such as:–Observation of the marine environment and sea-ice monitoring–Surveillance of maritime transport zones–Land surface mapping, e.g., vegetation cover and surface deformation,–Polar environment monitoring (e.g., ice shelves and glaciers)–Climate Change–Emergency Response and ManagementThe Sentinel-1 first generation comprises four satellite units developed in two batches. The first two (A and B) have been already launched and two recurrent (C&D) ones planned for launch ensuring continuity of measurement throughout the 2020’s. Sentinel-1C and D will overlap with other Copernicus SAR mission in development like ROSE-L [2] and the Sentinel-1 Next Generation [3].In this paper we discuss the status and evolution of the Sentinel-1 first generation.

This paper provides an overview of the Copernicus L-band SAR mission referred to as ROSE-L (Radar Observing System for Europe at L-band).In particular, the paper provides an overview of the ROSE-L spacecraft and focuses on the ROSE-L SAR instrument architecture, performance and critical technology developments.The current status of the instrument activities (project is in Phase C) will be presented, highlighting the main achievements and challenges.

This paper addresses the planned Copernicus Sentinel-1 Next Generation (NG) mission, which will provide enhanced C-band data continuity novel imaging capabilities beyond the next decade (2030) in support of operational Copernicus services that are routinely using Sentinel-1 data. We discuss potential SAR system concepts and their launcher compatibility along with key SAR instrument design parameters and their envisaged performance enhancements.In this context, we consider novel imaging capabilities in view of addressing challenging mission requirements, and existing and evolving applications.Furthermore, we consider modular and incremental observation concepts, involving NewSpace smallSat SAR constellations to complement Sentinel-1 NG C-band SAR acquisitions. In addition, we discuss the planned embarkation of the Automatic Identification System (AIS) payload in support of maritime surveillance.

The Sentinel-1 mission represented an unprecedented source of SAR imagery, on which Copernicus and other providers conveniently leveraged to build a continuously expanding catalogue of operational services. In the next two decades, the family of SAR instruments under the Copernicus umbrella will feature additional wavelength diversity, with the ROSE-L mission providing operational illumination in L-band, and will introduce with the next generation Sentinel-1 (Sentinel-1 NG) a significant step ahead in terms of imaging quality and coverage performance, while carefully guaranteeing data and service continuity with the current generation. The massive volumes of data in space, time, polarizations and frequencies are expected on one hand to significantly enhance the applications and services already in place and on the other to open the way to new mapping and monitoring solutions in land, water and cryosphere domains. This paper will address such new perspectives.

This paper addresses the planned Copernicus Sentinel-1 Next Generation (NG) mission, which will provide enhanced C-band data continuity beyond the next decade (2030) in support of operational Copernicus services that are routinely using Sentinel-1 data. In particular, it discusses the envisaged SAR performance enhancements and novel imaging capabilities. It focusses on potential SAR system concepts comprising the definition of SAR instrument designs and the analysis of their performance, the launcher compatibility, and pre-development activities for critical technologies. In addition, it discusses the planned embarkation of the Automated Identification System (AIS) payload and the novel VHF Data Exchange System (VDES) in support of maritime surveillance. The Sentinel-1 Next Generation will consider modular and incremental observation concepts, involving NewSpace smallSat SAR constellations to complement Sentinel-1 NG C-band SAR acquisitions.

This paper addresses the planned Copernicus Sentinel-1 Next Generation (NG) mission, which will provide enhanced C-band data continuity beyond the next decade (2030) in support of operational Copernicus services that are routinely using Sentinel-1 data. In particular, we discuss potential SAR and SAR interferometry (InSAR) performance enhancements and novel imaging capabilities for vessel detection and velocity estimation for vessels and ocean surface currents, respectively. In addition, we present results of the preliminary mission analysis, addressing the coverage, revisit time, and repeat-orbit interval for SAR interferometry. Further, we discuss different SAR system concepts, which were considered during the feasibility study phase.

In this paper we provide an overview of the evolution of the Copernicus SAR Space Component: the Sentinel-1 Space Segment, including the Spacecraft development status, the ROSE- L mission development status and the approach for the development of Sentinel-1 Next Generation mission. In particular, we discuss the objectives and implementation approaches and related challenges for the evolution.

In the last ten years, ESA's Earth Observation (EO) program has been based on three main pillars, i.e. Copernicus, Meteorology and Earth Science Explorer and on some crosscutting activities covering international cooperation and preservation of historical data. In the framework of the Copernicus program, the Sentinel-1 mission is the workhorse for acquiring systematically and providing routinely a large volume of C-band SAR data to the Copernicus services and the global scientific and commercial user community. As part of the Copernicus expansion, ESA completed the study phase for an L-band SAR mission (ROSE-L) last October 2019 and issued the corresponding Request for Proposal for the development of two spacecraft. On the other hand, the availability of high-resolution X-band data is ensured through national European SAR missions, such as TerraSAR-X, Cosmo-SkyMed and PAZ, which are referred to as Copernicus Contributing Missions. L-band SAR data are required for applications, such as surface deformation mapping, monitoring of cryosphere dynamics, sea-ice classification and land cover mapping, among others. As such, L-band data provide complementary information to C- and X-band data. Besides ESA's ROSE-L, Germany is perusing the implementation of the proposed Tandem-L mission, at national level. Recently, disruptive NewSpace smallSat SAR companies have emerged on the EO market. This has triggered discussions on whether or to what extent smallSats can eventually replace or complement large institutional SAR missions. In this paper we provide the overview of the evolution of the Copernicus SAR Space Component: the Sentinel-1 Space Segment and the Spacecraft development status, the ROSE-L development approach and we also discuss the challenges for the evolution. its objectives and implementation, the systematic data acquisition strategy including coverage and revisit frequency, and the end-to-end SAR performance

The paper provides the overview of the evolution of the Copernicus Sentinel-l Space Segment and the Spacecraft development status. Following the successful launch and in-orbit Commissioning of Sentinel-1A in 2014 and Sentinel-1B in 2016, ESA is currently developing the Sentinel-1C and -1D models. The paper addresses the improvements in system robustness and performance. In addition, it discusses the main characteristics of the Automatic Identification System (AIS) instrument to augment the SAR payload data for ship marine traffic applications and the Optical Communication Payload (OCP) for payload data downlink via inter-satellite laser-link with the European Data Relay System (EDRS). Finally, it will address the novel solutions to make Sentinel-1C and Sentinel-1D design fully compliant with the latest Space Debris code-of-conduct and the required casualty risks at re-entry.

This paper addresses the results of the instrument and product performance verification, radiometric and geometric calibration achieved since the end of the respective Sentinel-1 A and B commissioning phases.

The paper provides an overview of the evolution of the Copernicus Sentinel-1 mission, which is part of the Copernicus European Earth Observation program. Following the successful launch and in-orbit Commissioning of Sentinel-1A in 2014 and Sentinel-1B in 2016, ESA is currently developing the Sentinel-1 C and D models. The paper addresses the expected improvements in system robustness and performance. In addition, it discusses the main characteristics of the Automatic Identification System (AIS) instrument to augment the SAR payload data for ship marine traffic applications and the Optical Communication Payload (OCP) for payload data downlink via inter-satellite laser-link with the European Data Relay System (EDRS). Finally, the design of Sentinel-1C and Sentinel-1D incorporates novel solutions that will make both satellites fully compliant with the latest Space Debris code-of-conduct and the required casualty risks at re-entry.

Sentinel-1A, the first component of the Copernicus Space Segment developed by the European Space Agency, was launched on 3 April 2014. It was commissioned in orbit during the following months leading to a In-Orbit Commissioning Review in September 2014. The launch of the identical Sentinel-1B is planned in April 2016, two years after Sentinel-1A with which will complete the Copernicus Sentinel-1 constellation. After launch, the LEOP Phase is expected to last three days where all subsystems and the SAR instrument will be checked. It will immediately be followed by the four-month Commissioning Phase that will include the in-orbit Calibration and Characterisation, and the verification of the satellite, in order to deliver a full functional and well performing satellite to the mission operations. This paper will present the LEOP and Commissioning activities already completed, and the status of Sentinel-1B Calibration, Characterisation and Verification activities of the Commissioning in place.

Sentinel-1 (S-1) has an unparalleled mapping capacity. In interferometric wide swath (IW) mode, three subswaths imaged in the novel Terrain Observation by Progressive Scans (TOPS) SAR mode result in a total swath width of 250 km. S-1 has become the European workhorse for large area mapping and interferometric monitoring at medium resolution. The interferometric processing of TOPS data however requires special consideration of the signal properties, resulting from the ScanSAR-type burst imaging and the antenna beam steering in azimuth. The high Doppler rate in azimuth sets very stringent coregistration requirements, making the use of enhanced spectral diversity (ESD) necessary to obtain the required fine azimuth coregistration accuracy. Other unique aspects of processing IW data, such as azimuth spectral filtering, image resampling, and data deramping and reramping, are reviewed, giving a recipe-like description that enables the user community to use S-1 IW mode repeat-pass SAR data. Interferometric results from S-1A are provided, demonstrating the mapping capacity of the S-1 system and its interferometric suitability for geophysical applications. An interferometric evaluation of a coherent interferometric pair over Salar de Uyuni, Bolivia, is provided, where several aspects related to coregistration, deramping, and synchronization are analyzed. Additionally, a spatiotemporal evaluation of the along-track shifts, which are directly related to the orbital/instrument timing error, measured from the SAR data is shown, which justifies the necessity to refine the azimuth shifts with ESD. The spatial evaluation indicates high stability of the azimuth shifts for several slices of a datatake.

The orbit for Earth observation satellite synthetic aperture radar (SAR) missions is maintained within an Earth-fixed orbital tube to ensure ground-track coverage repeatability and, consequently, to enable repeat-pass interferometric compatibility between data takes. In this letter, it is shown that the size of the orbital tube may affect the interferometric performance in terms of azimuth spectral decorrelation and azimuth coregistration accuracy under the presence of squint. These effects require special consideration for SAR burst modes, such as ScanSAR or TOPS (i.e., Terrain Observation by Progressive Scans). This letter presents and analyzes these aspects in the frame of the Sentinel-1 mission.

A direct consequence of the TOPS acquisition geometry and the steering in azimuth of the antenna is the time-varying Doppler centroid within bursts. If this fact is not properly accommodated during SAR image formation, undesired distortions in both azimuth and range dimensions of the focused SAR images may appear. Azimuth distortions are caused by the local mismatch of both squint and topography. Range distortions arise from the inaccurate accommodation of the intrapulse motion of the platform, usually known as the stop-and-go approximation. Conventional spaceborne SAR image formation schemes will be, in general, unable to provide accurate TOPS SAR images. These distortions are discussed and evaluated for exemplary low-Earth-orbit SAR scenarios. Compensation strategies are presented and validated with TerraSAR-X TOPS data. A discussion of the potential impact on the Sentinel-1 interferometric-wide-swath and extra-wide-swath modes (i.e, TOPS) is also given.

The paper provides an overview of the Copernicus Sentinel-1 system capabilities and applications. In particular, the characteristics of the Sentinel-1 SAR imaging modes and their key performance parameters are described. In addition, the Sentinel-1 SAR interferometry (InSAR) capabilities, especially for TOPS InSAR and the strategy for maintaining the orbital baseline as well as the requirements for TOPS image co-registration are discussed.

The Copernicus Sentinel-1 Earth Radar Observatory, a mission funded by the European Union and developed by ESA, is a constellation of two C-band radar satellites. The satellites have been conceived to be a continuous and reliable source of C-band SAR imagery for operational applications such as mapping of global landmasses, coastal zones and monitoring of shipping routes. The Sentinel-1 satellites are built by an industrial consortium led by Thales Alenia Space Italia as Prime Contractor and with AIRBUS Defence and Space as SAR Instrument Contractor. The paper describes the general satellite architecture, AIT flow and the satellite key performances. It provides also an overview on the CSAR Instrument, its development status and prelaunch SAR performance prediction.

Sentinel-1A (S1A), launched by the European Space Agency (ESA) on April 3, 2014, is a state-of-the-art spaceborne Synthetic Aperture Radar (SAR) Earth observation platform. S1A products are expected to provide high and consistent geolocation accuracy. As of the end of May, 2014, the satellite has not yet reached its reference orbit. However, estimation of product geolocation accuracy is ongoing, and improvements are continually being made. The results reported here represent the early situation, with continued progress expected.

Sentinel-1A, the first component of the Copernicus Space Segment developed by the European Space Agency, has been launched 3 April 2014. The LEOP Phase is expected to last three days where all subsystems and the SAR instrument will be checked. It is immediately followed by the three-month Commissioning Phase that will include the in-orbit Calibration and Characterisation, and the verification of the satellite, in order to deliver a full functional and well performing satellite to the mission operations. This paper will present the LEOP and Commissioning activities in progress, and the status of Calibration, Characterisation and Verification activities of the Commissioning in place.

The paper provides an overview of the GMES Sentinel-1 system characteristics including the SAR imaging modes and their key performance parameters, the SAR interferometry capabilities, and the specifics of related attitude and orbit control modes (i.e., roll steering mode and zero-Doppler steering mode). Furthermore, the paper outlines the planned Sentinel-1 commissioning phase activities related to the in-orbit SAR system end-to-end performance verification and calibration.

This paper provides an overview of the Senitnel-1 Ground Segment and its main operations concepts. It presents the Sentinel-1 Payload data Ground Segment (PDGS), responsible during the Sentinel-1 mission operations for the Sentinel-1 mission planning, X-Band data downlink, data processing, quality performance, data dissemination, archiving activities and user interface, with the main objective to make the core ground segment products available to the Sentinel-1 users within the expected timeliness and quality. The paper describes as well the Sentinel- 1 operational user product family and their characteristics.

The on-orbit alignment of the antenna beams of both the X-band and C-band radar systems during operations of the shuttle radar topography mission/X-band synthetic aperture radar (SRTM/X-SAR) was a key requirement for achieving best interferometric performance. In this paper, we consider the X-SAR antenna beam alignment in azimuth. For a single-pass cross-track SAR interferometer, we establish the relation between yaw and pitch misalignment of the antenna beams and the resulting relative shift of the Doppler frequency bands. This relation is used to provide solutions for the mechanical adjustments of the outboard antenna and electronic beam steering to correct for azimuth misalignment. Furthermore, the effects of the X-SAR effective outboard antenna pattern on the azimuth beam alignment are analyzed. As a result, a so-called "relaxing" factor is derived, which increases the limit for the difference in antenna azimuth angle with respect to the requirement on spectral overlap, and hence spatial interferogram resolution. However, we also show that the alignment requirement is driven by the constraint on decreasing the azimuth ambiguity-to-signal ratio (AASR) for the effective outboard antenna pattern to reduce the resulting additional height error. The strategy for misalignment determination and correction is presented, and results of the analysis of the in-flight X-SAR antenna beam alignment are discussed.

Five ascending and four descending ERS-1/2 tandem-mode synthetic aperture radar (SAR) interferometry (InSAR) data pairs with useful scene coherence are used to measure the surface flow field of an alpine glacier in the Canadian Rocky Mountains. The topographic component of the interferogram phase is calculated by using a digital elevation model (DEM) of the terrain and precise orbit data to reconstruct the ERS InSAR imaging geometry. The DEM is derived from the Canada Centre for Remote Sensing (CCRS) Convair-580 airborne SAR interferometer. As dual line-of-sight (LOS) measurements are not sufficient to completely resolve the three-dimensional (3D) surface flow field, several different assumptions for determining the missing variables are considered, and the 3D surface flow field is estimated by using single and dual LOS measurements. The InSAR results agree with historic and coincident displacement measurements made using traditional point surveying techniques.

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed.>