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This paper provides an overview of the Copernicus SAR missions, namely Sentinel-1, ROSE-L and Sentinel-1 Next Generation (NG). In particular, we discuss the Sentinel-1 SAR performance and enabling techniques for SAR interferometry (InSAR). Further, we describe the key characteristics of the ROSE-L SAR instrument. For the Sentinel-1 NG mission, we discuss potential SAR performance enhancements and novel imaging capabilities. In addition, we present different SAR system concepts and results of the preliminary mission analysis, addressing coverage and revisit time. Finally, we discuss the ESA Earth Explorer BIOMASS P-band SAR mission and its SAR instrument.

One of the candidate missions in the evolution of the Copernicus Space Component (CSC) is the Copernicus polaR Ice and Snow Topography ALtimeter (CRISTAL). The aim of this mission is to obtain high-resolution sea-ice thickness and land ice elevation measurements and includes the capability to determine the properties of snow cover on ice to serve Copernicus’ operational products and services of direct relevance to the Polar Regions. The evolution of the CSC is foreseen in the mid-2020s to meet priority user needs not addressed by the existing infrastructure, and to reinforce the Copernicus services by expanding the monitoring capability in the thematic domains of anthropogenic emissions (CO2), polar and agriculture/forestry/emergency. This evolution will be synergetic with the enhanced continuity of services foreseen with the next generation of the existing Copernicus Sentinels. New high-priority candidate satellite missions have been identified by the European Commission (EC) for implementation in the coming years to address gaps in current capability and emerging user needs. This paper describes the CRISTAL mission objectives, main mission requirements driving its design, the payload complement currently under development and its expected contributions to the monitoring of important components of Earth’s cryosphere.

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-lC and Sentinel-lD design fully compliant with the latest Space Debris code-of-conduct and the required casualty risks at re-entry.

Sentinel-1 C&D SAR instruments are designed to continue the observations beyond the lifetime of Sentinel-1 A & B. They are to a high degree rebuilds of S-lA&B and will have the same imaging modes and interfaces to ground. Changes have been implemented within the SAR antenna by using a new Tile Amplifier design, which will contribute to improved radiometric stability and accuracy. The new tile amplifiers simplify the internal calibration approach by reducing the number of internal measurements from five to three. Another improvement is the introduction of interleaved noise measurements during image acquisition in addition to noise acquisitions in preamble and postamble. This is important as the surface brightness temperature have a significant impact on the acquired noise and can change the measured levels by up to 1 dB. A first tile for S-lC with the new design has been successfully tested. Results confirm the updated design and indicate improved measurement accuracy.

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 Copernicus Sentinel-1 mission, which includes Sentinel-1A (S-1A) and Sentinel-1B (S-1B) satellites, and the characteristics of its SAR system. Sentinel-1 uses pre-programmed SAR mode operations to provide a high revisit frequency and systematic global SAR image coverage. This is mainly based upon the operational use of the novel TOPS (Terrain Observation with Progressive Scans in azimuth) SAR imaging mode. In particular, we present results of the SAR system performance analysis focusing on the instrument stability and the achieved radiometric accuracy, as well as the Noise Equivalent Sigma Zero (NESZ). In addition, we discuss the cross-S-1A/S-1B SAR Interferometry (InSAR) performance considering the effects of burst synchronization and SAR antenna pointing on the achievable common Doppler bandwidth. Results of differential cross interferograms are presented showing the coseismic surface displacement caused by the central Italy earthquake.

In the frame of the Global Monitoring for Environment and Security (GMES) Space Component programme, the European Space Agency (ESA) undertook the development of a European Radar Observatory (Sentinel-1), a polar orbiting two-satellite constellation for the continuation and improvement of SAR operational services and applications. Satellite and payload are being built to provide routine, day-and-night, all-weather medium (typically 10 m) resolution observation capability. Ground infrastructure is provided for planning, mission control, data processing, dissemination and archiving. Free and open data access is provided. Data quality of the Sentinel-1 data products is shown along with uncertainty estimation of retrieved information products confirming specified performance and indicating application growth potential. The unique data availability performance of the Sentinel-1 routine operations makes the mission particularly suitable for emergency response support, marine surveillance, ice monitoring and interferometric applications such as detection of subsidence and landslides.

This paper concerns the performance of the Flexible Dynamic Block Adaptive Quantizer (FDBAQ), the on-board data compression scheme used by Sentinel-1A (S-1), the C-band Synthetic Aperture Radar (SAR) system for Earth Observation launched on 3rd April 2014. FDBAQ has been designed to deal with the high instrument data rate due to the high spatial resolution and large swath width. S-1 SAR is able to acquire long data take, corresponding to large volumes of data stored on-board. Since FD-BAQ has been implemented for the first time on S-1, the capabilities of such a compression scheme have not been tested on real data before. The purpose of this paper is to present the results of the analysis of real acquisitions acquired after the end of the Commissioning Phase, so in its full efficiency. FDBAQ is compared with the traditional Block Adaptive Quantizer (BAQ) compression scheme in terms of quantization noise level, average bit rate and signal to noise ratio.

This paper concerns the performance of the flexible dynamic block adaptive quantizer (FDBAQ), which is the onboard data compression scheme used by Sentinel-1 (S-1), i.e., the C-band synthetic aperture radar (SAR) constellation whose first satellite (Sentinel-1A) has been launched on April 3, 2014. The data rate that results from the fine resolution and the wide swath of S-1 would exceed, without data compression, the S-1 hardware limitations. The FDBAQ has been proposed as an efficient method to reduce the instrument data rate and limit the onboard storage requirement. The capabilities of such a compression scheme have not been tested on real data before. Preflight simulation and analysis were based on a simplified processing scheme and radar backscattering information taken from past missions. The purpose of this paper is to present the first results of the analysis of real acquisitions, comprising thousands of products, in every S-1 acquisition mode, acquired during and after the commissioning phase. Advantages and limits are presented in detail, comparing FDBAQ and the traditional block adaptive quantizer (BAQ) compression scheme, in terms of quantization noise level, signal-to-noise ratio, and average bit and data rates.

The ESA Sentinels constitute the first series of operational satellites responding to the Earth Observation needs of the EU-ESA Global Monitoring for Environment and Security (GMES) programme. The GMES space component relies on existing and planned space assets as well as on new complement ary developments by ESA. In contrast to SAR systems already existing in C-band like ASAR/ENVISAT or RADARSAT-2, high demands on the radiometric stability and accuracy are made for Sentinel-1. The mission depends on th e method of calibrating the entir e Sentinel-1 system in an efficient way. This paper describes the strategy and provides a plan of all activities required for in-flight calibration of Sentinel-1. Keywords: GMES, Sentinel-1, CSAR , Calibration, Validation 1. INTRODUCTION The Sentinel-1 synthetic aperture radar (SAR) constellation represents a completely new approach to SAR mission design by ESA in direct response to the operational needs for SAR data expressed under the EU-ESA Global Monitoring for Environment and Security (GMES) programme. The Sentinel-1 constellation is expected to provide near daily coverage over Europe and Canada, global coverage at least every 6 days – all vast improvements with respect to the existing SAR systems [1, 2]. The Sentinel-1 Synthetic Aperture Radar (SAR) instrument operated in two main operational modes: Interferometric Wide Swath Mode, Wave Mode, and two additional imaging modes: Strip Map Mode, and Extra-wide Swath Mode. Except of the Wave Mode all modes can be operated in dual polarization using two receiving channels. The front end of the instrument is based on an active phased array antenna driven by 280 transmit/receiver modules. Thus, by switching the instrument over a multitude of different beams, progressive scanning in azimuth is possible in order to reduce the scalloping effect (TOPS) [3] and by scanning in elevation a wide range of swath positions can be covered (up to 400 km ground range). The most important point with respect to the in-orbit calibration of this flexible SAR system is the tight performance with an absolute radiometric accuracy of only 1 dB (31 ) for all operational modes. Never before such a strong requirement (a few tenths of dB) has been defined for a satellite SAR system. Following the experience gained with ERS and ENVISAT it is necessary to have a set of precision radar transponders to act as point targets which can be automatically programmed and accessed du ring the Sentinel-1 commi ssioning phase and the remainder of the mission lifetime in order to achieve the absolu te radiometric accuracy requirement. This paper will describe aspects of the in-orbit calibration of the Sentinel-1 constellation. The concept of the Sentinel-1 transponder design and its development status will be presented.

The Sentinel-1 satellite carries on board a C-band Synthetic Aperture Radar built from 560 active radiating waveguide arrays. The 280 horizontally polarised waveguide arrays and the 280 vertically polarised waveguide arrays are arranged as dual-polarised pairs in suficient proximity to allow for grating lobe free electronic steering of the S-1 SAR antenna in the elevation plane. Each waveguide array is connected to a transmit-receive module (TRM) feeding or receiving signals via their common antenna port. The SAR instrument has an internal RF Characterisation mode exploiting the phase shifting capabilities of the TRMs, that allows monitoring of the individual excitations of each waveguide array in both Tx and Rx. The present paper reports on a novel Pulse Coded Calibration (PCC) scheme, that whilst maintaining some salient features of the Hadamard based PCC, also allows to optimise the antenna active return losses. A low active return loss is beneficial to minimise the RF stress of the TRM output circuitry and improves the accuracy of the RF Characterisation itself. (4 pages)

ENVISAT ASAR is successfully operating since March 2002 and resulting ASAR products are operationally distributed to the user community since December 2002. This paper provides an update of the ASAR performance, from the instrument status to the product quality assessment.