The present paper provides a focus on the ROSE-L instrument internal calibration (iCAL) design. The ROSE-L SAR Instrument has been conceived to realize a full Digital Beam Forming (DBF) architecture, requiring an innovative iCAL approach.

The ROSE-L SAR Instrument is the key payload of the corresponding ESA Copernicus Expansion Mission, which will complement the already operational Copernicus C-band SAR mission Sentinel-1 by adding an L-band high resolution wide swath synthetic aperture radar imaging capability. The paper will present an overview on the ROSE-L SAR Instrument development status close to its Critical Design Review (CDR) and on its predicted SAR Mission Performance.

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.

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 discusses multistatic SAR, highlighting the potential of constellations to deliver scalable performance, which allows for the simplification and reduction of the single units in terms of size and power. In particular, the paper illustrates the impact of technical challenges such as navigation control, clock synchronization, and data processing. The paper also includes the discussion of the main applications of multistatic SAR, including the measurement of single-pass interferometric and tomographic signatures as part of the calibration process. The paper is closed with examples of possible constellations offering comparable performance to SAR missions of the present and next generations.

In preparation of potential future Earth observation Synthetic Aperture Radar (SAR) missions, the European Space Agency (ESA) is conducting instrument preparatory activities. This paper presents the status and results of the instrument pre-developments for an L-band receive-only SAR, which would fly in formation with an active SAR satellite acting as an illuminator. Such formations would enable e.g. single-pass SAR interferometry, tomography as well as observations under large bistatic angles. The paper focuses on the development of the Radar Central Electronics and the Antenna front-end, which were performed in preparation of the SAOCOM-CS mission [1].

This correction refers to Eqs. (6), (7), and (19) in the above paper (ibid., vol. 48, no. 7, pp. 2994-3008, Jul. 2010).

In February 2011, the Polarimetric Airborne Radar Ice Sounder (POLARIS) was flown in Antarctica in order to assess the feasibility of a potential space-based radar ice sounding mission. The campaign has demonstrated that the basal return is detectable in areas with up to 3 km thick cold ice, in areas with up to several hundred meters thick warm shelf ice, and in areas with up to 700 m thick crevassed glacier ice. However, major gaps in the basal return are observed, presumably due to excessive absorption, scattering from ice inclusions in the firn, low basal reflectivity, and the masking effect of the surface clutter. Internal layers are observed down to depths exceeding 2 km. The polarimetric data show that the internal layers are strongly anisotropic at a ridge, where the ice flow is supposed to be highly unidirectional. In case of space-based ice sounding, the antenna pattern cannot offer sufficient surface clutter suppression, but improved clutter suppression has been demonstrated with novel multi-phase-center techniques.

The European Space Agency (ESA) is preparing candidates for the next Earth Explorer Core mission with the aim to select the 7thmission to be launched. Earth Explorers are the backbone of the science and research element of ESA's Living Planet Programme, providing an important contribution to the global endeavour of understanding the Earth system. Six candidate missions were originally selected and investigated in preliminary studies (Phase 0). A down-selection was made after a User Consultation Meeting in January 2009. Three of the candidate missions (Biomass, CoReH2O and PREMIER) were retained for more detailed feasibility investigations (Phase A). Each mission has been prepared through two parallel and competing industrial studies and many complementary science and technology activities. The final down-selection will be in 2013, followed by implementation and planned launch in 2019. This paper gives an overview of the CoReH2O requirements, mission concept and profile, satellite, payload, and status of the mission.

Multichannel synthetic aperture radar (SAR) makes it possible to obtain high-resolution wide-swath imagery, thus overcoming an inherent limitation of conventional SAR. To cope with a nonuniformly sampled data array in azimuth caused by variations of the pulse repetition frequency, these systems require appropriate coherent processing such as the multichannel reconstruction algorithm. This letter presents the applicability of this algorithm to airborne measured multichannel X-band data. In this context, impact and performance of different channel-balancing methods are investigated. Furthermore, the analytic prediction of residual azimuth ambiguities is verified in the measured data by means of a point target analysis.

This paper reviews advanced multi-channel SAR system concepts for the imaging of wide swaths with high resolution. Several novel system architectures employing both direct radiating arrays and reflector antennas fed by a digital array are introduced and compared to each other with regard to their imaging performance. In addition, innovative SAR imaging modes are proposed which enable the mapping of ultra-wide swaths with high azimuth resolution. The new techniques and technologies have the potential to enhance the imaging performance of future SAR systems by one order of magnitude if compared to state of the art SAR sensors like TerraSAR-X, ALOS, Radarsat-2 or Sentinel-1.

Due to a system-inherent limitation, conventional synthetic aperture radar (SAR) is incapable of imaging a wide swath with high geometric resolution. This restriction can be overcome by systems with multiple receive channels in combination with an additional digital signal processing network. So far, the application of such digital beamforming algorithms for high-resolution wide-swath SAR imaging has been restricted to multichannel systems in stripmap operation. However, in stripmap mode, the overall azimuth antenna length restricts the achievable swath width, thus preventing very wide swaths as requested by future SAR missions. Consequently, new concepts for ultrawide-swath imaging are needed. A promising candidate is a SAR system with multiple azimuth channels being operated in burst mode. This paper analyzes innovative ScanSAR and Terrain Observation by Progressive Scans (TOPS) system concepts with regard to multichannel azimuth processing. For this, the theoretical analyses, performance figures, and SAR signal processing, which had previously been derived for multichannel stripmap mode, are extended to systems operating in burst modes. The investigations reveal that multichannel ScanSAR systems enable the imaging of ultrawide swaths with high azimuth resolution and compact antenna lengths. These considerations are embedded in a multichannel ScanSAR system design example to demonstrate its capability to image an ultrawide swath of 400 km with a high geometric resolution of 5 m. In a next step, this system is adapted to TOPS mode operation, including an innovative “staircase” multichannel processing approach optimized for TOPS.

Synthetic aperture radar (SAR) systems with multiple receive channels allow for high-resolution wide-swath imaging thus overcoming a fundamental limitation of conventional single-aperture SAR. By using multiple apertures in azimuth, additional samples are received for each transmitted pulse. This allows for a reduced pulse repetition frequency (PRF) thereby enabling a wider swath. However, a nonoptimum PRF is associated with a nonuniform sample spacing in azimuth and needs to be compensated by a multichannel reconstruction algorithm. For strong deviations from the optimum PRF, the inverse character of such an algorithm might result in a degraded performance. This can be overcome by an innovative advanced transmit antenna architecture which allows for a pulse-to-pulse shift of the phase center. Such an antenna enables the adaptive adjustment of the system's phase center positions to the respective PRF, thereby ensuring constant performance over a clearly extended PRF range. In particular, in combination with conventional multichannel processing strategies, this technique represents the next step toward a fully active multiple-input multiple-output (MIMO) SAR and has a great potential for future systems.

Multi-channel synthetic aperture radar (SAR) systems enable high-resolution wide-swath imagery thus overcoming the inherent limitation of conventional SAR. A possible realization based on the combination of multi-aperture SAR signal reconstruction in azimuth with digital beamforming on receive in elevation is given in [1]. The present paper turns focus to advanced concepts for the imaging of even wider swaths while still providing high azimuth resolution [2]. In this regard, the operation of multi-channel SAR systems in burst modes like ScanSAR or TOPS is introduced and aspects of applying the multi-aperture reconstruction algorithm to burst mode data are analyzed. The influence of the digital processing network on performance parameters as signal-to-noise-ratio and azimuth ambiguity-to-signal-ratio in multi-channel burst mode systems is considered and embedded in the design example of a ScanSAR system that allows for the imaging of a 400 km wide swath with a geometric resolution of 5 m. Finally, first results for a multi-channel TOPS system are presented and an optimized TOPS processing approach is introduced.

The paper deals with the performance of next generation SAR sensors, here referred to as SMART (Smart Multi Aperture Radar Techniques) equipped with digital beamforming capabilities. Apart from representing a technological jump, these sensors offer the flexibility of actually deciding on the (possibly hybrid) mode(s) of operation on-ground after the data have been acquired. The paper presents the performance of SMART system configurations and modes of operation for a digital beamforming SAR which covers a large swath with a high resolution.

This paper introduces the innovative concept of multidimensional waveform encoding for spaceborne synthetic aperture radar (SAR). The combination of this technique with digital beamforming on receive enables a new generation of SAR systems with improved performance and flexible imaging capabilities. Examples are high-resolution wide-swath radar imaging with compact antennas, enhanced sensitivity for applications like alongtrack interferometry and moving object indication, and the implementation of hybrid SAR imaging modes that are well suited to satisfy hitherto incompatible user requirements. Implementation-specific issues are discussed and performance examples demonstrate the potential of the new technique for different remote sensing applications.

This paper introduces and analyses the innovative paradigm of multidimensional waveform encoding for space- borne synthetic aperture radar (SAR). The combination of this technique with digital beamforming on receive enables a new class of highly performant SAR systems employing novel and highly flexible radar imaging modes. Examples are adaptive high-resolution wide-swath SAR imaging with compact antennas, enhanced parameter estimation sensitivity for applications like along-track interferometry and moving object indication, and the implementation of hybrid SAR imaging modes that are well suited to satisfy the hitherto incompatible user requirements for frequent monitoring and detailed mapping. Implementation specific issues will be discussed and examples demonstrate the potential of the new technique for different remote sensing applications.

Multi-aperture synthetic aperture radar (SAR) systems in combination with an appropriate coherent processing of the individual aperture signals enable high resolution wide swath (HRWS) SAR imaging [1]-[8]. An innovative reconstruction algorithm for such a digital beamforming on receive was presented in [9]-[12] that allows for HRWS even in case of a non-uniformly sampled data array in azimuth. This paper will compare this algorithm to different azimuth processing strategies regarding their performance in dependency of the overall sampling. Further, optimization strategies are discussed to maximize the system's performance by pattern tapering on transmit and "Pre-Beamshaping on Receive" networks that allow for pattern tapering on receive and adaptively adjust the virtual sample positions.

The displaced phase centre (DPC) technique enables a wide swath SAR with high azimuth resolution. In classic DPC systems, the pulse repetition frequency (PRF), sensor velocity and antenna length underlie a stringent timing requirement and any deviation will result in a non-uniform sampling of the syn­thetic aperture. This restriction can be overcome by the use of a recon­struction algorithm, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling. This paper ex­plains limitations of the reconstruction imposed by the processing and the impacts on the ambiguity suppression. The potential of the algorithm when applied to DPC systems like TerraSAR-X with its split receive antenna is demon­strated and the benefits re­sulting from the additional receive ap­ertur e regarding swath width and resolution are pointed out. Further on, the impact of ad­ditive and phase noise on the recon­struction and its sensitivity against these perturbations are shown.

The displaced phase centre (DPC) technique enables a wide swath SAR with high azimuth resolution. In a classic DPC system, the PRF has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF results in a non-uniform sampling of the synthetic aperture. This paper shows that an unambiguous reconstruction of the SAR signal is also possible in case of such a non-optimum PRF. For this, an innovative reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling of the synthetic aperture. This algorithm also has a great potential for multistatic satellite constellations as well as the dual receive antennas in Radarsat II and TerraSAR-X

The displaced phase center (DPC) technique will enable a wide-swath synthetic aperture radar (SAR) with high azimuth resolution. In a classic DPC system, the pulse repetition frequency (PRF) has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This letter derives an innovative reconstruction algorithm and shows that an unambiguous reconstruction of a SAR signal is possible for nonuniform sampling of the synthetic aperture. This algorithm will also have great potential for multistatic satellite constellations as well as the dual receive antenna mode in Radarsat 2 and TerraSAR-X.