This paper introduces a novel architectural design for wideband spaceborne Earth Observation Synthetic Aperture Radars (SAR). In particular the paper is focused on an innovative architecture conceived for the transmission chain of the internal electronics of the radar. The presented solution has been developed in the frame of the program "COSMO - SkyMed di Seconda Generazione" (CSG), to address challenging system requirements in terms of transmitted bandwidth and signal quality. This architecture is based on the direct Radio-Frequency (RF) synthesis of the radar signal and relies on the possibility of configuring the impulse response function of high speed Digital to-Analog-Converters (DACs) to increase the intermediate frequency of the transmitted signal and on the availability of a high performance digital signal generation section with pre compensation capabilities. For the future, this approach paves the way towards a possible direct conversion at RF of the radar transmitted signal, therefore avoiding the performance limits and the issues typically related to up-conversions. The presented solution drastically simplifies the design of the RF section of spaceborne radars, avoiding most of the typical distortions which impact on SAR systems image quality.

The CSG SAR is the heart of the remote sensing system conceived by the Italian Space Agency (ASI) and by the Italian Ministry of Defence (I-MoD) for taking the baton from "COSMO - SkyMed" (CSK). This microwave imaging sensor is a multi-mode X-band radar, designed to implement a variety of acquisition techniques, with a wide span of performance and functionalities. The requirements of the system have been defined by ASI and I-MoD and negotiated with Thales Alenia Space Italia S.p.A. (TAS-I) to provide improved performance exploiting the full bandwidth that will be permitted by the updated ITU regulation, including additional modes and novel acquisition techniques (patented by TAS-I), together with a new set of experimental modes operating also in squinted modalities. In addition to that, CSG will assure continuity with the services already provided by CSK. This paper gives an outline of the architecture of the CSG SAR, illustrates the key features of the hardware designed for enabling the new required capabilities, and presents the results of a performance prediction based on the current stage of development of the radar.

This paper focuses on COSMO SECONDA GENERAZIONE (CSG) satellite that, thanks to its outstanding performances and enhancements, both guarantees operational continuity to the currently operating COSMO-SkyMed "first generation", Ref. [1], and improves its performances and functionalities. The CSG programme is funded by the Italian Ministry of Research and Italian Ministry of Defence (I-MoD) and managed by the Italian Space Agency (ASI) in conjunction with I-MoD.

COSMO Second Generation (CSG) system has been conceived, according to the requirements stated by ASI and I-MoD, at the twofold need of ensuring operational continuity to the currently operating “first generation” COSMO-SkyMed (CSK) spacecraft constellation, while achieving a generational step ahead in terms of functionality and performance. The improved quality of the imaging service is among the foremost characteristics of CSG (see [5]), providing the End Users with new/enhanced capabilities in terms of higher number of images and increased image quality (i.e. larger swath, and finer resolution) with respect to COSMO-SkyMed (first generation) spacecrafts currently in operation, along with additional capabilities (e.g. full polarimetric SAR acquisition mode). The greater operative versatility in system resources management is one of the key aspects of the design approach. Some examples are the satellite agility both at platform and antenna level, used to increase the density of acquisitions in a fixed region, the capability to adapt operative profiles to system environment (e.g. sun illumination, downlink scenarios), service request planning process not only function of the priority but also able to maximize the system resources exploitation.

COSMO-SkyMed is the most important Italian Earth Observation space program. The program is funded by the Italian Ministry of Research and Italian Ministry of Defence (I-MoD) and conducted by the Italian Space Agency (ASI) in conjunction with I-MoD. COSMO Second Generation (CSG) system has been conceived, according to the requirements stated by ASI and I-MoD, at the twofold need of ensuring operational continuity to the currently operating "first generation" COSMO-SkyMed (CSK) spacecraft constellation, while achieving a generational step ahead in terms of functionality and performances. In order to ensure such continuity, the new CSG satellites will be ready for operations timely to replace the previous generation satellites whenever they are being progressively phased out at the end of their lifetime.In the current days, after having defined the mission fundamentals of the CSG space borne imaging radar system, the detailed design of both space and ground segments elements has been undertaken. In this frame this paper delineates the key concepts of the CSG system in terms of service improvement and relation with CSK.The improved quality of the imaging service is among the foremost characteristics of CSG, providing the End Users with new/enhanced capabilities in terms of higher number of images and increased image quality (i.e. larger swath, and finer resolution) with respect to COSMO-SkyMed (first generation) spacecraft currently in operations, along with additional capabilities (e.g. full polarimetric SAR acquisition mode) and a greater operative versatility in programming and sharing the system resources among different typologies of Users that request images of different characteristics.Further, while describing the above mentioned topics, this paper shows the key aspects of the CSG engineering approach adopted in order to conceive CSG, that starting from the User requirements ends with the design of the lowest-level system building blocks. Besides, key elements both at space and ground segments are highlighted within this paper.

"COSMO - SkyMed di Seconda Generazione" (COSMO SG) is a programme funded by the Italian Ministry of Research and by the Italian Ministry of Defence (I-MoD), and conducted by the Italian Space Agency (ASI) with I-MoD at the aim of pursuing a twofold goal: assuring SAR data continuity to the users of "COSMO - SkyMed" (CSK) and enhancing the capability of that system in terms of functionalities and performance. In accordance with the mentioned objectives, COSMO SG will enable astonishing Earth observation capabilities, satisfying emerging needs of both civilian and military users. Within the frame of this programme, to comply to the applicable user's requirements, Thales Alenia Space Italia S.p.A is charged of developing an innovative multi-mode X-band Synthetic Aperture Radar (SAR), to confirm the image quality performance of CSK, to improve the resolution achievable by the system and to provide the novel capability of supporting acquisitions based on simultaneous dual polarisation on receive. This paper provides a description of the SAR instrument design, gives an outline of the key parameters of the instrument and describes the main enabling technologies developed in order to implement this design.

Ka-Band interferometry offers new opportunities in Earth observation for science and civil security applications due to the unique characteristics of this higher frequency band. Several Ka-Band satellite missions and instruments are currently under development. The first Ka-band instrument, Altika Altimeter [ 1], is in orbit and has shown remarkable performance confirming the feasibility to use this frequency for EO application despite higher atmospheric losses. However for Ka-band interferometric SAR operating from a single platform the link budget is critical and requires signal recovery techniques. Scan-on-receive combined with digital beam forming overcomes these restrictions and offers additional features leading to high performance systems. This paper discusses possibilities to apply digital beam forming techniques to Ka-band instruments enhancing the performance.

A brand-new design of the Synthetic Aperture Radar (SAR) instrument has been conceived, capable to make the space resolution of the "narrow field images" finer than COSMO-SkyMed First Generation satellites (CSK), while providing multi-polarization. The technologies necessary to sustain improved performances interest all SAR payload elements, realizing completely renewed design of SAR central electronics and active phased array antenna with respect to CSK. A renewed Payload Data Handling and Transmission (PDHT) design significantly improves the performances of the PDHT currently in use in CSK, in terms of on-board data storage capacity (doubled), space-to-ground data transmission throughput (doubled), data reception rate from SAR. The technology innovations relate to all composing elements of PDHT, such as on-board memory cells, command & control software, data encryption, modulation scheme, communication devices. The Satellite Platform has been enhanced with respect to CSK, in terms of augmented electrical power (necessary to cope with the increased peak power required by the payload), an Avionics Subsystem (AVS) new state-of-the-art design (enhanced sensors technology and a very high satellite agility), a new transponder with enhanced data rates and an increased propulsion fuel tank capacity for an extended operative lifetime. This paper describes the COSMO Second Generation challenging technologies and design put in place in the LEO SAR Satellites context.

The paper proposes a COMmunication SATellite (COMSAT) compatible Synthetic Aperture RADAR (SAR), with regional coverage and continuous observations. Such a system could provide deformations and water-vapour maps over regions of hundreds of kilometers with resolutions in time-space otherwise impossible with that coverage. The basic monostatic concept is reviewed together with its multistatic evolution, capable of exploiting the present clusters of COMSATs at the same longitudinal node. Attention is brought to the most critical issues, such as atmospheric turbulence, target coherence, and clutter decorrelation.

In the frame of the "Study into Ka-band SAR", a project funded by the European Space Agency (ESA), the authors investigated new instrument concepts to implement a spaceborne high resolution interferometric SAR operating at Ka-band. In particular, thanks to the antenna separation which is required at these frequencies to achieve accurate height measurements, the analysis was focused on concepts related to single pass interferometry from a single platform. This paper illustrates the definition of the instrument concepts elaborated during the Study, gives an insight of the performance that they are capable to achieve and lays the foundations for the preparation of the roadmap that will conclude the Study paving the way for possible future developments.

Earth Explorer is an ESA Program aimed to provide an important contribution for the understanding of the Earth System. Earth Explorer missions form the science and research element of ESA's Living Planet Program and focus on the observation of atmosphere, biosphere, hydrosphere and cryosphere. In this context, the CoReH2O mission was conceived in order to characterize snow cover spatial distribution and its relevant properties: snow depth, Snow Water Equivalent (SWE), sea ice and glacier features. Electromagnetic properties of the geophysical parameters of interest, and the need to retrieve them accurately on a wide geographical scale, envision the mission around a Synthetic Aperture Radar (SAR) providing the key features of wide coverage, “Simultaneous Dual Polarisation on Receive” capability, “Simultaneous Dual Band” (Ku - X) capability.

Antenna beam pointing accuracy and stability are key issues for obtaining reliable and high quality remote sensing data in space-borne SAR sensors. A wide set of causes, related to technological aspects and environmental conditions acting at both Bus and Payload level, contribute to misalign the actual antenna bore sight from the theoretical direction. Even very small error angles on the yaw, pitch and roll axes directly reflect on antenna pointing, impacting on key image quality parameters such as resolution, swath width, signal to ambiguity ratio. Particularly, two major types of errors can be considered: time invariant (static) errors and time-variant (dynamic) errors. The different SAR image quality parameters show different sensitivity to mispointing and therefore are affected in different ways by satellite attitude. In this paper we analyze the effects of static and dynamic errors and we predict their impact of the most relevant SAR image quality parameters, by assuming as reference a generic X-band SAR mission.

COSMO-SkyMed is the Italian Remote Sensing programme which foresees the utilization of a constellation of four SAR Satellites in Low Earth Orbit, dedicated to the management, control and exploitation of Earth resources for civil and defence applications. The program is completely funded by the Italian Government, mainly through the Italian Ministry of Research (MIUR) and the Ministry of Defence (I-AD). Thales Alenia Space Italia is responsible for the design, development and verification of the complete constellation. Satellites will take SAR images of the Earth in the X-band for a variety of government, commercial and scientific users, providing data with unprecedented quality in terms of numbers of images, resolution and accuracy. Following the canonical space qualification and acceptance processes customers and Thales Alenia Space Italia decided to pursue an end-to-end experimental verification of the SAR instrument in order to provide evidence of its capabilities. With respect to the classical approach for the on-ground verification of space-borne SAR which is done through the verification by parts and the final analytical compilation, it was decided to set-up an outdoor verification Test able to exploit all radar functionalities and performance in an integrated approach i.e. radar electronics, antenna and calibrated targets all together. In this paper they are described the test-set-up and the results of the experimental verification campaign made through the qualification hardware of the SAR.

In the frame of the study "Innovative radar altimeter concepts", founded by the European Space Agency (ESA), the authors analyzed potential advanced measurement concepts for radar altimeters of future generation, studied the feasibility of the identified techniques and proposed a design for an instrument based on the most promising system concept. This paper summarizes the major results of the study.