This work is focused on the forthcoming ROSE-L mission, developed by the European Space Agency (ESA) as part of the Copernicus Expansion Programme. Among the different advanced engineering solutions that will be exploited by the system, we concentrate on the ScanSAR acquisition mode and show how to enable ROSE-L for a high gain two-look configuration. More specifically, we propose a solution aimed at achieving different goals.The first goal is focused on better tailoring the ROSE-L system, originally designed for a one-look ScanSAR mode configuration, to a more attractive two-look one. The second goal is to retain the azimuth resolution and the range swath of the original system design. The third goal is to be compliant with the main system specifications, with respect to the one- look mode configuration.To achieve these goals, we propose to properly shape the radiated azimuth beam, without upsetting the original design of the ROSE-L radar antenna and taking advantage of the degrees of freedom offered by its current layout.

This work shows that additional ScanSAR capabilities, with respect to those achievable through the current synthetic aperture radar (SAR) system of the forthcoming Radar Observation System for Europe at L-band (ROSE-L) mission, may be easily enabled through a proper shaping of the azimuth pattern of the TX radar antenna. In particular, we show that by properly acting only on the distribution of the input excitations of the elements of the currently designed TX antenna array, we can move from a single azimuth-look ScanSAR configuration to a more attractive two-look one. This result is achieved without upsetting the current system architecture and without changing the current mission parameters [such as azimuth resolution, range swath, and pulse repetition frequency (PRF)], all tailored to a one-look ScanSAR configuration. On the other hand, the proposed two-look mode requires to double the azimuth beamwidth with respect to the one-look mode, thus leading to an unavoidable antenna gain decrease, whose amount is approximately 3 dB. The presented analysis also shows that, by still acting on the distribution of the input excitations of the TX antenna array, the scalloping effect can be significantly mitigated with respect to that of the current system design, in both scenarios relevant to the original one-look ScanSAR configuration and the proposed two-look one.

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.

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.

In support of ESA's Mission Advisory Group for ROSE-L (Radar Observing System for Europe at L-band), a project team consisting of experts from operational ice services, universities and research institutes has been investigating the benefits of using data from L-band SAR in addition to C-band SAR imagery for monitoring of sea ice and detection of icebergs. The project work is still ongoing. Here, we introduce the technical background and present first results.

In the future ROSE-L mission, supported by the European Space Agency (ESA) as part of the Copernicus Expansion Programme, different advanced acquisition techniques will be simultaneously experienced, namely, ScanSAR, Scan On Receive and Digital Beam Forming on receive. This work shows that additional ScanSAR capabilities with respect to those achievable through the current ROSE-L system design may be enabled through proper shaping of the azimuth pattern of the TX radar antenna. In particular, we show that without upsetting the current system architecture, and properly acting only on the distribution of the input excitations of the elements of the currently designed TX array antenna, we can obtain a significant mitigation of the scalloping effect and/or move from a single azimuth look ScanSAR configuration to a more attractive two-look one.

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.

The Radar Observing System for Europe at L-band (ROSE-L) is part of the Copernicus Expansion Programme which focuses on new missions that have been identified by the European Commission (EC) as priorities for implementation in the coming years. ROSE-L provides additional capabilities above and beyond those of the current Sentinel missions, filling observation gaps as well new and emerging user needs not yet addressed.

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 September 2019, the German research icebreaker Polarstern started the largest multidisciplinary Arctic expedition, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to ice floes at high Arctic for a whole year, thus including the winter season, the main goal of the expedition is to better understand and quantify relevant processes within the atmosphere-ice-ocean system that impact the sea ice, ultimately leading to improved climate models. Satellite remote sensing, specially multi-frequency synthetic aperture radar (SAR) plays a major role to achieve this goal. Two major objectives in SAR based remote sensing of sea ice is on the one hand to have a large coverage, and on the other hand to obtain a radar response that carries as much information as possible. A comprehensive set of C- and L- band SAR images were acquired during the course of MOSAiC. In this initial study we evaluate the effects of seasonal changes on C- and L-band backscatter in respect to three different sea ice types, i.e., Young Ice, Smooth Ice and Rough/Deformed Ice along with the performance of sea ice type retrieval of a established algorithm. Areas of deformed, smooth and young sea ice were observed in the vicinity of R/V Polarstern and these areas are included whenever possible in the yearlong time series. For both frequencies a change in all backscatter channels values can be observed during the early melt season. This is first noticeable in the C-band images and later followed by a change in the L-band images, probably caused by their different penetration depth and volume scattering sensitivities.

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.

This brief note introduces a study that aims at quantifying the gain for sea ice observations which is achieved when combining L- and C-band SAR imagery for the retrieval of ice conditions and iceberg occurrences. An L-band SAR mission is currently under discussion at the European Space Agency (ESA) as one of the six Copernicus High Priority Candidate Missions (HPCMs). Since the emphasis of the study is on operational monitoring and ice charting, it involves contributions from different ice services that are members of the International Ice Charting Group (IICWG). Preliminary results confirm findings of earlier investigations on the use of L-band for sea ice monitoring and extend them with first systematic investigations of iceberg detection at L-band.

This paper takes stock of a Sentinel-1 (S-1) surface soil moisture (SSM) product, developed in the ESA SEOM project “Exploitation of Sentinel-1 for Surface Soil Moisture Retrieval at High Resolution” (Exploit-S-1). The characteristics of the product are illustrated and the benefits of the synergy with the future L-band Radar Observation System for Europe (ROSE-L) mission are discussed.

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

This paper investigates the sensitivity of Sentinel-1 (S-1) interferometric coherence to crop structure and near surface soil moisture (SSM) content. The study analyzes a data set collected in 2017 over the Apulian Tavoliere agricultural site (Southern Italy). The data set includes: i) in situ data over more than 600 agricultural fields monitored during the 2017 winter and spring growing seasons; ii) time-series of S-1 IW VV & VH backscatter & interferometric coherence; iii) time series of S-1 SSM maps. The temporal behavior of S-1 coherence and VH backscatter has been assessed over the monitored agricultural fields. Initial results indicate a stronger sensitivity of S-1 coherence than VH backscatter to crop geometric structure. In addition, an analysis at site scale, conducted before and after an important rain event, indicates a change of SSM from 0.18 to 0.30 m3/m3along with a change of S-1 coherence from 0.61 to 0.53.

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.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.As part of the Copernicus expansion, ESA has initiated the study phase for an L-band SAR mission (ROSE-L). At national level, Germany is perusing the implementation of the proposed Tandem-L mission.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 Sentinel-1 Space Segment and the Spacecraft development status and we also discuss the challenges for the evolution of the Copernicus SAR Space Component, based upon a review of the Sentinel-1 mission, i.e. its objectives and implementation, the systematic data acquisition strategy including coverage and revisit frequency, and the end-to-end SAR performance.

The objective of this study is to cross-compare three algorithms for retrieving surface soil moisture (SSM) from ESA's Sentinel-1 (S-1) data. The context is provided by the large scientific and application interest in SSM products at high resolution and regional/continental scale that can be retrieved from S-l data alone or in combination with other missions such as NASA/SMAP and ESA/SMOS. Of the three investigated algorithms, one inverts a scattering model exploiting a Bayesian approach, whereas the other two are change detection approaches. The cross-comparison is carried out by using both simulated and experimental data. Strengths and weaknesses of the three algorithms are identified and discussed.

Soil moisture content is an essential climate variable that is operationally delivered at low resolution (e.g. 36-9 km) by earth observation missions, such as ESA/SMOS, NASA/SMAP and EUMETSAT/ASCAT. However numerous land applications would benefit from the availability of soil moisture maps at higher resolution. For this reason, there is a large research effort to develop soil moisture products at higher resolution using, for instance, data acquired by the new ESA's Sentinel missions. The objective of this study is twofold. First, it presents the validation status of a pre-operational soil moisture product derived from Sentinel-1 at 1 km resolution. Second, it assesses the possibility of integrating Sentinel-2 data and additional ancillary information, such as parcel borders and high resolution soil texture maps, in order to obtain soil moisture maps at “field scale” resolution, i.e. ~0.1 km. Case studies concerning agricultural sites located in Europe are presented.

The systematic retrieval of near surface soil moisture (SSM) fields at high resolution (e.g., 0.1-1.0 km) is a challenging task that requires the exploitation of new retrieval algorithms and SAR data with advanced observational capabilities (in terms of spatial/temporal resolution, radiometric accuracy, very large swath, long-term continuity and rapid data dissemination). The launch of the Sentinel-1 (S-1) constellation provides these capabilities and calls for the development and validation of pre-operational SSM products at high resolution. The objective of this paper is to present and initially assess a SSM retrieval algorithm developed in view of S-1 data exploitation. The activity is supported by a large scientific community engaged in fostering a more effective interaction between researchers working in the field of high and low resolution SSM retrieval.

The concept of a passive receiving small satellite flying in formation with an active satellite for bistatic Synthetic Aperture Radar (SAR) imaging has been the subject of numerous national and international studies. In 2013, ESA received an offer from the National Commission for Space Activities of Argentina (CONAE) to launch a small satellite with the SAOCOM-1b satellite, and to collaborate during the mission exploitation phase. The main SAOCOM-1b payload is an L-band polarimetric SAR instrument. This offer, provides a unique opportunity to the Earth observation science community to demonstrate at global scale the science capabilities of an L-band active-passive satellite constellation through dedicated in-orbit experiments and to secure valuable feedback within a short time frame on the scientific potential of L-band SAR mission constellations.

In the above paper[1], there is an error inTable I. The value “30” in the bottom row, fifth column should be “350.” The corrected table is provided here.

The current paper aims to provide a brief overview of the ESA activities relevant to Polarimetric SAR missions mission development and exploitation, present achievements and discuss future opportunities for research.

The telecommunications sector has proposed to use the 5.350–5.470 GHz frequency band for ground-based communication services. The Sentinel-1, RadarSAT-2, and future RadarSAT constellation SAR satellites are operating in the same band. Here we assess the impact of these ground-based uncorrelated radio frequency interference (RFI) sources to radar interferometry-based ground motion analysis. Apart from a theoretical assessment, a Persistent Scatterer Interferometry analysis is performed based on a combination of real ENVISAT data and simulated RFI noise at different levels. The analysis shows that the RFI sources significantly reduce the applicability of radar interferometry, with a reduction of detected Persistent Scatterers with more than 50%. If the telecommunication sector would proceed with this plan, operational ground motion services based on Sentinel-1 data would no longer be possible.

Satellite radar altimeter (RA) measurements are important for continued monitoring of rapidly changing polar regions. In 2010, the European Space Agency launched CryoSat-2 carrying SIRAL, a Ku-band RA with objectives of determining the thickness and extent of sea ice and the topography of the ice sheets. One difficulty with Ku-band radar surveys over snow and ice is unknown penetration of RA signal into snow cover. Improving our understanding of the interactions of RA signals with snow and ice is needed to produce accurate elevation products. To this end, we developed a low-power, ultrawideband (12-18 GHz) RA for airborne surveys to provide fine resolution measurements capable of detecting both scattering from the surface and layers within sea ice and ice sheets. These measurements provide a means of identifying the dominant scattering location of lower resolution RA measurements comparable to satellite-based instruments. We generated two products: a full-bandwidth waveform (FBW) to identify scattering targets at fine resolution and a reduced-bandwidth waveform (RBW) to represent conventional RA measurements. Retrackers are used to generate height estimates over various surface conditions for comparisons. Over ice sheets, the leading-edge tracker provided consistent ice-surface elevation measurements between the FBW and RBW results; however, there were significant differences between the results from the centroid tracker. Over sea ice, the location of the dominant return between the results from snow-covered sea ice is highly variable. This paper provides an overview of RA surveys in polar regions, a description of the CReSIS system, and a discussion of the results.

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.

In this letter, a C-band SAR classification algorithm mapping agricultural crops dominated by surface or volume scattering is derived and assessed. The algorithm is an adaptive thresholding method based on the iterative solution of the Kittler-Illingworth method applied to exploit temporal series of cross-polarized SAR data. The performances of the classification algorithm have been assessed on ENVISAT ASAR data acquired over Görmin (Germany) during the AgriSAR'06 campaign and on RADARSAT-2 data acquired over Flevoland (The Netherlands) and Indian Head (Canada) during the ESA AgriSAR'09 campaign. The results indicate that the classification method improves the accuracy with respect to the one obtained by the threshold method based on a constant value, unless the data distributions are mono-modal. The algorithm is fast and robust versus changes of site location and it is expected to achieve an average overall accuracy better than 80%.

A significant source of error in the retrieval of sea ice freeboard from pulse-limited radar altimeters arises when scattering from off-nadir leads dominates the power echo causing the onboard tracker to “snag” and overestimate the two-way travel time. This range overestimate translates into an ocean elevation underestimate relative to the ice surface and an overestimate of the sea ice freeboard. We demonstrate using interferometric CryoSat-2 data that it is possible to infer the across-track angle of return to off-nadir leads and their location in the CryoSat-2 footprint and hence correct for the associated range error for the first time. It is found that specular scattering from leads can dominate the radar echo some 1530 m off nadir. Over the region studied, the mean ocean elevation bias is closely associated with the “pulse peakiness” (PP) parameter used for identifying specular waveforms. Considering only the most specular waveforms, the elevation bias was measured to be -1.21 ±0.93 cm. However, lowering the PP threshold includes lower power waveforms originating from higher off-nadir angles, and the elevation bias becomes -4.06 ±1.66 cm. Unaccounted for, these biases represent an ~ 10-40-cm overestimate in ice thickness. Despite the relatively large error on the mean bias, correcting for off-nadir ranging contributes only a small amount to the elevation uncertainty when combined with range and orbit determination uncertainties. We found that making use of CryoSat-2's interferometric mode over sea ice ultimately decreases the uncertainty on the area-averaged ocean elevation by allowing the inclusion of more waveforms in the analysis.

The use of Ka-Band in remote sensing creates new opportunities in Earth observation for science and civil security applications due to the unique characteristics of this higher frequency range. Several Ka-Band satellite missions and instruments are currently under development or close to launch (e.g. ALTIKA altimeter, SWOT satellite, etc). In addition, studies into future interferometric SAR missions are on-going and there is an increasing interest in the capabilities offered by radar systems at higher frequencies. This paper reports on major trends as derived from the 1st International Workshop on Ka-band Earth Observation Radar Missions (KEO'12), which was organized by the European Space Agency at ESA/ESTEC (The Netherlands) in November 2012.

The European Space Agency (ESA) is preparing candidates for the next Earth Explorer Core mission with the aim to select the 7th Earth Explorer mission to be launched towards the end of this decade. Earth Explorers are the backbone of the science and research element of ESA's Living Planet Programme, providing an important contribution to the global endeavor of understanding the Earth's system, particularly in view of global climate change. Six candidate missions were selected and investigated in the preliminary feasibility studies (Phase 0). A further down-selection was made after the User Consultation Meeting held in Lisbon, Portugal, in January 2009. Three candidate missions (Biomass, CoReH2O and PREMIER) were selected for further feasibility investigations (phase A). Each of the candidate missions has been defined in detail through two parallel and competing industrial studies and many complementary science and technology studies, aiming to the final down-selection in 2013, followed by the mission implementation with a planned launch in 2019. This paper will give an overview of the observation requirements, satellite system, payload and general status of the Biomass mission.

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 mapping and monitoring of sea ice regions represents a key application area for spaceborne synthetic aperture radar (SAR) missions. The European Space Agency (ESA) is under-taking the development of Sentinel-1, an imaging radar mission at C-Band for the continuation of SAR operational applications. Monitoring sea ice zones and the arctic environment is one of the major application areas supported by Sentinel-1. Other spaceborne SAR missions are being developed or considered by a number of space organizations. The study described herein focuses on evaluating the contribution of SAR constellations to operational and scientific monitoring of sea ice conditions through the analysis of multi-parameter SAR datasets (airborne, spaceborne) and through the development and exploitation of a simulation tool able to predict sea ice radar signatures as a function of the ice type and condition and of sensor parameters.

In this paper, a C-band SAR classification algorithm mapping agricultural crops dominated/non-dominated by volume scattering is described and assessed. The algorithm exploits cross-polarized SAR data and it is a part of the SMOSAR algorithm (“Soil MOisture retrieval from multi-temporal SAR data”) developed in view of the forthcoming Sentinel-1 data. The performances of the classification algorithm have been assessed on RADARSAT-2 data acquired over Flevoland (The Netherlands) and Indian Head (Canada) during the ESA AgriSAR'09 campaign. The results indicate that the selected method is fairly robust versus changes of site location and in average it is expected to achieve an overall accuracy equal or better than 80%.

The BIOMASS mission is designed to map the full range of the world's above-ground forest biomass, for the needs of national scale inventory and global carbon flux calculations. This objective is achieved with advanced P-band SAR techniques. The P-band biomass measurement concept was based on previous work over the past two decades. During the preparatory phase, new campaigns have been conducted to address critical issues on the biomass retrieval algorithms, over tropical and boreal forests. The collected datasets comprise accurate and complete sets of in situ data and advanced P-band SAR data. This paper presents the retrieval algorithms developed using the collected datasets.

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 complementary developments by ESA. This paper describes the Sentinel-1 mission, an imaging synthetic aperture radar (SAR) satellite constellation at C-band. It provides an overview of the mission requirements, its applications and the technical concept for the system.

The TropiSAR campaign has been conducted in August 2009 in French Guiana with the ONERA airborne radar system SETHI. The main objective of this campaign was to collect data to support the Phase A of the 7th Earth Explorer candidate mission, BIOMASS. Several specific questions needed to be addressed to consolidate the mission concept following the Phase 0 studies, and the data collection strategy was constructed accordingly. More specifically, a tropical forest data set was required in order to provide test data for the evaluation of the foreseen inversion algorithms and data products. The paper provides a description of the resulting data set which is now available through the European Space Agency website under the airborne campaign link. First results from the TropiSAR database analysis are presented with two in-depth analyses about both the temporal radiometric variation and temporal coherence at P-band. The temporal variations of the backscatter values are less than 0.5 dB throughout the campaign, and the coherence values are observed to stay high even after 22 days. These results are essential for the BIOMASS mission. The observed temporal stability of the backscatter is a good indicator of the expected robustness of the biomass estimation in tropical forests, from cross-polarized backscatter values as regarding environmental changes such as soil moisture. The high temporal coherence observed after a 22-day period is a prerequisite for SAR Polarimetric Interferometry and Tomographic applications in a single satellite configuration. The conclusion then summarizes the paper and identifies the next steps in the analysis.

The acquisition of Snow Water Equivalent (SWE) at spatial resolutions higher than those of the present methods relying on inversion of coarse-scale passive microwave observations is a possible application for space-borne SAR imagery. The presented experimental campaign NoSREx (Nordic Snow Radar Experiment) was initiated to contribute to the knowledge of snowpack backscattering and emission properties, in particular, to help develop methods to retrieve SWE from high-resolution two-frequency SAR observations (at X and Ku band). Another objective was to provide data for studies exploring the synergistic use of active and passive microwave observations for monitoring of snow properties. The NoSREx campaign began in November 2009, and has recently concluded a second winter period of observations.

The European Space Agency (ESA) released a Call for Proposals for the next Earth Explorer Core Mission in March 2005, with the aim to select the 7thEarth Explorer (EE-7) mission for launch in the next decade. Twenty-four proposals were received and subject to scientific and technical assessment. Six candidate missions were selected and further investigated in the preliminary feasibility studies (Phase 0). A further down-selection was made after the User Consultation Meeting held in Lisbon, Portugal in January 2009. Three candidate missions were selected for further feasibility investigations (phase A). Each of the candidate missions is now being defined in detail through two parallel and competing industrial studies and many complementary science and technology studies, aiming to the final down-selection in 2011/12, followed by the mission implementation with a planned launch in the 2016/17 timeframe.

The TropiSAR campaign has been conducted in August 2009 in French Guiana with the ONERA airborne system SETHI. The main objective of this campaign was to collect data to support the Phase A of the Earth Explorer candidate mission, Biomass. Several specific questions need to be addressed to answer the recommendations of the ESAC group and the data collection strategy has been constructed accordingly. The first part of the paper lists these specific questions. We then describe the selected test sites, followed by a summary on the radar instrument and the radar configuration (geometry and waveform). The data acquisition plan is provided and the temporal behaviour of the P-Band data is explored.

We present initial results from an experimental campaign aiming to acquire a comprehensive, full-snow season dataset of simultaneous backscatter and brightness temperature measurements of snow covered ground. The campaign is a part of Phase A activities in support of the proposed CoReH2O mission, aiming both to contribute to investigations on interpreting snow properties from active microwave observations, and to explore the possibilities for synergistic use of active measurements with existing passive microwave instruments. The campaign period covers the winter season of 2009-2010. Microwave observations are complemented by detailed in situ data of snow cover properties.

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 complementary developments by ESA. This paper describes the Sentinel-1 mission, an imaging synthetic aperture radar (SAR) satellite constellation at C-band. It provides an overview of the mission requirements, its applications and the technical concept for the system.

The choice of synthetic aperture radar (SAR) system design parameters such as radiometric calibration uncertainty and noise-equivalent sigma zero has a significant impact on applications exploiting SAR image data. However, methods for quantitatively translating the impact of system and mission parameter choices into the application context are lacking. This letter addresses this subject and derives a closed-form algebraic expression for translating radiometric biases due to calibration uncertainties-an important SAR engineering specification-into estimates of classification uncertainties for the restricted case of two homogeneous classes characterized by different backscatter intensity levels. The expression is exploited within this letter to estimate the potential impact of radiometric uncertainty on SAR-derived thematic maps. The results indicate that classification results based on the joint use of data from future SAR constellations in particular may be significantly degraded due to calibration uncertainties.

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 complementary developments by ESA. This paper describes the Sentinel-1 mission, an imaging synthetic aperture radar (SAR) satellite constellation at C-band. It provides an overview of the mission requirements, its applications and the preliminary technical concept for the system.

A new call for Core Earth Explorer Ideas was released by the European Space Agency in March 2005. The Call focused on the global carbon and water cycles, atmospheric chemistry and climate, as well as the human element as a cross cutting issue. The proposals were peer reviewed by scientific panels, and also appraised technically and programmatically by ESA. This paper describes the Earth Explorer cycle and gives an overview of the six candidate missions selected for assessment studies.

Land surface process modelling might be limited due to lack of reliable model input data. Key surface variables as land cover information or soil moisture conditions have been proven to be observable by remote sensing systems. The integration of remote sensing data into land surface process models might therefore help to improve their simulations results. Longer wavelength SAR data has a higher sensitivity to soil moisture content than higher frequency systems. Recent (ALOS) and planed (e.g. TerraSAR-L) SAR systems are therefore expected to provide valuable information about soil moisture dynamics. The present study investigates the potential to retrieve land cover information and geophysical parameters from L-band SAR data. The retrieval results are assimilated into a state-of-the-art land surface model to evaluate the merit of L-band SAR data assimilation.

Soil roughness greatly affects the scattering process of microwaves to the soil surface. Previous studies showed that the values of roughness parameters increase asymptotically with increasing profile length. In this paper, 25-m profiles are used to study the influence of profile length on the roughness parameters and on the shape of the autocorrelation function. It is further investigated whether correct soil roughness parameters, as obtained from long surface roughness profiles, can be determined from 4-m-long profiles. Therefore, the extrapolation of an empirical relationship between roughness parameters and profile length is investigated, for three different roughness classes. The technique yields parameter values which are comparable to the 25-m roughness parameters.

ASIRAS is an airborne system designed for sea-ice and ice sheet monitoring. It has been developed by ESA under a Technology Research Program contract. The main sensor of this system is a high resolution Ku-band radar altimeter with 1GHz bandwidth. The observation concept is based on a scaled configuration of SIRAL sensor on board CryoSat. The principle of the measurements is based on a combination of ranging, SAR and Interferometric techniques. The development and the validation of ASIRAS are now completed. The system will be extensively used during the Calibration and Validation campaigns of CryoSat mission. This paper describes the key design drivers and the main features of the system. The key operational parameters of the instrument are discussed, with particular focus on the link between the space-based and the airborne configuration. Finally, the performance of the instrument is presented, based on the results obtained from technical flights and a validation campaign.

The objectives of the TerraSAR-SIM campaign were to quantify the impact of the time intervals between SAR acquisitions at different wavelengths on agricultural applications. In 2 flight campaigns in 5 similar flight programs suitable multipolarised L,-X- and C-band radar data were acquired in a test site in Barrax. The different processing qualities of the level 1b data were analysed with different evaluation methods such as separability analysis, scatter plots, histogram analysis, biomass correlation, classification. Particularly the separability analysis was used in order to assess the influence and quality of the different radar wavelength, polarisations, acquisition dates/time lags and of level 1B processing parameters on the quality of agricultural and land use applications and retrieval algorithms. Campaign and analysis results are presented in the following paper.

In this paper is proposed an alternative description of the roughness state of bare soil surfaces at the scale of the "homogenous" agricultural field. As a first step, the roughness power spectra of experimental profiles acquired over various test-sites in Europe are thoroughly investigated to characterize the main features of the different tillage states. Then, a novel roughness parameter is obtained by integrating the filtered power spectral density of the surface over a frequency band centered on the resonant Bragg frequency. This parameter can describe the roughness effectively seen by the SAR sensor at the scale of the field. Finally, the roughness parameter stability and its impact on the backscattered /spl sigma//spl deg/ are assessed with a view on investigating issues of parameters retrieval.

This paper aims to establish the joint roughness statistics for rms height s and correlation length l for agricultural bare soil fields and a variety of tillage conditions. To do so, we make use of a unique pan-European database of profile measurements covering five different sites and containing approximately 1.5 km of profile data. A preliminary assessment of the validity of the derived roughness statistics for electromagnetic scattering models is also carried out by comparing /spl sigma//sup 0/ predictions obtained using the integral equation model with derived roughness statistics and European Remote Sensing 1 and 2 (ERS 1/2) synthetic aperture radar observations. The results are then summarized within the overall context of roughness description and we discuss the implications in terms of forward modeling and inversion. The limitations of s and l parameters as roughness descriptors are also underlined.

The objective of this paper is to quantify the impact of the type of surface-profiling instrument on the roughness measurements in radar remote sensing studies. Particularly, the use of mechanical profilers as compared to more precise laser profilers is investigated. The motivations for this study are twofold. First, simple and inexpensive mechanical profilers will probably still be used extensively for in situ ground measurements in the next few years, e.g., to investigate the use of multipolarization, multiincidence angle satellite data, i.e., Advanced Synthetic Aperture Radar (ASAR) onboard the European Space Agency Environmental Satellite. Second, a great amount of roughness data have been acquired in the past by means of mechanical profilers and, to date, a quantification of the error budget affecting these measurements is still missing. The paper focuses on modeling and quantifying the measurement errors associated with profiles a few meters long. To determine the errors, we compare soil roughness measurements obtained using laser and mechanical profilers over agricultural surfaces with different roughness characteristics. The analyzed datasets consist of roughness measurements acquired over the Matera site (Italy) and the Marestaing site, near Toulouse (France), in 1998 and 2000, respectively. Analytical expressions for first and second statistical moments of roughness parameters as a function of different sources of measurement errors are derived and compared to experimental values. The results show that mechanical measurements, once appropriately calibrated, are in overall good agreement with laser measurements. Practical indications of the most appropriate profiler length and number of independent measurements to be recorded are also derived in the paper.

In order to improve a better quantitative understanding of the effect of soil moisture of bare soils on C-band SAR data, five dedicated "weather" stations with soil moisture probes, rain gauges, and temperature thermometers have been installed through the Flevoland test site (The Netherlands) since April 2000. In addition to the in-situ data, spaceborne SAR data at C-band measured by ERS-2 are also collected (3 images every 70 days), taking advantage that the test site is close-by the locations of the ESA transponders used for calibration of the SAR data. In this paper, the variations of the backscattering coefficient due to soil moisture changes are shown as well as the effect of rain precipitation's on the soil moisture at different depths. Diurnal variations of the soil moisture have been observed during drying periods and soil temperature measurements allow a precise monitoring of this effect.

Assesses the feasibility of retrieving soil moisture content over smooth bare-soil fields using European Remote Sensing synthetic aperture radar (ERS-SAR) data. The roughness conditions considered in this study correspond to those observed in agricultural fields at the time of sowing. Within this context, the retrieval possibilities of a single-parameter ERS-SAR configuration is assessed using appropriately trained neural networks. Three sources of error affecting soil moisture retrieval (inversion, measurement, and model errors) are identified, and their relative influence on retrieval performance is assessed using synthetic datasets as well as a large pan-European database of ground and ERS-1 and ERS-2 measurements. The results from this study indicate that no more than two soil moisture classes can reliably be distinguished using the ERS configuration, even for the restricted roughness range considered.

The surface roughness parameters commonly used as inputs to electromagnetic surface scattering models (SPM, PO, GO, and IEM) are the root mean square (RMS) height s, and autocorrelation length l. However, soil moisture retrieval studies based on these models have yielded inconsistent results, not so much because of the failure of the models themselves, but because of the complexity of natural surfaces and the difficulty in estimating appropriate input roughness parameters. In this paper, the authors address the issue of soil roughness characterization in the case of agricultural fields having different tillage (roughness) states by making use of an extensive multisite database of surface profiles collected using a novel laser profiler capable of recording profiles up to 25 m long. Using this dataset, the range of RMS height and correlation values associated with each agricultural roughness state is estimated, and the dependence of these estimates on profile length is investigated. The results show that at spatial scales equivalent to those of the SAR resolution cell, agricultural surface roughness characteristics are well described by the superposition of a single scale process related to the tillage state with a multiscale random fractal process related to field topography.