The European Space Agency's (ESA) BIOMASS mission is a pioneering Earth observation satellite mission launched on April 29, 2025. Utilizing a P-band synthetic aperture radar (SAR), the objective of BIOMASS is to deliver estimates of above-ground forest biomass, forest height (FH), and forest disturbance (FD), with unprecedented accuracy. The mission's primary scientific goal is to quantify the distribution and changes in forest biomass, thereby reducing uncertainties in carbon flux estimates and informing climate models. The satellite's advanced instrumentation and innovative approach allow it to penetrate dense forest canopies, capturing data even in challenging environments. The mission will operate in two distinct phases: the tomographic phase and the interferometric phase, which will support polarimetric interferometric SAR (Pol-InSAR) and tomographic SAR (TomoSAR) processing. Additionally, BIOMASS will provide valuable observational data for ice sheets, deserts, the ionosphere, below canopy topography, and other domains.

Reliable crop monitoring is paramount to achieve the objectives of the Common Agricultural Policy (CAP) and Food and Agriculture Organization. Synthetic Aperture Radar (SAR) provides high-resolution imaging and all-weather data acquisition capabilities for crop monitoring. This study investigates the sensitivity of parcel-level Sentinel-1 interferometric coherence to farming activities (e.g. planting, emergence, harvest and tillage) and weather events. A methodology to detect activities was developed and validated using ground-truth data from four crop types, collected over four years. The proposed approach was able to detect over 60% of all nine different farming activities. The results show that interferometric coherence is a reliable indicator for farming activities that can be considered as events resulting in a clear structural change (e.g. tillage 100%), but less reliable for gradual changes (e.g. Emergence 40%).

This paper presents a multi-channel ground-based bistatic SAR receiver architecture designed to perform single-pass tomography using the Sentinel-1 satellites as transmitters of opportunity. The bistatic receiver presents only 3 imaging channels, which is an extreme case for single-pass tomographic estimation. The three antennas are placed in a non-uniform configuration, such that the two antenna separations are in a 2:1 ratio. For a fixed array length, the non-uniform 3-element array will extend the maximum unambiguous height (relative to the 3-element uniform array), while keeping the elevation resolution cell around the Rayleigh limit. In the proposed processing flow, for each Sentinel-1 overpass on the envisaged orbits, the bistatic SAR image of each channel is focused on a two-dimensional grid, and afterwards the elevation profile of a given area is computed using the Capon estimator. The proposed architecture was evaluated in a measurement campaign performed between June-November 2021 using an electronic target with two transmit antennas placed on a vertical pole situated at 58.5 m from the ground receiver. For an array length of 2.6 m, the overall root mean squared error of the relative height was below 10 cm, while the unambiguous interval and the height resolution cell were around 3.75 m and 1.2 m, respectively. The experimental data from this measurements campaign provide the first quantitative assessment of spaceborne transmitter/stationary receiver single-pass bistatic SAR tomography in a controlled environment. In the long term, these results may contribute to future multi-static spaceborne SAR missions for which a single-pass tomographic capability is envisioned.

The Biomass mission is the 7th Earth Explorer Mission within the frame of the ESA Earth Observation Programme. The primary objective of Biomass is to determine the worldwide distribution of forest above-ground biomass in order to reduce the major uncertainties in calculations of carbon stocks and fluxes associated with the terrestrial biosphere. To meet these objectives Biomass will carry, for the first time in space, a fully polarimetric P-band synthetic aperture radar (SAR) supporting also interferometric acquisitions. This paper provides an overview of the Biomass system design and development status.

The systematic high temporal coverage of Sentinel-1 Synthetic Aperture Radar (SAR) is ideal for agricultural monitoring. The availability of these data on cloud computing infrastructure eliminates the need for massive computing power to process imagery. However, their distribution as SAR imagery still limits their accessibility for non-expert users. In Agricultural SandboxNL, Copernicus Sentinel-1 imagery on the Google Earth Engine (GEE) was mined to produce a database of spatially-tagged, parcel-level backscatter for every agricultural parcel in the Netherlands from 2017 to 2019. The database includes descriptors from the publicly available Basisregistratie Gewaspercelen, allowing the user to query the database by crop type and administrative boundary for any region of interest within The Netherlands. Publication of this database reduces the burden of processing and extracting a large volume of Sentinel-1 SAR data for experts. More importantly, it provides easy access to the Sentinel-1 data for agriculture/agronomy experts with limited SAR processing experience. In addition, the GEE package Sen1byParcel developed for Agricultural SandboxNL is made publicly available so that Sentinel-1 imagery can be extracted for any user-provided shapefile.

Using a combination of multi-directional SAR and TIR measurements, the Harmony Earth Explorer 10 mission candidate will provide high resolution simultaneous measurements of surface stress, surface currents SST and wave spectra over oceans, 3-D deformation vectors over solid Earth, and time-series of surface elevation changes over volcanic areas and land ice masses. This will serve a series of science objectives aimed at better understating multi-scale processed and feedbacks in the Earth System.

Scheduled for launch in 2023, ESA's seventh Earth Explorer Mission, BIOMASS, will carry the first P-band synthetic aperture radar (SAR) to be flown in space, to gather fully polarimetric acquisitions over forested areas worldwide in interferometric and tomographic modes. This paper presents the algorithms developed to estimate biophysical parameters from BIOMASS measurements and their implementation in the BIOMASS level 2 (L2) prototype processor. The L2 processor will generate global maps of forest Above Ground Biomass (AGB), Forest Height (FH), Forest disturbance (FD). Accurate generation of these products requires the L2 processor to be closely inter-linked with the BIOMASS interferometric processor, in order to produce phase-calibrated interferometric stacks, retrieve sub-canopy terrain topography, and generate a 3D representation of forest structure by use of SAR tomography. AGB estimation results are here shown using BIOMASS-like acquisitions derived from campaign data acquired over six tropical forests in South America and Equatorial Africa.

This paper describes the rationale and development of the estimation techniques for the level-2 data products of the European Space Agency's 7th Earth Explorer BIOMASS mission. BIOMASS is planned for launch in 2023 and will carry the first-ever P-band synthetic aperture radar (SAR) onboard a satellite. It has been designed to produce consistent global maps of the Earth's forests during a nominal five-year lifetime. Fully polarimetric SAR data will be collected and the satellite orbit will be selected for repeat-pass interferometry and tomography in separated mission phases. Mission requirements call for three level-2 data products: above-ground biomass, forest height and forest disturbance. The paper also discusses the expected limitations of the estimation techniques and remaining problems to be addressed.

This paper presents a time-domain synthetic aperture radar (SAR) processor designed for Sentinel-l Terrain Observation by Progressive Scans (TOPS) monostatic data. The processor focuses Interferometric Wide (IW) swath and Extra Wide (EW) swath data on a selected region-of-interest (ROI) and consists of the following main stages: decoding of Level-0 data, selection of the relevant burst and pulses for the targeted ROI, range compression, azimuth frequency unfolding and resampling, and image focusing by a fast subaperture-based version of the back-projection algorithm. The performances of the developed processor are assessed on datasets acquired in IW and EW imaging modes. Such a time-domain processor can be regarded as a first step towards a geometry/frequency-agnostic SAR processing kernel for future monostatic/multi static spaceborne SAR missions.

Synthetic Aperture Radar Tomography (TomoSAR) is one primary remote sensing technique for deriving elevation estimations and recovering the 3D spatial information of an observed scene. This article presents a novel method for improved single-pass bistatic SAR tomography estimation, in the case of a spaceborne transmitter-stationary receiver architecture, with only three imaging channels at the receiver. The approach is based on the use of the coarray space to create a virtual set of acquisitions, as received from an array with a larger number of antenna elements. The proposed configuration is evaluated through simulations.

The paper proposes a methodology to perform azimuth focusing of spaceborne transmitter-stationary receiver bistatic synthetic aperture radar (SAR) data across multiple along-track apertures to increase azimuth resolution. The procedure uses as input several azimuth apertures (continuous groups of range compressed pulses) from one or more satellite bursts and comprises the following stages: azimuth antenna pattern compensation, slow time resampling, reconstruction of missing azimuth samples between neighbouring sets of pulses using an auto-regressive model and back-projection focusing of the resulting multi-aperture range image. The approach is evaluated with real bistatic data acquired over an area of Bucharest city, Romania.

This paper addresses the feasibility of exploiting a radargrammetric procedure for the retrieval of height estimates using stereo images acquired in a space-surface (spaceborne transmitter-stationary receiver) bistatic geometry. Currently, the research interest concerning this particular direction is still in its infancy, as there are very few papers partially covering the subject. The method proposed in this study is applied to a set of SAR images (displaying an urban area of the Bucharest city) in order to assess the elevation of a group of selected targets within the remotely sensed zone.

Space-based radio echo sounding of the continental ice sheets can potentially provide full coverage with uniform sampling and data quality as well as detection of change in environmentally sensitive areas. This paper addresses the feasibility of sounding the Antarctic ice sheets with a space-based P-band radar. The assessment firstly makes use of an electromagnetic model of the ice sheets where the key model parameters are determined from data that have been acquired in Antarctica with an airborne P-band ice sounding radar. The performance of a space-based radar with a nadir-looking geometry but otherwise similar to ESA's Biomass SAR, is then simulated for a set of Antarctic scenarios that are defined based on the statistics of key ice regions. It is found that in about 2/3 of the simulation scenarios clutter and/or thermal noise will obscure the echo from the ice bed.

This paper presents a Synthetic Aperture Radar (SAR) simulator designed to assess the performance of bi-static SAR missions. It is a modular software able to simulate realistic SAR data (including injection of the system non-idealities), to estimate the SAR performance at radiometric and interferometric level. In order to ensure accurate measures of the bi-static performance, it simulates raw data exploiting a time-domain approach, without assumptions on the acquisition geometry. This feature makes the simulator a useful tool for the design of new SAR mission concepts. We also report sample results considering the SAOCOM-CS mission case as an example of application of the simulator.

The European Space Agency (ESA) STEAM (SaTellite Earth observation for Atmospheric Modelling) project aims at investigating new areas of synergy between high-resolution numerical atmosphere models and data from spaceborne remote sensing sensors, with focus on Copernicus Sentinels 1, 2 and 3 satellites. An example of synergy is the ingestion of surface information derived from Sentinel data in numerical weather prediction models. The rationale is that Sentinels 1, 2 and 3 are able to provide high spatio-temporal resolution information on the surface boundary (as well as the atmosphere column) and that an inaccurate representation of the boundary conditions represents a major source of uncertainty for weather forecasts. For a profitable ingestion of EO data in numerical weather prediction models, a critical aspect is the choice of a suitable model. Once the numerical model is chosen, the problem of the selection of the Sentinel-derived surface variables that have to be ingested in the model has to be tackled. While some data, such as sea and land surface temperature, are directly available, other surface data, such as soil moisture, have to be retrieved. Being STEAM currently in its initial phase, this paper gives a general overview of the project and focuses on the first activities performed in its framework. In particular, it describes the rationale behind the choice of the Numerical Weather Prediction Model and the multi-temporal approach designed to retrieve soil moisture from Sentinel-1 data. Moreover, the first results of the ingestion of Sentinel derived soil moisture, land surface temperature and sea surface temperature data into the selected model are shown. These results concern an extreme weather event that occurred in Tuscany (central Italy) in September 2017.

Companion SAR missions offer a cost-effective solution to enhance the added value of existing SAR satellites. In particular, they offer new possibilities to extend the observation space and provide one or several single-pass interferometric channels for the acquisitions. The paper aims to provide a description of an end-to-end performance simulation for companion SAR missions, including the evaluation of two exemplary configurations under realistic conditions and with the incorporation of the major error sources affecting these systems. A critical discussion of the results will be included of the final version of the paper drawing from the analysis relevant conclusions for the design of payload and concepts for future companion SAR missions.

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.

Ka-band may lead to important applications for the next generation of SAR spaceborne sensors (e.g.: DEM, disaster management, GMTI, subsidence, ocean currents, vegetation height). Nevertheless, the lack of trusted references on backscatter at Ka-band revealed to be the main limitation for the investigation of future applications. The paper, supported by the ESA project “Ka-band SAR backscatter analysis in support of future applications”, is aimed at studying the wave interaction at Ka-band for a widely varying range of targets in order to define a set of well calibrated and reliable KA-band backscatter coefficients. Here, we propose several examples of backscatter data resulting from a critical survey of available datasets at Ka-band. The reliability of the results will be assessed via a preliminary comparison with Electromagnetic Models (EM).

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 work we report the main conclusions of the European Space Agency (ESA) Metawave project (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects) for what concerns the Synthetic Aperture Radar Interferometry (InSAR) viewpoint. The Atmospheric Phase Screen (APS) estimated with the Permanent Scatterers (PS) technique in the test sites of Roma and Como has been compared with MM5 simulations, Meris Water Vapor (WV) data and GPS Zenith Wet Delays (ZWD). The experiment shows that, even though MM5, Meris and GPS data detect the similar absolute amount of WV, their accuracy is not enough to compensate the InSAR sensitivity to the WV spatial variability. In particular, Numerical Weather Prediction models look promising for correcting long WV spatial wavelengths in presence of topography; GPS measurements reveal the best performances toward short WV spatial wavelengths, while Meris data in the analyzed area show generally poor reliability.

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as tectonic movements, landslide monitoring and digital elevation model extraction. One of its major limitation is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which introduces an unknown delay in the signal propagation. This paper describes the general approach and some results achieved in the framework of an ESA funded project devoted to the mapping of the water vapour with the aim to mitigate its effect in InSAR applications. Ground based (microwave radiometers, radiosoundings, GPS) and spaceborne observations (AMSR-E, MERIS, MODIS) of columnar water vapour were compared with Numerical Weather Prediction model runs in Central Italy during a 15-day experiment. A dense network of GPS receivers was deployed close to Como, in Northern Italy, to complement the operational network in order to derive Zenith Total Delay as well as Slant Delay which can support InSAR processing. A comparison with Atmospheric Phase Screens (APS) derived from a sequence of Envisat multi pass interferometric acquisitions processed using the Permanent Scatters technique on the two test sites has been also performed. The acquired experimental data and their comparison give a valuable idea of what can be done to gather information on water vapour, which, besides InSAR applications, plays a fundamental role in weather prediction and radio propagation studies. The work has been carried out in the framework of an ESA funded project, named "Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects" (METAWAVE). This paper presents the general approach an the various methodologies exploited in the project, together with the overall intercomparison of the results. In deep details on the comparison with the InSAR APS maps derived by the PS technique, as well as on GPS receiver processing and water vapour tomography are reported in two companion papers.

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.

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as monitoring tectonic movements and landslides or extracting digital elevation models. One of its major limitations is the atmospheric variability, and in particular the high water vapor spatial and temporal variability, which introduces an unknown delay in the signal propagation. On the other hand, these effects might be exploited, so as InSAR could become a tool for highresolution water vapor mapping. This paper describes the approach and some preliminary results achieved in the framework of an ESA funded project devoted to the mitigation of the water vapor effects in InSAR applications. Although very preliminary, the acquired experimental data and their comparison give a first idea of what can be done to gather valuable information on water vapor, which play a fundamental role in weather prediction and radio propagation studies.

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.

In a recent paper, Younis et al. propose an apparently interesting methodology for the computation of the interference received by a spaceborne passive sensor from terrestrial interferences. However, the paper seems to require some clarifications, as some of the conclusions are questionable. This comments paper aims at identifying the most outstanding issues of the publication.

This paper presents an overview of the microwave instruments currently in development under the Future Programmes of the ESA's Earth Observation Envelop Programme. The description of the instruments will be structured according to two broad categories of future missions, i.e. the Earth Explorer and Earth Watch candidates.

At the World Radiocommunication Conference 2003 (WRC-03) of the International Telecommunication Union (ITU) several issues related to Earth observation will be on the agenda and decisions will be taken with respect to these so-called agenda items. In this paper the current status of some of the WRC-03 agenda items will be given where Earth observation is directly involved through its active instruments, the so-called Earth Exploration Satellite Service (active), or its passive instruments, the so-called Earth Exploration-Satellite Service (passive). The paper discusses and presents the status up-to-date for the following agenda items for WRC-03: (1) Agenda Item 1.5: introduction of Radio Local Area Networks (RLANs) in the bands 5150-5350 MHz and the band 5470-5725 MHz. The 5250-5350 MHz band is an extensively used band for remote sensing by SARs, scatterometers and altimeters. This agenda item also asks for an extension of the EESS (active) band from 5460-5570 MHz to facilitate wideband (up to 320 MHz) active sensors. (2) Agenda Item 1.38: the possible allocation of 6 MHz for EESS (active) in the frequency range 420-470 MHz (P-band). A new frequency allocation in P-band would enable a future satellite project to carry a P-band radar for e.g. penetrating forest canopies for biomass estimation and ice-sheet sounding on Antarctica for retrieval of the bedrock topography. (3) Agenda Item 1.8.2: the protection of EESS (passive) sensors from unwanted emissions in adjacent and nearby bands. The issue of unwanted emissions is difficult to tackle both from a technical and regulatory point of view especially when linked to the protection of exclusive passive band At the time of the IGARSS conference itself, the outcome of these WRC-03 agenda items including the upcoming agenda items for the next World Radiocommunication Conference (planned in 2007) will be known and will be presented. Consequentially, the Earth observation community will informed at a very early stage which issues are selected for the next World Radiocommunication Conference where EESS (both active and passive) is directly involved as well as the implications of the outcome of the issues leading to WRC-03.

A new simple scatterometer concept combines the advantages of both the fixed, multiple beam, sidelooking radar such as AMI-Wind (ERS-1/2) and NSCAT (ADEOS), and the conically scanning pencil-beam radar such as SeaWinds. A wide, fanbeam antenna is rotated around a vertical axis with a slow rotation rate. For a satellite at an altitude of 725 km, the antenna footprint sweeps a circular donut of 1500 km diameter. Such a slow conical scan combined with the motion of the satellite at /spl ap/7 km/s ground speed results in highly overlapping successive sweeps such that an image pixel is revisited up to 10-11 times during an overpass. The pixels in the radial direction are resolved by range-gating the radar echo. Depending on the across-track position of the imaged pixel, the measurement acquisitions during an overpass consist of a set of /spl sigma//spl deg/ at different combinations of the azimuth and incident angles. A preliminary optimization of the system resulted in a C-band radar concept with a 15 km multiple-look spatial resolution and global coverage in two days. A sketch of the developed concept, preliminary system design, and predicted performance are described.