Convective systems are responsible for energy transfers between the lower and upper atmospheric layers and play a fundamental role in the water cycle, weather and climate evolution. With a tandem of high resolution and wide swath all-sky atmospheric sounders, the C2OMODO concept allows the estimation of vertical dynamics within deep convective systems.

This paper reports on the main results of SMOS-HR instrument technical study, a new interferometric radiometer dedicated to Soil Moisture and Ocean Salinity measurement from space. The instrument aims at providing enhanced spatial resolution with respect to SMOS and integrating robust RFI (RF Interference) mitigation technique. The instrument key performance requirements and the architecture features and trade-offs are exposed in this paper.

Recent applications of passive L-band observations from space are summarized for ocean, land surface and cryosphere applications. The main limitation of the measurements performed by the current generation of sensors is the spatial resolution. The need of a mission ensuring the continuation of L-band measurements from space with high spatial resolution (10-15 km) is discussed.

Digital Beam Forming (DBF) and Synthetic Aperture Inter-ferometry (SAI) are signal processing techniques that mixes the signals collected by an antenna array to produce high resolution images. This study aims at comparing these two approaches with the aid of simulations conducted at microwaves frequencies within the frame of the Soil Moisture and Ocean Salinity (SMOS) mission which is providing for more than a decade systematic passive L-band measurements from space. Although the two techniques are using the same signals and sharing the same goal, there are few differences that deserve attention. This is the case of the reconstruction floor error whose level and angular signature are significantly lower with the DBF paradigm than with the SAI one.

International audience

The Soil Moisture and Ocean Salinity (SMOS) satellite has provided, for the very first time, systematic passive L-band (1420 - 1427 MHz) measurements from space with a spatial resolution of ~v40 Km. Within the frame of the studies conducted by CESBIO and CNES for the next generations of high-resolution L-band imaging radiometers based on aperture synthesis, the concept of unconnected interferometry plays a key role in the roadmap because it is a solution for improving the spatial resolution. Before deploying such a mission, many issues have to be solved. This is why CNES has initiated the Unconnected L-band Interferometer Demonstrator (ULID) which aims at demonstrating the capability to operate unconnected interferometry in orbit. ULID system relies on a small constellation of three identical nano-satellites flying in close range formation and transmitting to ground the signals acquired by similar detectors onboard all satellites to allow synchronization and correlation computation. This contribution is concerned by the demonstration of our ability to cope with synchronization problems between the detectors.

The Soil Moisture and Ocean Salinity (SMOS) satellite has provided, for the very first time, systematic passive L-band (1420 - 1427 MHz) measurements from space with a spatial resolution of ~40 Km. Preliminary results of studies conducted within the frame of a High Resolution (HR) follow-on mission are presented. The SMOS-HR project has undergone a Phase 0 study by the French space agency. The aim of this contribution is to improve the spatial resolution capabilities of SMOS-HR from ~10 Km to ~4 Km with the aid of a swarm of nano-satellites orbiting close to the connected array selected for SMOS-HR. After SMOS and SMOS-HR, this third generation named SMOS-NEXT will be the very first one to perform aperture synthesis from space with both connected and unconnected interferometric measurements.

The SMOS mission, launched in 2009, has been followed by Aquarius and SMAP, but follow-on missions are still in the preliminary phases. One of the main expected improvements is on the spatial resolution, for which a 10-fold increase is needed. Regardless of the choice on acquisition principle (real aperture or interferometry) such a massive improvement cannot be addressed with current technology. But interferometry has an advantage here in the sense that it can be distributed over multiple satellites. The mission described in this paper is the first step towards a complete system to satisfy these challenging requirements. Such a massive improvement cannot be addressed with current technology and requires a major revisit of the acquisition of interferometric measurements. Of course, technological advances targeted by this mission concept is of far wider interest than L-band interferometry. The mission described in this paper is the first step towards a complete system to satisfy these challenging requirements.

The Soil Moisture and Ocean Salinity (SMOS) satellite is performing systematic L-band observations since 2009, allowing a large number of science and operational applications. Several recent studies have shown the need of the continuity of L-band observations, in particular with an increased angular resolution. In this contribution, two instrumental concepts are presented to reach native resolutions of 5–10 km. In addition, using airborne data, it is also shown that the accuracy of downscaling coarser resolution L-band data to 5–10 km using a high resolution auxiliary data set, is significantly lower than that of native high resolution observations.

After almost 10 years in operation (SMOS- Aquarius - SMAP) the very high potential of L band radiometry is clearly demonstrated. Several applications are already operational (assimilation at ECMWF, for hurricanes, for sea ice etc.) so it is crucial to maintain such measurements. To do so while satisfying the current missions specifications is also of prime importance. Degrading spatial resolution is thus a significant step back which will impact science and applications). These missions are now getting older and the goal of the study presented in this paper is to assess which planned mission could fulfill the requirements to ensure data continuity. For this purpose, an extensive users' requirements study was performed in 2018-2019 assessing what would be required in the near future as well as when L band radiometry was absolutely necessary to satisfy the requirements. From the gathered results a cluster analysis was performed and the only.

The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) has been providing the longest consistent data record of passive L-band (1.4 GHz) observations for more than ten years. SMOS, as well as the NASA missions SMAP and Aquarius have demonstrated the interest of L-band observations for land, ocean and cryosphere studies. The continuity of L-band observations must be assured taking into account that the spatial resolution (~ 40 km) of SMOS and SMAP is too coarse for some applications. Disaggregation strategies can be implemented but using airborne data, we show that the quality of the downscaled data cannot match that of an instrument with higher native resolution. The goal of the SMOS-HR (High Resolution) mission is to ensure the continuity of L-band observations while increasing the native resolution to 10 km. SMOS-HR will carry an array of ~ 230 antennas to perform aperture synthesis. The antenna distribution has been optimized to reduce the aliasing in the reconstructed images and SMOS-HR will incorporate advanced on-board Radio Frequency Interferences (RFI) mitigation techniques.

Continuation of brightness temperature measurements at L- band is a major asset for soil moisture and ocean salinity studies in the long term. The SMOS mission, launched in 2009, has been followed by Aquarius and SMAP, but follow-on missions are still in the preliminary phases. One of the main expected improvements is on the spatial resolution, for which a 10-fold increase is needed.Such a massive improvement cannot be addressed with current technology and requires a major revisit of the acquisition of interferometric measurements.The mission described in this paper is the first step towards a complete system to satisfy these challenging requirements.

The wave scatterometer, SWIM, will be on-board the Chinese French oceanographic mission, CFOSAT. It will complete the Chinese wind scatterometer, SCAT. They will provide the scientific community with joint wind and wave measurements for the very first time. The launch is now coming soon: autumn 2018. SWIM is a Ku-band real-aperture radar with 6 rotating fan-beams pointing near nadir. The main characteristics and performance of the instrument measured during the Satellite Integration Campaign, products and ground segment development are presented in this paper, as well as predicted performances estimated from simulations.

This paper provides an overview of the surface waves investigation and monitoring (SWIM) instrument which will be one of the two payload instruments carried by China France Oceanography SATellite (CFOSAT) with a planned launch date in mid-2018. SWIM is a real aperture wave scatterometer operated at near-nadir incidence angles and dedicated to the measurement of directional spectra of ocean waves. The SWIM flight model is currently being assembled and tested, its performance is being assessed and its prototype data processing algorithm is being developed. The aim of this paper is to provide a complete overview on the motivations and scientific requirements of this mission, together with a description of the design and characteristics of the SWIM instrument, and the analysis of its expected performances based on a prelaunch study. An end-to-end simulator has been developed to evaluate the quality of the data products, thus allowing the overall performance of the instrument to be assessed. Simulations run with two subsets of full orbit subsets show that the performances of the instrument and the inversion algorithms will meet the scientific requirements for the mission.

SWIM is part of the CFOSAT satellite mission payload. It is designed for the measurement of directional ocean wave spectra. It is a Ku-band real-aperture radar with 6 rotating fan-beams pointing near nadir. The main characteristics of the instrument, data, products are presented in this paper, as well as performances estimated from simulations.

The CFOSAT mission is an innovative spatial mission for oceanography: for the very first time, both wind and wave vectors will be measured at the global ocean surface. This paper presents the wave scatterometer, SWIM and its associated scientific performances.

SWIM (Surface Wave Investigation and Monitoring) is a spaceborne radar pointing at nadir and small incidence angles, scanning in azimuth. It is designed for the measurement of directional ocean wave spectra and will be embarked on the CFOSAT (China France Oceanography SATellite) mission to be launched in 2014. The CFOSAT project is now in the C/D phase (manufacturing phase). Taking into account the very last definition of the instrument, we present here the expected performances for estimates of significant wave height and spectral parameters of long ocean waves. These performances have been obtained using numerical simulations taking into account instrument specifications and realistic sea surface conditions, in particular those corresponding to the Atlantic storm of November 2002, which caused the Prestige ship sinking and its terrible oil slick.

In the frame of the development of the instrument SWIM (Surface Waves Investigation and Monitoring) on the CFOSAT program (Chinese French Oceanographic Satellite) funded by CNES, Thales Alenia Space is currently developing a new multi beam rotating antenna in Ku Band. This single reflector offset antenna includes a rotating feed comprising 6 beams. The SWIM instrument is the first ever space radar concept that is mainly dedicated to the measurement of ocean waves directional spectra and surface wind velocities through multi-azimuth and multi-incidence observations. Orbiting on a 500 km sun-synchronous orbit, its multiple Ku-band (13,575 GHz) beams illuminating from nadir to 10° incidence and scanning the whole azimuth angles (0-360°) provide with a 180 km wide swath and a quasi global coverage of the planet between the latitude of -80 and 80°. Such a wide range of observations requiring high range resolution (about 20 m on the ground) have led to design an instrument whose architecture and technology goes beyond what has been done on altimeter and scatterometer systems. At antenna subsystem level, multi-azimuth and multi-incidence observations requirements have led to design an ambitious antenna subsystem that rotates at 6 rotations per minute while transmitting RF signals towards 6 differents beams in Transmit and Receive Modes. Thales Alenia Space started in January 2009 under CNES contract phase B studies on the design of this multi beam rotating antenna in order to contribute to the System Preliminary Design Review held successfully in January 2010. B Phase complementary activities are currently under progress to prepare the C/D Phase planned to start beginning of 2011. This paper aims at giving an overview of the SWIM antenna preliminary design and performances.

SWIM is a Ku-band radar designed for wave directional spectrum estimation. This radar operates at six incidence angles (from 0° to 10°) with a complete azimuth scanning covering a swath of 180 km. The phase B (addressing preliminary design) of SWIM is currently under finalization. In, the preliminary design and associated performance analysis have been published taking into account the first results of Phase B design. This paper is focused on the last performance assessment of this phase B for all the measurements performed by the SWIM instrument.

This paper summarizes a study done by the EADS ASTRIUM and founded by the CNES (French spatial agency) in the field of the innovative focal planes for sub-millimetre wave radiometers. The objectives are to improve performance of space sub-millimetre wave instruments for two main applications: atmospheric chemistry study and ice clouds and precipitations observations. The areas for improvement are focused on global instrument architecture and on some specific focal plane components such as dichroïc filters and mixers.

The instrument SWIM (Surface Waves Investigation and Monitoring) on the CFOSAT program (Chinese French Oceanographic Satellite) is a state of the art radar for several reasons. At first, SWIM is the first ever space radar concept that is mainly dedicated to the measurement of ocean waves directional spectra and surface wind velocities through multi-azimuth multi-incidence observations. Orbiting on a 500 km sun-synchronous orbit, its multiple Ku-band (13, 575 GHz) beams illuminating from nadir to 10° incidence and scanning the whole azimuth angles (0-360°) provide with a 180 km wide swath and a quasi global coverage of the world between -80 and 80°. Secondly, such a wide range of observations requiring high range resolution (about 20 m on the ground) have led to design an instrument whose architecture and technology goes beyond what has been done on altimeter and scatterometer systems. The global coverage and the reduction of telemetry budgets have required to perform onboard range compression. The variety of signals at different incidences, the impact of the complex moving geometry of observation and the required real-time signal processing have led to propose onboard complete digital range compression on backscattered 320 MHz bandwidth signals. Finally, multi-azimuth multi-incidence observations requirements have led to design a complex antenna subsystem that rotates at 6 rounds per minute while transmitting high power RF signals towards tunable directions.

SWIM is a Ku-band radar designed for wave directional spectrum estimation. This radar operates at six incidence angles (from 0° to 10°) with a complete azimuth scanning. SWIM is currently in Phase B (concept and design phase). In [1, 2], the preliminary design and associated performance analysis have been published taking into account the end of Phase A design. This paper is focused on the performance assessment of the SWIM instrument based on the new developments which occur during Phase B. In addition, major reviews have been carried out on the performance analysis.

For current total power radiometers, the measurement of two different reference temperatures at least are necessary to be able to calibrate the radiometric receiver. In addition, we can note that two terms are essential to characterize the performance of a microwave radiometer : the radiometric sensitivity and the radiometric accuracy. On one hand, this paper will highlight the impact of the calibrations on the radiometric sensitivity. For that, some key elements as the gain stability or the number of calibration and their weighting are discussed. We will notably see that a trade off on these different parameters can be obtained in order to optimize this sensitivity. On the other hand, this paper will present the different elements that could affect the radiometric accuracy and it will focus on the elements related to the calibration.

In a study proposed by CNES, EADS ASTRIUM has analysed the feasibility and the design of Synthetic Aperture Radars within the stringent envelope of micro satellites. The primary mission objective is high resolution (2 metres for -17 dB.m2/m2 sensitivity) for a 5 km swath width, in X band. Two options have been analysed for this study. The first one was based on a passive reflector. Platform agility is required to achieve steering of the SAR beams in elevation. The second option was based on an active reflector antenna designed by THALES which detailed performances are currently studied under a Research and Technology study with CNES. This paper presents the definition and performances of a micro-satellite based on passive reflector antenna. This satellite design is compatible of a launch of up to three satellites at a time on low earth orbit, and offers Stripmap and ScanSAR modes capabilities. Finally, this short overview identifies the technological developments required to achieve the SAR on a micro satellite concept in the mid term

The interferometric cartwheel (CNES patent) is composed of three passive identical microsatellites set in a particular orbital geometry and flying behind or ahead of an active synthetic aperture radar (SAR) satellite. This satellite illuminates a ground swath and the reflected signals are received by the microsatellites with specific viewing configurations. The obtained data are mainly used for the computation of a Digital Elevation Model (DEM). This paper details first the across-track interferometry principle specific to the cartwheel geometry. General system and satellite characteristics are then presented as well as their main constraints. Finally, a performance budget based on a typical satellite configuration is carried out and leads to the topographic accuracy of the DEM.