French Space Research Articles

THE BIRTH OF SPACE OCEANOGRAPHY: TECHNOLOGICAL QUESTIONS AND CLIMATOLOGICAL OPPORTUNITY (UNITED STATES, FRANCE, 1950–1980)

ABSTRACT This article analyzes the formation of space oceanography as a scientific specialty, in France and in the United States. Throughout much of its history, oceanography has relied upon a broad range of instrumentation (bathyscaphes, tide gauges, and so forth). The importance of instrumentation meant that many of the exchanges during major scientific meetings in the 1960s focused on engineering problems. As a result, institutional investments by NASA and the French space agency, the Centre National d'Études Spatiales (CNES) supported advances in instrumentation. The emergence of the climate change issue made it possible to merge several factors (technical, geopolitical, and institutional) into the specialty of space oceanography. The birth of a scientific specialty requires the conjunction of several determining factors: a powerful disciplinary basis, a technological innovation resulting in major advances, and scientific politicians capable of tackling new problems. The development of space oceanography provides an excellent example of the origin of a new scientific specialty. The purpose of this article is to trace the history of the combination of the technical and scientific factors that resulted in the origin of space oceanography. This article will focus on specific events that led to the origin of space oceanography, in particular on a series of meetings organized by researchers interested in very specific technical questions. Many of the classical questions of oceanography could be addressed and dealt with by developing and using new instruments (e.g. radar altimeters). To document how the specialty of space oceanography developed, I propose to follow American and French examples of the transformations induced by space oceanography. Such a comparison makes it possible to measure the differential scientific ‘maturity’ of a nascent speciality. The emergence of climate change research, starting in the 1970s, reorganized many of the oceanographic research questions and legitimized the extension of the discipline into geospatial research. One goal of this article is to understand how this development of science policy influenced interactions between different disciplines.

The interactions between surface Kuroshio transport and the eddy field east of Taiwan using satellite altimeter data

Based on the daily sea surface height and absolute geostrophic velocity data from 1993 to 2015 provided by the AVISO Center of French Space Agency, the surface Kuroshio transport east of Taiwan and its adjacent eddy field (sea surface height anomaly) were analyzed. Four main periods of the surface Kuroshio transport and eddy field east of Taiwan were obtained, which were used to reveal their interactions. The main conclusions are as follows: (1) Based on the wavelet analysis, the surface Kuroshio transport east of Taiwan and its nearby eddy field showed significant seasonal, annual and interannual periods. In addition to the obvious periods of 182 days (0.5 year) and 365 days (1 year), there were also more obvious periods of about 860 days (2.35 years) and 2 472 days (6.8 years) for the surface Kuroshio transport. There were also four more obvious periods corresponding to the eddy field of 200 days (0.55 year), 374 days (1 year), 889 days (2.43 years) and 2 374 days (6.5 years), although there were latitudinal variations. (2) Based on both the correlation and causal analysis, the correlation between the surface Kuroshio transport and the nearby eddy field over the above four periods was analyzed, and different Kuroshioeddy interactions, with period and latitudinal variability, were revealed.

Validation of Copernicus Sentinel-2 Cloud Masks Obtained from MAJA, Sen2Cor, and FMask Processors Using Reference Cloud Masks Generated with a Supervised Active Learning Procedure

The Sentinel-2 satellite mission, developed by the European Space Agency (ESA) for the Copernicus program of the European Union, provides repetitive multi-spectral observations of all Earth land surfaces at a high resolution. The Level 2A product is a basic product requested by many Sentinel-2 users: it provides surface reflectance after atmospheric correction, with a cloud and cloud shadow mask. The cloud/shadow mask is a key element to enable an automatic processing of Sentinel-2 data, and therefore, its performances must be accurately validated. To validate the Sentinel-2 operational Level 2A cloud mask, a software program named Active Learning Cloud Detection (ALCD) was developed, to produce reference cloud masks. Active learning methods allow reducing the number of necessary training samples by iteratively selecting them where the confidence of the classifier is low in the previous iterations. The ALCD method was designed to minimize human operator time thanks to a manually-supervised active learning method. The trained classifier uses a combination of spectral and multi-temporal information as input features and produces fully-classified images. The ALCD method was validated using visual criteria, consistency checks, and compared to another manually-generated cloud masks, with an overall accuracy above 98%. ALCD was used to create 32 reference cloud masks, on 10 different sites, with different seasons and cloud cover types. These masks were used to validate the cloud and shadow masks produced by three Sentinel-2 Level 2A processors: MAJA, used by the French Space Agency (CNES) to deliver Level 2A products, Sen2Cor, used by the European Space Agency (ESA), and FMask, used by the United States Geological Survey (USGS). The results show that MAJA and FMask perform similarly, with an overall accuracy around 90% (91% for MAJA, 90% for FMask), while Sen2Cor’s overall accuracy is 84%. The reference cloud masks, as well as the ALCD software used to generate them are made available to the Sentinel-2 user community.

Propagation Experiment at <italic>Ka</italic>-Band in French Guiana: First Year of Measurements

ONERA, the French Aerospace Lab, and CNES, the French Space Agency, are currently running a Ka -band propagation experiment at the Guiana Space Centre (CSG) in Kourou (French Guiana). A rain gauge and a beacon receiver able to record the 20.2 GHz beacon signal of the Amazonas 3 satellite have been deployed. The equipment is operational since January 1, 2017, and the duration of the experiment has been set to three years. This letter addresses some results of the first year of measurements (from January 2017 to December 2017). The annual and monthly complementary cumulative distribution functions of rainfall rate and rain attenuation are presented as well as a comparison with the rain attenuation prediction method recommended in ITU-R P.618-13.

Charging characteristics and micromechanism of space electrons irradiated polymers

The charging characteristics and microscopic mechanism of space electrons irradiated polymers are the basis for the study and protection of spacecraft polymer charging and discharging characteristics. Monte Carlo method is used to simulate the scattering process of space electrons, and the fast secondary electron model simulates the generation of secondary electrons. The finite difference method is used to solve the charge transport process of charge continuity equation, current density equation and Poisson equation. The capture process realizes the transmission process of space electrons through the equation based on the Poole-French effect. Based on the electronic scattering/transport synchronization model and combined with the geostationary earth orbit electronic spectrum distribution theoretical formula of the French National Aeronautics and Space Research Agency (ONERA) and the ground experimental method of the agency (SIRNE), a scattering model based on the electron spectrum distribution in geosynchronous orbit is established. The numerical simulation of the charging process of space electrons irradiated polymers is carried out. The space charge density, space potential, electric field distribution and the space potential of polymer sample under the irradiation of single- and multi-energy electrons in space environment are obtained. The relationship among charging characteristics, microscopic parameters and surface potential of the sample is clarified. The surface potential characteristics of space electrons irradiated polymer are consistent with the experimental results. The single energy charge potential and strength are higher than those of multi-energy electrons. When the charging reaches a steady state, the electron mobility is smaller (less than 10<sup>–11</sup> cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>), and the absolute value of the space potential is significantly enhanced with the decrease of the electron mobility. When the composite rate is large (greater than 10<sup>–14</sup> cm<sup>3</sup>·s<sup>–1</sup>), the absolute value of the spatial potential increases with recombination rate increasing. The study of the charging characteristics of space electrons is not comprehensive because only the mode of single-energy electron irradiation is taken into consideration. The research results are of great scientific significance and practical value for revealing the charging characteristics and microscopic mechanism of space electrons irradiated polymer and improving the research level of spacecraft charge and discharge fault mechanism.

Averaging bias correction for the future space-borne methane IPDA lidar mission MERLIN

Abstract. The CNES (French Space Agency) and DLR (German Space Agency) project MERLIN is a future integrated path differential absorption (IPDA) lidar satellite mission that aims at measuring methane dry-air mixing ratio columns (XCH4) in order to improve surface flux estimates of this key greenhouse gas. To reach a 1 % relative random error on XCH4 measurements, MERLIN signal processing performs an averaging of data over 50 km along the satellite trajectory. This article discusses how to process this horizontal averaging in order to avoid the bias caused by the non-linearity of the measurement equation and measurements affected by random noise and horizontal geophysical variability. Three averaging schemes are presented: averaging of columns of XCH4, averaging of columns of differential absorption optical depth (DAOD) and averaging of signals. The three schemes are affected both by statistical and geophysical biases that are discussed and compared, and correction algorithms are developed for the three schemes. These algorithms are tested and their biases are compared on modelled scenes from real satellite data. To achieve the accuracy requirements that are limited to 0.2 % relative systematic error (for a reference value of 1780 ppb), we recommend performing the averaging of signals corrected from the statistical bias due to the measurement noise and from the geophysical bias mainly due to variations of methane optical depth and surface reflectivity along the averaging track. The proposed method is compliant with the mission relative systematic error requirements dedicated to averaging algorithms of 0.06 % (±1 ppb for XCH4=1780ppb) for all tested scenes and all tested ground reflectivity values.

Los "filmeurs" Joseph Morder y Alain Cavalier. Gesto fílmico de despojamiento y epistemología de la no manipulación

El presente artículo pretende analizar la práctica cinematográfica del filmeur a través de dos de sus máximos representantes en el espacio francés: Joseph Morder y Alan Cavalier. Se trata, por tanto, de determinar los planteamientos epistemológicos y las características estéticas de esta experiencia fílmica desarrollada en soledad, en la que la filmación se convierte en un “acto corporal y estético” caracterizado por la subjetividad, la intimidad, la inmediatez y la observación. El análisis de diferentes obras pertenecientes a ambos autores –Lettre de Joseph Morder à Alain Cavalier (2005), Joseph Morder par Alain Cavalier (2006), J’aimerais partager le printemps avec quelqu’un (2007), Le Filmeur (2005) y otras– permitirá evidenciar cómo estas experiencias de realidad van más allá de las prácticas diarísticas o autobiográficas, ya que la narración queda relegada en pos de la vivencia presente y espontánea del situarse “en el interior del acto de filmar”. Estas prácticas intimistas y minimalistas de un gesto cinematográfico de despojamiento están determinadas por la evolución de la tecnología utilizada y sus automatismos; en el caso de Morder desde el súper 8mm al teléfono móvil y en el de Cavalier a través de su pequeña cámara digital. Esta experiencia fílmica se define por una epistemología de la no manipulación que se convierte en transgresión de la ortodoxia cinematográfica.

Characterizing the dead time of the ECLAIRs camera on board the mission SVOM

French (CNES) and Chinese (CNSA) space agencies collaborate to build the SVOM (Space-based multi-band Variable Object Monitor) mission due to be launched in 2021 to study gamma-ray bursts and high-energy transients. The SVOM prime instrument, ECLAIRs, will detect and localize GRBs autonomously as well as provide a spectral and temporal characterization of the GRB prompt emission. ECLAIRs is expected to detect around 200 GRBs during the 3 year nominal lifetime of the mission. ECLAIRs is a wide-field (\(\sim 2 \text {sr}\)) coded mask camera with a detection plane made of 8 independent sectors of 800 Schottky CdTe detectors working in the 4-150 keV energy range. Each sector is connected to independent readout electronics. In this paper, we focus on the study of the temporal performance and we estimate how dead time will affect bright transient lightcurves. We discuss the analytical model based on simulations over a large range of source count rates on a dedicated test bench. We show that dead time will not significantly affect ECLAIRs data, even for the brightest GRBs (3.7% of lost counts for a count rate of 105 counts.s− 1 over the detection plane in the energy range 4−150 keV) and our model can nicely correct the parts of the lightcurves which are the most affected by dead time effects for very bright GRBs.

A strategy to implement a Software Defined Networking controller in a space launcher

Nowadays, networks need to take care about several metrics. In the case of space launcher, the Quality of Service (QoS) items are availability, real time and observability. In addition, events like failure or stage separation need a modification of the configuration during the flight respecting QoS purposes. In order to unify these QoS items and apply an online reconfiguration, a SDN centralized architecture is chosen. This paper proposes a methodology to implement a SDN controller that computes the forwarding plane taking into account the end-to-end delays requirement. Then, the methodology is considered in the case study of a space launcher application with the French Space Agency (CNES).

Satellites for What? Creating User Communities for Space-based Data in France: The Case from LERTS to CESBIO.

This article uses a French case to explore the who, how, and why of satellite remote-sensing development and its transition towards routine utilization in the domain of ecosystems ecology. It discusses the evolution of a community of technology developers promoting remote-sensing capabilities (mostly sponsored by the French space agency). They attempted to legitimate quality scientific practices, establish the authority of satellite remote-sensing data within academic institutions, and build a community of technology users. This article, hence, is intended to contribute to historical interest in how a community of users is constructed for a technological system.

Brief Introduction about the SVOM Mission

SVOM is a mission dedicated for studying <i>γ</i>-Ray Bursts, and will also be a powerful target-ofopportunity observatory for the whole astronomy community. The mission has been approved jointly by both Chinese and French space agencies. It is planned to be in the orbit in 2021 with an altitude ≤ 600 km and an inclination ≤ 30&#176;.

On the Simulation of Complex Visibilities in Imaging Radiometry by Aperture Synthesis

The basic observables of an imaging interferometer by aperture synthesis are the complex visibilities. Under some conditions, they can be simulated with the aid of the van Cittert–Zernike theorem. However, owing to underlying assumptions, some important effects that may alter them cannot be taken into account. This paper is devoted to the numerical simulation of complex visibilities without any reference to the van Cittert–Zernike theorem, in such a way that these effects can be taken into account. The emission from an extended source is modeled using a linear superposition of random waves emitted by a collection of point sources, which are all assumed to behave like black bodies at thermal equilibrium. These random waves are numerically generated with the aid of white noises filtered in such a way that their power spectral densities follow the shape of Planck distributions at the temperature of the point sources over a wide range of frequencies. The radio signal is then transported to the antennas, where the voltage patterns are taken into account as well as the filters response of the bandpass receivers. It is, therefore, sent to the correlator unit for being cross-correlated. From emission to correlation, perturbing effects can be introduced at any time. To illustrate this modeling method, numerical simulations are carried out in the L-band around 1413.5 MHz in reference to the SMOS- next project led by the French Space Agency. The results are discussed and compared with the estimates provided by the van Cittert–Zernike theorem. Owing to the amount of calculations to be performed, massive parallel architectures like that found in GPU have been required.

MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane

The MEthane Remote sensing Lidar missioN (MERLIN) aims at demonstrating the spaceborne active measurement of atmospheric methane, a potent greenhouse gas, based on an Integrated Path Differential Absorption (IPDA) nadir-viewing LIght Detecting and Ranging (Lidar) instrument. MERLIN is a joint French and German space mission, with a launch currently scheduled for the timeframe 2021/22. The German Space Agency (DLR) is responsible for the payload, while the platform (MYRIADE Evolutions product line) is developed by the French Space Agency (CNES). The main scientific objective of MERLIN is the delivery of weighted atmospheric columns of methane dry-air mole fractions for all latitudes throughout the year with systematic errors small enough (&lt;3.7 ppb) to significantly improve our knowledge of methane sources from global to regional scales, with emphasis on poorly accessible regions in the tropics and at high latitudes. This paper presents the MERLIN objectives, describes the methodology and the main characteristics of the payload and of the platform, and proposes a first assessment of the error budget and its translation into expected uncertainty reduction of methane surface emissions.

A demonstrator of an Ethernet based embedded network in space launchers

The relationships between the French Space Agency (CNES) and the CRAN laboratory are 10 years old. In this framework, the CRAN has studied how the Ethernet standardized network may advantageously replace the old MIL-STD-1553B communication bus which is embedded today in the European launchers. Some classical requirements had to be respected, but specific constraints of the spatial field have been also met. Theoretical studies were leaded, and it was expected by the CNES to validate the academic results through real experimentations on which the results should be confirmed. A demonstrator has been designed which has fulfilled its role, but has also induced new unexpected problematics.

Hayabusa2 Mission Overview

The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU3) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. The Haybusa2 spacecraft developed by Japan Aerospace Exploration Agency (JAXA) was successfully launched on December 3, 2014 by an H-IIA launch vehicle and performed an Earth swing-by on December 3, 2015 to set it on a course toward its target Ryugu. Hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on Ryugu, especially about the origin of water and organic materials transferred to the Earth’s region. Hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (ONC-T), a laser altimeter (LIDAR), a near-infrared spectrometer covering the 3-μm absorption band (NIRS3), and a thermal infrared imager (TIR). It also has three small rovers of MINERVA-II and a small lander MASCOT (Mobile Asteroid Surface Scout) developed by German Aerospace Center (DLR) in cooperation with French space agency CNES. MASCOT has a wide angle imager (MasCam), a 6-band thermal radiator (MARA), a 3-axis magnetometer (MasMag), and a hyperspectral infrared microscope (MicrOmega). Further, Hayabusa2 has a sampling device (SMP), and impact experiment devices which consist of a small carry-on impactor (SCI) and a deployable camera (DCAM3). The interdisciplinary research using the data from these onboard and lander’s instruments and the analyses of returned samples are the key to success of the mission.

SENTINEL-2 GLOBAL REFERENCE IMAGE VALIDATION AND APPLICATION TO MULTITEMPORAL PERFORMANCES AND HIGH LATITUDE DIGITAL SURFACE MODEL

Abstract. In the frame of the Copernicus program of the European Commission, Sentinel-2 is a constellation of 2 satellites with a revisit time of 5 days in order to have temporal images stacks and a global coverage over terrestrial surfaces. Satellite 2A was launched in June 2015, and satellite 2B will be launched in March 2017. In cooperation with the European Space Agency (ESA), the French space agency (CNES) is in charge of the image quality of the project, and so ensures the CAL/VAL commissioning phase during the months following the launch. This cooperation is also extended to routine phase as CNES supports European Space Research Institute (ESRIN) and the Sentinel-2 Mission performance Centre (MPC) for validation in geometric and radiometric image quality aspects, and in Sentinel-2 GRI geolocation performance assessment whose results will be presented in this paper. The GRI is a set of S2A images at 10m resolution covering the whole world with a good and consistent geolocation. This ground reference enables accurate multi-temporal registration of refined Sentinel-2 products. While not primarily intended for the generation of DSM, Sentinel-2 swaths overlap between orbits would also allow for the generation of a complete DSM of land and ices over 60° of northern latitudes (expected accuracy: few S2 pixels in altimetry). This DSM would benefit from the very frequent revisit times of Sentinel-2, to monitor ice or snow level in area of frequent changes, or to increase measurement accuracy in areas of little changes.

MICROSCOPE: five months after launch

MICROSCOPE is a French Space Agency mission that aims to test the Weak Equivalence Principle in space down to an accuracy of 10−15, two orders of magnitude better than the current constraints. The MICROSCOPE satellite was launched on April 25, 2016. We describe the MICROSCOPE mission, its measurement principle and instrument, and report on the status of its in-orbit commissioning as of September 2016.

PPP-method realization for the determination of Low Earth Orbit Satellite motion parameters using on-board GPS-observations

The results of development and testing of the domestic realization of PPP method (Precise Point Positioning) for high-precision determination of Low Earth Orbit satellites (LEOS) movement parameters using the results of on-board GPS-observations and the kinematic (geometric) positioning mode only without LEOS dynamic movement models are presented. The features of the proposed variant of the PPP method of processing the GPS-observations with using of precise ephemerides and clock estimates of GPS satellites, as well as other information from the IGS international service and the French space agency CNES are described. The components of the observation error model and the technique of “a priori” and “a posteriori” estimates of the accuracy of coordinate determinations are described. Using the example of the processing of the on-board GPS-observations from specialized foreign LEOS COSMIC it is indicated that for observation intervals of 30–40 minutes and more there can be achieved sub-decimeter accuracy of LEOS positioning. The results of comparison of the convergence of “float” and discrete/integer methods of carrier-phase ambiguity resolution are presented.

PSUP: A Planetary SUrface Portal

The large size and complexity of planetary data acquired by spacecraft during the last two decades create a demand within the planetary community for access to the archives of raw and high level data and for the tools necessary to analyze these data. Among the different targets of the Solar System, Mars is unique as the combined datasets from the Viking, Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions provide a tremendous wealth of information that can be used to study the surface of Mars. The number and the size of the datasets require an information system to process, manage and distribute data. The Observatories of Paris Sud (OSUPS) and Lyon (OSUL) have developed a portal, called PSUP (Planetary SUrface Portal), for providing users with efficient and easy access to data products dedicated to the Martian surface. The objectives of the portal are: 1) to allow processing and downloading of data via a specific application called MarsSI (Martian surface data processing Information System); 2) to provide the visualization and merging of high level (image, spectral, and topographic) products and catalogs via a web-based user interface (MarsVisu), and 3) to distribute some of these specific high level data with an emphasis on products issued by the science teams of OSUPS and OSUL. As the MarsSI service is extensively described in a companion paper (Quantin-Nataf et al., companion paper, submitted to this special issue), the present paper focus on the general architecture and the functionalities of the web-based user interface MarsVisu. This service provides access to many data products for Mars: albedo, mineral and thermal inertia global maps from spectrometers; mosaics from imagers; image footprints and rasters from the MarsSI tool; high level specific products (defined as catalogs or vectors). MarsVisu can be used to quickly assess the visualized processed data and maps as well as identify areas that have not been mapped yet. It also allows overlapping of these data products on a virtual Martian globe, which can be difficult to use collectively. The architecture of PSUP data management layer and visualization is based on SITools2 (Malapert and Marseille, 2012) and MIZAR (Module for Interactive visualiZation from Astronomical Repositories) respectively, two CNES generic tools developed by a joint effort between the French space agency (CNES) and French scientific laboratories. Future developments include the addition of high level products of Mars (regional geological maps, new global compositional maps…) and tools (spectra extraction from hyperspectral cubes). Ultimately, PSUP will be adapted to other planetary surfaces and space missions in which the French research institutes are involved.

Experimental study of hypervelocity impacts on space shields above 8 km/s

This paper deals with hypervelocity impacts of millimeter size space debris on space structures at velocity regime between 6 and 15 km/s. Millimeter size debris present a real threat to space structures since they cannot be tracked nor detected by radars. At the opposite, for larger debris, 5-10 cm size, avoidance manoeuvre can be conducted remotely from earth to shift the space structure from the threat trajectory. A lot of works (tests and simulations) have been done for debris smaller than 5 cm size. For debris smaller than 1 cm, the maximum impact velocity reachable with available facilities is mainly up to 8-8.5 km/s. As a result, the ballistic limit equation (BLE) for single plate, whipple shield and honeycomb structures are only based on analytical and numerical investigations for higher threat velocity.There is no efficient facility available to generate hypervelocity impacts in the 8-12 km/s regime for millimeter size projectile. To fulfil this need, the French space agency CNES granted a R&T contract to Thiot Ingenierie company for performing hypervelocity tests between 8 and 12 km/s. The contract specified Thiot Ingénierie for performing the analysis and the development of a special hypervelocity device that will be able to propel 1 to 3 mm aluminium sphere at this high velocity regime. With this innovative launcher, impacts of 1 mm sphere diameter at a speed of 10km/s and above is now reachable.The present study presents hypervelocity impacts on different types of targets: single plate, whipple shield and honeycomb structure have been tested. Impact velocities ranging from 7 to 10 km/s have been reached. Specific diagnostic tools (very high speed camera, X-rays flash photography …) are used to analyse the tests. Results, in terms of ejecta projection, post-impact damage are presented. The effects of ejecta tunnelling in the case of honeycomb shield is highlighted.