The accurate calibration of the line of sight (LOS) is very important for a high-resolution imaging satellite, especially in a system as Co3D, whose mission is to produce 3D elevation models. A calibration error immediately translates into an altimetry error. Co3D has a matrix and the reading of the lines is done in rolling shutter, each line is read at a different date. So, the geometry of the image is affected by the dynamic perturbations of the attitude during the acquisition time.The objective of the study is to propose a calibration method accurate to 0.1 pixel at 90 percentile. The images needed for calibration must only require one or two satellite passes over the same site, and be compatible with the pointing agility. The method must be robust to residual errors in attitude knowledge.The assumptions of the simulations have been modified in this article to keep the performance of Co3D confidential.

Pleiades-HR is a high resolution remote sensing system developed by the French Space Agency (CNES) for civil and military users. The constellation is composed of two identical satellites PHR1A launched on 2011, December 17th and PHR1B launched one year after, on 2012, December 2nd. More than 600 images can be daily acquired by each satellite in various viewing angles conditions: the satellites are able to target images with viewing angles greater than 47°. Since the launch of the first satellite, major improvements have been integrated in the ground processing to enhance the quality of products and offer new options. Starting from a Pleiades-HR system overview, this paper offers a description of the ground processing and presents an assessment of the different products available now, including image quality performances.

The PLEIADES program is a space Earth Observation system led by France, under the leadership of the French Space Agency (CNES). Since it was successfully launched on December 17th, 2011, Pleiades 1A high resolution optical satellite has been thoroughly tested and validated during the commissioning phase led by CNES. The whole system has been designed to deliver submetric optical images to users whose needs were taken into account very early in the design process. This satellite opens a new era in Europe since its off-nadir viewing capability delivers a worldwide 2- days access, and its great agility will make possible to image numerous targets, strips and stereo coverage from the same orbit. Its imaging capability of more than 450 images of 20 km x 20 km per day can fulfill a broad spectrum of applications for both civilian and defence users. For an earth observing satellite with no on-board calibration source, the commissioning phase is a critical quest of wellcharacterized earth landscapes and ground patterns that have to be imaged by the camera in order to compute or fit the parameters of the viewing models. It may take a long time to get the required scenes with no cloud, whilst atmosphere corrections need simultaneous measurements that are not always possible. The paper focuses on new in-flight calibration methods that were prepared before the launch in the framework of the PLEIADES program : they take advantage of the satellite agility that can deeply relax the operational constraints and may improve calibration accuracy. Many performances of the camera were assessed thanks to a dedicated innovative method that was successfully validated during the commissioning period : Modulation Transfer Function (MTF), refocusing, absolute calibration, line of sight stability were estimated on stars and on the Moon. Detectors normalization and radiometric noise were computed on specific pictures on Earth with a dedicated guidance profile. Geometric viewing frame was determined with a particular image acquisition combining different views of the same target. All these new methods are expected to play a key role in the future when active optics will need sophisticated in-flight calibration strategy.

In the frame of its earth observation missions, CNES created a library called QPEC, and one of its launcher called Medicis.QPEC / Medicis is a sub-pixel two-dimensional stereo matching algorithm that works on an image pair.This tool is a block matching algorithm, which means that it is based on a local method.Moreover it does not regularize the results found.It proposes several matching costs, such as the Zero mean Normalised Cross-Correlation or statistical measures (the Mutual Information being one of them), and different match validation flags.QPEC / Medicis is able to compute a two-dimensional dense disparity map with a subpixel precision.Hence, it is more versatile than disparity estimation methods found in computer vision literature, which often assume an epipolar geometry.CNES uses Medicis, among other applications, during the in-orbit image quality commissioning of earth observation satellites.For instance the Pléiades-HR 1A & 1B and the Sentinel-2 geometric calibrations are based on this block matching algorithm.Over the years, it has become a common tool in ground segments for in-flight monitoring purposes.For these two kinds of applications, the two-dimensional search and the local sub-pixel measure without regularization can be essential.This tool is also used to generate automatic digital elevation models, for which it was not initially dedicated.This paper deals with the QPEC / Medicis algorithm.It also presents some of its CNES applications (in-orbit commissioning, in flight monitoring or digital elevation model generation).Medicis software is distributed outside the CNES as well.This paper finally describes some of these external applications using Medicis, such as ground displacement measurement, or intra-oral scanner in the dental domain.

In the frame of the Copernicus program of the European Commission, Sentinel-2 offers multispectral high-spatial-resolution optical images over global terrestrial surfaces. In cooperation with ESA, the Centre National d’Etudes Spatiales (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. Sentinel-2 is a constellation of 2 satellites on a polar sun-synchronous orbit with a revisit time of 5 days (with both satellites), a high field of view - 290km, 13 spectral bands in visible and shortwave infrared, and high spatial resolution - 10m, 20m and 60m. The Sentinel-2 mission offers a global coverage over terrestrial surfaces. The satellites acquire systematically terrestrial surfaces under the same viewing conditions in order to have temporal images stacks. The first satellite was launched in June 2015. Following the launch, the CAL/VAL commissioning phase is then lasting during 6 months for geometrical calibration. This paper will point on observations and results seen on Sentinel-2 images during commissioning phase. It will provide explanations about Sentinel-2 products delivered with geometric corrections. This paper will detail calibration sites, and the methods used for geometrical parameters calibration and will present linked results. The following topics will be presented: viewing frames orientation assessment, focal plane mapping for all spectral bands, results on geolocation assessment, and multispectral registration. There is a systematic images recalibration over a same reference which is a set of S2 images produced during the 6 months of CAL/VAL. This set of images will be presented as well as the geolocation performance and the multitemporal performance after refining over this ground reference.

In the frame of the Copernicus program of the European Comission, Sentinel-2 will offer multispectral high-spatial-resolution optical images over global terrestrial surfaces. In cooperation with ESA, the Centre National d'Etudes Spatiales (CNES) is in charge of the image quality of the project, and will so ensure the CAL/VAL commissioning phase during the months following the launch.Sentinel-2 is a constellation of 2 satellites on a polar sun-synchronous orbit with a revisit time of 5 days (with both satellites), a high field of view - 290km, 13 spectral bands in visible and shortwave infrared, and high spatial resolution - 10m, 20m and 60m. The Sentinel-2 mission offers a global coverage over terrestrial surfaces. The satellites acquire systematically terrestrial surfaces under the same viewing conditions in order to have temporal images stacks. The first satellite has been launched in June 2015. Following the launch, the CAL/VAL commissioning phase will then last during 6 months for geometrical calibration.This paper first provides explanations about Sentinel-2 products delivered with geometric corrections. Then this paper details calibration sites, and the methods used for geometrical parameters calibration and presents the first linked results. The following topics are presented: viewing frames orientation assessment, focal plane mapping for all spectral bands, first results on geolocation assessment, and multispectral registration. There is a systematic images recalibration over a same reference which will be a set of S2 images produced during the 6 months of CAL/VAL. As it takes time to have all needed images, the geolocation performance with ground control points and the multitemporal performance are only first results and will be improved during the last phase of the CAL/VAL. So this paper mainly shows the system performances, the preliminary product performances and the way to perform them.

Sentinel-2 is a multispectral, high-resolution, optical imaging mission, developed by the European Space Agency (ESA) in the frame of the Copernicus program of the European Commission. In cooperation with ESA, the Centre National d’Etudes Spatiales (CNES) is responsible for the image quality of the project, and will ensure the CAL/VAL commissioning phase. Sentinel-2 mission is devoted the operational monitoring of land and coastal areas, and will provide a continuity of SPOT- and Landsat-type data. Sentinel-2 will also deliver information for emergency services. Launched in 2015 and 2016, there will be a constellation of 2 satellites on a polar sun-synchronous orbit, imaging systematically terrestrial surfaces with a revisit time of 5 days, in 13 spectral bands in visible and shortwave infra-red. Therefore, multi-temporal series of images, taken under the same viewing conditions, will be available. So as to ensure for the multi-temporal registration of the products, specified to be better than 0.3 pixels at 2σ, a Global Reference Image (GRI) will be produced during the CAL/VAL period. This GRI is composed of a set of Sentinel-2 acquisitions, which geometry has been corrected by bundle block adjustment. During L1B processing, Ground Control Points will be taken between this reference image and the sentinel-2 acquisition processed and the geometric model of the image corrected, so as to ensure the good multi-temporal registration. This paper first details the production of the reference during the CALVAL period, and then details the qualification and geolocation performance assessment of the GRI. It finally presents its use in the Level-1 processing chain and gives a first assessment of the multi-temporal registration.

This paper describes a simple pushbroom camera model for Earth observation satellites and proposes a new algorithm to refine the orientation parameters of a camera from a set of ground control points. The relative importance of the various orientation parameters are analyzed. On the last generation of very high resolution satellites such as Pléiades and WorldView, the attitude angles are shown to be the main contributors to localization errors. Thus the proposed algorithm focuses on refining the attitude angles. It is based on a simple polynomial fitting method. Numerous experiments, which can be reproduced through the online demo associated to this paper, show that the proposed algorithm is able to reduce the localization error by one order of magnitude with only a few ground control points. A geometric simulator for the proposed model is implemented, as well as the attitude refinement algorithm.

PLEIADES earth observing system consists of two satellites designed to provide optical 70cm resolution images to civilian and defense users. The first Pleiades satellite 1A was launched on December 2011 while the second satellite Pleiades 1B was placed on orbit, one year after, on December 2012. The calibration operations and the assessment of the image of the two satellites have been performed by CNES Image Quality team during the called commissioning phase which took place after each launch and lasted each time less than 6 months. The geometric commissioning activities consist in assessing and improving the geometric quality of the images in order to meet very demanding requirements. This paper deals with the means used and methods applied, mainly the innovative ones, in order to manage these activities. It describes both their accuracy and their operational interest. Finally it gives the main results for geometric image quality performances of the PHR system.

Pleiades est le système d'observation de la Terre civil le mieux résolu développé en Europe. Ce programme d'imagerie est conduit par le Centre National d'Etude Spatial français (CNES). Le premier satellite a été lancé le 17/12/2011 et le second le 02/12/2012. Chaque satellite est conçu pour fournir des images optiques aux utilisateurs civils et défense. Les images sont acquises simultanément en Panchromatique (PA) et multi-spectral (XS), ce qui permet en condition d'acquisition nadir d'obtenir des scènes de 20 km de large, en couleurs naturelles ou fausses couleurs, avec une résolution de 70 cm sur les produits PA+XS fusionnés. La couverture est quasi-mondiale avec une période de revisite de 24h avec les 2 satellites.L'évaluation de la Qualité Image et les opérations d'étalonnage ont été réalisées par l'équipe Qualité Image du CNES pendant les recettes en vol de 6 mois qui ont suivi le lancement de chacun des satellites. Ces activités couvrent plusieurs thèmes comme l'étalonnage absolu, le calcul des coefficients d'égalisation, les opérations de refocalisation, l'estimation de la FTM, l'étalonnage du modèle géométrique, l'estimation de la précision de localisation, la registration multi-spectrale, les stabilités statiques et dynamiques, les précisions planimétriques et altimétriques. Ces opérations nécessitent des réglages spécifiques de la charge utile ainsi que des guidages particuliers de la plateforme du satellite. Les nouvelles capacités offertes par l'agilité des satellites Pleiades nous ont autorisées à imaginer de nouvelles méthodes d'étalonnage et de mesures des performances.Après quelques rappels sur les caractéristiques principales des satellites, la présentation décrit les opérations d'étalonnage qui ont été menées pendant les recettes en vol et fournit les principaux résultats de Qualité Image.

This paper deals with the problem of retrieving attitude perturbances in the framework of the PLEIADES-HR optical satellites. Thus, two complementary methods are compared. The first one uses the high agility capacity of satellites to acquire stars in an inertial steering mode. The second method exploits the fact that multispectral CCD arrays are shifted in the telescope focal plane in the velocity direction: for a same ground point, the resulting images are not affected by the same attitude perturbances. The resulting misregistrations can be exploited to deduce information about the attitude platform. Both methods have been applied to PLEIADES-HR satellites, during commissioning period.

In the early phase of the Pleiades program, the CNES (the French Space Agency) specified and developed a fully automatic mosaicing processing unit, in order to generate satellite image mosaics under operational conditions. This tool can automatically put each input image in a common geometry, homogenize the radiometry, and generate orthomosaics using stitching lines. As the image quality commissioning phase of Pleiades1A is on-going, this mosaicing process is being tested for the first time under operational conditions. The French newly launched high resolution satellite can acquire adjacent images for French Civil and Defense User Ground Segments. This paper presents the very firsts results of mosaicing Pleiades1A images. Beyond Pleiades’ use, our mosaicing tool can process a significant variety of images, including other satellites and airborne acquisitions, using automatically-taken or external ground control points, offering time-based image superposition, and more. This paper also presents the design of the mosaicing tool and describes the processing workflow and the additional capabilities and applications.

Since SPOT1, the French national space centre (CNES) has worked on improving the geometry of Earth observation spacecrafts. The accuracy of sensor calibration is one of the main key points for any Earth observation application such as orthorectification, DEM generation or surface change detection. For the last twenty years CNES has developed two families of methods: absolute methods and relative methods. These methods are used to characterize a pushbroom acquisition along the detector line and the time line. By this way, the viewing directions are measured and the residual of the spacecraft’s attitude angles (not restituted by the Attitude and Orbit Control System) is estimated. This information can complete the geometric model of all the scenes acquired by the instrument and is used in all geometric applications. This paper presents new attitude assessment methods taking advantage of the capabilities of Pléiades-HR in terms of agility and focal plane arrangement – panchromatic band and multispectral (MS) bands.

The Pleiades system, ORFEO system optical component (Optical and Radar Federated Earth Observation) consists of a constellation of two satellites for very High Resolution panchromatic and multispectral optical observation of the Earth. Its mission is to cover all European civilian needs (mapping, tracking floods and fires) and defence in the category of metric resolution: 0.7m Nadir. The first Pleiades satellite was launched at the end of last year. One of the key objectives of the Pleiades HR (PHR) project is to achieve a location accuracy that will allow the use of images in GIS (Geographical Information System) without geometrical model improvement by refining on ground control points. The image location without refined model was specified with the precision of the most commonly used tool ie the civil GPS. So the location accuracy has been specified at less than 12m for 90% of the images on a nominal satellite configuration. Very special care has been taken all along the PHR project realization to achieve this very good location accuracy. The final touch is given during the in-orbit commissioning phase which lasts until June 2012. The geometric quality implies to tune the parameters involved in the geolocation model (geometric calibration): besides attitude and orbit restitution tuning (not considered here), it consists in estimating the biases between the instrument orientation and the AOCS reference frame, and also the sight line of each detector in the focal plane. This is called static geometrical model. The analysis of dynamic perturbations outside of the model are the second most important image quality objective of in-flight commissioning, not described in this paper. Finally “image quality assessment” consists in evaluating the image quality obtained in the final products. For geolocation model, it is quantified by the absolute geolocation and the pointing accuracies, and it is a main contributor in length alteration and planimetric and altimetric accuracies. In this paper we will present both the different practices we have adopted (their advantages, limitations and complementarities) and the means we are using for the operational assessment of the location quality of PHR images. We will focus on the innovative methods and mention the improvements in progress. To conclude, we will present the very first accuracy results assessed after PHR1A launch on L1 and Sensor products.

The new French high resolution earth observing satellite PLEIADES-HR will be launched in 2011. A specific design and new technologies have been embarked to provide great agility. These capabilities offer new methods to perform the image quality activities during the commissioning period. Some of them depend on dedicated guidance of the satellite platform and specific targets on the Earth or beyond. For instance, one concerns the so-called AMETHIST method to compute the normalization coefficients of the radiometric model. Another one is based on a controlled slow-motion to get a reference image line whose deviation along the image will give information on radiometric noise or attitude perturbations. Another uses the stars to measure the line-of-sight dynamic stability or the instrument refocusing needs. These originals methods and some more are briefly presented in this paper after an introduction of PLEIADES-HR capacities.

Since SPOT1, the French national space center (CNES) has worked on improving the geometry of Earth observation spacecrafts. The accuracy of sensor calibration is one of the main key points for any Earth observation application such as orthorectification, DEM generation or surface change detection [7]. Two families of methods have been developed by CNES for twenty years: absolute methods and relative methods. These methods are used to characterize a pushbroom acquisition along the detector line and the time line. By this way, the viewing directions are measured and the residual of the spacecraft's attitude angles (not restituted by the AOCS) are estimated. This information can complete the geometric model of all the scenes acquired by the instrument and is used in all geometric applications. We will first consider the absolute methods and then the relative methods.

The CNES (the French Space Agency) has specified and developed a fully automatic mosaicing processing unit, in order to generate satellite image mosaics under operational conditions. This tool, called SIGMA, can automatically put each input image in a common geometry, homogenize the radiometry, and generate orthomosaics using stitching lines.

In-flight Image Quality calibration and performance assessment activities depend on specific acquisitions and, for some of them, on dedicated guidance of the satellite platform. The operational constraints may be tedious during the commissioning phase. Moreover, the length of the requested data collection may be conditioned by uncontrolled parameters such as climatic hazard. The new French high resolution earth observing satellite Pleiades-HR will be launched at the beginning of 2010. A specific design and new technologies have been embarked to provide great agility. These capabilities offer new methods to perform the image quality activities. Two are described in this paper. The first one concerns the so-called AMETHIST method to compute the normalization coefficients of the radiometric model. The second one uses the stars to measure the line-of-sight dynamic stability.

Pleiades is a high-resolution optical Earth observation system developed by CNES, for civilian and militarian users. It is the French part of the French-Italian ORFEO program which also comprises COSMO-SkyMed, an Italian high-resolution radar system. The launch of the first Pleiades satellite is scheduled in 2008, the second, one year later. Their requirements were defined from users studies from the different spatial imaging applications, taking into account the trade-off between on-board technological complexity and ground processing capacity and trying to match the actual needs. The Pleiades satellites are in realisation phase. The precise definition of the image ground processing is running. This paper presents the main technical characteristics of the satellite (agility, stability, localisation accuracy...) and its optical instrument. It gives an overview of the different system products: level 1 image, "Perfect Sensor" image, orthoimage and orthomosaic. We then focus on the "Perfect Sensor" image: a basic product specially designed for the photogrammetric community and delivered with two geometric models: the physical model and a rational function model. We finally highlight the high geometric accuracy of the rational function model in the case of the "Perfect Sensor" image”.