A New Metric for Estimating the Disparity of Antenna Patterns in Synthetic Aperture Imaging Radiometry

The soil moisture and ocean salinity (SMOS) satellite has provided for about ten years systematic passive L -band measurements from space. For several months, phase 0 studies are conducted by the French space agency for a second-generation high resolution (HR) follow-on mission. This contribution is making the connection between this SMOS hr project and the SMOS mission by revisiting the following problematic: the impact of the disparity of the antenna patterns on the reconstruction floor error observed in the retrieved brightness temperatures. This impact is revisited in light of the progress made since that time and a new metric is introduced for estimating the disparity between antenna patterns. It would be helpful for the design of future missions based on imaging by aperture synthesis with interferometric arrays comprising a large number of antennas

On the reduction of the reconstruction bias in synthetic aperture imaging radiometry

International audienc

Impact of the Antenna Spacing on the Brightness Temperature Maps Retrieved with a Synthetic Aperture Imaging Radiometer

For almost five years, phase 0 and phase A studies have been conducted by the French space agency for a second generation of the Soil Moisture and Ocean Salinity (SMOS) satellite devoted to a High Resolution (HR) follow-on mission. Within the frame of the preliminary results obtained with a candidate array for this SMOS-HR project, this contribution focuses on what could happen to any synthetic aperture imaging radiometer when the shortest spacing between the antennas of the interferometric array becomes smaller than a geometrical limit below which the synthesized field of view seems to be wider than the field of view seen by each elementary antenna. It is shown that in such a situation, the inversion of the complex visibilities becomes unstable in presence of noise and this instability is characterized by the undesirable presence of a phantom in the retrieved brightness temperature maps. The origin of this phantom is explained and a solution to cure the interferometric array from that issue is proposed and assessed with the aid of numerical simulations

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Real experiments are sometimes missing or highly expensive to implement when teaching modern physics. This is an important issue, especially when the theories are not intuitive. However, with the incorporation of computers into the classroom it has become much easier to illustrate some amazing effects of modern physics that cannot be brought to the attention of students without the aid of numerical simulations. Thanks to the performance of MATLAB langage, as well as to the easiness to code a theoretical problem, the students can really conduct numerical expriments and play with them almost in real time. This computer-based teaching approach is illustrate here with the capabilities to use MATLAB for solving initial values problems of ordinary differential equations encountered in relativistic electrodynamics Ordinary differential equations in Matlab In mathematics, an ordinary differential equation (or ODE) is a relation f that contains one or more derivatives of a dependent variable y with respect to a single independent variable t, usually referred to as time. Many studies have been devoted to the solution of ODEs. In the case where the equation is linear, it can be solved by analytical methods. Unfortunately, most of the interesting ODEs are non-linear and, with a few exceptions, cannot be solved analytically. However, in science and in engineering, a numeric approximation to the solution is often good enough to solve a problem. Numerical integration is that part of numerical analysis which studies the numerical solutions of ODEs with the aid of iterative solvers. MATLAB offers several numerical algorithms to solve a wide variety of ODEs. These solvers are designed to handle only explicit ODEs of the form y = f (t, y), linearly implicit ODEs of the form M(t, y) · y = f (t, y) as well as fully implicit ones of the form f (t, y, y ) = 0. Generall

Brightness temperature maps reconstruction from dual-polarimetric visibilities in synthetic aperture imaging radiometry

International audienc

Impact of the Antenna Spacing on the Brightness Temperature Maps Retrieved with a Synthetic Aperture Imaging Radiometer

For almost five years, phase 0 and phase A studies have been conducted by the French space agency for a second generation of the Soil Moisture and Ocean Salinity (SMOS) satellite devoted to a High Resolution (HR) follow-on mission. Within the frame of the preliminary results obtained with a candidate array for this SMOS-HR project, this contribution focuses on what could happen to any synthetic aperture imaging radiometer when the shortest spacing between the antennas of the interferometric array becomes smaller than a geometrical limit below which the synthesized field of view seems to be wider than the field of view seen by each elementary antenna. It is shown that in such a situation, the inversion of the complex visibilities becomes unstable in presence of noise and this instability is characterized by the undesirable presence of a phantom in the retrieved brightness temperature maps. The origin of this phantom is explained and a solution to cure the interferometric array from that issue is proposed and assessed with the aid of numerical simulations

Image reconstruction methods for remote sensing by aperture synthesis.

In the study of the spaceborne instrument MIRAS (Microwave Imaging Radiometer by Aperture Synthesis), two types of interferometric devices had to be examined: the T and Y configurations. The imaging properties of the corresponding devices (field-aliasing effects, error propagation, multiresolution aspects, etc.) motivated the final choice for the Y configuration. To conduct this study it was therefore essential to master the inverse problems of Fourier synthesis as well as the difficulties related to phase calibration. A general survey of the corresponding techniques is presented

Redundant spacing calibration: phase restoration methods.

New methods for redundant spacing calibration (RSC) are proposed. These are based on recent studies concerning phase calibration and the related phase unwrapping problem. In the corresponding theoretical framework, two subspaces of the baseline phase space, the unknown-spectral-phase space K and the aberration baseline phase space L, play an important role. An interferometric device for which the intersection of K and L is reduced to {0} is said to be of full phase. For any imaging device of this type, including those for which the traditional recursive approach fails, the phase restoration problem can be solved in the least-squares sense. When the closure phases are strongly blurred, global instabilities may occur. Their analysis appeals to concepts of algebraic number theory: Z-lattice, reduced basis, and nearest lattice point. In all cases, the separation angle between K and L must be as large as possible. The imaging devices based on the RSC principle should be designed accordingly. All these problems are illustrated by considering the phase restoration problems encountered in passive remote sensing by aperture synthesis.The difficulties related to possible correlator failures are examined in this context

Reconstruction d'image pour la mission SMOS

Les radiomètres imageurs à synthèse d'ouverture sont des instruments très prometteurs pour l'observation de la Terre dans le domaine des micro-ondes. C'est dans ce contexte que l'Agence Spatiale Européenne poursuit les développements de la mission SMOS (Soil Moisure and Ocean Salinity) dédiée à la mesure de l'humidité des sols et de la salinité de surface des océans à une échelle globale depuis l'espace à l'aide d'un interféromètre opérant en bande L. Cette mission constitue la première tentative d'appliquer à l'observation de la Terre le concept d'imagerie radiométrique à synthèse d'ouverture, technique initialement développée en radio-astronomie. Cet article s'intéresse à la reconstruction de cartes de température de brillance à partir de mesures interférométriques. Plus exactement, il étend la méthode d'inversion sélectionnée par l'Agence Spatiale Européenne au cas du traitement de données interférométriques obtenues en polarisation verticale et horizontale