Comparison of regularized inversion methods in synthetic aperture imaging radiometry

This paper is concerned with the reconstruction of radiometric brightness temperature maps from interferometric measurements. The corresponding inverse problem is often ill-posed unless a regularizing constraint is introduced in order to provide a unique and stable solution. Standard regularizing approaches are compared and illustrated with numerical simulations carried out in reference to the Soil Moisture and Ocean Salinity space mission led by the European Space Agency.     

Two-dimensional synthetic aperture images over a land surface scene

The Soil Moisture and Ocean Salinity (SMOS) space mission is currently undergoing phase-B studies at the European Space Agency. The SMOS payload is an L-band interferometric radiometer based on a two-dimensional aperture synthesis concept. This paper presents the first images obtained by a demonstrator of the SMOS instrument over land surfaces at the Avignon test site in 1999     

Geophysical characterization of the large-scale internal structure of a waste rock pile from a hard rock mine

A geophysical investigation was conducted on a waste rock pile of a polymetallic mine to define its internal structure. Three different areas of the pile were investigated using electrical resistivity imaging, ground penetrating radar, and electromagnetic conductivity techniques. The surveys were conducted on the top of the pile, along the slope of the upper bench and in several boreholes drilled into the pile. Laboratory testing was also undertaken on samples taken from three exploratory trenches dug into the top surface in order to ascertain their geochemical and hydrogeological properties. The geophysical surveys indicated a general horizontal layering in the core of the pile and dipping stratification parallel to the slope along the edges. These features are related to the method of construction and, to a lesser extent, to a change in the waste rock characteristics. Integrating all the data confirmed that such geophysical investigations can provide valuable information to assess the internal structure of a waste rock pile. The ensuing structural model can then be used to construct a hydrogeological model which can form a basis for evaluating the flow of water (and gas) in the pile.     

Brightness Temperature Map Reconstruction from Dual-Polarimetric Visibilities in Synthetic Aperture Imaging Radiometry

Synthetic aperture imaging radiometers are powerful sensors for high-resolution observations of the Earth at low microwave frequencies. Within this context, the European Space Agency is currently developing the soil moisture and ocean salinity (SMOS) mission devoted to the monitoring of SMOS at global scale from L-band spaceborne radiometric observations obtained with a 2-D interferometer. This paper is concerned with the reconstruction of radiometric brightness temperature maps from interferometric measurements. More exactly, it extends the concept of ldquoband-limited resolving matrixrdquo to the case of the processing of dual-polarimetric data.     

A resolving matrix approach for synthetic aperture imaging radiometers

Synthetic aperture imaging radiometers (SAIRs) are potential powerful instruments for high-resolution observation of planetary surfaces at low microwave frequencies. This paper deals with the reconstruction of radiometric brightness temperature maps from SAIR interferometric measurements. It is demonstrated that the corresponding inverse problem is not well-posed and must, therefore, be regularized in order to provide a unique and stable solution. A new approach is presented by referring to the notion of modeling operator and to the concept of a resolving matrix of the instrument. To illustrate the theory, numerical simulations are carried out in reference to the Soil Moisture and Ocean Salinity space mission led by the European Space Agency. The results are discussed with emphasis on stability and error analysis.     

Apodization functions for 2-D hexagonally sampled synthetic aperture imaging radiometers

It is now well established that synthetic aperture imaging radiometers promise to be powerful sensors for high-resolution observations of the Earth at low microwave frequencies. Within this context, the European Space Agency is currently developing the Soil Moisture and Ocean Salinity (SMOS) mission. The Y-shaped array selected for SMOS is fitted with equally spaced antennae and leads to a natural hexagonal sampling of the Fourier plane. This paper deals with the choice of the apodization function to be applied to the complex visibilities. The aim of this function is to reduce the Gibbs phenomenon produced by the finite extent of the star-shaped frequency coverage and the resulting sharp frequency cut-off. A large number of windows are introduced. A comparison of these in terms of their spatial domain properties is given, according to criteria relevant for remote sensing of the Earth's surface. This paper also describes how discrete Fourier transform calculations over hexagonal grids can be performed using a simple algorithm. Actually, standard fast Fourier transform algorithms designed for Cartesian grids and which have a long track record of optimization can be reused. Finally, an interpolation formula is given for resampling data from hexagonal grids without introducing any aliasing artifacts in the resampled data.     

On the Reduction of the Reconstruction Bias in Synthetic Aperture Imaging Radiometry

Synthetic aperture imaging radiometers (SAIRs) are powerful instruments for high-resolution observation of planetary surfaces at low microwave frequencies. This paper is concerned with the reconstruction of radiometric brightness temperature maps from SAIR interferometric measurements. Even in the absence of modeling errors and radiometric noise, a systematic error, or bias, has been observed in the reconstructed maps. The origin of this bias is analyzed and an efficient solution is proposed for reducing it. The core reconstruction procedure is not changed, and no additional measurements are needed. Throughout the scientific rationale, particular emphasis is laid on numerical simulations carried out for the Soil Moisture and Ocean Salinity space mission, a project led by the European Space Agency and devoted to the remote sensing of soil moisture and ocean salinity from a low-orbit platform