Minimum Redundancy Wavenumber Illumination for FDM MIMO spaceborne SAR Tomography

This work presents a recently proposed concept to finely resolve the vertical structure of natural media by a formation of spaceborne Synthetic Aperture Radars (SAR) on-board different satellites. The formation is assumed to operate in Multiple Input Multiple Output (MIMO) mode by implementing a Frequency Division Multiplexing (FDM) access scheme, where all satellites transmit simultaneously on different frequency bands and receive the echoes scattered by the Earth’s surface in all transmitted bands. In so-doing, a formation on N satellites is used to produce N<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SAR images. By the principle of Diffraction Tomography, each of these images represents a distinct set of wavenumbers, i.e. a distinct region of the spatial spectrum of the observed scene. Fine vertical resolution is achieved by developing a novel approach to deploy the satellites in such a way that the resulting interferometric differential wavenumbers form an almost uniformly-spaced array of maximum length under the constraint of a given height of ambiguity and interferometric coherence magnitude. This approach, which we refer to as Minimum Redundancy Wavenumber Illumination (MRWI), is shown to provide the equivalent of 17 and 26 monostatic acquisitions while using formations of just 4 or 5 satellites, respectively. Such figures are comparable to the best airborne and ground-based tomographic systems available as of today, and indicate the concrete possibility to image the vertical structure of natural targets from space at fine resolution. The analysis is supported by results from synthetic data generated by numerical simulations.