Radar tomography (RT) is a challenging nonlinear inverse problem of electromagnetic wave scattering. It is used to map the global permittivity distribution of a target object, such as asmall solar system body (SSSB), interior. Such imaging requires intensive forward computations to model wave propagation from the transmitting antenna to the receiver through the target domain, and advanced inversion algorithms to yield an accurate reconstruction of the internal structure based on the forward data. In the planetary scientific investigations, the target domain is often very large in comparison to the measurement wavelength, the measurement configuration is sparse by neccesity of the measurement being performed in deep space, and the measurement frequency is a balance between achieving optimal penetration and resolution in an environment where power consumption and the payload of the measurement devices are limited.
Our group, led by Prof. Sampsa Pursiainen (sampsa.pursiainen@tuni.fi) investigates the RT problem by advanced finite element time domain (FETD) methods and the associated inversion algorithms. We use Graphics Processing Unit (GPU) acceleration to speed up the computations and can currently simulate target domains of approximately 40 meters at 60 MHz radar signal, or 400 meters at 6 MHz signal. The FETD solvers, and the associated inversion algorithms for forward data reconstruction are the openly available as GPU-ToRRe software package for the 2D domain modelling, and GPU-Torre-3D package for 3D domains.
We have also developed Asteroid Wireframe Package (AWP) which can be used to build a permittivity-controlled, 3D-printable analogue object based on a numerical finite element mesh. The produced wireframe can be manufactured with a standard fused filament fabrication printer and commercially available dielectric plastic filament, and be measured in a laboratory by a tomographic microwave radar. This has enabled us to validate the numerical solvers with measurement data.
Funding support
This research is being funded by Academy of Finland Centre of Excellence in Inverse Modelling and Imaging 2018-2025, and the Academy of Finland ICT 2023 project FETD-Based Tomographic Full-Wave Radar Imaging of Small Solar System Body Interiors (project number 336151)