Internal probing of an asteroid analogue by electromagnetic method

The internal structure of small solar bodies are not well-known yet. The imaging of the interior of asteroids and comet will provide important information about their formation. In this paper, we aimed to provide a fast and efficient method to roughly image the shape and the interior of small bodies of the Solar system. We focused on monostatic measurements on two analogues of the 25143 Itokawa asteroid. The back-propagation technique was applied to promptly image the shape and internal structure of the analogues. The result shows the external shape of the analogue and that the inner void core can be reached and distinguished.acceptedVersionPeer reviewe

Investigation of wavelength-induced uncertainties in full-wave radar tomography of high contrast domain : An application to small solar system bodies

This paper aims to reconstruct the internal structure of a two-dimensional test object via numerically simulated full-wave time domain radar tomography with the presence of wavelength-induced (WI) uncertainties, following from a complex domain structure, and domain diameters 21 or 64 times the wavelength of the signal propagating inside the target. In particular, we consider an application in planetary scientific studies of reconstructing the interior structure of an arbitrary high contrast small Solar System Body (SSSB), i.e., an asteroid, with a probing signal wavelength limited by the instrument and mission payload requirements. Our uncertainty reduction model finds the reconstruction via averaging multiple inverse solutions assuming that the WI deviations in the solutions correspond to random deviations, which we assume to be independent and identically distributed (IID). It incorporates error marginalisation via a randomised signal configuration, spatial-averaging of candidate solutions, frequency-based error marginalisation, and the truncated singular value decomposition (TSVD) filtering technique, based on our assumptions of the phase discrepancy of the signal, domain parameters, and the full-wave forward model. The numerical experiments are performed for 20 and 60 MHz centre frequencies proposed for CubeSat-based radars, the latter being the centre frequency of the Juventas Radar which will be aboard Hera mission to investigate the interior structure of asteroid Dimorphos. A benchmark reconstruction of the target was obtained with the spatial averaging, sparse point density and frequency randomised configuration for both 20 and 60 MHz frequency systems.publishedVersionPeer reviewe

Highly Adaptive and Automated Tetrahedral Mesh Generator for Multi-Compartment Human Head Model with Deep Brain Structures in EEG

This paper introduces a highly adaptive and automated approach for generating Finite Element (FE) discretization for a given realistic multi-compartment human head model obtained through magnetic resonance imaging (MRI) dataset. We aim at obtaining accurate tetrahedral FE meshes for electroencephalographic source localization. We present recursive solid angle labeling for the surface segmentation of the model and then adapt it with a set of smoothing, inflation, and optimization routines to further enhance the quality of the FE mesh. The results show that our methodology can produce FE mesh with an accuracy greater than 1 millimeter, significant with respect to both their 3D structure discretization outcome and electroencephalographic source localization estimates. FE meshes can be achieved for the human head including complex deep brain structures. Our algorithm has been implemented using the open Matlab-based Zeffiro Interface toolbox with it effective time-effective parallel computing system.

Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement dataII. The time domain approach

International audienceContext. The internal structures of small solar system bodies (SSSBs) are still poorly understood. In this paper, we find an experimental tomographic reconstruction of coarse high-contrast details inside a complex-structured target object using multipoint full-wave radar data. Aims. Our aim is to advance the development of inversion techniques to be used in potential planetary scientific radar investigations targeting SSSBs, which have complex shapes and whose internal structure is largely unknown. Finding out the structure is an important scientific objective of Solar System research in order to understand its history and evolution. Methods. This is the second part (Paper II) of a joint study considering the methods to analyse and invert quasi-monostatic microwave measurement data of an asteroid analogue. We focused on incorporating advanced, full-wave, forward simulation in time domain with experimental data obtained from multiple measurement points. In particular, this study investigates multiple scattering and multipath effect suppression (MES) to reduce artefacts in the reconstructions. MES is necessary since the high-contrast and complex-shaped target and, especially, its back wall in high curvature regions cause intense reflections that deteriorate the reconstruction quality if not treated correctly. We considered the following two approaches to obtain MES: (i) geometrical optics-based pathlength thresholding and (ii) a peak detection method to investigate whether a data-driven approach could be used. At the inversion stage, we investigated marginalisation of random effects due to modelling by splitting a larger point set into several sparse sets of measurements. Results. Based on the results, MES is crucial to localise a void inside the complex analogue target. A reconstruction can be found when the maximum signal propagation time approximately matches that of the first back-wall echo for each measurement point. The marginalisation approach allows us to find a reconstruction that is comparable in quality to the case of full data, while reducing the computation effort per subsystem, which is advantageous when inverting a large data set