Abstract
Context.Information carried by the full wave field is particularly important in applications involving wave propagation, backpropagation, and a sparse distribution of measurement points, such as in tomographic imaging of a small Solar System body.Aims.With this study, our aim is to support the future mission and experiment design, such as for example ESA’sHera, by providing a complete mathematical and computational framework for the analysis of structural full-wave radar data obtained for an asteroid analogue model. We analyse the direct propagation and backpropagation of microwaves within a 3D printed analogue in order to distinguish its internal relative permittivity structure.Methods.We simulate the full-wave interaction between an electromagnetic field and a three-dimensional scattering target with an arbitrary shape and structure. We apply the Born approximation and its backprojection (the adjoint operation) to evaluate and backpropagate the wave interaction at a given point within the target body. As the data modality can have a significant effect on the distinguishability of the internal details, we examine the demodulated wave and the wave amplitude as two alternative data modalities and perform full-wave simulations in frequency and time domain.Results.The results obtained for a single-point quasi-monostatic measurement configuration show the effect of the direct and higher-order scattering phenomena on both the demodulated and amplitude data. The internal mantle and void of the analogue were found to be detectable based on backpropagated radar fields from this single spatial point, both in the time domain and in the frequency domain approaches, with minor differences due to the applied signal modality.Conclusions.Our present findings reveal that it is feasible to observe and reconstruct the internal structure of an asteroid via scarce experimental data, and open up new possibilities for the development of advanced space radar applications such as tomography.
Highlights
This article concerns the modelling of full-wave propagation and backpropagation with an asteroid analogue model as the target
This is due to the size of the target and its contrast, and suggests the inadequacy of linear propagation models as they omit the effects of multiple scattering or multiple coupling including multiple reflections and refractions, which are referred to as multi-path effects determined by the second term on the right-hand side of Eq (3)
At 10 GHz, the target is larger in terms of the wavelength, that is, the main dimension of the analogue is equal to 12.6 λm, and the field inside includes fine ripples which correspond to multiple paths and scattering effects due to the high contrast between the permittivity of the analogue and that of the vacuum
Summary
This article concerns the modelling of full-wave propagation and backpropagation with an asteroid analogue model as the target. The possibilities provided by these techniques continue to expand thanks to the rapidly increasing computing resources which enable modelling of the full wave propagation in an arbitrary domain and at high frequency. Our focus is on potential radar investigations of future space missions (Hérique et al 2018, 2019; Takala et al 2018; Sorsa et al 2019, 2020; Eyraud et al 2020). Our objective is to provide a complete mathematical and computational framework for the analysis of structural full-wave radar measurements obtained for a structurally complex asteroid analogue model, thereby supporting the related future space mission and laboratory experimental design. We consider the 3D printed analogue of Eyraud et al (2020) which is based on the optical high-resolution shape model of asteroid 25143 Itokawa
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