Analysis of full microwave propagation and backpropagation for a complex asteroid analogue via single-point quasi-monostatic data

Information carried by the full wave field is particularly important in applications involving wave propagation, backpropa- gation, and a sparse distribution of measurement points, such as in tomographic imaging of a small Solar System body. With this study, our aim is to support the future mission and experiment design, such as for example ESA’s HERA, 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. 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. 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. 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.