  In this paper, we investigate full-wave computed radar tomography (CRT) using
a rubble-pile asteroid model in which a realistic shape (Itokawa) is coupled
with a synthetic material composition and structure model. The aim is to show
that sparse bistatic radar measurements can distinguish details inside a
complex-structured rubble-pile asteroid. The results obtained suggest that
distinct local permittivity distribution changes such as surface layers, voids,
low-permittivity anomalies, high-permittivity boulders, and cracks can be
detected with bistatic CRT, when the total noise level in the data is around
-10 dB with respect to the signal amplitude. Moreover, the bistatic measurement
set-up improves the robustness of the inversion compared to the monostatic
case. Reconstructing the smooth Gaussian background distribution was found to
be difficult with the present approach, suggesting that complementary
techniques, such as gravimetry, might be needed to improve the reliability of
the inference in practice.
