“…Moreover, the high permittivity of the asteroid minerals [17,18,19,20] is likely to lead to strongly randomized or noisy reflections ‡ due to which the present inversion strategy utilizing the direct part of the signal can be advantageous [5]. In addition to asteroid tomography, other potential applications of the present sparse source inversion approach include on-site material testing and inspection [21,22,23,24,25,26,27], biomedical ultrasonography [28,29,30,31,32], as well as plenty of atmospheric, pedospheric, geological, and biological investigations utilizing travel time data [33,34,35], such as recovery of the root-zone structure of a tree [36]. The objectives above were studied in a laboratory experiment in which three 22-41 mm onyx stones were to be detected from the central part of a 150 mm synthetic reson cube based on travel time of a 55 kHz (35 mm wavelength) ultrasonic signal.…”