Voids may be natural or human made, have different shapes, and exist in various geological environments at depths of 1 m to much greater. Their only common property, which is a sharp contrast with their surroundings, has been the focus of decades of research aiming at their detection. Nonetheless, no definitive “silver bullet” has been found for this yet unresolved challenge, which is essential for engineering, security, and various academic disciplines counting on near-surface geophysical methods.

This special section reports the newest approaches attempting to solve this difficult problem. It contains 13 papers, beginning with a historical review of seismic...

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