3aEAa2. Development of a portable system for acoustical reconstruction of tunneland cave geometries.

Session: Wednesday Morning, May 25

Author: David L. Bowen
Location: Acentech Inc., 33 Moulton St., Cambridge, MA 02138, <emailhref="dbowen@acentech.com">dbowen@acentech.com


Noninvasive remote determination of the geometry of caves, tunnels, andpiping complexes has value for both military and commercial activities. Troopsthat must enter caves, tunnels, or urban storm sewer piping systems, for example,would be greatly aided by first knowing the distance to the next turn, opening,branch, or closure. A system employing a sound source and a pair of acousticsensors was developed to do this, based on the medical techniques of acousticlaryngometry and rhinometry, and has been demonstrated both in laboratoryand in fullscale field situations. Acoustical reflectometry techniques arefirst used to compute an area versus distance profile of the passageway underinterrogation. Other procedures are then used to classify and characterizethe various types of “junctions” that could give rise to the observedchanges in area (branching versus a simple area expansion, etc.). Resultsobtained using a prototype field system in fullscale tests indicate thatsmall arms fire can be used in place of a loudspeaker as the sound source(with hydrophones as the sensing elements), thus increasing the portabilityof the system. Other techniques for remote geometry mapping of tunnellikespaces will also be discussed. [Work supported by the U.S. Army Corps of Engineers.]