Acoustics – Geophysical or subsurface exploration – Seismic source and detector
Reexamination Certificate
2000-04-25
2003-03-25
Lobo, Ian J. (Department: 3662)
Acoustics
Geophysical or subsurface exploration
Seismic source and detector
C181S401000, C073S636000, C073S639000, C367S178000
Reexamination Certificate
active
06536553
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates in general to acoustic sensors and in particular to the use of acoustic sensors to identify underground objects.
More than 100 million landmines have been deployed throughout the world, resulting in tens of thousands of people dead or maimed every year. U.S. soldiers are deeply immersed in peacekeeping, humanitarian, and military operations in areas of the world cluttered with mines. There are diverse technologies for detecting mines and explosive ordnance with varying degrees of performance, cost, and practicality.
Magnetometers are used to detect ferromagnetic objects such as mines. However, many mines are made of plastic with minimal metal components, and metallic debris often confounds magnetometer detections. The use of thermal imaging for mine detection relies on the mine releasing or storing thermal energy at different rates than its surrounding. Explosive vapor sensors are effective, but are big and slow. Thermal neutron activation for bulk explosive detection has practical limits. X-ray backscatter, mm-wave emissivity, chemical/biosensors, ultra-wide and mm-wave radars are also promising (See Gros & Bruschini, Int'l Symp. on Meas. & Control in Robotics, Brussels, May 1996).
Ground penetrating radar emits electromagnetic waves and monitors the reflections from the soil caused by dielectric variations from underground objects. However, non-metallic mines are only detectable if their dielectric properties strongly contrast with their surrounding. Target-specific resonances can be present in the reflected signal (See Peters, Daniels, Young, “Ground Penetrating Radar as Subsurface Environmental Sensing Tools” Proc. IEEE, Vol. 82, No. 12, December. 1994, pp. 1802-1822).
Seismic sensors can also detect resonances for discrimination between metal, plastic, wood, and rocks. Seismic echo-rangers observe mine echoes via generation and detection of scattered Rayleigh and/or surface compressional waves reflecting off a buried mine and returning to a sensor array (See BBN Systems and Technologies Corp., “Feasibility of Acoustic Landmine Detection: Final Technical Report,” Report No. BBN-TR-7677, May 19, 1992).
Acoustic (ultrasonic) imagery is commonplace in medicine. Broadband acoustic detection is effectively employed in underwater warfare and the detection of underwater mines buried in sea-bottom silt. Reflections at material discontinuities, as well as mine dimension, shape, materials, and depth contribute to the distortion of the induced and resultant sound field. These effects, often subtle modifications to amplitude, phase, and frequency, are easily monitored to extract information relating to an object within its surroundings.
Acoustic systems are capable of good penetration through very wet and heavy ground, such as clay, “but are likely to experience problems at the air-ground interface.” (See Bruschini & Gros, “A survey of Current Sensor Technology Research for the Detection of Landmines,” Int'l Workshop on Sustainable Humanitarian Demining (SusDem'97), Sep. 29 -Oct. 1, 1997 Zagreb, Croatia). Successful imaging with 15 MHz was conducted on a mine submerged slightly underwater, like deployed in rice fields. Such high frequencies will not normally penetrate the ground, and more appropriate frequencies and coupling should be used. Transmitting 3 kHz pulse bursts into the ground has permitted detecting objects down to 12 inches, and shown that rock-reflected signals exhibit irregular axes of reflections (See Morita. “Land Mine Detection System,” TRW Final Report AT-73-2, Feb. 23, 1973).
The introduction of soliton-like shock waves into the ground showed they had weak interaction with the ground, which causes minimal dispersion, and can provide much information from mine reflected energy (See Sen, Physical Review Letters, vol. 74, p. 2686-2689, 1995 and Physical Review E, vol. 54, pp. 6857-6865, 1996). Millisecond acoustic burst/impulse techniques provide advantages over continuous wave (CW) techniques. Return pulse gating allows interpretation of travel path and spectral modifications, since the pulse contains typically 200 Hz to 20 kHz data (See Rogers and Don, “Location of Buried Objects by and Acoustic Impulse Technique,” Acoustics Australia 22 5-9, 1994). A significant problem lies in isolating small object pulses from other, often dominant, signals, and coping with ground contours and irregularities (See Don, “Using Acoustic Impulses to Identify a Buried nonmetallic Object,” Abstract 2aPA3, 127th Meeting of the Acoustical Society of America, May 1994). CW and broadband acoustics may impart more energy to better induce structure resonances.
A US Army study found that disturbed soil covering a mine absorbed acoustic energy while the surrounding undisturbed soil reflected the acoustic energy. Where the acoustic energy was absorbed, the ground vibrated at seismic frequencies that depended on the acoustic input, soil properties, and on the mine (See More, Dilworth, Lewis, Wesolowicz, and Stanich, “Acoustic Mine Detection,” Daedalus Enterprises Final Report, Feb. 7, 1990). This implies that complementary sensor technologies, such as passive/active acoustic/seismic can enhance detection and identification through sensor fusion.
The present invention employs acoustic array techniques to localize buried objects and interpret the landmine's environment. One embodiment of the present invention is a low-cost, hand-held mine detector that rolls or slides across the ground, suitable for a soldier to inspect and clear, for example, a two-foot wide path for him to walk. In some embodiments, the invention incorporates data from seismic and electromagnetic sensors to enhance detection and reduce false alarms. Acoustic coupling and imaging can also aid in the nondestructive evaluation of materials and structures.
SUMMARY OF THE INVENTION
In accordance with the invention an apparatus for detecting an underground object comprises a container in contact with a ground surface; a medium disposed in the container; at least one acoustic sensor disposed in the medium in the container, for detecting acoustic noise; and an output device connected to the acoustic sensor. The apparatus further comprises at least one acoustic source that emits acoustic noise. The medium is at least one of liquid and gel. At least a portion of the container that contacts the ground surface is substantially acoustically transparent. The at least one acoustic source may be disposed in the medium in the container.
The portion of the container that contacts the ground surface is made of a substantially flexible material such that the portion of the container that contacts the ground surface substantially conforms to a contour of the ground surface. The substantially flexible material is one of rubber, polyethylene, polyvinylchloride, vinyl and a plastic material. The medium is one of water, oil and oil well drilling mud. The output device comprises a visual display, an auditory device or a tactile device.
In one embodiment the container is a roller having a generally cylindrical shape, the roller including a shaft that passes through the roller wherein the at least one acoustic sensor is mounted on the shaft. At least one acoustic source that emits acoustic noise may also be mounted on the shaft. A handle may be attached to the shaft for moving the roller across the ground surface. The acoustic noise is one of swept sine impulsive, broadband and continuous wave.
Preferably, an acoustic impedance of the medium is substantially the same as an acoustic impedance of material around the underground object.
The apparatus may further comprise a data processor connected between the at least one acoustic sensor and the output device. The data processor compares data from the at least one acoustic sensor and the at least one acoustic source. The data are compared for variations in at least one of phase, amplitude, frequency, time of arrival and echoes.
The apparatus may further comprise a rear wheel assembly attached to the handle, for decreasing loading of the ro
Adams William V.
Clohan, Jr. Paul S.
Lobo Ian J.
The United States of America as represented by the Secretary of
LandOfFree
Method and apparatus using acoustic sensor for sub-surface... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus using acoustic sensor for sub-surface..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus using acoustic sensor for sub-surface... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3073042