Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
  • G01V1/02—Generating seismic energy

Definitions

• the invention relates to a device for generating elastic waves in a body and for seismic prospection with at least one airborne sound source.
• Soil geophysical methods of investigation are known, e.g. seismic and dynamic soil investigations with which layer boundaries, deposits and cavities can be localized in the subsurface.
• the investigations can be carried out from the surface of the site or in boreholes and are used for large-scale outcrops.
• the wave propagations in the subsurface and their speeds are measured.
• seismic waves are generated by artificial excitation, e.g. by explosions in air (US Pat. No. 2,912,060) or by vibrators, which propagate underground, are broken and reflected at the geological interfaces and back to the earth's surface return where they are registered with geophones.
• the waves arrive with different running times. From this, the structure of the subsurface can be determined with great accuracy, down to depths of several kilometers, with the corresponding measuring effort.
• the disadvantage of known methods is that that the surface layer is only recorded with a low resolution down to a depth of one hundred meters, with this soil layer being of particular interest, for example because of the exploration of the subsoil, the location of cavities, the mapping of archaeological sites and the mapping of contaminated sites. Since this uppermost layer is the most inhomogeneous layer of earth, it has also led to disturbances in the measurement signals in the hitherto known prospecting methods for greater depths, so that a correction of the measurement signals was necessary.
• An underwater location system is known from US Pat. No. 3,237,151, in which airborne noise is generated by an aircraft flying over the location area.
• the aircraft can also be provided with a siren, the sound of which is picked up by couplers floating on the water surface, which use the ultrasound frequencies for an active sonar signal, hydrophones arranged below the coupler picking up the reflected ultrasound signals.
• the invention has for its object to provide a device of the type mentioned, which enables better resolution of the measurement signals in the depth range up to 100 m.
• the features of the main claim serve to achieve this object.
• the use of an electro-magnetic loudspeaker working in the frequency range between 100 and 1500 Hertz enables the prospection to be optimized to a desired depth of penetration in layers near the surface, which advantageously enables an examination and mapping of layers and deposits near the surface up to a depth of 100 meters with high Resolution is possible.
• the device according to the invention has the advantage of being inexpensive and simple. With short sound impulses, the noise pollution is extremely low.
• the device can be assembled in an extremely compact manner, which makes it particularly suitable for measurements in urban areas, not least because of the low noise pollution. Since the device uses sophisticated technical elements, it is also highly reliable.
• the airborne sound preferably has an arbitrarily selectable amplitude and frequency characteristic within the specified range.
• the airborne sound can be varied within the frequency range 100 to 1500 Hz with regard to frequency, waveform, intensity curve, sound pulse sequence, etc.
• the adaptation of the amplitude and frequency characteristics makes it possible to achieve a resolution in the dm range in the upper layers and in the m range in deeper layers, whereby measurements not only in the solid rock but also in the loose rock are possible.
• a higher frequency generally leads to a higher resolution but also to a lower penetration depth.
• the preferred application of the device is in high-resolution reflection measurements in structures near the surface in loose and solid rock up to a depth of about 100 m. It allows these structures to be imaged with great accuracy using their reflective properties.
• the device can be used in the usual way for mapping, profile measurement, com-on-mid-point measurement and for vertical seismic profiling.
• the resolution of the measurement signals allows e.g. the static correction of seismic signals which are falsified by the inhomogeneous layer near the surface.
• the high resolution also enables the device to be used for site investigation, for mapping old sites, for mapping archaeological sites or for recording and checking aquifers.
• the signal generator consists of a signal generator with selectable amplitude and frequency characteristics, whereby the frequency, the waveform and intensity as well as the temporal intensity curve as well as the repetition rate, pulse train but also continuous pulses can be set in an advantageous manner and thus adapted to body properties in order to provide a high-resolution measurement signal receive. Frequency-modulated sound waves can also be generated.
• the airborne sound source has at least one loudspeaker arranged at an adjustable distance from the body, which is decoupled from the body via a soft suspension.
• the adjustable height makes it possible to avoid resonances, the attachment of the loudspeakers via a soft suspension, for example soft rubber buffers, resulting in a virtually complete decoupling of the chassis of the airborne sound source from the body to be examined.
• An impedance converter can be arranged between the body and the loudspeaker and / or a structure-borne sound sensor. This impedance converter reduces reflections on the body surface and improves the coupling of the sound impulses.
• An intermediate layer can be arranged between the impedance converter and the body, which facilitates displacement of the loudspeaker or the structure-borne sound sensor.
• the intermediate layer makes it possible to shift measuring devices, namely the sound source on the one hand and sound pickups on the other hand, onto the body surface, so that various measurement signal evaluation methods, such as mapping, profile measurement and common mid-point measurements, can be used.
• the structure-borne noise transducers can also be arranged at different depths in the body to be examined, thereby permitting highly precise speed measurements and e.g. with geophysical application an exact devil assignment for the calibration of the measuring method.
• Geophones with a natural frequency ⁇ IOO Hertz can be used as structure-borne sound sensors.
• the noise level at low frequency, e.g. from traffic-related vibrations is reduced.
• the natural frequency of the geophones is chosen to be as high as possible in order to exclude low-frequency noises.
• the invention is explained in more detail below with reference to the single figure.
• the figure shows a movable arrangement 1 of a loudspeaker 2 which is suspended at an adjustable height above the floor 3 in a suitable frame construction 4.
• Decoupling devices for example soft suspensions, are provided in the frame for decoupling the loudspeaker from the ground. In this way, the generation of surface waves is reduced and the signal form generated by the loudspeaker is fed into the loose and solid rock of the ground 3 essentially undisturbed.
• the loudspeaker chassis 6 can be connected to the decoupled part of the frame 4 via an additional decoupling device 7.
• an impedance converter 8 can be attached to the base 3 in a fixed or movable manner below the loudspeaker 2. With many loose rocks, however, an impedance converter 8 can be dispensed with. The conversion of airborne sound into structure-borne sound is only supported to the extent necessary by the impedance converter 8.
• the reflected echo signals are received in the usual way with structure-borne sound transducers 9 on the floor 3, which can also be adapted in terms of their impedance via a fixed or movable impedance converter 10.
• Geophones with a natural frequency> 100 Hertz are preferably used.
• the signals from the structure-borne noise transducers 9, for example the geophone, are amplified by an amplifier 12 which can be controlled by a computer 11 and fed to the computer 11 via an A / D converter 14.
• the signal is generated by a signal generator 16, the output signal of which can be adjusted with regard to amplitude, frequency, waveform and frequency modulation and is supplied to the electromagnetic loudspeaker 2 via a power amplifier 17.
• the signal can also be generated via the computer 11, by means of which an even better variation of the signal characteristics is possible.
• the digital signals from the computer 11 are fed to the power amplifier 17 via a D / A converter 18.
• loudspeakers it is also possible to provide these loudspeakers with different signals, e.g. different frequency to supply.
• the output power of the amplifier 17 should be at least 500 W. With regard to the frequency, it can generally be said that a higher frequency results in a higher resolution, albeit with a somewhat lower penetration depth. The penetration depth is correspondingly higher at lower frequencies.
• the computer 11 also serves to register the measured values, coordinate the emitted signal pulses and the received reflection pulses, temporarily store and evaluate the results, etc. With the aid of the computer 11, signal stacking can also be carried out, which is very precisely reproducible because of the negligible deformation of the body 3.
• a current generator 19 can be provided to supply power to the electrical devices.
• the sound source arrangement 1 and the structure-borne sound recording device 20 can be arranged displaceably on the floor 3 via an intermediate layer 22 arranged between the arrangements and the body or floor 3.
• the structure-borne noise transducers 9 can also be arranged in a bore in different depths in order to enable very precise speed measurements and thus depth assignments in the sense of a calibration of the measuring devices.

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• Engineering & Computer Science (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Acoustics & Sound (AREA)
• Environmental & Geological Engineering (AREA)
• Geology (AREA)
• General Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• Geophysics (AREA)
• Geophysics And Detection Of Objects (AREA)

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• 1989
  • 1989-04-21 DE DE3913178A patent/DE3913178C1/de not_active Expired - Lifetime
• 1990
  • 1990-04-10 WO PCT/EP1990/000569 patent/WO1990013051A1/de not_active Application Discontinuation
  • 1990-04-10 AU AU54185/90A patent/AU5418590A/en not_active Abandoned
  • 1990-04-10 EP EP90905465A patent/EP0468984A1/de not_active Withdrawn
  • 1990-04-20 DD DD90339903A patent/DD299681A5/de not_active IP Right Cessation
  • 1990-04-20 PL PL28487290A patent/PL284872A1/xx unknown
  • 1990-04-20 ZA ZA903004A patent/ZA903004B/xx unknown
  • 1990-04-21 CN CN90103612A patent/CN1046609A/zh active Pending

Non-Patent Citations (1)

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