This paper presents a new interferometric measurement technique which makes it possible to determine the spatial refractive index distribution inside asymmetrical transparent objects. The suggested set-up, consisting of mirror galleries for producing several projections, a holographic beam coupling system including a method for suppressing possible object self radiation, and only one camera in combination with a differential interferometer, is described in detail. Advantages and properties of the numerical tomographic reconstmtion method developed for this experimental set-up are discussed. Results of test experiments demonstrate that these concepts work in practice. and further results indicate the general usefulness of the technique.

A sound wave vibration using a scanning laser Doppler vibrometer are used as a method of exploring and imaging an extremely shallow underground. Flat speakers are used as a vibration source. We propose a method of distinguishing a buried object using a response range of a frequencies corresponding to a vibration velocities. Buried objects (plastic containers, a hollow steel can, an unglazed pot, and a stone) are distinguished using a response range of frequencies. Standardization and brightness imaging are used as methods of discrimination. As a result, it was found that the buried objects show different response ranges of frequencies. From the experimental results, we confirmed the effectiveness of our proposed method.

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We propose a new detection method for buried objects using the optimum frequency response range of the corresponding vibration velocity. Flat speakers and a scanning laser Doppler vibrometer (SLDV) are used for noncontact acoustic imaging in the extremely shallow underground. The exploration depth depends on the sound pressure, but it is usually less than 10 cm. Styrofoam, wood (silver fir), and acrylic boards of the same size, different size styrofoam boards, a hollow toy duck, a hollow plastic container, a plastic container filled with sand, a hollow steel can and an unglazed pot are used as buried objects which are buried in sand to about 2 cm depth. The imaging procedure of buried objects using the optimum frequency range is given below. First, the standardized difference from the average vibration velocity is calculated for all scan points. Next, using this result, underground images are made using a constant frequency width to search for the frequency response range of the buried object. After choosing an approximate frequency response range, the difference between the average vibration velocity for all points and that for several points that showed a clear response is calculated for the final confirmation of the optimum frequency range. Using this optimum frequency range, we can obtain the clearest image of the buried object. From the experimental results, we confirmed the effectiveness of our proposed method. In particular, a clear image of the buried object was obtained when the SLDV image was unclear.

We propose a method of distinguishing a buried object using the optimum frequency response range corresponding to the vibration velocity. Air-borne sound and a scanning laser Doppler vibrometer are used for noncontact acoustic imaging in the extremely shallow underground. Flat speakers that have a sharp directivity are used as vibration sources. Plastic container, hollow steel can, unglazed pot, and stone are used as buried objects and they are buried in the sand about 2 cm deep. First, noise waves are used for the confirmation of the buried object’s frequency response range. The ground surface imaging result by scanning laser Doppler vibrometer is used to confirm the position of the buried objects. To confirm the frequency range, the difference of the vibration velocities is used. Next, burst waves are emitted again to make a clear image. The frequency of the burst waves is set near the frequency response range. Finally, the buried object’s frequency response range is checked again the same way. The clear image is made by using the optimum frequency. From the indoor experimental results, we confirmed the frequency response range of each buried objects and the effectiveness of our proposed method.