JP5517429B2 - Sound imaging device - Google Patents

Description

  The present invention relates to an acoustic imaging apparatus, and more particularly to an acoustic imaging apparatus in water such as a sonar.

  An imaging technique using an acoustic technique is being studied as a technique for imaging the structure in the seabed sedimentary layer and the objects in the seabed sedimentary layer. Light is not transmitted inside the seabed and the electromagnetic transmission of the seawater / sedimentary layer is extremely low, so acoustic images using sonar (SONAR) are used for imaging in the seabed. The method is the first choice. However, the sediment has a characteristic that the attenuation rate of the acoustic wave is remarkably larger than that of seawater. In particular, since the attenuation rate increases exponentially as the frequency of sound waves increases, this is a great barrier to attempts to improve the spatial resolution of sonar images by increasing the sonar frequency (shortening the wavelength). Therefore, an acoustic imaging method and a signal processing method / algorithm for generating an image in the seafloor sediment layer with high contrast and a high S / N ratio (signal / noise ratio) beyond this barrier are desired.

  Regarding technologies that consider the effects of seabed sedimentary layers, there are the following. Japanese Patent Application Laid-Open No. 2002-311136 obtains a difference in lag time from a received signal of a sonar that is divided into two vertically, and determines whether a target is buried on the seabed or below the seabed using a threshold value. Technology is disclosed. Japanese Patent Application Laid-Open No. 9-304527 discloses a technique for estimating acoustic parameters represented by the density and attenuation coefficient of a deposited layer from reflection loss using BL (Bottom Loss) data. According to the present technology, it is possible to estimate the density and the attenuation rate when it is assumed that the deposited layer has uniform characteristics in the depth direction. Japanese Patent Application Laid-Open No. 10-221444 discloses a technique for measuring a density distribution in the depth direction by irradiating a sound wave whose frequency is gradually changed in the depth direction of the deposited layer. In addition, WO1999004287A1 focuses on the object buried in the deposition layer, and uses the fact that the acoustic distortion deformation of the object appears as a nonlinear distortion to the reflected sound signal. A technique for detecting is disclosed.

JP 2002-311136 A Japanese Patent Laid-Open No. 9-304527 Japanese Patent Laid-Open No. 10-221444 WO1999004287A1

  Conventionally, a technique for estimating the physical characteristics of the deposited layer and a technique for estimating acoustic parameters by comparing the characteristics of the deposited layer as a pre-existing database with acoustic data are known. However, there has been no technique for correcting the influence of sound wave propagation in the seabed sedimentary layer, that is, image shift or distortion caused by the presence of the sedimentary layer, during image processing.

  The present invention relates to an acoustic imaging apparatus capable of forming a high-definition, high-resolution acoustic image by eliminating positional deviation, low contrast (blurring), and contour distortion caused by the presence of a seabed sediment layer. The purpose is to provide.

  The acoustic imaging apparatus of the present invention includes an image processing algorithm that corrects the influence of acoustic propagation by the seabed sedimentary layer. In this image processing algorithm, first, the physical parameters of the deposited layer are estimated, and calculation parameters during sonar image processing are corrected from the estimated physical parameters. A sonar image is generated using the corrected calculation parameter to obtain a sonar image in which a received signal or image deviation or distortion caused by acoustic wave propagation in the deposited layer is corrected. Further, the corrected sonar image is compared with the reference image, and the residue is fed back to further correction to improve the accuracy of the correction.

  Furthermore, the acoustic imaging apparatus of the present invention uses the physical parameter of the deposited layer estimated in the compensation to control and give the transmission condition of the acoustic wave to the physical parameter of the deposited layer that varies depending on the location. And a sound wave transmission algorithm for transmitting and receiving sound waves under more suitable conditions.

  According to the present invention, the influence of the sound wave propagation characteristics in the seabed sedimentary layer on the soundwave image is corrected to eliminate the image shift and distortion, and the resolution of the soundwave image, the S / N ratio, the contrast, and the seabed deposition. The detection sensitivity of objects in the layer can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, imaging in the sea and in the bottom sedimentary layer will be described with reference to FIGS. 1 and 2. Next, an image processing algorithm in the sound wave imaging apparatus of the present invention will be described in detail with reference to FIGS. Thereafter, with reference to FIG. 9 to FIG. 25, a specific example of the acoustic imaging apparatus according to the present invention will be described in more detail with the explanation of various processes in the image processing algorithm and the result of the acoustic wave propagation simulation in the deposited layer. Give an explanation.

  FIG. 1 is a schematic view of a sound wave imaging device in the sea. Sound imaging in the sea is performed using a sonar 102 provided on the hull 100 and the navigation body 101. In the hull 100, for example, a hull sonar provided under the hull is used. Hull sonar can only be operated from sea level, so in recent years it has been called unmanned underwater vehicles (UUVs) and autonomous underwater vehicles (AUVs). Underwater and seabed acoustic imaging using the traveling body 101 has been actively studied. By using UUV or AUV, it is possible to acquire a sound image at a deep water depth. The transmitted sound wave 103 from the sonar 102 reaches the object 104 and the sea bottom surface 105, and the reflected sound becomes the received sound wave 106 and is received by the sonar 102. By combining the received sound waves 106 received in a plurality of directions and different places, a sonar image 107 reflecting the shapes of the object 104 and the sea floor 105 is created.

Usually, such a sonar image is created assuming the propagation of sound waves in the sea. For example, when a reflected sound wave from the object 104 with respect to the transmitted sound wave transmitted from the sonar 102 at an angle θ = 60 ° is received in the sonar 102 after 0.1 second, the horizontal distance d from the sonar of the object. Using one-way acoustic wave propagation time t = 0.05 [s] and sound velocity c = 1,522 [m / s] in seawater,
d = c × t × cos θ = 1,522 [m / s] × 0.05 [s] × cos 60 ° = 38.05 [m]
And is drawn on the sonar image 107 as an image 108 of the object. On the other hand, the existence of the seabed sediment layer 109 becomes a problem in such acoustic image acquisition in the sea. For example, as shown in FIG. 1, the object 110 may be buried in the seabed sediment layer 109. At this time, when the object 110 is imaged as a sonar image, it is obvious that the sound wave propagation characteristics inside the surrounding seabed sediment layer 109 are greatly affected.

  With reference to FIG. 2, the influence of the sound wave propagation characteristics inside the seafloor sediment layer on the generation of the sonar image will be described. First, when there is an object in the sea, the sound wave 201 transmitted from the sonar 200 propagates only in the sea and reaches the object 202. Therefore, similarly to the sonar image 107 in FIG. 1, the object 204 is imaged in the sonar image 203. On the other hand, when the target object 206 exists in the sedimentary layer 205, the transmission sound wave 207 from the sonar enters the seafloor sedimentary layer. Since the sound velocity of the ocean bottom sediment layer is different from the sound velocity in the sea, the refraction of sound waves occurs and the sound propagation path is different from that in the sea. In addition, since the sound attenuation rate in the seafloor sedimentary layer is larger than that in the sea, the magnitude of sound waves is also reduced. Furthermore, since the sea bottom is a density discontinuity between the sea water and the sedimentary layer, the reflection at the sea bottom is not small. As a result of these, the image 209 of the object 206 appearing in the obtained sonar image 208 has a positional deviation due to refraction and a small sound wave size when compared with the image formed in the sea. Low contrast (blurring), distortion of the contour of the image due to scattering at the sea bottom, and the like are caused. Furthermore, if the degree of refraction, attenuation and scattering is further increased due to the characteristics of the sedimentary layer, the object in the seafloor sedimentary layer may not be imaged (no image) in the sonar image. That is, in order to accurately image the seabed sediment or to image the object in the seabed sediment, the following inconveniences are caused: (a) the position of the sonar image is shifted by the influence of the seabed sediment. There are two points that need to be resolved: blur and contour distortion, and (b) the object does not form an image in the sonar image due to the influence of the seabed sedimentary layer.

  In the present invention, the above inconvenience is solved by two methods. First, (1) To correct the deviation due to the sound wave propagation characteristics of the deposited layer during the sonar image generation process, and to create an image in which the influence of the deposited layer is corrected. Next, (2) transmitting a sound wave under a sound wave transmission condition suitable for the characteristics of the deposited layer. 3 to 7 illustrate an example of the processing algorithm (1), and FIG. 8 illustrates an example of the processing algorithm (2). 3 to 8 show an image processing algorithm and a skeleton of a sound wave imaging apparatus including such an image processing algorithm, and details of parameters, images, and data appearing in the algorithm will be described later.

  FIG. 3 shows an embodiment of the image processing algorithm according to the present invention together with the embodiment of the sound wave imaging apparatus according to the present invention. The algorithm shown in FIG. 3 is the basic algorithm of the present invention that compensates for deposited layer acoustic wave propagation characteristics. In the present embodiment, a sonar transmission / reception unit 300 is provided as a first transmission / reception unit. The sonar transmission / reception unit 300 transmits and receives sound waves. When the seabed sedimentary layer exists in the direction in which the sound wave is transmitted, the received signal is affected by the seabed sedimentary layer as shown in FIGS. On the other hand, in this case, it is clear that the received signal includes information on the sound propagation characteristics of the seabed. Accordingly, the received signal 301 of the sonar is transmitted to the bottom sediment calculation unit 302 which is the first calculation unit. As will be described later in detail, the “sediment” represents one or a set of a plurality of physical parameters such as a density distribution in the sedimentary layer and a hydraulic conductivity. Based on the received signal received by the sonar transmission / reception unit, the bottom sediment calculation unit 302 estimates a physical parameter representing the sediment of the deposited layer, that is, a calculation parameter 303.

  Next, the calculation parameter 303 is transmitted to the image compensation calculation unit 304 which is a second calculation unit. The image compensation calculation unit 304 calculates the deposition layer correction data 305. The correction data 305 is, for example, a compensation amount of a deposited layer in a sonar image processing process and a compensation coefficient inside the processing process. Next, the correction data 305 is transmitted to the compensation image processing unit 306 which is a third calculation unit. At the same time, the sonar received signal 307 is also transmitted to the compensation image processing unit 306. The compensation image processing unit 306 generates correction image data 308 in which the sound wave propagation characteristics of the deposited layer are compensated using the correction data 305 when image processing is performed on the received signal of the sonar to generate a sonar image. In the process of generating the corrected image data 308 so far, the processing for compensating the primary sediment bottom sediment is completed. The sonar image generated by the compensation image processing unit 306 is displayed on the image display unit.

  In the present invention, the corrected image data 308 is further transmitted to the reference information generation unit 309 which is the fourth calculation unit. A reference image 310 is input to the contrast information generation unit 309 separately. In the reference information generation unit 309, the reference image 310 and the corrected image data 308 subjected to the primary compensation of the deposited layer are compared to calculate the reference information 311, that is, an amount representing the effect of correcting the deposited layer. Further, the control information 311 is transmitted to the bottom sediment parameter correction unit 312 which is the fifth calculation unit. In this bottom sediment parameter correction unit, using the control information 311, a corrected calculation that represents the correction amount of the calculation parameter calculated by the bottom sediment calculation unit 302 or the more likely sediment bottom sediment after the correction. Calculate the parameters. As described above, according to the embodiment shown in FIG. 3, it is possible to calculate the sonar image in which the influence of the acoustic wave propagation characteristics of the deposited layer is primarily corrected and the physical parameters of the modified deposited layer.

  FIG. 4 shows an embodiment of the sound wave imaging apparatus of the present invention and an embodiment of the image processing algorithm. FIG. 4 shows a more detailed example of the reference image 310 in FIG. The reference image 310 is image data input to the contrast information generation unit 309, and there are two examples of the image data.

  First, one embodiment will be described with reference to FIG. Here, a normal sonar image processing unit 400 as a sixth calculation unit is provided. In the normal sonar image processing unit 400, based on the sound wave signal received by the sonar transmission / reception unit 300, a sound image by the normal sonar is generated without passing through the primary processing of the deposited layer correction according to the present invention shown in FIG. . That is, the normal sonar image processing unit receives the received signal 401 (the same information as 307 in FIG. 3) of the sonar transmission / reception unit, and generates an original image, that is, a normal sonar image 402. The normal sonar image 402 can be used as it is as the reference image 310 to be input to the control information generation unit 309. The comparison information generation unit 309 compares the normal sonar image 402 as the reference image 310 with the correction image 308 sent from the compensation image processing unit 306, and how much correction is performed from the normal sonar image 402. That is, the amount of change from the normal sonar image 402 is calculated. The magnitude of this correction amount is the reference information 311 here.

  Another embodiment will be described with reference to FIG. In the case of the present embodiment, a reference image storage unit 403 which is a memory / storage unit is provided. The reference image storage unit 403 holds an optimal compensation image prepared in advance, and this optimal compensation image 404 is used as a reference image. This optimal compensation image 404 can be used as the reference image 310 that is input to the contrast information generation unit 309 as it is. In the reference information generation unit 309, the optimum compensation image 404 as the reference image 310 is compared with the correction image 308 sent from the compensation image processing unit 306, and how much the correction approaches the optimum compensation image 404. That is, an amount representing an asymptotic degree with the optimal compensation image 404 is calculated. The amount representing the asymptotic degree is the reference information 310 here.

  Furthermore, an embodiment in which both of the two reference image output blocks are provided will be described with reference to FIG. In this embodiment, either the normal sonar image 402 or the optimal compensation image 404 is selected and used as the reference image. In this case, as shown in FIG. 4, both the normal sonar image processing unit 400 as the sixth calculation unit and the reference image storage unit 403 as the memory / storage unit are provided, and the reference information as the fourth calculation unit. The first input switching unit 405 is configured to switch the reference image 310 input to the generation unit 309 to either the normal sonar image 402 that is the original image or the optimum compensation image 404 in the memory / storage unit.

  FIG. 5 shows an embodiment provided with a feedback loop for calculation parameters as one embodiment of the sound wave imaging apparatus of the present invention and one embodiment of the image processing algorithm. Here, the corrected calculation parameter 500 calculated by the bottom sediment parameter correction unit 312 which is the fifth calculation unit is newly used as an input to the image compensation calculation unit 304 which is the second calculation unit. Further, FIG. 5 includes an input switching unit 501 that is a second input switching unit, and the bottom sediment is primarily calculated by the bottom sediment calculation unit 302 using the input switching unit 501. The calculation parameter 303 and the corrected calculation parameter 500 may be switched to be the calculation parameter 502 that is newly input to the image compensation calculation unit. In this embodiment, by providing a calculation parameter feedback loop, the physical parameter of the deposited layer that is primarily estimated from the received signal 301 received by the transmitting / receiving unit 300 of the sonar is corrected, thereby calculating the calculation parameter. It is possible to move closer to physical parameters that are considered to represent the actual bottom sediment, less deviation, improved contrast ratio, less blurring of contours, high-quality, high-resolution acoustic wave propagation in the deposited layer A sonar image with corrected characteristics can be obtained.

  FIG. 6 illustrates a case where a bottom sediment measuring device 600 as a second transmitting / receiving unit is provided as one example of the acoustic imaging apparatus of the present invention and an example of the image processing algorithm. The bottom sediment measuring instrument 600 is a transmission / reception unit that transmits and receives sound waves independently of the first transmission / reception unit, and transmits sound waves different from the first transmission / reception unit toward the seabed sedimentary layer. Receives the reflected sound. The signal received by the bottom sediment measuring instrument 600 can be used as a reception signal 601 as a calculation parameter 603 input to the bottom sediment calculation unit 302 as the first calculation unit.

  In the sonar transmission / reception unit 300 as the first transmission / reception unit, there is a restriction that transmission / reception of sound waves is performed in order to obtain a sonar image. By providing the bottom sediment measuring instrument 600 separately from the sonar transceiver 300, it is possible to transmit and receive sound waves specialized only for estimation of bottom sediment parameters. For example, the sonar transmission / reception unit 300 can transmit a frequency of 5 kHz, while the bottom sediment measuring device 600 can transmit and receive a sound wave of 100 kHz. Thus, in the sonar image creation, the received sound wave with respect to the transmitted sound wave of 5 kHz received by the sonar transmission / reception unit 300 is used, while the bottom sediment estimation, that is, the computation parameter estimation in the present invention, is received by the bottom sediment measuring device 600. A physical parameter representing a more detailed bottom sediment can be estimated using a reception signal with respect to a transmission sound wave of 100 kHz. In the present embodiment, the third input switching unit 602 switches between the reception signal 301 received by the sonar transmission / reception unit 300 and the reception signal 601 received by the bottom sediment measuring device 600, You may comprise so that it can be set as the input signal 603 transmitted to the bottom sediment calculation part 302. FIG.

Next, the case where the known density distribution data 604 which is a database part is provided is demonstrated as one of the Example of the sound wave imaging device of this invention, and the Example of an image processing algorithm using FIG. In some cases, the bottom sediment of the sea area where the sonar is imaged is known in advance. This is a case where physical parameter information such as density distribution in the sedimentary layer has been acquired by prior operations or sediment investigation. At this time, it may be provided with a database portion for storing bottom sediment data of the seabed sedimentary layer, that is, a calculation parameter in the present invention, that is, known density distribution data 604. The known density distribution data 604 can output an operation parameter 605 that is input to the second calculation unit. In addition, the known density distribution data 604 can be input to the second input switching unit 501 as a known calculation parameter 605, and the second input switching unit 501 further performs the calculation calculated by the bottom sediment calculation unit 302. For the image compensation calculation unit 304, which is the second calculation unit, by switching any one of the calculation parameter 500, the calculation parameter 500 modified by the fifth calculation unit, and the known calculation parameter 605. You may comprise so that it can output as the parameter 606 for a calculation transmitted.
The bottom sediment measuring instrument 600 and / or the known density distribution data 604 which is a database unit may be added to the acoustic imaging apparatus shown in FIGS.

  With reference to FIG. 7, a case where there is a calculation parameter adjustment unit will be described as one embodiment of the sound wave imaging apparatus of the present invention and one embodiment of the image processing algorithm. In the present embodiment, a bottom sediment parameter knob portion 700 which is an adjustment portion is provided. Here, the bottom sediment parameter knob unit 700 can adjust the value of the operation parameter (502, 606, etc.) input to the image compensation calculation unit 304 as the second calculation unit. It can be input to the image compensation calculation unit 304 as the use parameter 702. Further, the image compensation calculation unit 304 calculates the correction data 305 using the adjusted calculation parameter. Further, the bottom sediment parameter knob 700 that is an adjustment unit may be added to the acoustic imaging apparatus shown in FIGS.

  FIG. 7 further illustrates a case where there is a calculation parameter display unit 703 as one of the embodiments of the sound wave imaging apparatus of the present invention and the image processing algorithm. Here, the calculation parameters calculated by the bottom sediment calculation section, which is the first calculation section, the calculation parameters prepared in the database section (these are shown as bottom sediment parameters 704 in FIG. 7) and the adjustment A bottom sediment display unit 703 which is a display unit for displaying one or a plurality of combinations of computation parameter values among the computation parameters 705 adjusted by the bottom sediment parameter knob unit which is a unit. The bottom sediment display unit 703 may be added to the acoustic imaging apparatus shown in FIGS.

  The embodiment of the acoustic imaging device of the present invention and the embodiment of the image compensation algorithm for the seabed sedimentary layer have been described above with reference to FIGS. 3 to 7, but physical parameters representing the sediment quality of the seabed sedimentary layer are calculated. This is one of the characteristics of the present invention, and this physical parameter can be used not only for image processing but also for controlling the transmission conditions of the sonar. That is, it can also be used to determine sonar transmission conditions that take into account the influence of the deposited layer, depending on the spot where the sonar is used.

  FIG. 8 shows an embodiment of the sound wave imaging device of the present invention in view of the above. The present embodiment includes a sonar transmission signal control unit 800. The sediment parameter calculation is performed in block 801 of the image processing algorithm shown in FIGS. The sonar transmission signal control unit 800 may receive the input 802 of any calculation parameter described in FIGS. For example, even if the calculation parameter is a value obtained by estimating the physical parameter of the bottom sediment calculated in the bottom sediment calculation unit which is the first calculation unit, or the calculation parameter stored in the database unit, The calculation parameter corrected in the bottom sediment parameter correction unit, which is the five calculation unit, may be used. The sonar transmission signal control unit 800 uses one of the transmitted calculation parameters 802 to determine a sound wave transmission condition suitable for the target deposition layer. For example, when 5 kHz is used as the frequency of the transmitted sound wave in the sonar transmission / reception unit, the frequency that propagates in a straight line inside the seabed sedimentary layer is calculated from the calculated calculation parameters. When the frequency is 8 kHz, a transmission sound wave 804 having a frequency of 8 kHz controlled by the sonar transmission / reception unit 300 can be newly transmitted by inputting the control signal 803 to the sonar transmission / reception unit 300 as the first transmission / reception unit. it can.

  As a result, it is possible to perform image processing that compensates the seabed sedimentary wave propagation characteristics based on the received signal acquired under more suitable sound wave irradiation conditions, with less deviation, improved contrast ratio, and further contouring. It is possible to obtain a sonar image in which the sound wave propagation characteristics of the deposited layer are corrected with high image quality and high resolution.

  As described above, the skeleton relating to the acoustic imaging device according to the present invention and the image processing algorithm for correcting the sound propagation characteristics of the seabed sediment layer has been shown using FIGS. Hereinafter, the blocks, various parameters, correction data, and sonar images appearing in FIGS. 3 to 8 will be described with reference to FIGS.

  First, the “bed sediment” of the seabed sedimentary layer will be described with reference to FIG. As shown in FIG. 9, the seabed sedimentary layer 900 constitutes a porous medium as a mixture of solid particles 901 and interstitial fluid 902 that is a liquid such as seawater existing between the solid particles. The parameter that characterizes the “bed sediment” of the seabed sediment layer the most is the average particle diameter d of the solid particles 901 constituting the seabed sediment layer. In general, those having an average particle size d of 3.9 μm or less are called Clay (mud), those having an average particle size of 62.5 μm or more are called Sand (sand), and those having an average particle size between them are called Silt. There are various other physical parameters of the seabed sediment layer, but basically this average particle diameter d largely governs the sound wave propagation characteristics of the seabed sediment layer.

Next, the parameter representing the “bed sediment” of the important seabed sediment is the porosity β. The porosity β is an amount of 0 to 1 that represents the volume fraction of the pore fluid 902 contained in the seabed sedimentary layer 900. That is, the density ρ (density as a mixture of liquid and solid) of the seabed sedimentary layer can be expressed by the following equation (1) using the density ρ _r of the solid particles 901 and the density ρ _f of the pore fluid 902. .
ρ = ρ _r (1−β) + ρ _f β (1)

  As apparent from the equation (1), the porosity β is closely related to the “density as a mixture” of the seabed sedimentary layer, and is a very important physical parameter of the seabed sedimentary layer. On the other hand, between the average particle diameter d of the seabed sediment layer and the porosity β, the porosity β generally decreases as the average particle diameter increases, as indicated by 904 in the lower diagram of FIG. There is a correlation. Therefore, if the average particle diameter d of the seabed sedimentary layer is known, the approximate porosity β can be predicted, and if the porosity β is known, the approximate average particle diameter d of the seabed sedimentary layer can be predicted. Furthermore, the porosity β is also an important parameter for predicting the sedimentary layer physical parameters described later, and is one of the most important parameters representing the “sediment” of the seabed sedimentary layer.

  Next, selection of the frequency of the transmission sound wave transmitted from the transmission / reception unit will be described with reference to FIG. The horizontal axis of the graph of FIG. 10 is the frequency of sound waves expressed in Hz (Hertz), and the vertical axis is the attenuation rate expressed in dB / m of sound waves in the seafloor sedimentary layer. Moreover, the line in a figure represents the simulation result of the attenuation factor of the sound wave in various bottom sediments. The bottom sediment here means the particle size of the particles in the sediment. The cases of Silty Sand, Sandy Silt, Silt, Clayey Silt, and Clay are arranged in the direction of decreasing particle size in order from the particle size Sand. It also shows. As described with reference to FIG. 9, β and the average particle size have a one-to-one correspondence. Also, the plot ◇ in FIG. 10 is past experimental data (E. L. Hamilton, “Geoacoustic modeling of the sea floor,” J. Acoust. Soc. Am., 68 (5), 1313-1340 (1980)).

  FIG. 10 shows that the attenuation rate increases as the frequency increases, although there are some values depending on the particle size. Here, when the frequency of the sound wave is 1 MHz, the attenuation rate is almost 100 dB / m. This means that when a sound wave having a magnitude of 200 dB is incident on the deposited layer, the sound wave propagates to a depth of 1 m and returns, and when it returns, the magnitude of the sound wave becomes substantially zero. The attenuation at 100 kHz is 10 dB / m or more for almost all sediment. At this time, the attenuation of the sound wave is 20 dB or more in a round trip of 1 m, that is, the magnitude of the received sound wave is 1/10 or less. As described above, in the present invention, the transmission frequency of the sound wave from the sonar transmission / reception unit is 1 MHz or less. More preferably, the frequency is 100 kHz or less.

With reference to FIG. 11, the depth direction distribution of the porosity β, which is an important physical parameter of the sedimentary layer representing the sediment, will be described. FIG. 9 explains that the porosity β in the sediment is correlated with the diameter d of the solid particles in the sediment. On the other hand, the size of the porosity β has a characteristic that it gradually decreases as it becomes deeper from the surface of the seabed sediment layer. FIG. 11 shows the depth distribution of the porosity of the deposited layers at two different locations (location A and location B). The plot ◇ in the figure indicates the measurement result at the location A, and the plot ♦ indicates the measurement result at the location B. These measurement results can be approximated by the following equation (2) using the depth z of the deposited layer.
β = β _min + (1−β _min ) exp (−pz ^−q ) (2)

Β _min in the equation (2) corresponds to the final porosity in a deep place. Therefore, the porosity β indicated by the data 904 in FIG. 9 corresponds to this β _min . Moreover, p and q, which are coefficients of the exponential function, are values that determine the shape of the approximate curve in FIG. By using the equation (2), the porosity distribution of the seabed sedimentary layer including the distribution in the depth direction can be expressed using three constants β _min , p, and q. That is, these three values β _min , p, and q can be considered as three main parameters representing the sediment of the seabed sedimentary layer. For example, the approximate curve 1102 of the porosity distribution at the location A shown in FIG. 11 is β _min = 0.72, p = 0.54, q = 0.54, and the approximate curve 1103 at the location B is β _min = 0.52, p = 0.37, and q = 0.74. By determining the values of β _min , p, and q, the porosity distribution in the deposited layer can be determined. Further, as described above, the porosity β has a correlation with the average particle diameter d of the solid particles of the sediment, and by determining these values, it is possible to know what kind of sediment the seabed sediment layer is. It will be.

The β _min , p, and q correspond to the calculation parameters in the present invention. Using the received signal 301 from the sonar transmission / reception unit, the bottom sediment calculation unit 302 calculates β _min , p, q which are the porosity distribution of the seabed sedimentary layer. Next, these calculation parameters are transmitted to the image compensation calculation unit (second calculation unit) 304. Here, β _min , p, and q have been described as values indicating the physical parameter distribution in the depth direction of the seabed sediment layer. In the present invention, the physical parameter distribution in the depth direction of the seabed sediment layer is indicated. Any number of parameters may be used as calculation parameters, and of course, an approximate expression other than the expression (2) may be used.

The estimation of physical parameters in the seafloor sedimentary layer other than β _min , p, and q will be described with reference to FIG. In addition to β _min , p, and q, there are many parameters that affect the sound propagation characteristics in the seafloor sedimentary layer. All of these parameters can be estimated by using β _min , p, and q. It is. For example, the permeability coefficient k of the seabed sedimentary layer is expressed by the following equation (3) using the porosity β.
^{k = d 2 β 3/180} (1-β 2) (3)

Therefore, the distribution of the permeability coefficient k in the depth direction of the deposition layer as shown in FIG. 12 using the porosity distribution at each of the places A and B (as shown in FIG. 11) In the place B, it can be calculated like a one-dot chain line 1201. Further, water permeability in addition coefficient, it is possible to calculate the gap size parameters, structure factor, bulk modulus, the key parameters that characterize the sound propagation seabed sediments, such as modulus of porosity beta, beta _min, By using p and q as basic calculation parameters, physical parameters in the seabed sedimentary layer can be clarified.

In this way, as a value indicating the distribution of physical parameters in the depth direction of the seabed sedimentary layer, for example, by using the characteristics of the seabed sedimentary layer obtained by selecting β _min , p, q, the acoustic wave propagation in the sedimentary layer It is possible to calculate how much the difference is compared with the case where there is no deposited layer, that is, the deviation of the sound wave propagation. The image compensation calculation unit (second calculation unit) 304 receives the input of the calculation parameter 303 and calculates a deviation of the sonar image due to the sound wave propagation in the seabed sedimentary layer. First, calculation of the deviation of the sound wave will be described with reference to FIGS. An embodiment of a method for calculating a shift in image compensation will be described with reference to FIGS. 15 and 16.

  FIG. 13 shows the calculation result of the acoustic wave propagation characteristics in the sedimentary layer when the transmitted acoustic wave 1302 is irradiated from the sonar 1301 to the seafloor sedimentary layer 1300 at an incident depression angle of θ = 30 °. Here, in the coordinate system, the direction 1303 parallel to the seabed sedimentary layer is the direction of the acoustic wave arrival range, and the direction 1304 perpendicular to the seabed sedimentary layer surface is the depth direction of the seabed sedimentary layer. Further, the graph 130 shows the change in sound velocity with respect to the deposition layer depth, the graph 131 shows the size of the range where the sound wave reaches the deposition layer depth, and the graph 132 shows the intensity of the sound wave with respect to the arrival range. It shows how it becomes.

  First, it can be seen from the graph 130 in FIG. 13 that the speed of sound in the seabed sedimentary layer is greatly different in the locations A and B which are different sediments. These sound velocities have a distribution in the depth direction. The solid line 1305 is the sound velocity distribution at the location A in FIG. 11, and the alternate long and short dash line 1306 is the sound velocity distribution at the location B. In both 1305 and 1306, the sound velocity gradually increases as the depth of the sedimentary layer increases from the acoustic velocity of 1533 m / s (sound velocity in seawater) on the surface of the sedimentary layer (0 m point). On the other hand, the degree of change in the sound speed differs depending on the location, and the sound velocity at the depth of 1 m of the deposited layer is 1555 m / s at the location A and 1660 m / s at the location B. On the other hand, if the porosity distribution (bottom quality) of the sedimentary layer is known, the sound velocity distribution corresponding to the location where the bottom sediment is different can be calculated. Further, in the graph 130, a dotted line 1307 indicates the speed of sound when there is no sedimentary layer and only seawater. Naturally, the speed of sound is constant at 1533 m / s. Therefore, by comparing the sound velocity distribution 1305 at location A and the sound velocity distribution 1306 at location B with the sound velocity 1307 in seawater, the difference between the sound velocity distribution in the sedimentary layer when no sedimentary layer is present (when only seawater is present) is obtained. Values can also be calculated.

  Next, looking at the graph 131 of FIG. 13, it can be seen that the sound wave travels through different paths with different refractions depending on the location when propagating into the deposited layer. A solid line 1308 indicates a propagation path of sound waves in the deposition layer at the location A, and a dashed line 1309 indicates a propagation path of sound waves in the deposition layer at the location B. In both cases, the incident depression angle to the deposited layer is 30 °. In the place A, the reach range is 15.6 m at the depth of the deposited layer 1 m, but in the place B, the reach range is about 16.5 m. It can be seen that when the distance is 1 m in depth, the displacement is close to 1 m. On the other hand, if the porosity distribution (sediment) in the deposited layer is known, it is possible to calculate the propagation path of the sound wave according to the location where the sediment is different. Further, in the graph 131, a dotted line 1310 indicates a propagation path of a sound wave when there is no sedimentary layer and only seawater. Naturally, since the physical parameter does not change, it is a linear propagation path. Therefore, by comparing the propagation path 1308 of the place A and the propagation path 1309 of the place B with the propagation path 1310 in seawater, the propagation path in the sedimentary layer and when there is no sedimentary layer (when only seawater is present) The difference value can also be calculated.

  Next, it can be seen from the graph 132 in FIG. 13 that the degree of change in the intensity of the sound wave varies depending on the location. The solid line 1311 is the intensity of sound waves expressed in dB (decibel) with respect to the arrival range of sound waves at the location A, and the alternate long and short dash line 1312 is the intensity of sound waves expressed in dB relative to the arrival range of the sound waves at the location B. The intensity of the sound wave is represented by a change from the intensity of the sound wave when entering the deposited layer. That is, when the intensity of the sound wave is 100 dB on the surface of the deposited layer (point of 0 m), for example, in the place B, the intensity is 100-10 dB = 90 dB in the reach range of 15.6 m. Comparing place A and place B, the reach range where the intensity of sound waves is −10 dB is about 15.6 m at place A and about 16.5 m at place B. You can see that On the other hand, if the porosity distribution (sediment) in the deposited layer is known, it is possible to calculate the distribution of attenuation of sound waves according to the different locations of the sediment. Further, in the graph 132, a dotted line 1313 indicates a change in the intensity of sound waves when there is no sedimentary layer and only seawater. Since sea water has a very small attenuation rate of 0.01 dB / m, there is no change in the intensity of sound waves with respect to movement in the range direction of at most several meters as shown in the graph 132. Therefore, by comparing the sound wave intensity distribution 1311 at the place A and the sound wave intensity distribution 1313 at the place B with the sound wave intensity distribution 1313 in the seawater, when there is no sedimentary layer (only the seawater And the difference between the distributions of the intensity of sound waves in the deposited layer can be calculated.

  As described above, using the graph 130, the graph 131, and the graph 132 in FIG. 13, it is shown that the propagation characteristics of the sound wave greatly differ in the sediment layer having different sediment depending on the location, and at the same time, the sediment of the sediment layer. If the (porosity distribution in the depth direction here) is known, it is possible to calculate how much the sound wave propagation characteristic is shifted, that is, the amount of deviation compared to when there is only seawater. These deviations are also deviations to a normal sonar image that is made assuming that there is no deposited layer, and the quality of the sonar image can be improved by correcting these deviations.

  A description will be given of how to use the deviation of the sound wave propagation characteristics as an image compensation value with reference to FIGS. This corresponds to the embodiment of the image compensation value of the deposited layer calculated by the image compensation calculation unit 304 as the second calculation unit, that is, the correction data 305.

  Prior to the detailed description, a mode of acquiring an image in the deposited layer with a sonar will be briefly described with reference to FIG. First, the sonar 1400 acquires an image while moving when forming the image. The moving direction is shown at 1402. The sonar movement direction is referred to as an azimuth direction 1403. The horizontal distance in the direction in which sound waves are emitted from the sonar is referred to as a range direction 1404. A sonar image 1405 is a collection of reflected sounds of sound waves emitted from the sonar 1400 one by one. The azimuth direction 1403 and the range direction 1404 in the sonar image 1405 are also shown in the figure. The sound wave transmitted from the sonar propagates in the seawater 1401, reaches the surface of the seabed sedimentary layer 1406, and forms a projection surface 1407. When imaging the bottom of the sea, a sonar image 1405 is created as a collection of the reflected sounds from the sound projection surface 1407 on the bottom of the sea. When acquiring an image in the sedimentary layer, It must be considered that after the sound wave reaches the bottom of the sea, it propagates into the bottom sediment layer 1406 and becomes a sound projection surface 1408 in the bottom sediment layer. Therefore, the sonar image is created by collecting the reflected sound signals 1409 from the sound wave projection surface 1408 in the seabed sediment layer one by one. Here, as described above, the reflected sound signal 1409 includes deviations such as the sound speed, the propagation path, and the attenuation due to the characteristics of the acoustic wave propagation in the deposition layer.

  Compensation for these deviations will be described with reference to FIG. FIG. 15 illustrates three preferred embodiments of the correction data according to the present invention, that is, the sound speed correction data 150, the propagation path correction data 151, and the attenuation correction data 152. Each of the correction data corresponds to the calculation result of the acoustic velocity distribution in the deposition layer, the propagation path in the deposition layer, and the intensity of the sound wave in the deposition layer, which has been described with reference to FIG.

First, the sound speed correction data 150 will be described. Here, the sound velocity distribution calculated from the sediment of the sedimentary layer described with reference to the graph 130 in FIG. 13 is used. Since the depth direction of the sound-velocity distribution c of the deposited layer (z) is known, (for only seawater, 1500) If there is no deposited layer distance L wave propagation time of the using the speed of sound c ₀ of seawater , T = L / c When it takes ₀ seconds, in the deposited layer (1501), the propagation time t ′ of the sound wave can be calculated from the following equation (4).

  Here, θ is the magnitude of the incident depression angle on the deposition layer, z is the depth direction of the deposition layer, Z is the depth of the deposition layer to be corrected, and at a point of a distance L (= Z / sin θ) in the propagation direction of the sound wave. Correspond.

  Thus, the deviation of the propagation time of the sound wave caused by the presence of the deposited layer can be obtained as (t′−t) seconds. This misalignment (t′−t) can be calculated for any point constituting the sonar image as indicated by an arrow 1502. Further, as in 1503, it is possible to individually give to each piece of data (corresponding to one transmission / reception of sound waves) of each original reception signal constituting the sonar image.

  Next, the propagation path correction data 151 will be described. Here, the sound wave propagation path calculated from the bottom sediment in the deposition layer, which is described in the graph 131 of FIG. 13, is used. When a sound wave propagates in the deposition layer, it is refracted in the deposition layer unlike the propagation path 1504 of the seawater only sound wave, and the propagation path changes like 1505. At this time, a deviation 1506 in the range direction due to the difference in the propagation path occurs at the point of the depth Z in the deposited layer. This range direction deviation can be calculated for any point on the sonar image, as indicated by the arrow 1507, in the same way as the image deviation due to the sound velocity distribution described above. Further, like 1508, the original received signal constituting the sonar image can be individually provided for each piece of data (corresponding to one transmission / reception of sound waves).

  Third, the attenuation correction data 152 will be described. Here, the distribution of the intensity of the sound wave calculated from the bottom sediment in the deposited layer described with reference to the graph 132 in FIG. 13 is used. As described with reference to the graph 132 in FIG. 13, when the sound wave propagates in the sedimentary layer, the sound wave is significantly attenuated compared to the case of only seawater, and the degree of attenuation differs depending on the sediment. Such a difference in the degree of attenuation has a one-to-one correspondence with the strength of the received signal, and lowers the luminance of the final image. When correcting such attenuation, the propagation distance of the sound wave in the deposited layer becomes important. As indicated by 152 in FIG. 15, the sound wave transmitted from the sonar 1509 has the propagation distance 1510 in the deposition layer a, b, c until reaching the depth of Z in the deposition layer depending on the incident angle to the deposition layer. , D are different. Therefore, as the distance in the range direction increases in the order of “a”, “b”, “c”, and “d”, the attenuation amount that the sound wave receives in the deposited layer also increases. Therefore, as shown in the lower diagram of FIG. 15, when the horizontal axis is the range direction and the vertical axis is the intensity of the sound wave received by the sonar, the intensity 1513 of the received sound wave with respect to the range direction decreases as the length in the range direction increases. . This tendency itself is the same when sound waves are transmitted through seawater. However, since the attenuation rate of the seabed sedimentary layer is remarkably larger than that of seawater as indicated by 132 in FIG. 13, the attenuation in the seabed sedimentary layer becomes substantially dominant in the influence of the attenuation accompanying the sound wave propagation. Therefore, the curve 1513 can be used as correction data for the sonar image as the attenuation amount of the sound wave at the point of the seabed Z. The attenuation amount of the sound wave corresponds to the luminance of the image, and can be calculated as a correction amount of the luminance distribution at an arbitrary point on the sonar image as indicated by 1514. Further, by using the curve 1513 as it is, it can be individually given to each piece of original received signal (corresponding to one transmission / reception of sound waves) constituting the sonar image as in 1515. .

  Up to this point, the form of the correction data 305 is a form in which a correction amount is calculated and given for an arbitrary point on the sonar image, or a correction amount given to each piece of individual data received by the sonar. As described above, the target to which the correction amount is given may be any data format that appears in the process of the sound wave reception signal to the sonar image generation. Further, as the amount represented by the correction data, not only the sound velocity correction data 150, the propagation path correction data 151, and the attenuation amount correction data 152, but also the deviation due to the sound wave propagation in the deposition layer in the sonar image is compensated. Any data can be used.

  In the present invention, the correction data 305 is further transmitted to the compensation image processing unit 306 which is a third calculation unit. Not only the correction data 305 but also the received signal 307 of the sonar are transmitted to the compensation image processing unit 306. Here, the sonar image is actually synthesized. Further, corrected image data 308 is generated using the correction data 305 to compensate for the influence of the sound wave propagation characteristics of the deposited layer.

  Hereinafter, two correction image data generation methods will be described with reference to FIGS. 16 and 17. First, the case where the correction data 305 is a correction amount for an arbitrary point of the sonar image will be described with reference to FIG. For example, the compensation image processing unit 306 sums the received signal 1601 from the sonar transmission / reception unit and the correction data 1602. The received signal 1601 from the transmission / reception unit of the sonar includes a shift 1603 due to the deposited layer at each point of the sonar image, but the correction data 1602 is compensation for the shift at each point. It has the quantity 1604 as a value. Therefore, by shifting the position of each pixel on the sonar image 1601 according to the shift compensation amount 1604 of the correction data 1602, the shift due to the sound wave propagation of the deposited layer can be eliminated. By combining the compensated data by the sonar image processing process 1605, a sonar image that has been subjected to deposition layer compensation, that is, corrected image data 1606 is generated. This corrected image data is the same as the corrected image data 308 in FIG.

  FIG. 17A is an explanatory diagram of a method of giving correction data 305 as a correction amount for each piece of data received by a sonar as another example of the method of creating corrected image data. Here, the correction related to the intensity distribution of the sound wave, that is, the attenuation amount shown in FIGS. 13 and 15 will be described as an example. Reference numeral 1701 denotes a received signal itself from the sonar signal. As time increases, the sound is reflected from a distant object in the range direction. As described above with reference to FIGS. 13 and 15, the attenuation amount from the deposited layer increases as the received signal becomes farther in the range direction. Therefore, the attenuation correction amount 1702 corresponding to each point in time of the received signal 1701 can be used as correction data. Here, the reception signal 1701 and the attenuation correction amount 1702 are multiplied to calculate a corrected reception signal 1703 in which the attenuation of the deposited layer is corrected. This process is sequentially performed on each received signal data 307 used when synthesizing the sonar image, and the data is synthesized by the sonar image processing process 1704, thereby correcting the attenuation of the deposited layer. A sonar image, that is, corrected image data 1705 is generated. This corrected image data is the same as the corrected image data 308 in FIG. In actual application, one of the three types of corrections shown in FIG. 15 may be used, or a plurality of corrections may be combined. Further, not only the correction of the sound velocity / propagation path / attenuation shown in FIG. 15 but also the sound wave that appears due to the difference in the sediment bottom layer such as the change of the frequency component / the change of the nonlinear component of the sound wave / the waveform distortion of the received sound wave. Any correction may be used in any combination as long as the correction uses an amount reflecting the difference in propagation characteristics.

  With the above process, in the embodiment described with reference to FIG. 3, (1) the sediment layer sediment is calculated, (2) sonar image correction data depending on the sediment is created, and (3) the sonar received signal. Using the correction data, the corrected image data in which the deposited layer is corrected is created, and the process for compensating the primary sediment layer sediment is completed. However, the calculation parameter that is primarily estimated may be a value close to the true sediment, but is not necessarily a correct value. It is also conceivable that when the correction data is entered during the sonar image processing process, the deposited layer cannot be corrected completely. In addition, as described with reference to FIG. 6, the bottom sediment measuring instrument 600 that is the second transmission / reception unit may be used as the calculation parameter representing the sediment of the deposited layer, and the known density distribution data 604 that is the database unit may be used. Sometimes used. In summary, the operational parameters used in the primary deposition layer correction process are “close” to the bottom sediment of the target deposition layer, but are generally not true.

  The following will describe how the uncertainty (displacement from the true value) of the calculation parameter as described above appears. FIGS. 16B and 17B show sonar images 1608 and 1707 when correction data is not used. The corrected image data 1606 has less deviation of the object in the image than the sonar image 1608 without correction, and the corrected image data 1705 has less luminance unevenness in the image than the sonar image 1707 without correction. . On the other hand, the influence of the sound wave propagation of the deposited layer cannot be completely eliminated, and in the corrected image data 1606, there are still a residue and a blur of the outline from the true image formation position. In the corrected image data 1705, a slight luminance unevenness or an image having a slightly low luminance in the range direction is obtained.

  Therefore, in the present invention, the contrast information is generated by comparing the corrected image data that has been primarily corrected with the reference image. Thereafter, a modified calculation parameter was further calculated using the reference information, and a feedback loop for bringing the calculation parameter closer to the true value was added. This configuration is as described with reference to FIGS. Here, the comparison information is a comparison between the corrected image data and the reference image data, the value of one or a combination of any one of an image difference value, an image correlation amount, and an image signal level. Is a value obtained by converting the difference between the corrected image and the original image data into the signal intensity, and the corrected calculation parameter is based on the reference information. Calculating a value obtained by converting any one or a combination of a plurality of physical parameters of the seabed sediment layer calculated from the value into a signal intensity and using the value as a calculation parameter input to the second calculation unit. Features. Hereinafter, with reference to FIGS. 18 and 19, the reference image 310 used for comparison with the corrected image data and the contrast information 311 calculated by the contrast information generation unit (fourth calculation unit) 309 described with reference to FIGS. 3 to 5. The corrected calculation parameter 500 calculated in the bottom sediment parameter correction unit (fifth calculation unit) 312 will be described in detail.

  A case where a normal sonar image (original image) 402 generated by the normal sonar image processing unit (sixth calculation unit) 400 in FIG. 4 is used as the reference image 310 will be described with reference to FIG. In this process, for example, a residue from the true image formation position and blurring of the outline as shown in FIG. 16 can be further eliminated. FIG. 18 shows corrected image data 1801 and a normal sonar image 1800 in which the deposited layer correction is primarily performed. A value indicating how much the image quality is improved in these two images is calculated. This value is the contrast information 311 calculated by the contrast information generation unit (fourth calculation unit) 309. Two examples of the contrast information 311 are considered here. One is a value indicating how clearly the object is depicted. Specifically, the differential value of the image representing the contrast value of the object and the sharpness of the contour is calculated. The other is an amount representing an improvement in the correction of the displacement of the position of the object, and this can be the amount of movement 1803 of the center of gravity of the object. These values are values indicating that the image quality is improved if the value increases (or decreases), although the “optimum value” is not given.

Next, the control information 311 is transmitted to the bottom sediment parameter correction unit (fifth calculation unit) 312, where the calculation parameter that is a parameter representing the sediment of the sedimentary layer is re-estimated and corrected calculation Generate parameters. Using the contrast information 311 calculated by the contrast information generation unit 309, the calculation parameters are corrected so as to further improve the image quality. As shown in FIG. 5, the corrected calculation parameter 500 is transmitted to the input switching unit (second input switching unit) 501. Here, the calculation parameter calculated by the first calculation unit 302 and which one is used as the calculation parameter are switched and sent to the image compensation calculation unit 304 to generate a corrected image again. In FIG. 18, the corrected calculation parameters β _min , p, q (1804) are shown. Here, the calculation parameter is corrected by, for example, a method of changing one or more values of β _min , p, and q by 1%. Further, the correction of the calculation parameter is selected so that the reference information 311 changes in a direction indicating the improvement of the image.

  The lower graph of FIG. 18 shows changes in control information (for example, contrast value and differential value) with respect to the number of calculations (the number of times the loop is rotated: the number of times the image is reconstructed using the modified calculation parameter). Is. Here, there are two methods for setting the calculation parameter correction completion by the feedback loop. The first method is a method of setting an upper limit such as n = 10 times for the number of calculations, and the second method is that the difference 1807 between the value of the reference information and the value 1808 in the normal sonar image data is set to a substantially constant value. It is a method of completing the calculation when it has settled down and no longer changes. Also, in this embodiment, when the quality of the image has deteriorated as a result of correction (1809), it is possible to return to the optimum direction (1810) by correcting the calculation parameter again. effective.

  A case where an optimal image 404 prepared in advance in the reference image storage unit (memory / storage unit) 403 in FIG. 4 is used as the standard image 310 will be described with reference to FIG. In this process, for example, when the attenuation amount correction in the deposition layer as shown in FIG. 17 is performed, the luminance unevenness of the image that could not be removed by the primary deposition layer correction can be removed. FIG. 19 shows corrected image data 1900 that has been primarily subjected to accumulated layer correction, and an optimal image 1901 prepared in advance in the reference image storage unit. Here, the optimum image may be, for example, a sonar image created in seawater, or one of sonar images in which deposition layer correction is completely performed. In any case, any image may be used as long as the image data has a shape in which the influence of the deposited layer does not exist in the sonar image.

Here, one piece of data 1902 in the azimuth direction in the sonar image is taken out, and the difference in image luminance value between the two images 1900 and 1901 is obtained. If the effect of the deposited layer is completely eliminated, this value is zero for all range directions. On the other hand, when the estimation of bottom sediment parameters is not complete, an influence that cannot be completely removed appears with a distribution in the range direction as in 1903. This is smaller than the luminance unevenness 1904 in the sonar image when the deposited layer compensation is not performed, but a residue 1905 that cannot be removed remains. Therefore, the residue 1905 becomes the contrast information 311 calculated by the contrast information generation unit (fourth calculation unit) here. Further, this reference information is transmitted to the bottom sediment parameter correction section (fifth calculation section) 312 in the same manner as in the description of FIG. 18, and here, the calculation parameter, which is a parameter indicating the sediment bottom sediment, is restored. An estimation is performed to generate a modified calculation parameter 1906. The use of, for example, β _min , p, q (1906) as calculation parameters is the same as in the embodiment of FIG. When the optimum image 404 prepared in advance in the reference image storage unit (memory / storage unit) 403 is used as the standard image 310, the value of the contrast information, which is a difference value from the reference image, approaches zero. The calculation parameters β _min , p, and q are corrected.

  The lower graph of FIG. 19 shows the change in the contrast information (here, the difference in the image luminance value) with respect to the number of calculations (number of times the loop is rotated: the number of times the image is reconstructed using the modified calculation parameter). is there. As described above, since the difference value from the optimum image is used as the contrast information here, the value of the contrast information varies in the vicinity of zero (dotted line 1910). Therefore, the loop process is such that the difference 1909 from zero gradually decreases as the number of times the loop is turned. The closer this difference value (control information value) is to zero, the more accurately the deposited layer is compensated. Therefore, the loop process may be terminated when the difference value with the reference information falls below a certain threshold T. Similarly to the case of FIG. 18, the number of loops may be determined in advance, such as the number of loops n = 10, empirically.

Here, with respect to the contrast information calculated between the reference image and the corrected image data, in addition to the examples of the contrast information described with reference to FIGS. Any difference between images, such as a difference in size, may be used. In addition, the reference information used at that time can be re-estimated for the operation parameter in the bottom sediment parameter correction unit (fifth calculation unit) from the value of the reference information as in the case of FIGS. Information. In addition, β _min , p, and q have been described as the modified calculation parameters. This is a physical parameter in the depth direction of the seabed sedimentary layer calculated using equation (2) as described above. A value indicating the distribution. Of course, as with the previous calculation parameter, any of a plurality of parameters indicating the physical parameter distribution in the depth direction of the seafloor sedimentary layer may be used as the corrected calculation parameter. Of course, an approximate expression other than the expression (2) may be used. As described above, the skeleton of deposited layer compensation in the present invention, that is, (1) creating a sonar image in which the deposited layer is corrected from the bottom sediment parameter of the deposited layer, and (2) determining and feeding back the effect of the image correction. The loop of creating a sonar image with a better deposited layer correction was described.

  Next, with reference to FIG. 20, the case where the bottom sediment measuring instrument 600 as the second transmission / reception unit shown in FIG. 6 is used as the calculation parameter and the case where the known density distribution data 604 as the database unit is used will be described. . First, FIG. 20A shows an example in the case where a bottom sediment measuring instrument as a second transmitting / receiving unit is provided in the traveling body 2001. Here, the traveling body 2001 is also provided with a sonar transmission / reception unit 2002 which is a first transmission / reception unit. As a first embodiment, an example in which a calculation parameter, which is a parameter representing sediment, is estimated using a received signal by the sonar transmission / reception unit 2002 can be considered. This corresponds to the case shown in the embodiments of FIGS. A sonar sound wave is transmitted from the sonar transmission / reception unit 2002 to the deposition layer 2003, and a corrected image in which the sonar original image is generated and the sediment is compensated is generated for the received sound wave. Here, in Fig.20 (a), the bottom measuring instrument 2004 which is a 2nd transmission / reception part is further comprised. The bottom sediment measuring instrument 2004 transmits and receives a sound wave for bottom sediment measurement to the deposited layer 2003. The reception signal received by the sonar transmission / reception unit 2002 and the reception signal received by the bottom sediment measuring instrument 2004 are transmitted to an image processing block 2005 for generating a sonar image that compensates for the deposited layer below the input switching unit 602.

  Here, the frequency of the sound wave in the second transmitting / receiving unit is 5 kHz or more and 10 MHz or less, more preferably 100 kHz or more and 10 MHz or less. When transmitting and receiving sound waves as a bottom sediment measuring instrument, the purpose is to sufficiently transmit sound waves into the deposited layer using sound waves of a relatively low frequency of 100 kHz or less, and relatively high frequencies of 100 kHz or more. There are two ways in which the purpose is to measure the density distribution and porosity distribution inside the deposited layer with high spatial resolution by shortening the wavelength using the sound wave. Therefore, the frequency of the bottom sediment measuring instrument 2004 is 5 kHz or more and 10 MHz or less, more preferably 100 kHz or more and 10 MHz or less.

  Next, in FIG. 20B, the bottom sediment measuring instrument 2007 as the second transmitting / receiving unit is provided physically separated from the traveling body 2001. In this case, the bottom sediment measuring device may be a sediment core sampler that acquires a core sample inside the sediment and physically measures the density distribution and porosity distribution instead of the second transmitting / receiving unit. Instead of using transmission and reception of sound waves, a deposit physical parameter measuring device such as an electromagnetic transducer may be used. Of course, sound waves may be transmitted and received. In that case, the frequency of the bottom sediment measuring instrument 2007 is 5 kHz to 10 MHz, more preferably 100 kHz to 10 MHz. At this time, similarly to FIG. 20A, the received signal received by the sonar transmission / reception unit 2002 and the received signal received by the bottom sediment measuring device 2007 generate a sonar image that compensates for the deposited layer below the input switching unit 602. To the image processing block 2005 for

  FIG. 20C shows an example in the case of using a calculation parameter representing the bottom sediment of the deposited layer from the database unit 2009 prepared in advance. This corresponds to the case where the information of the known density distribution data 604 in FIG. 6 is used by the image compensation calculation unit 304 as the second calculation unit. In this case, without using a bottom sediment measuring device, the received signal received by the sonar transmission / reception unit 2002 and the calculation parameters stored in the database unit 2009 generate a sonar image that compensates for the deposited layer below the input switching unit 501. Is transmitted to an image processing block 2005.

  FIG. 21 is used to show several examples of the method for measuring sediment layer bottom sediment parameters using acoustic waves. FIG. 21 (a) is an explanatory diagram of a bottom sediment estimation method using the fact that the attenuation rate varies depending on the sediment bottom sediment. Here, sound waves are irradiated from the bottom sediment measuring device 2101. The left side is a diagram measuring the deposited layer 2102 at the location A, and the right side is a diagram measuring the deposited layer 2103 at the location B. At this time, the received sound waves received by the receiving unit include sound waves 2106 and 2107 returning from the inside of the deposited layer in addition to the sound waves 2104 and 2105 reflected by the surface of the deposited layer. Here, the reception signals 2106 and 2107 from the inside of the deposited layer have a difference in the reception level. This is because, as shown in FIG. 10, the attenuation rate of the sound wave varies depending on the sediment of the deposited layer, and the respective sediment parameters can be estimated from the values of the amplitudes 2106 and 2107 of the sound wave from the inside. For example, when the value of 2104 is 10, when the value of 2106 is 5, the attenuation amount is simply −6 dB. By comparing with the simulation result as shown in FIG. The size can be estimated.

  FIG. 21B is an explanatory diagram of a bottom sediment estimation method using the fact that the arrival range of sound waves in the sedimentary layer varies depending on the sediment of the sedimentary layer. Prior to the description of the estimation method, how the reach range changes with respect to the sediment will be described with reference to FIG.

  FIG. 22 is a graph showing a simulation result by a sound wave propagation calculation of the deposition layer, and showing a relationship between the bottom sediment (sediment density) of the deposition layer and the reach range of the sonar. Here, the reach range of the sonar has a one-to-one correspondence with a range in which a sound wave image can actually be acquired. In the graph, a line 2201, a line 2202 and a line 2203 correspond to the sound wave frequencies of f1, f2 and f3, respectively, and the frequency increases as the number increases. Further, as shown in the graph, it can be seen that the size of the reach range varies greatly depending on the sediment of the deposited layer. When the deposit density is small, the reach range becomes large, and the reach range may be 100 m or more. On the other hand, it can also be seen that the reach range is at most 20 m when the sediment density is high. The fact that the size of the reach range changes in this way is nothing other than the drastic change in the expected performance of the sonar (how efficiently it can be explored) depending on the sediment. In addition, it is clear from the graph of FIG. 22 that this tendency varies greatly depending on the frequency of the sound wave. Therefore, it can be seen that the bottom sediment of the deposited layer can be calculated backward if the range reached by the sound wave of a certain frequency can be measured.

  Returning to FIG. 21B, the left side is a place A (density = 2.1) where the deposit density is low, and the right side is a place B (density = 1.7) where the deposit density is high. At this time, referring to FIG. 22, when the frequency is f1, the reach range of the place A is 45 m, and the reach range of the place B is 20 m. FIG. 21 illustrates the reach range 2110 of the place A and the reach range 2111 of the place B. Here, it can be seen that the location where the reference object 2109 starts to appear in the sonar image is different between the location A and the location B by placing a reference object 2109 in the deposition layer. At location A, the reference object begins to appear from a location at a distance 2112 that is relatively far from the sonar. On the other hand, at the location B, the image of the reference object 2109 cannot be seen unless the distance 2113 from the sonar is close. Here, it can be seen that the distance 2112 and the distance 2113 have values depending on the density of the deposited layer. By measuring this distance on the sonar image, the sediment of the deposited layers 2102 and 2103 can be estimated. In this case, by calculating backward from the distance, it can be seen that the density of the deposited layer is 2.1 at location A and 1.7 at location B, respectively.

  FIG. 21C is an explanatory diagram of a bottom sediment estimation method using the fact that the critical angle on the surface of the deposited layer changes depending on the sediment quality. Prior to the description of the estimation method, how the critical angle of sound waves changes with respect to the sediment will be described with reference to FIG.

  FIG. 23 is a graph showing a result of simulation by sound wave propagation calculation of the deposited layer, and showing a relationship between the bottom sediment (sediment density) of the deposited layer and the sonar incident critical angle. Here, the incident critical angle is an angle at which the sound wave is not transmitted into the deposited layer. Even if the sound wave is incident on the deposited layer at an angle smaller than the incident critical angle, the sound wave is transmitted into the deposited layer. I won't go. In the graph, lines 2301, 2302, 2303, 2304, and 2305 indicate the relationship between the bottom sediment and the critical angle when the frequencies are f1, f2, f3, f4, and f5, respectively, and the numbers increase from f1 to f5. As the frequency increases, the frequency increases. From the graph of FIG. 23, it can be seen that the critical angle of incidence of the sonar varies greatly depending on the sediment. That is, it is shown that the amount of sound waves transmitted through the deposited layer varies greatly depending on the sediment of the deposited layer. In addition, it is shown in the graph that this tendency changes greatly depending on the frequency of the sound wave. Therefore, it can be seen that if the magnitude of the sonic critical angle at a certain frequency is known, the bottom sediment of the deposited layer can be calculated backward.

  Here, returning to FIG. 21C, the sound wave transmitted from the sound wave transmitter 2115 only causes total reflection at an incident angle equal to or smaller than a certain angle. Therefore, by preparing the receiver row 2116, there is a place where the signal intensity rapidly increases depending on the receiver position, as shown in a graph 2117. The critical angle can be measured from the receiver position. Therefore, from this embodiment, the bottom sediment of the deposited layer can be estimated by measuring the critical angle.

  FIG. 24 is a diagram illustrating an example of an image display unit, a sediment parameter display unit, an input switching unit, and a sediment parameter adjustment unit in the acoustic imaging apparatus of the present invention. As shown in FIG. 24A, the acoustic imaging apparatus 2400 includes a reference image display unit 2401 that displays a reference image and a correction image display unit that displays a correction image. However, as shown in FIG. 24B, the reference image display unit 2401 may not be provided, and only the corrected image display unit 2402 may be provided. The sound wave imaging apparatus 2400 of this example is provided with three input switching units. In the example of the figure, three input switching units are prepared in the apparatus housing. However, switching may be performed inside the apparatus, and the number of input switching units provided in the acoustic imaging device casing is any number from 0 to 3. But you can. Here, a first input switching unit 2404 that separates the image data of the memory / storage unit and the image data from the sonar transmission / reception unit as a reference image is provided. Further, the calculation parameter switching is performed by adjusting the known density distribution data, the calculation parameter calculated by the first calculation unit, the corrected calculation parameter when performing the automatic image quality improvement loop, and the adjustment unit 2407 manually. A second switching unit 2405 is provided for switching between the four calculation parameters of the adjusted calculation parameter. Finally, a third input switching unit 2406 is provided for switching which one of the received signals of the sonar transmission / reception unit and the bottom sediment measuring device is used as an input to the first calculation unit.

Further, the acoustic imaging apparatus 2400 includes a calculation parameter adjustment unit 2407. The adjustment unit 2407 may be a knob or a lever, and it is sufficient that the calculation parameters can be substantially adjusted. Further, a plurality of calculation parameters may be adjusted, and therefore a plurality of calculation parameter adjustment units 2407 may exist. In the example shown in the figure, an adjustment unit that adjusts β _min , p, and q, which are parameters representing the porosity distribution of the deposited layer described in FIG. A display portion 2408 is included. In the calculation parameter display unit 2408, the physical values of the calculation parameters used to create the corrected image data at that time are displayed. Here, a plurality of calculation parameters may be displayed, and therefore there may be a plurality of calculation parameter (bottom sediment parameter) display units 2408. Here, according to the switching of the input switching unit 2405, the known density distribution data, the calculation parameter calculated by the first calculation unit, the corrected calculation parameter when performing an automatic image quality improvement loop, and the adjustment unit 2407 manually adjust Any one of the four calculation parameters of the adjusted calculation parameter is displayed. In FIG. 24, since the input switching unit 2405 is in the Auto position, the corrected value of the parameter for calculation is displayed on the display unit 2408. Further, FIG. 24 shows values when β _min is 0.72, p is 0.54, and q is 0.53.

  As described above, the acoustic imaging apparatus shown in FIG. 24 allows the operator to adjust the sediment parameters while referring to the reference image and the compensation image, and further the calculation parameters, so that compensation close to a true image can be achieved. An image can be obtained, and more suitable corrected image data of the deposited layer can be automatically obtained according to the feedback loop shown in FIGS.

  With reference to FIG. 25, a method of changing the sound wave irradiation conditions of the sonar using the calculation parameters will be described. FIG. 25A shows an example of changing the search range by one scan according to the bottom sediment. When the bottom sediment is estimated, the reachable range corresponding to the bottom sediment can be estimated as described with reference to FIG. Therefore, in the example of FIG. 25 (a), for example, in the sediment A (2501), the search is performed five times, and in the sediment B (2502), the search is performed twice. Control the conditions.

  Further, as described in FIG. 22, the reach range is variable depending on the frequency. In FIG. 25 (b), adaptive reach range change by frequency change is performed using it. As shown in the left figure, at the frequency A (2507), since the reach range 2504 is short, it is assumed that a reach range sufficient to image the buried object 2506 cannot be obtained. At this time, as shown in the right figure, by controlling the frequency and changing the frequency to B (2508), transmission / reception of ultrasonic waves having a sufficient reach range 2505 for imaging the buried object 2506 can be performed. it can.

  In addition to the method shown in FIG. 25, the control of any sound wave irradiation condition that enables more efficient sound wave transmission / reception depending on the sediment of the deposited layer belongs to the scope of the present invention. For example, the change of the transmission sound pressure in consideration of the attenuation rate, the change of the beam pattern, the change of the waveform of the sound wave pulse, the change of the sound wave transmission interval, and the like are also within the scope of the present invention.

1 is a schematic view of an acoustic imaging device in the sea and in the seabed sedimentary layer. Explanatory drawing which shows the part for the gap | deflection and distortion of a sound wave image by a seabed sedimentary layer. The figure which shows the basic Example of the sound wave imaging device by this invention, and an image processing algorithm. The figure which shows the Example of the sound wave imaging device and image processing algorithm by this invention. The figure which shows the Example of the sound wave imaging device and image processing algorithm by this invention. The figure which shows the Example of the sound wave imaging device and image processing algorithm by this invention. The figure which shows the Example of the sound wave imaging device and image processing algorithm by this invention. The figure which shows the Example of the sound wave imaging device and image processing algorithm by this invention. The figure explaining the bottom sediment parameter of a seabed sedimentary layer. The graph showing the attenuation rate in a deposition layer with respect to a sonar frequency. The figure which shows the measured value in the location A and the location B of the porosity with respect to the deposition layer depth. The figure which shows the example of a calculation of the physical parameter in a deposited layer. The figure which shows the difference in the speed of sound by the difference in a place, an arrival range, and the intensity of a sound wave. The figure explaining imaging in a deposition layer by a sonar. The figure which shows the image correction parameter of a deposited layer. The figure which shows an example of correction | amendment image data. The figure which shows an example of correction | amendment image data. The figure which shows an example of contrast information and calculation parameter correction. The figure which shows an example of contrast information and calculation parameter correction. The figure which shows the Example of a sediment measuring device and a database part. The figure which shows the Example of the bottom sediment estimation method by a bottom sediment measuring device. The figure which shows the relationship between a reachable range and a density. The figure which shows the relationship between an incident critical angle and a density. The figure which shows the example of the display part of the sound wave imaging device by this invention. The figure which shows the Example of sonar transmission signal control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Hull 101 Navigation body 102 Sonar 103 Transmission sound wave from sonar 104 Object 105 Sea bottom surface 106 Reception sound wave to sonar 107 Sonar image 108 Imaging image of object on sonar image 109 Seabed sedimentation layer 110 Embedded in seabed sedimentation layer Object 200 sonar 201 transmitted sound wave from sonar 202 object 203 sonar image 204 of the object in the sea image formation image 205 of the object on the sonar image sedimentary layer 206 object 207 in the seafloor sedimentary layer Transmitted sound wave 208 from irradiated sonar Sonar image 209 when there is an object in the seabed sediment layer 300 Object 300 in the seabed sedimentary layer on the sonar image Sonar transmission / reception unit (first transmission / reception unit)
301 Sonar received signal 302 Bottom sediment calculation unit (first calculation unit)
303 Operation Parameter 304 Image Compensation Calculation Unit (Second Calculation Unit)
305 Correction data 306 Compensation image processing unit (third calculation unit)
307 Sonar received signal 308 corrected image data 309 target information generation unit (fourth calculation unit)
310 Reference Image 311 Control Information 312 Bottom Sediment Parameter Correction Unit (Fifth Calculation Unit)
400 Normal sonar image processing unit (sixth calculation unit)
401 sonar received signal 402 normal sonar image 403 reference image storage unit (memory / storage unit)
404 Optimal compensation image 405 Input switching unit (first input switching unit)
500 Modified calculation parameter 501 Input switching unit (second input switching unit)
502 Parameter for calculation 600 after switching Bottom sediment measuring instrument (second transmitter / receiver)
601 Received signal 602 of bottom sediment measuring instrument Input switching unit (third input switching unit)
603 Parameters for calculation input to bottom sediment calculation unit 604 Known density distribution data (database unit)
605 Known calculation parameter 606 Calculation parameter 700 transmitted to the image compensation calculation section Bottom sediment parameter knob section 701 Calculation parameter adjustment signal 702 Adjusted computation parameter 703 Bottom sediment display section (display section)
704 Calculation parameters (sediment parameters) input to the bottom sediment display
705 Adjusted calculation parameter 800 Sonar transmission signal control unit (signal control unit)
801 Block of image processing algorithm 802 Optional parameter 803 in the image processing algorithm Control signal 804 of sonar transmission / reception unit Controlled sonar transmission signal 900 FIG. 901 showing the structure of the seabed sediment layer 901 Solid particles 902 in the seabed sediment layer Seabed Interstitial fluid 904 in sedimentary layer Relationship between average particle diameter d and porosity β 1102 Approximate curve of porosity distribution at location A 1103 Approximate curve of porosity distribution at location B 1200 Distribution of hydraulic conductivity at location A in the depth direction of the sedimentary layer Estimated result 1202 Estimated result 130 of the distribution of the permeability coefficient in the depth direction at location B 130 Graph representing the change in sound velocity with respect to the deposited layer depth 131 Graph representing the change in reachable range with respect to the deposited layer depth Graph 1300 showing changes in the intensity of sound waves Seabed sediment layer 1301 Receiving unit 1302 Transmission sound wave from sonar 1303 Component horizontal to seabed sediment layer in direction of sound wave transmission (direction of arrival range)
1304 Depth direction of seabed sediment layer 1305 Sound velocity distribution at location A 1306 Sound velocity distribution at location B 1307 Sound velocity of seawater 1308 Sound wave propagation route 1309 at location A Sound wave propagation route 1310 at location B Sound wave propagation route 1311 when the medium is seawater Sound wave intensity 1312 with respect to the sound wave arrival range at A A Sound wave intensity 1313 with respect to the sound wave arrival range at the location B FIG. 1400 shows a change in sound wave intensity when there is no sediment layer and only seawater. Medium 1402 Moving direction of sonar (sonar) 1403 Azimuth direction 1404 Range report 1405 Sonar image 1406 Seabed sedimentary layer 1407 Sound projection surface 1408 Seafloor sedimentation surface 1408 Sound projection surface 1409 in seafloor sedimentation layer 1409 Sound projection in seafloor sedimentation layer Reflected sound signal 150 from the surface Sound speed correction data 151 Propagation path correction data 152 Attenuation correction data 1500 Sound wave propagation time 1501 when there is only seawater Sound wave propagation time 1502 when there is a deposited layer Sound velocity correction amount given to an arbitrary point in the sonar image (t′−t)
1503 Sound velocity correction amount 1504 given to one received signal Wave propagation path 1505 in the case of seawater only Wave propagation path 1506 in the sedimentary layer Position in the range direction in the case of seawater at the depth Z and in the case of the sedimentary layer Difference 1507 Propagation path correction amount 1508 given to an arbitrary point Propagation path correction amount 1509 given to one received signal Sonar 1510 Propagation distance 1513 in the deposition layer Strength of received sound wave 1514 in range direction On sonar image Luminance distribution correction amount 1515 given to an arbitrary point of the luminance correction amount 1601 given to one received signal Received signal 1602 from the sonar transmission / reception unit 1602 Correction data 1603 Deviation due to deposited layer 1604 Deviation compensation amount 1605 Sonar Image processing process 1606 corrected image data 1608 normal sonar image 1701 Received signal 1702 attenuation correction amount 1703 corrected received signal 1704 sonar image processing process 1705 corrected image data 1707 normal sonar image 1800 normal sonar image 1801 corrected image data 1803 in which the accumulation layer correction is primarily performed 1804 movement amount 1804 of the center of gravity Modified calculation parameter 1807 Difference in value of contrast information from value in normal sonar image 1808 Contrast information 1809 in normal sonar image When image quality has dropped 1810 Image quality re-improvement 1900 Image data for correction 1901 Optimum image 1902 prepared in advance One image data 1903 in the azimuth direction 1903 Distribution of residue after compensation of deposited layer 1904 Distribution of luminance unevenness 1905 in normal sonar image 1906 Amount of residue 1906 Corrected calculation parameter 909 difference value 1910 ordinate zero line 2001 Kohashikarada of zero 2002 sonar transceiver 2003 deposited layer 2004 sediment analyzer (second transmitting and receiving unit)
2005 Image processing block 2007 Bottom sediment measuring instrument 2009 Database part (known density distribution data)
2101 Bottom sediment measuring instrument 2102 Location A deposition layer 2103 Location B deposition layer 2104 Location A surface scattering 2105 Location B surface scattering 2106 Received signal 2107 from location A deposition layer 2107 Received signal 2109 from location B deposition layer Reference object 2110 Arrival range 2111 of place A Arrival range 2111 of place B Object detection distance 2113 of place A Object detection distance 2115 of place B Sonic wave transmitter 2116 Receiver array 2117 Distribution of signal intensity 2201 of receiver array Frequency f1 Relationship between bottom sediment and sonar reach range at frequency f2 2202 Relationship between bottom sediment and sonar reach range at frequency f2 2301 Relationship between bottom sediment and sonar reach range at frequency f3 2301 Bottom sediment and critical angle at frequency f1 Relationship 2302 Relationship between bottom sediment and critical angle at frequency f2 2303 at frequency f3 Relationship between quality and critical angle 2304 Relationship between sediment and critical angle at frequency f4 2305 Relationship between sediment and critical angle at frequency f5 2400 Ultrasonic imaging device housing 2401 Reference image display unit 2402 Correction image display unit 2404 1-input switching unit 2405 2nd input switching unit 2406 3rd input switching unit 2407 Calculation parameter adjustment unit 2408 Calculation parameter display unit 2501 Minesweeping plan 2502 for bottom sediment A 2504 Minesweeping plan 2504 for sediment B Range 2505 Range 2506 at frequency B Object 2507 Transmitted sound wave 2508 at frequency A Transmitted sound wave at frequency B

Claims (15)

A first transmission / reception unit for transmitting a sound wave toward a seabed sediment layer in the sea and receiving a reflected wave to generate a reception signal;
A first calculation unit for calculating a calculation parameter representing a physical parameter of a seabed sediment layer based on a reception signal of the first transmission / reception unit;
A second calculation unit that generates correction data for correcting a shift of a sonar image caused by acoustic wave propagation in the seafloor sediment using the calculation parameter or the corrected calculation parameter ;
A third calculation unit that generates correction image data obtained by correcting the deviation using the correction data with respect to the reception signal generated from the first transmission / reception unit;
A fourth calculator that compares the corrected image data with reference image data and generates contrast information indicating a correction effect for a shift;
A fifth calculator for correcting the calculation parameter based on the control information and generating the corrected calculation parameter ;
And wherein said possess an image display unit for displaying the sonar image based on the corrected image data, to modify closing conditions, <br/> repeating the processing from the second calculating portion to the fifth calculator Sound imaging device.   The sixth calculation unit that generates sonar image data based on a reception signal of the first transmission / reception unit, wherein the fourth calculation unit uses the sonar image data as the reference image data. The sound wave imaging device described in 1.   2. The acoustic imaging according to claim 1, further comprising a storage unit that stores image data prepared in advance, wherein the fourth calculation unit uses image data stored in the storage unit as the reference image data. apparatus. A second transmitter / receiver for generating a reception signal by transmitting a sound wave and receiving a reflected wave independently of the first transmitter / receiver toward an undersea sedimentary layer in the sea; and any one of claims 1 to 3, characterized in that calculating a calculation parameter that represents the physical parameters of the seabed sediments on the basis of the received signal of the second transmitting and receiving part in place of the receiving signal of the first transmitting and receiving part The sound wave imaging device described in 1. 5. The acoustic imaging apparatus according to claim 4 , wherein a frequency of a sound wave transmitted from the second transmission / reception unit is 5 kHz or more and 10 MHz or less. A measuring device for measuring physical parameters of the seabed sedimentary layer, wherein the first calculation unit calculates the physical parameters of the seabed sedimentary layer based on the signal measured by the measuring device instead of the received signal of the first transmitting / receiving unit; calculating a calculation parameter representing ultrasonic imaging apparatus according to any one of claims 1 to 3, characterized in. A database unit storing a plurality of calculation parameters representing physical parameters of the seabed sedimentary layer, wherein the second calculation unit generates the correction data using the calculation parameters stored in the database unit; ultrasonic imaging apparatus according to any one of claims 1 to 6, wherein. Adjust the value of the operation parameter, ultrasonic imaging apparatus according to calculation parameters which is adjusted to any one of claims 1 to 7, characterized in that it has an adjusting section to be output to the second calculator . Ultrasonic imaging apparatus according to any one of claims 1 to 8 having a display section for displaying the value of said operational parameter. The image display unit, ultrasonic imaging apparatus according to any one of claims 1 to 9, characterized in that an image can be displayed based on the sonar image and aligned the reference image data. The arithmetic parameter, sound waves according to any one of claims 1 to 10, characterized in that a coefficient that determines the density of the seabed sediments, porosity, or the permeability of the depth of the distribution profile Imaging device. The reference information is generated by comparing values of one or a plurality of combinations of an image difference value, an image correlation amount, and an image signal level between the corrected image data and the reference image data. is the sound wave imaging apparatus according to any one of claims 1 to 11, characterized in that the difference between the corrected image and the original image data is converted value to the signal strength. In the fifth calculation unit, based on the reference information, any one or a combination of a plurality of physical parameters of the seabed sediment layer calculated from the value of the reference information expressed as the difference of the image data is the signal intensity. the converted value was calculated, ultrasonic imaging apparatus according to any one of claims 1 to 12, characterized by using as said modified operation parameter that is input to the second calculator. Using the value of the operation parameter, according to any one of claims 1 to 13, further comprising a transmission control unit for controlling the transmission condition of the sound wave transmitting from said first transmitting and receiving part Acoustic imaging device. The sound wave imaging device according to any one of claims 1 to 14 , wherein a frequency of a sound wave transmitted by the first transmission / reception unit is 1 MHz or less.

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