CN115598217B - Device and method for in-situ measurement of low-frequency acoustic characteristics of seabed sediments - Google Patents

Abstract

The invention discloses a device and a method for in-situ measurement of low-frequency acoustic characteristics of a seabed sediment layer, wherein the device comprises a deck subsystem and an underwater detection subsystem, the deck subsystem comprises a hydraulic unit and a display control unit, and the underwater detection subsystem comprises an acoustic transmitting unit and an acoustic receiving unit; the acoustic transmitting unit comprises a transmitting transducer and a transmitting circuit module; the acoustic receiving unit comprises a conical probe, a first acoustic probe, a receiving circuit probe and a second acoustic probe. The deck subsystem and the underwater detection subsystem are powered and communicated through a four-core cable, and real-time state display and remote control of the deck subsystem on the underwater detection subsystem are achieved. The acoustic receiving unit is based on a hydraulic unit, and can penetrate into a hard deposition layer to obtain the acoustic characteristics of the deposition layer with a large depth profile. The method is suitable for the in-situ measurement of the large-depth low-frequency acoustic characteristics of the seabed sediment layer, can accurately obtain the sound velocity and the sound attenuation coefficient of the sediment layer in situ, and is used for ocean sound field calculation and seabed engineering geological exploration.

Description

An in-situ measurement device and method for low-frequency acoustic characteristics of seafloor sediments

Technical Field

The invention belongs to the technical field of acoustic property measurement of seabed sediment layers, and in particular relates to an in-situ measurement device and method for low-frequency acoustic properties of seabed sediment layers.

Background Art

Acoustic properties are important environmental factors of the ocean and are widely used in marine science and marine engineering. The acoustic properties of the seafloor surface sediment layer, as the lower boundary of sound wave propagation in the ocean, and the acoustic properties of the ocean water body jointly constrain the propagation of sound waves in the ocean, and are one of the key parameters for calculating the ocean acoustic field. At the same time, the seafloor sediment layer is also the direct object of marine engineering construction. Its acoustic properties are closely related to elastic mechanics and are an important part of marine engineering geological evaluation. There are two methods for measuring the acoustic properties of seafloor sediments: one is sampling measurement and the other is in-situ measurement. Sampling measurement is to collect samples of the sediment layer from the seabed and measure them in the laboratory. This measurement method brings two problems: on the one hand, the sample collection and transportation process causes disturbance of the sediment and changes its original physical state; on the other hand, it is separated from the original temperature and pressure environment of the seabed and changes its original environmental conditions. The physical state and environmental conditions of the sediment have an important influence on the acoustic properties. Based on this, both internationally and domestically, in-situ measurement technology is actively developed to insert measuring instruments into the seabed sediments for in-situ measurement.

At present, the in-situ measurement of the acoustic characteristics of the submarine sediment layer is mainly carried out on the surface layer, using the equipment's own weight to penetrate into the sediment layer, and the penetration depth is usually less than 10 meters. This measurement technology can meet the needs of ocean acoustic field calculation. However, marine engineering construction requires the measurement of the acoustic characteristics of submarine sediment layers at greater depths. The method of using the equipment's own weight to penetrate cannot meet the geological exploration requirements of submarine engineering construction, and it is difficult to carry out acoustic characteristic measurements of deep sediment layers. At the same time, it is not suitable for low-frequency measurement operations.

Summary of the invention

The purpose of the present invention is to provide an in-situ measurement device and method for the low-frequency acoustic characteristics of seabed sediments in view of the deficiencies in the prior art. The present invention has high integration and is easy to install. Based on a hydraulic unit, it can penetrate deeper seabed sedimentary strata, is suitable for low-frequency operations, and can be used repeatedly.

The present invention is realized by the following technical scheme: an in-situ measurement device for low-frequency acoustic characteristics of a seabed sediment layer, the device comprising a deck subsystem and an underwater detection subsystem; the deck subsystem comprises a hydraulic unit and a display and control unit; the underwater detection subsystem comprises an acoustic transmitting unit and an acoustic receiving unit; the acoustic transmitting unit comprises a hemispherical directional low-frequency transmitting transducer and a hemispherical directional high-frequency transmitting transducer; the acoustic receiving unit comprises a second acoustic probe rod, a receiving circuit probe rod, a first acoustic probe rod and a conical probe, which are sequentially connected from top to bottom to form a probe rod;

The first acoustic probe rod has a first receiving transducer and a second receiving transducer embedded in it; the second acoustic probe rod has a third receiving transducer and a fourth receiving transducer embedded in it;

The first acoustic probe rod is provided with a first 4-hole sound-transmitting window and a second 4-hole sound-transmitting window, and the second acoustic probe rod is provided with a third 4-hole sound-transmitting window and a fourth 4-hole sound-transmitting window. The radial inward depression of all the sound-transmitting windows is 1mm. The first receiving transducer, the second receiving transducer, the third receiving transducer and the fourth receiving transducer are respectively installed and embedded in the first 4-hole sound-transmitting window, the second 4-hole sound-transmitting window, the third 4-hole sound-transmitting window and the fourth 4-hole sound-transmitting window, and a plurality of sound attenuation grooves are provided on the outer wall of the probe rod. The first acoustic probe rod and the receiving circuit probe rod, as well as the receiving circuit probe rod and the second acoustic probe rod, are communicated and powered by a 4-core socket cable. The 4-core socket cable consists of a first plug, an electric slip ring and a second plug, with two cores for power supply and two cores for communication.

The hemispherical directional high-frequency transmitting transducer is used to transmit sound waves to measure the distance between each receiving transducer, and the hemispherical directional low-frequency transmitting transducer is used to transmit sound waves, which are received by the acoustic receiving unit to further measure the acoustic characteristics;

The hydraulic unit is used to penetrate the acoustic receiving unit into the seabed sediment layer through hydraulic pressure; the display and control unit is used to control the transmission parameters of the transmitting transducer on the acoustic transmitting unit and receive the data collected by the receiving transducer on the acoustic receiving unit.

Furthermore, the display and control unit is used for controlling the acoustic transmitting unit and collecting data of the acoustic receiving unit, and controls the transmission and data collection based on a clock synchronization signal.

Furthermore, the acoustic emission unit also includes an underwater sound velocity meter for measuring the sound velocity in water.

Furthermore, the conical probe has a diameter 2 mm larger than the diameters of the first acoustic probe and the second acoustic probe, and expands the hole when penetrating into the seabed sediment layer.

Furthermore, the distances between the two receiving transducers respectively installed on the first acoustic probe rod and the second acoustic probe rod are the same; and the polarization directions of the four adjacent receiving transducers installed on the first acoustic probe rod and the second acoustic probe rod are opposite.

Furthermore, a posture sensor is configured inside the receiving circuit probe rod to monitor the posture of the probe rod in the seabed sediment layer in real time.

Furthermore, the first acoustic probe is provided with a displacement sensor to obtain the penetration depth of the entire probe into the sediment.

The present invention also provides a method for in-situ measurement of low-frequency acoustic characteristics of a seafloor sediment layer, the method comprising the following steps:

(1) During operation, the acoustic transmitting unit is deployed, and after the acoustic transmitting unit is seated on the bottom, the acoustic receiving unit is penetrated into the seabed sediment layer through the hydraulic unit;

(2) During the process of penetrating into the seabed sediment layer, underwater measurement is started; after the acoustic receiving unit penetrates into the sediment layer, the acoustic characteristics of the sediment layer are measured using the same transmission frequency as in the water;

(3) The acoustic receiving unit collects the acoustic wave data in the sediment layer and water body, transmits it to the display and control unit, and performs post-processing on the data to obtain the in-situ acoustic characteristic parameters of the seabed sediments.

The beneficial effects of the present invention are as follows: based on the hydraulic penetration unit of the deck subsystem, the designed probe device can penetrate into the seabed sediment layer at a greater depth to carry out in-situ measurement of acoustic characteristics. Through the acoustic window design of the probe rod, it can ensure the reception of sound waves in the sediment layer at a greater depth, and effectively protect the receiving transducer from the stress in the sediment layer at a great depth, and maintain the receiving sensitivity of the receiving transducer. The present invention uses a discretely arranged transmitting transducer, can use a larger-sized low-frequency acoustic transducer, and integrates a high-frequency transducer with an underwater sound velocity meter to complete the relative distance measurement between the transmitting transducer and the receiving transducer; the present invention realizes the in-situ low-frequency measurement of the acoustic characteristics of the seabed sediment layer at a greater depth, and provides an effective means for conducting elastic mechanical evaluation of the seabed sediment layer in the field of marine engineering.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

FIG1 is a schematic diagram of the overall structure of the present invention.

FIG. 2 is a schematic diagram of an acoustic emission unit of the present invention.

FIG. 3 is a schematic diagram of an acoustic receiving unit of the present invention.

FIG. 4 is a schematic diagram of a connection scheme between an acoustic probe rod and a receiving circuit probe rod of the present invention.

FIG. 5 is a schematic diagram showing calculation of the measurement method of the present invention.

In the figure, hydraulic unit 1.1, display and control unit 1.2, acoustic transmitting unit 2.1, acoustic receiving unit 2.2, hemispherical directional low-frequency transmitting transducer 2.1.1, hemispherical directional high-frequency transmitting transducer 2.1.2, underwater sound velocity meter 2.1.3, conical probe 2.2.1, first acoustic probe rod 2.2.2, receiving circuit probe rod 2.2.3, second acoustic probe rod 2.2.4, first receiving transducer 2.2.2.1, second receiving transducer 2.2.2.2, third receiving transducer 2.2.4.1, fourth receiving transducer 2.2.4.2, first 4-hole sound-transmitting window 2.2.2.3, second 4-hole sound-transmitting window 2.2.2.4, third 4-hole sound-transmitting window 2.2.4.3, fourth 4-hole sound-transmitting window 2.2.4.4.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Fig. 1 to Fig. 3, an in-situ measurement device for low-frequency acoustic characteristics of a seabed sediment layer of the present invention comprises a deck subsystem and an underwater detection subsystem; the deck subsystem comprises a hydraulic unit 1.1 and a display and control unit 1.2; the underwater detection subsystem comprises an acoustic transmitting unit 2.1 and an acoustic receiving unit 2.2; the transmitting unit comprises a hemispherical directional low-frequency transmitting transducer 2.1.1 and a hemispherical directional high-frequency 100kHz to 200kHz transmitting transducer 2.1.2, the frequency of the hemispherical directional low-frequency transmitting transducer 2.1.1 is 1kHz to 8kHz, and the frequency of the hemispherical directional high-frequency transmitting transducer 2.1.2 is 100kHz to 200kHz; the acoustic receiving unit includes a conical probe 2.2.1, a first acoustic probe rod 2.2.2, a receiving circuit probe rod 2.2.3 and a second acoustic probe rod 2.2.4; the first acoustic probe rod 2.2.2 is installed with a first receiving transducer 2.2.2.1 and a second receiving transducer 2.2.2.2; the second acoustic probe rod 2.2.4 is installed with a third receiving transducer 2.2.4.1 and a fourth receiving transducer 2.2.4.2; the receiving circuit probe rod 2.2.3 is located between the first acoustic probe rod 2.2.2 and the second acoustic probe rod 2.2.4, and the conical probe 2.2.1, the first acoustic probe rod 2.2.2, the receiving circuit probe rod 2.2.3 and the second acoustic probe rod 2.2.4 are connected into an acoustic probe rod by threads.

The hemispherical directional high-frequency transmitting transducer 2.1.2 is used to transmit sound waves to measure the distance between each receiving transducer, and the hemispherical directional low-frequency transmitting transducer 2.1.1 is used to transmit sound waves, which are received by the acoustic receiving unit 2.2 to further measure the acoustic characteristics;

The hydraulic unit 1.1 is used to penetrate the acoustic receiving unit 2.2 into the seabed sediment layer through hydraulic pressure; the display and control unit 1.2 is used to control the transmission parameters of the transmitting transducer on the acoustic transmitting unit 2.1, and receive the data collected by the receiving transducer on the acoustic receiving unit 2.2, and control the transmission and data collection work based on the clock synchronization signal.

As shown in FIG. 2 , the acoustic transmitting unit 2.1 includes an underwater sound velocity meter 2.1.3 for measuring the sound velocity in water.

The conical probe 2.2.1 has a diameter 2 mm larger than that of the first acoustic probe rod 2.2.2 and the second acoustic probe rod 2.2.4, and expands the hole when penetrating into the seabed sediment layer.

As shown in Figure 3, the first acoustic probe rod 2.2.2 is provided with a first 4-hole sound-transmitting window 2.2.2.3 and a second 4-hole sound-transmitting window 2.2.2.4, the second acoustic probe rod 2.2.4 is provided with a third 4-hole sound-transmitting window 2.2.4.3 and a fourth 4-hole sound-transmitting window 2.2.4.4, all the sound-transmitting windows are recessed by 1mm, the first receiving transducer 2.2.2.1, the second receiving transducer 2.2.2.2, the third receiving transducer 2.2.4.1 and the fourth receiving transducer 2.2.4.2 are respectively installed and embedded in the first 4-hole sound-transmitting window 2.2.2.3, the second 4-hole sound-transmitting window 2.2.2.4, the third 4-hole sound-transmitting window 2.2.4.3 and the fourth 4-hole sound-transmitting window 2.2.4.4, and a plurality of sound attenuation grooves are provided on the outer wall of the probe rod.

As shown in Fig. 4, the first acoustic probe 2.2.2, the receiving circuit probe 2.2.3 and the second acoustic probe 2.2.4 communicate and are powered via a 4-core socket cable. The 4-core socket cable consists of a first plug 2.2.2.5, an electric slip ring 2.2.2.6 and a second plug 2.2.2.7. The probes are connected by threads.

The distances between the two receiving transducers respectively installed on the first acoustic probe rod 2.2.2 and the second acoustic probe rod 2.2.4 are the same; the polarization directions of the four adjacent receiving transducers installed on the first acoustic probe rod 2.2.2 and the second acoustic probe rod 2.2.4 are opposite.

The receiving circuit probe rod 2.2.3 is internally configured with a posture sensor, which can monitor the posture of the probe rod in the seabed sediment layer in real time.

The first acoustic probe 2.2.2 is provided with a displacement sensor, which can obtain the depth of penetration of the probe into the sediment.

After the survey ship is installed and debugged, the in-situ measurement device for low-frequency acoustic characteristics of seabed sediment provided by the present invention deploys an acoustic transmitting unit 2.1 into the seabed, and the underwater sound velocity meter 2.1.3 measures the sound velocity of the seawater. Then, based on the hydraulic unit 1.1, the acoustic receiving unit 2.2 probe rod is deployed. The first receiving transducer 2.2.2.1, the second receiving transducer 2.2.2.2, the third receiving transducer 2.2.4.1 and the fourth receiving transducer 2.2.4 in the probe rod are .2 After entering the water, the hemispherical directional high-frequency transmitting transducer 2.1.2 transmits sound waves in the water. The propagation time of the sound waves received by the four receiving transducers is used to calculate the distances between the hemispherical directional high-frequency transmitting transducer 2.1.2 and the first receiving transducer 2.2.2.1, the second receiving transducer 2.2.2.2, the third receiving transducer 2.2.4.1 and the fourth receiving transducer 2.2.4.2 based on the underwater sound speed measured by the underwater sound speed meter 2.1.3. After the probe touches the bottom, it begins to penetrate the seabed sediment layer at a uniform speed. The hemispherical directional low-frequency transmitting transducer 2.1.1 transmits sound waves. The sound wave propagation time and sound wave amplitude received by the four receiving transducers are used, and based on the horizontal projection distance and penetration depth between the hemispherical directional low-frequency transmitting transducer 2.1.1 and the four receiving transducers, the distance between the hemispherical directional low-frequency transmitting transducer 2.1.1 and the four receiving transducers is converted, thereby calculating the sound velocity and sound attenuation coefficient of the seabed sediment layers at different levels.

、

、

及

，发射换能器与接收换能器之间的声传播时间分别为

、

、

及

，其中，水中声速为声速仪测得的

。4只接收换能器的间距分别为

、

及

，发射换能器与探杆的水平投影距离为L，接收换能器相对于发射换能器水平投影点的改正值为

。As shown in Figure 5, at a certain moment, the distances between the transmitting transducer and the four receiving transducers of the acoustic probe are

,

,

and

, the acoustic propagation time between the transmitting transducer and the receiving transducer is

,

,

and

, where the speed of sound in water is the speed of sound measured by the sound velocity meter

The spacing between the 4 receiving transducers is

,

and

, the horizontal projection distance between the transmitting transducer and the probe is L, and the correction value of the receiving transducer relative to the horizontal projection point of the transmitting transducer is

.

、

、

及

，利用发射换能器与接收换能器在海底沉积层中的传播时间，求得沉积层的声速与声衰减系数。Based on the above formulas (1), (2), (3), (4) and (5), the distance between the transmitting transducer and the receiving transducer at a certain time is obtained:

,

,

and

, the propagation time of the transmitting transducer and the receiving transducer in the seabed sediment layer is used to obtain the sound velocity and sound attenuation coefficient of the sediment layer.

On the other hand, the present invention also provides a method for realizing in-situ measurement of low-frequency acoustic characteristics of seabed sediment layers by using the above-mentioned device. During operation, the acoustic transmitting unit 2.1 is deployed, and after the acoustic transmitting unit is seated on the bottom, the acoustic receiving unit 2.2 is penetrated into the seabed sediment layer by the hydraulic unit 1.1; during the process of penetrating into the seabed sediment layer, underwater measurement is started; after the acoustic receiving unit 2.2 penetrates into the sediment layer, the acoustic characteristics of the sediment layer are measured using the same transmission parameters as those in water; the acoustic wave data in the sediment layer and the water body are collected by the acoustic receiving unit 2.2, and transmitted to the display and control unit 1.2, and the data is post-processed to obtain the in-situ acoustic characteristic parameters of the seabed sediments.

The specific implementation steps are as follows:

Step 1: System Installation

1.1) Check and confirm that all the components of the units are normal;

1.2) Assemble the deck subsystem and underwater detection subsystem separately.

Step 2: System debugging

2.1) Use a 4-core socket cable to connect the display and control unit 1.2 with the acoustic transmitting unit 2.1 and the acoustic receiving unit 2.2 of the underwater detection subsystem;

2.2) Carry out power supply and communication debugging according to specific operation requirements.

Step 3: System deployment

3.1) Use a winch to lower the acoustic transmitting unit 2.1 and place it in the water;

3.2) After the acoustic transmitting unit 2.1 touches the bottom, the deployment is stopped;

3.3) Using the hydraulic unit 1.1, the acoustic receiving unit 2.2 is deployed. When the conical probe 2.2.1, the first acoustic probe rod 2.2.2, the receiving circuit probe rod 2.2.3 and the second acoustic probe rod 2.2.4 are all submerged in water, the hemispherical directional high-frequency transmitting transducer 2.1.2 of the acoustic transmitting unit 2.1 transmits sound waves, the four receiving transducers record the propagation time of the sound waves, and the underwater sound velocity meter 2.1.3 measures the sound velocity of seawater;

3.4) Using the hydraulic unit 1.1, the conical probe 2.2.1, the first acoustic probe rod 2.2.2, the receiving circuit probe rod 2.2.3 and the second acoustic probe rod 2.2.4 are further inserted into the seabed sediment layer. The hemispherical directional low-frequency transmitting transducer 2.1.1 of the acoustic transmitting unit 2.1 transmits sound waves, and the four receiving transducers record the propagation time of the sound waves.

3.5) When the probe reaches the predetermined depth of the seabed sediment layer or encounters a hard stratum, the penetration is stopped and the probe is recovered.

Step 4: System recovery

4.1) After the operation is completed, recover the underwater detection subsystem to the deck;

4.2) Disassemble the underwater detection subsystem, rinse with fresh water and store in a cool and dry place.

The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims (7)

1. An in-situ measuring device for low-frequency acoustic characteristics of a seabed sediment layer is characterized by comprising a deck subsystem and an underwater detection subsystem; the deck subsystem comprises a hydraulic unit (1.1) and a display control unit (1.2); the underwater detection subsystem comprises an acoustic transmitting unit (2.1) and an acoustic receiving unit (2.2); the acoustic emission unit (2.1) comprises a hemispherical directional low-frequency emission transducer (2.1.1) and a hemispherical directional high-frequency emission transducer (2.1.2); the acoustic receiving unit (2.2) comprises a conical probe (2.2.1), a first acoustic probe (2.2.2), a receiving circuit probe (2.2.3) and a second acoustic probe (2.2.4), which are sequentially connected from bottom to top into a probe rod;

the first acoustic probe rod (2.2.2) is internally embedded with a first receiving transducer (2.2.2.1) and a second receiving transducer (2.2.2.2); a third receiving transducer (2.2.4.1) and a fourth receiving transducer (2.2.4.2) are embedded and installed in the second acoustic probe (2.2.4);

the first acoustic probe rod (2.2.2) is provided with a first 4-hole sound-transmitting window (2.2.2.3) and a second 4-hole sound-transmitting window (2.2.2.4), the second acoustic probe rod (2.2.4) is provided with a third 4-hole sound-transmitting window (2.2.4.3) and a fourth 4-hole sound-transmitting window (2.2.4.4), all the sound-transmitting windows are radially recessed by 1mm, and a first receiving transducer (2.2.2.1), a second receiving transducer (2.2.2.2), a third receiving transducer (2.2.4.1) and a fourth receiving transducer (2.2.4.2) are correspondingly embedded in the first 4-hole sound-transmitting window (2.2.3), the second 4-hole sound-transmitting window (2.2.2.4), the third 4-hole sound-transmitting window (2.2.4.3) and the fourth receiving transducer (2.2.4.4.2) are respectively and internally provided with a plurality of sound-transmitting grooves;

the first acoustic probe rod (2.2.2) and the receiving circuit probe rod (2.2.3) and the second acoustic probe rod (2.2.4) are communicated and powered through a 4-core socket cable, the 4-core socket cable consists of a first plug (2.2.2.5), an electric slip ring (2.2.2.6) and a second plug (2.2.2.7), and the two-core power supply and the two-core communication are realized;

the hemispherical directional low-frequency transmitting transducer (2.1.1) is used for transmitting sound waves and measuring sound wave signals of a sedimentary deposit, the acoustic characteristics are further measured by receiving through the acoustic receiving unit (2.2), the hemispherical directional high-frequency transmitting transducer (2.1.2) is used for transmitting the sound waves and measuring the distance between the receiving transducers, and the acoustic propagation signals in the water body are received through the acoustic receiving unit (2.2);

the acoustic emission unit (2.1) further comprises an underwater sound velocity meter (2.1.3) for measuring the sound velocity in water;

the hydraulic unit (1.1) is used for penetrating the acoustic receiving unit (2.2) into the seabed sedimentary deposit through hydraulic pressure;

the display and control unit (1.2) is used for controlling the transmitting parameters of the transmitting transducer on the acoustic transmitting unit (2.1) and receiving the data collected by the receiving transducer on the acoustic receiving unit (2.2).

2. The in-situ measuring device for the low-frequency acoustic characteristics of the seabed sediment layer as claimed in claim 1, wherein the display and control unit (1.2) is used for controlling the acoustic emission unit (2.1) and acquiring data of the acoustic receiving unit (2.2), and the emission and data acquisition work is controlled based on a clock synchronization signal.

3. An in situ device for measuring the low frequency acoustic properties of sediment at the seabed as claimed in claim 1, wherein the cone shaped probe (2.2.1) has a diameter 2mm larger than the diameter of the first acoustic probe (2.2.2) and the second acoustic probe (2.2.4) and is reamed when penetrating the sediment at the seabed.

4. The in-situ measuring device for the low frequency acoustic characteristics of the seabed sediment as claimed in claim 1, wherein the distance between the 2 receiving transducers respectively arranged on the first acoustic probe (2.2.2) and the second acoustic probe (2.2.4) is the same; the polarization direction of the first acoustic probe (2.2.2) is opposite to that of 4 adjacent receiving transducers arranged on the second acoustic probe (2.2.4).

5. The in-situ measurement device for the low-frequency acoustic characteristics of the seabed sediment as claimed in claim 1, wherein the receiving circuit probe rod (2.2.3) is internally provided with an attitude sensor for monitoring the attitude of the probe rod in the seabed sediment in real time.

6. An in situ measurement device of low frequency acoustic properties of sedimentary layers on the seabed as claimed in claim 1, wherein the first acoustic probe (2.2.2) is provided with a displacement sensor to obtain the depth of the whole probe penetrating into the sediment.

7. An in-situ measuring method for the acoustic properties of a seabed sediment layer based on the in-situ measuring device for the low-frequency acoustic properties of the seabed sediment layer as claimed in any one of claims 1 to 6, which comprises the following steps:

(1) During operation, arranging the acoustic transmitting unit (2.1), and after the acoustic transmitting unit sits on the bottom, penetrating the acoustic receiving unit (2.2) into a seabed sedimentary layer through the hydraulic unit (1.1);

(2) In the process of penetrating into the seabed sedimentary deposit, beginning to carry out underwater measurement; when the acoustic receiving unit (2.2) penetrates into the sedimentary deposit, the acoustic characteristics of the sedimentary deposit are measured by using the same transmitting frequency as that in water;

(3) Acoustic data in the sedimentary deposit and the water body are collected through the acoustic receiving unit (2.2) and transmitted to the display control unit (1.2), and post-processing of the data is carried out to obtain in-situ acoustic characteristic parameters of the submarine sediments.

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