Ocean depth acoustic wave measurement method and device

Abstract

The invention mainly solves the problem of how to reduce the measurement error of the ocean depth when a ship sails. An ocean depth sound wave measuring method is characterized by comprising the following steps: acquiring the average depth h of a measured area, and setting the navigational speed of a ship as v and the propagation speed of sound waves in water as w during measurement; a sound wave transmitting transducer and a receiving transducer are installed below a ship body, the receiving transducer is located behind the transmitting transducer, and the distance s between the receiving transducer and the transmitting transducer is equal to 2vh / w; the transmitting transducer transmits sound waves vertically downwards, the receiving transducer receives the returned sound waves, and the water depth of the measured area is calculated according to the round-trip time of the sound waves. The device has the beneficial effects that the distance s between the receiving transducer and the transmitting transducer is equal to 2vh / w, after the transmitting transducer vertically transmits sound waves downwards, because a ship is moving, when the receiving transducer receives the sound waves, the receiving transducer is located at the original position of the transmitting transducer or is not far away from the transmitting transducer, so that the influence caused by the movement of the ship body is effectively reduced, and the measurement is more accurate.

Description

Technical Field

[0001] The present invention relates to the field of measurement technologies, and in particular, to a method and device for measuring the ocean depth by sound waves. Background Art

[0002] Currently, the most commonly used method for measuring the ocean depth is the acoustic method. Commonly used instruments include echo sounders, which are developed based on the principle of echo ranging. It is installed at the bottom of a ship. During operation, the transmitting transducer emits sound waves downward from the sea surface. The sound waves propagate downward in the water, reach the seabed, reflect back, and are received by the receiving transducer on the sea surface. By combining the propagation speed of sound waves in water and the time interval from transmission to reception, the ocean depth can be calculated. However, since the ship is usually moving during measurement, the ship is no longer at the original position when receiving the sound waves, which will introduce measurement errors. Summary of the Invention

[0003] The main problem to be solved by the present invention is how to reduce the measurement error of the ocean depth when the ship is sailing.

[0004] A method for measuring the ocean depth by sound waves, characterized by comprising the following steps: Obtain the average depth h of the measured area, assume the ship speed during measurement is v, and the propagation speed of sound waves in water is w; Install the sound wave transmitting transducer and the receiving transducer below the hull. The receiving transducer is located behind the transmitting transducer, and the distance between them is s = 2vh / w; The transmitting transducer vertically emits sound waves downward, and the receiving transducer receives the returned sound waves. According to the round-trip time of the sound waves, calculate the water depth of the measured area.

[0005] The beneficial effect is that the receiving transducer is s=2vh / w away from the transmitting transducer. After the transmitting transducer transmits the sound wave vertically downward, since the ship is moving, when the receiving transducer receives the sound wave, it is located at the original position of the transmitting transducer or not far away from it, which effectively reduces the influence of the movement of the hull and makes the measurement more accurate; the sound wave propagation path is in the vertical up and down direction, there is no inclination angle, the sound wave propagation path is a standard straight line, and the measurement is very accurate; in addition, the distance between the receiving transducer and the transmitting transducer fully utilizes the length of the hull itself, and usually it can be directly installed under the hull without adding extension equipment. For example, if the average depth of the measured area is 3000m, the speed of the ship during measurement is 10m / s, and the propagation speed of the sound wave in the water is 1500m / s, then s=40m, which is almost the same as the length of the measuring ship itself, and the length of the measuring ship can be fully utilized. It should be noted that since the depth change is not too large within the fixed measurement range of the hull, the average depth h is meaningful. As for the specific value of the average depth h, it can be obtained in advance based on other measurement data. The method of the present invention is applicable to the ocean because the ocean depth is large, the round trip time of the sound wave is long, and the movement of the hull needs to be considered for accurate measurement. Since the seabed can be regarded as a plane with a high probability at a small area sound wave reflection place, the sound wave reflection angle and the sound wave receiving position are basically determined, that is, the sound wave is reflected vertically upward, so that it can be ensured that the sound wave receiving transducer receives a strong reflected sound wave signal. Even if the seabed has a slope, since the positive and negative offsets of the seabed slope are large in a large range, the probability of the near-view plane is still very large, and it can be ensured that the sound wave receiving transducer receives a strong reflected sound wave signal within a large probability range.

[0006] Assuming the round trip time of the sound wave is t, the water depth is wt / 2.

[0007] The beneficial effect is that the method for calculating the water depth is the same as in the prior art, but because the receiving transducer is located at or near the original location of the transmitting transducer when it receives the sound wave, the measurement is more accurate.

[0008] A device for measuring ocean depth acoustic waves, characterized in that it comprises a transmitting transducer and a receiving transducer, wherein the transmitting transducer transmits acoustic waves vertically downward, the transmitting transducer and the receiving transducer are installed below a ship hull, the receiving transducer is located behind the transmitting transducer, and the distance between the two is s=2vh / w, wherein h is the average depth of the measured area, v is the speed of the ship during measurement, and w is the propagation speed of the acoustic waves in water; the transmitting transducer transmits acoustic waves vertically downward, the receiving transducer receives the returned acoustic waves, and the water depth of the measured area is calculated according to the round trip time of the acoustic waves.

[0009] The beneficial effects are as follows: The receiving transducer and the transmitting transducer are separated by a distance of s = 2vh / w. After the transmitting transducer vertically emits sound waves downward, due to the movement of the ship, when the receiving transducer receives the sound waves, it is located at or near the original position of the transmitting transducer, effectively reducing the influence brought by the movement of the hull and making the measurement more accurate; the sound wave propagation route is in the vertical up-and-down direction without any inclination angle, and the sound wave propagation route is a standard straight line, so the measurement is very accurate; in addition, the distance between the receiving transducer and the transmitting transducer makes full use of the length of the hull itself. Usually, it can be directly installed under the hull without adding new extension equipment.

[0010] Assume the round-trip time of the sound wave is t, then the water depth is wt / 2.

[0011] The beneficial effect is that the water depth calculation method is the same as that of the prior art, but since the receiving transducer is located at or near the original position of the transmitting transducer when it receives the sound wave, the measurement is more accurate. An ocean depth acoustic measurement method, characterized by comprising the following steps: Obtain the average depth h of the measured area, assume the ship speed during measurement is v, and the sound wave propagation speed in water is w; Install a sound wave transmitting transducer and n receiving transducers under the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the sound wave transmitter is s = 2vh / w; The transmitting transducer vertically emits sound waves downward, and the receiving transducer receives the returned sound waves. According to the round-trip time of the sound wave, calculate the water depth of the measured area. Select the sound wave received by one receiving transducer to calculate the water depth. Assume the round-trip time of the sound wave is t, then the water depth is wt / 2.

[0012] The beneficial effects are as follows: By selecting the sound wave received by a receiving transducer to calculate the water depth, when the receiving transducer receives the sound wave, it is located at or near the original position of the transmitting transducer, effectively reducing the influence caused by the movement of the hull and making the measurement more accurate; the sound wave propagation path is in the vertical up-and-down direction without any inclination angle, and the sound wave propagation path is a standard straight line, resulting in very accurate measurement; in addition, the distance between the receiving transducer and the transmitting transducer makes full use of the length of the hull itself. Usually, it can be directly installed under the hull without the need to add additional extension equipment. Of course, if the water depth is relatively large, the maximum distance between the transmitting transducer and the receiving transducer may exceed 100 meters. If it exceeds the length of the ship, it is also very easy to install the receiving transducer by extending a certain distance at the stern. When the water depth is less than the average depth, the sound wave received by the receiving transducer closer to the transmitting transducer can be used because when the water depth is shallow, the measurement time is short and the distance the ship moves is short.

[0013] All receiving transducers receive the sound wave simultaneously, and the water depth is calculated based on the time t when the sound wave is received first.

[0014] The beneficial effect is that the sound wave is received first, that is, the receiving transducer that receives the sound wave first is located at or near the original position of the transmitting transducer, making the measurement more accurate.

[0015] Alternatively, which receiving transducer's received sound wave is used to calculate the water depth can be selected according to the water depth of the measured area. For example, when the water depth is close to the average depth, the sound wave received by the (n + 1) / 2-th (i.e., the middle-positioned) receiving transducer is used; when the water depth is less than the average depth, the sound wave received by the receiving transducer closer to the transmitting transducer can be used; when the water depth is greater than the average depth, the sound wave received by the receiving transducer farther from the transmitting transducer can be used. For example: There are 3 receiving transducers, which are used to measure the depths of the shallow water, medium water, and deep water areas in the measured area respectively. First, the sound wave received by the 2nd receiving transducer is used to calculate the water depth. When the water depth is shallow, the sound wave received by the 1st receiving transducer is used; when the water depth is medium, the sound wave received by the 2nd receiving transducer is used; when the water depth is deep, the sound wave received by the 3rd receiving transducer is used.

[0016] The beneficial effect is that determining which receiving transducer's received sound wave to use according to the water depth can basically ensure that within the measured range, when the receiving transducer receives the sound wave at different water depth areas, it is located at or near the original position of the transmitting transducer, effectively reducing the influence caused by the movement of the hull and making the measurement more accurate. When the water depth is shallow, the sound wave received by the 1st receiving transducer is used because when the water depth is shallow, the measurement time is short and the distance the ship moves is short. An ocean depth acoustic wave measurement device, characterized by comprising one transmitting transducer and n receiving transducers. The transmitting transducer and the receiving transducers are installed under the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the acoustic wave transmitter is s = 2vh / w, where h is the average depth of the measured area, v is the speed of the ship during measurement, and w is the propagation speed of the acoustic wave in water. The transmitting transducer emits acoustic waves vertically downward, and the receiving transducers receive the returned acoustic waves. According to the round-trip time of the acoustic wave, the water depth of the measured area is calculated. Select the acoustic wave received by one receiving transducer to calculate the water depth. Suppose the round-trip time of the acoustic wave is t, then the water depth is wt / 2.

[0017] The beneficial effects are as follows: Select the acoustic wave received by one receiving transducer to calculate the water depth. When the receiving transducer receives the acoustic wave, it is located at or near the original position of the transmitting transducer, effectively reducing the influence brought by the movement of the hull and making the measurement more accurate. The propagation route of the acoustic wave is in the vertical up-and-down direction without an inclination angle, and the propagation route of the acoustic wave is a standard straight line, so the measurement is very accurate. In addition, the distance between the receiving transducers and the transmitting transducer makes full use of the length of the hull itself. Usually, it can be directly installed under the hull without adding new extension equipment. Of course, if the water depth is relatively large, the maximum distance between the transmitting transducer and the receiving transducer may exceed 100 meters. If it exceeds the length of the ship, it is also very easy to install a receiving transducer by extending a certain distance at the stern. When the water depth is less than the average depth, the acoustic wave received by a receiving transducer closer to the transmitting transducer can be used because when the water depth is relatively shallow, the measurement time is short and the moving distance of the ship is short.

[0018] All receiving transducers receive the acoustic wave simultaneously, and calculate the water depth based on the time t when the acoustic wave is received first.

[0019] The beneficial effect is that the acoustic wave is received first, that is, the receiving transducer that receives the acoustic wave first is located at or near the original position of the transmitting transducer, and the measurement is more accurate.

[0020] Or, which receiving transducer's received acoustic wave is used to calculate the water depth can be selected according to the water depth of the measured area. For example, when the water depth is close to the average depth, the acoustic wave received by the (n + 1) / 2th (that is, the middle-positioned) receiving transducer is used. When the water depth is less than the average depth, the acoustic wave received by a receiving transducer closer to the transmitting transducer can be used. When the water depth is greater than the average depth, the acoustic wave received by a receiving transducer farther from the transmitting transducer can be used. For example: There are 3 receiving transducers, which respectively measure the depths of the shallow water, middle water, and deep water in the area where they are located. First, the sound waves received by the 2nd receiving transducer are used to calculate the water depth. When the water depth is shallow, the sound waves received by the 1st receiving transducer are used; when the water depth is medium, the sound waves received by the 2nd receiving transducer are used; when the water depth is deep, the sound waves received by the 3rd receiving transducer are used.

[0021] The beneficial effect is that, according to the water depth, it is determined which receiving transducer's received sound waves are used, which can basically ensure that within the measured range, at different depths of the water area, when the receiving transducer receives the sound waves, it is located at or near the original position of the transmitting transducer, effectively reducing the influence brought by the ship's movement and making the measurement more accurate. When the water depth is shallow, the sound waves received by the 1st receiving transducer are used because when the water depth is shallow, the measurement time is short and the distance the ship moves is short. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 . Schematic diagram of the present invention when using 1 receiving transducer; Figure 2 . Schematic diagram of the present invention when using 3 receiving transducers.

[0023] In the figure: 1. Transmitting transducer, 2. Receiving transducer, 3. Ship's hull. DETAILED DESCRIPTION OF THE INVENTION Embodiment

[0024] As Figure 1 described, a method for measuring the depth of the ocean by sound waves is characterized by including the following steps: Obtain the average depth h of the measured area, assume the ship's speed during measurement is v, and the propagation speed of sound waves in water is w; Install the sound wave transmitting transducer and the receiving transducer under the ship's hull. The receiving transducer is located behind the transmitting transducer, and the distance between the two is s = 2vh / w; The transmitting transducer vertically emits sound waves downward, and the receiving transducer receives the returned sound waves. According to the round-trip time of the sound waves, the water depth of the measured area is calculated.

[0025] Assume the round-trip time of the sound wave is t, then the water depth is wt / 2. Embodiment

[0026] As Figure 1As described above, an ocean depth acoustic wave measuring device, characterized in that it includes a transmitting transducer and a receiving transducer. The direction in which the transmitting transducer emits acoustic waves is vertically downward. The transmitting transducer and the receiving transducer are installed below the hull. The receiving transducer is located behind the transmitting transducer, and the distance between the two is s = 2vh / w, where h is the average depth of the measured area, v is the speed of the ship during measurement, and w is the propagation speed of acoustic waves in water. The transmitting transducer emits acoustic waves vertically downward, and the receiving transducer receives the returned acoustic waves. According to the round-trip time of the acoustic waves, the water depth of the measured area is calculated.

[0027] Assume the round-trip time of the acoustic wave is t, then the water depth is wt / 2. Embodiment

[0028] As Figure 2 As described above, an ocean depth acoustic wave measuring method, characterized in that it includes the following steps: Obtain the average depth h of the measured area. Assume the speed of the ship during measurement is v, and the propagation speed of acoustic waves in water is w. Install a sound wave transmitting transducer and n receiving transducers below the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the sound wave transmitter is s = 2vh / w. The transmitting transducer emits acoustic waves vertically downward, and the receiving transducer receives the returned acoustic waves. According to the round-trip time of the acoustic waves, the water depth of the measured area is calculated. Select the acoustic wave received by one receiving transducer to calculate the water depth. Assume the round-trip time of the acoustic wave is t, then the water depth is wt / 2.

[0029] All receiving transducers receive acoustic waves simultaneously, and use the time t when the acoustic wave is received first to calculate the water depth.

[0030] The receiving transducers are 3. They respectively measure the depths of three water areas of shallow water, medium water, and deep water in the area where they are located. First, use the acoustic wave received by the 2nd receiving transducer to calculate the water depth. When the water depth is shallow, use the acoustic wave received by the 1st receiving transducer. When the water depth is medium, use the acoustic wave received by the 2nd receiving transducer. When the water depth is deep, use the acoustic wave received by the 3rd receiving transducer. Embodiment

[0031] As Figure 2 As described above, an ocean depth acoustic wave measuring method, characterized in that it includes the following steps: Obtain the average depth h of the measured area. Assume the speed of the ship during measurement is v, and the propagation speed of acoustic waves in water is w. Install a sound wave transmitting transducer and n receiving transducers under the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the sound wave emitter is s = 2vh / w; The transmitting transducer emits sound waves vertically downward, and the receiving transducer receives the returned sound waves. According to the round-trip time of the sound waves, the water depth of the measured area is calculated. Select the sound waves received by one receiving transducer to calculate the water depth. Let the round-trip time of the sound waves be t, then the water depth is wt / 2.

[0032] The receiving transducers are 3 in number, and are used to measure the depths of three water areas of shallow water, medium water and deep water in the area where they are located. First, use the sound waves received by the 2nd receiving transducer to calculate the water depth. When the water depth is shallow, use the sound waves received by the 1st receiving transducer. When the water depth is medium, use the sound waves received by the 2nd receiving transducer. When the water depth is deep, use the sound waves received by the 3rd receiving transducer. Embodiment

[0033] As Figure 2 described, a marine depth sound wave measuring device, characterized in that it includes 1 transmitting transducer and n receiving transducers. The transmitting transducer and the receiving transducers are installed under the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the sound wave emitter is s = 2vh / w, where h is the average depth of the measured area, v is the speed of the ship during measurement, and w is the propagation speed of sound waves in water; the transmitting transducer emits sound waves vertically downward, and the receiving transducer receives the returned sound waves. According to the round-trip time of the sound waves, the water depth of the measured area is calculated. Select the sound waves received by one receiving transducer to calculate the water depth. Let the round-trip time of the sound waves be t, then the water depth is wt / 2.

[0034] All receiving transducers receive sound waves simultaneously, and use the time t when the sound waves are received first to calculate the water depth.

[0035] The receiving transducers are 3 in number, and are used to measure the depths of three water areas of shallow water, medium water and deep water in the area where they are located. First, use the sound waves received by the 2nd receiving transducer to calculate the water depth. When the water depth is shallow, use the sound waves received by the 1st receiving transducer. When the water depth is medium, use the sound waves received by the 2nd receiving transducer. When the water depth is deep, use the sound waves received by the 3rd receiving transducer. Embodiment

[0036] As Figure 2As described, an ocean depth acoustic wave measurement device, characterized in that it includes 1 transmitting transducer and n receiving transducers. The transmitting transducer and the receiving transducers are installed below the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase in sequence. The n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the acoustic wave transmitter is s = 2vh / w, where h is the average depth of the measured area, v is the ship's speed during measurement, and w is the propagation speed of the acoustic wave in water; the transmitting transducer vertically emits acoustic waves downward, and the receiving transducers receive the returned acoustic waves. According to the round-trip time of the acoustic wave, the water depth of the measured area is calculated. Select the acoustic wave received by one receiving transducer to calculate the water depth. Let the round-trip time of the acoustic wave be t, then the water depth is wt / 2.

[0037] The receiving transducers are 3, which are respectively used to measure the depths of three water areas of shallow water, medium water, and deep water in the area where they are located. First, use the acoustic wave received by the 2nd receiving transducer to calculate the water depth. When the water depth is shallow, use the acoustic wave received by the 1st receiving transducer. When the water depth is medium, use the acoustic wave received by the 2nd receiving transducer. When the water depth is deep, use the acoustic wave received by the 3rd receiving transducer.

Claims

1. A method for measuring ocean depth by acoustic wave, characterized by comprising the following steps: Obtain the average depth h of the area to be measured. Let the ship speed during measurement be v, and the propagation speed of acoustic wave in water be w; Install an acoustic wave transmitting transducer and a receiving transducer below the hull. The receiving transducer is located behind the transmitting transducer, and the distance between them is s = 2vh / w; The transmitting transducer vertically emits acoustic waves downward, and the receiving transducer receives the returned acoustic waves. Calculate the water depth of the area to be measured according to the round-trip time of the acoustic wave.

2. The method for measuring ocean depth acoustic wave according to claim 1, characterized in that, Let the round-trip time of the acoustic wave be t, then the water depth is wt / 2.

3. An ocean depth acoustic wave measuring device, characterized in that, It includes a transmitting transducer and a receiving transducer. The direction of the acoustic wave emitted by the transmitting transducer is vertically downward. The transmitting transducer and the receiving transducer are installed below the hull. The receiving transducer is located behind the transmitting transducer, and the distance between them is s = 2vh / w, where h is the average depth of the area to be measured, v is the ship speed during measurement, and w is the propagation speed of acoustic wave in water; the transmitting transducer vertically emits acoustic waves downward, and the receiving transducer receives the returned acoustic waves. Calculate the water depth of the area to be measured according to the round-trip time of the acoustic wave.

4. The marine depth acoustic wave measuring device according to claim 3, characterized in that, Let the round-trip time of the acoustic wave be t, then the water depth is wt / 2.

5. A method for measuring ocean depth by acoustic wave, characterized by comprising the following steps: Obtain the average depth h of the area to be measured. Let the ship speed during measurement be v, and the propagation speed of acoustic wave in water be w; Install one acoustic wave transmitting transducer and n receiving transducers below the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the first to the nth receiving transducers and the transmitting transducer increase in sequence. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the acoustic wave transmitter is s = 2vh / w; The transmitting transducer vertically emits acoustic waves downward, and the receiving transducer receives the returned acoustic waves. Calculate the water depth of the area to be measured according to the round-trip time of the acoustic wave. Select the acoustic wave received by one receiving transducer to calculate the water depth. Let the round-trip time of the acoustic wave be t, then the water depth is wt / 2.

6. A method for measuring ocean depth sound waves according to claim 5, characterized in that, All receiving transducers receive acoustic waves simultaneously, and calculate the water depth based on the time t when the acoustic wave is received first.

7. A method for measuring ocean depth sound waves according to claim 5, characterized in that, The receiving transducers are three, which respectively measure the depths of the shallow water, medium water, and deep water areas in the area. First, use the acoustic wave received by the second receiving transducer to calculate the water depth. When the water depth is shallow, use the acoustic wave received by the first receiving transducer. When the water depth is medium, use the acoustic wave received by the second receiving transducer. When the water depth is deep, use the acoustic wave received by the third receiving transducer.

8. An ocean depth acoustic wave measuring device, characterized in that, It includes one transmitting transducer and n receiving transducers. The transmitting transducer and the receiving transducers are installed under the hull. The receiving transducers are located behind the transmitting transducer. The n receiving transducers are arranged at equal intervals. The distances between the 1st to the nth receiving transducers and the transmitting transducer increase successively. n is an odd number, and the distance between the (n + 1) / 2th receiving transducer and the acoustic wave emitter is s = 2vh / w, where h is the average depth of the area to be measured, v is the ship speed during measurement, and w is the propagation speed of acoustic waves in water. The transmitting transducer emits acoustic waves vertically downward, and the receiving transducers receive the returned acoustic waves. According to the round-trip time of the acoustic waves, the water depth of the area to be measured is calculated. Select the acoustic waves received by one receiving transducer to calculate the water depth. Suppose the round-trip time of the acoustic waves is t, then the water depth is wt / 2.

9. The ocean depth acoustic wave measuring device according to claim 8, characterized in that, All receiving transducers receive acoustic waves simultaneously, and calculate the water depth based on the time t when the acoustic waves are received first.

10. The marine depth acoustic wave measuring device according to claim 8, characterized in that, There are 3 receiving transducers, which respectively measure the depths of three water areas of shallow water, medium water, and deep water in the area where they are located. First, use the acoustic waves received by the 2nd receiving transducer to calculate the water depth. When the water depth is shallow, use the acoustic waves received by the 1st receiving transducer. When the water depth is medium, use the acoustic waves received by the 2nd receiving transducer. When the water depth is deep, use the acoustic waves received by the 3rd receiving transducer.

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