JP2556625B2 - Active sonar for upward monitoring - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active monitoring sonar for upward monitoring, which is installed under the sea or near the sea floor and detects a target existing in the sea in the direction of the sea surface using sound waves.

[0002]

2. Description of the Related Art As shown in FIG. 2, an active monitoring sonar of this type has an upper monitoring active sonar 100 supported at a depth D2 by an anchor 102 and a mooring line 101 on a seabed 300 having a depth D1. The target 200 existing at the depth D3 is detected by the monitoring active sonar 100.

Next, a conventional upward monitoring active sonar will be described with reference to FIG. As shown in FIG. 3, the active sonar for upward monitoring has a transmitter 1 for transmitting a sound wave 11 into water, a transmitter 3 for supplying a transmission signal 31 to the transmitter 1, and a reception sound wave reflected from a target 200 or the like. A receiver 2 for converting 21 into a reception signal 22 and a TV for amplifying the reception signal 22 from the receiver 2 by changing the gain with time.
A G (Time Varied Gain) receiver 4;
A period timer 5 that determines the transmission / reception timing, a range gate generator 6 that stops the receiving function for a predetermined time, and a target detection that generates a target signal 71 by applying a certain threshold to the TVG receiver output signal 41. Depth meter 8 for measuring the depth of vessel 7 and active sonar for upward monitoring
have.

The operation will be further described with reference to FIGS. 3 and 4. When the active upper sonar shown in FIG. 3 is activated, the periodic timer 5 is activated and the trigger signal 51 is applied to the transmitter 3. A transmission signal 31 pulse-modulated based on the trigger signal 51 is transmitted from the transmitter 3 and converted into a sound wave via the wave transmitter 1, and as a result, the transmitted sound wave 11 (waveform in FIG. 4A) is directed to the sea surface. Is emitted. The transmission cycle at this time is T1.

The signal received by the receiver 2 is shown in FIG. 4B. The first transmitted sound wave 11 (FIG. 4A1) shows the reverberation in the sea (FIG. 4B11) and the target echo (if there is a target). 4B12), the first (first) sea surface reflected wave (FIG. 4B131), and the second (secondary) sea surface reflected wave (FIG. 4B132) are generated. Here, the level EL of the target echo (FIG. 4B12) is given by the equation (1).

EL = SL-2TL + TS (1) SL = transmit level TL = 20 log R + αR (propagation loss) R = distance between underwater levitation body and target α = absorption loss count TS = target target strength The level SR1 of the first reflected wave on the sea surface is given by the equation (2).

SR1 = SL-TL1-SS (2) TL1-20log2 * D2 + 2 [alpha] * D2 D2 = floating body depth SS = sea surface reflection loss Further, the level SR2 of the second sea surface reflected wave is expressed by equation (3). Given in.

SR2 = SL-TL2-2 · SS-BS (3) TL2 = 20 log (2 · D2 + 2 · D1) + α (2 · D2 + 2 · D1) D1 = sea bottom depth BS = sea bottom reflection loss The echo generation time T2 is given by equation (4).

T2 = 2R / C (4) C = sound velocity in water (about 1500 m / s) The time T3 at which the first sea surface reflected wave is generated is given by equation (5).

T3 = 2D2 / C (5) Further, the second sea surface reflected wave generation time T4 is given by the equation (6).

T4 = (2 · D2 + 2 · D1) / C (6) Next, the reverberation B21, the target echo B22, and the first echo are also generated by the second transmitted acoustic wave 11 (FIG. 4A2). Sea surface reflected wave B231 and second sea surface reflected wave B232
Is generated and received.

The received sound wave 21 received by the receiver 2 is converted into an electric signal to become a reception signal 22, and the TVG receiver 4
Is input to The gain of the TVG receiver 4 is the trigger signal 5
In synchronization with 1, it changes so that it is low immediately after transmission and increases with time. This state is shown in FIG. 4C. Since this change in gain is generally matched with the change in reverberation (FIG. 4B11), the output signal 41 of the TVG receiver 4 does not generate output due to reverberation, as shown in FIG.
D12) and the first sea surface reflection signal (Fig. 4D131).
Only output.

The output signal 41 is sent to the target detector 7, and the range gate signal 61 (FIG. 4E) puts the target signal 71 into a reception stop state from immediately before the first sea surface reflection to the next transmission (T6). (FIG. 4F). The range gate signal 6 can receive the time T5 shown in FIG. 4E by the depth signal 81 from the depth meter 8 and the trigger signal 51 and stop receiving the time T6. This time T5 is given the depth D2 of the floating body by the depth signal 81, and is determined according to the equation (7).

T5 = 2D2 / C-T7 (7) T7 = Margin Further, the time T6 is determined by the equation (8).

T6 = T1-T5 (8) T1 = transmission cycle (FIG. 4A) Next, description will be made after the second transmission. The reverberation (FIG. 4B21), the target echo (FIG. 4B22), the first sea surface reflected wave (FIG. 4B231), etc. are generated by the second transmitted sound wave (FIG. 4A2) as in the first time. As above, but in addition to this, the first transmission (Fig. 4A1)
The second sea surface reflected wave (FIG. 4B132) due to is received before the target echo (FIG. 4B22). This signal is
Since it cannot be prohibited by the range gate signal 61, the target signal 7
1 is included as a signal F132, which causes a false detection. The same applies to the third transmission (Fig. 4A).
It also occurs after 3).

[0016]

As described above,
In the conventional active sonar for upward monitoring, since the transmission cycle (FIG. 4T1) is set to a predetermined constant value, it is inevitable that a malfunction due to the second sea surface reflected wave is unavoidable, as shown in FIG. 4F. There was a problem.

[0017]

According to the present invention, a transmitter that sends out sound waves into the sea at a certain transmission cycle, a receiver that receives reflected waves based on the transmitted sound waves, and a low value during the transmission cycle period. From the timing of receiving the primary sea surface reflected wave of at least the transmitted sound wave that has received the output of the reception amplifying means and has a gain that changes from 1 to a high value, to the next transmission timing. And a transmission cycle defining means for defining the transmission cycle so that the timing of receiving the secondary sea surface reflected wave of the transmitted sound wave and the next transmission timing substantially overlap each other. An active sonar is obtained which is characterized in that the detection signal is obtained from the output of the gate means.

The upward monitoring active sonar according to the present invention includes a wave transmitter for transmitting a sound wave into water, a transmitter for supplying a transmission signal to the wave transmitter, and a wave receiver for converting a reception sound wave into a reception signal. , TV that changes the gain of received signal over time
G receiver, a period calculator that calculates a transmission period according to the depth of the sonar and generates a trigger signal having a period according to the depth, and a range gate generator that stops the reception function for a certain time according to the depth of the sonar And a target detector that generates a target signal by applying a certain threshold to the output signal of the TVG receiver, and a depth gauge that measures the depth of the sonar.

[0019]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of the embodiment.

In FIG. 1, a wave transmitter, a wave receiver 2, a transmitter 3, a TVG receiver 4, a range gate generator 6, a target detector 7, and a depth gauge 8 have the same functions as in the prior art. Therefore, the above description is referred to and the description thereof is omitted here.

The period calculator 5A shown in FIG. 1 determines the transmission period (FIG. 5T11) by the depth signal 81 of the depth meter 8 according to the equation (9) and generates the trigger signal 51.

T11 = (2 · D2 + 2 · D1) / C (9) D2 = Underwater floating body depth (output from depth gauge) D1 = D2 + L (seafloor depth) L = length of rope As shown in FIG. 5, the second sea surface reflected wave (FIG. 5B132) by the first transmission overlaps with the reverberation (FIG. 5B21) by the second transmission and enters the timing when the gain of the TVG receiver is low. Second sea surface reflected wave (Fig. 5B
False detection by 132) can be avoided. As shown in equation (9), this transmission cycle (FIG. 5T11) changes with the installation depth even if the installation depth changes, and the second sea surface reflected wave and the reverberation due to the second transmission are always present. As mentioned above, false detection will not occur.

In the present embodiment, the transmission period of the active sonar for the underwater levitation body is defined as the time from the first transmission to the second arrival of the sea surface reflected wave. It is well known that it is desirable to obtain many echoes (increase the amount of data) in a short time. For example, after transmitting, it is desirable to perform the next transmission at the same time as the first sea surface reflection, but the most data amount is desirable,
As shown in the above equation (2), the level of the first reflected wave on the sea surface is extremely large, which is unsuitable because the level cannot be suppressed by the TVG receiver.

[0026]

As described above, according to the present invention, the depth of the sonar is set so that the timing of receiving the secondary sea surface reflected wave after the transmission of the transmission period of the upward monitoring active sonar overlaps with the timing of the next transmission. By controlling according to the depth of the seabed, there is an effect that malfunction due to sea surface reflected waves can be avoided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention,

FIG. 2 is a diagram showing an operating state of an active sonar for upward monitoring,

FIG. 3 is a block diagram of a conventional active sonar for upward monitoring,

FIG. 4 is a waveform chart of each part for explaining the operation of the conventional technique;

FIG. 5 is a waveform diagram of each part for explaining the operation of the present invention.

[Explanation of symbols]

 1 wave transmitter 2 wave receiver 3 transmitter 4 TVG receiver 5 period timer 5A period calculator 6 range gate generator 7 target detector 8 depth meter 100 upper monitoring active sonar 101 anchor line 102 anchor 200 target 300 seabed 400 Sea level

Front page continued (72) Inventor Kiyohiko Iwasaki 5-7-1, Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Mitsuhiro Numata 5-27-14 Tamagawa Gakuen, Machida, Tokyo (72) Invention Minato Kato 1-48-9 Hirao, Inagi-shi, Tokyo (56) Reference JP-A-50-133860 (JP, A) JP-A-1-262491 (JP, A) JP-A-57-91471 (JP, A) Japanese Patent Sho 63-61628 (JP, B2)

Claims (1)

(57) [Claims] 1. A transmitter that sends out sound waves in the sea at a certain transmission cycle, a receiver that receives a reflected wave based on the transmitted sound waves, and a gain that changes from a low value to a high value during the transmission cycle period. Reception amplification means for amplifying the output of the receiver,
Gate means for receiving the output of the receiving and amplifying means and for inhibiting output at least from the timing of receiving the primary sea surface reflected wave of the transmitted sound wave to the next transmission timing, and the secondary sea surface reflected wave of the transmitted sound wave. An upper monitoring actuator comprising: a transmission cycle defining unit that defines the transmission cycle so that the timing and the next transmission timing substantially overlap with each other, and a detection signal is obtained from the output of the gate unit. Tibsoner.