Multibeam image sonar

Single frequency&dual frequency multibeam image sonar

Due to its small size, it is an ideal device for application in micro platforms. At the same time, it has a sturdy structure and is also the preferred choice for large work level underwater robots and applications in measuring underwater terrain structures

Single frequency&dual frequencyMultibeam image sonar

Due to its small size, it is an ideal device for application in micro platforms. At the same time, it has a sturdy structure and is also the preferred choice for large work level underwater robots and applications in measuring underwater terrain structures



Nanjing Juhai Information Technology Co., Ltd

Multi beam image sonar is a new generation of compact image sonar with wide applications underwater. Due to their small size, they are ideal devices for applications in micro platforms, and they have a sturdy external structure, making them a choice for large work level underwater robots and measuring underwater terrain structures.

Multi beam image sonar has different voltage resistance options of 500m, 1000m, and 4000m.

M series: standard model, withstand voltage of 500m.

MT series: It has all the advantages of the M series, with a titanium shell and a pressure resistance of 1000m.

MD series: titanium shell, pressure resistant to 4000m, used for working in deep water environments.

Features:

1. The frequency range is 375kHz to 3.0MHz, with single frequency and dual frequency systems, suitable for underwater navigation, underwater situational awareness, and detection work.

2. Provide a wide viewing angle range, with a horizontal beam angle of 130 degrees and a vertical beam angle of 20 degrees.

3. Wide range capability, from 0 1m to 200m.

4. High definition image quality, with a minimum angular resolution of 0.25 degrees.

5. Outstanding image clarity, with a range resolution of up to 2mm.

6. Simple and intuitive operating software.

7. The update rate of real-time image output is as high as 40Hz.

Performance parameters:

mechanical parameters

M-Series MT-Series MD-Series

尺寸 125 mm (L) x 122mm (W) x 62mm (H) 125mm (L) x 122mm (W) x 62mm (H) 125mm (L) excluding connector x ø125mm

Material Aluminum Titanium Titanium

重量 980 g (Air), 360g (Water) 1350g (Air), 730g (Water) 2.5kg (Air), 1.45kg (Water)

Voltage resistance 500 m 1000m 4000m

Temperature range (working) -5 ° C up to+35 ° C -5 ° C up to+35 ° C -5 ° C up to+35 ° C

Temperature range (storage) -20 ° C up to+50 ° C -20 ° C up to+50 ° C -20 ° C up to+50 ° C up to

M370s M750d M1200d M3000d

MT370s MT750d MT1200d MT3000d

MD370s MD750d MD1200d MD3000d

频率 375 kHz 750kHz / 1.2MHz 1.2MHz / 2.1MHz 1.2MHz / 3.0MHz

Range (Maximum) 200m 120m/40m 40m/10m 30m/5m

Range (Minimum) 0.2m 0.1m 0.1m 0.1m

Range resolution 8 mm 4mm / 2.5mm 2.5mm / 2.5mm 2.5mm / 2mm

Maximum update rate 40 Hz 40Hz 40Hz 40Hz

Horizontal detection angle 130 ° 130 °/130 ° 130 °/60 ° 130 °/40 °

Vertical detection angle 20 ° 20 °/20 ° 20 °/12 ° 20 °/20 °

Number of beams 256 512 512 512

Angle resolution 2 ° 1 °/0.6 ° 0.6 °/0.4 ° 0.6 °/0.4 °

Beam spacing 0.5 ° 0.25 °/0.25 ° 0.25 °/0.16 ° 0.25 °/0.1 °

Electrical indicators

M-Series

MT-Series MD-Series

接口 Impulse IE55 Series, 6-way Impulse MC Series, 6-way (Schilling SeaNet / Burton option)

通讯 4- wire 100-BaseT Ethernet, 2-wire DSL extender module 4-wire 100-BaseT Ethernet, 2-wire DSL extender module

电压 12 V to 32V DC non-isolated 18V to 32V DC isolated

功率 10 W to 35W (model and range dependent*) 10W to 35W (model and range dependent*)

Temperature and pressure sensors for calculating sound velocity

working principle

Traditionally, sonar is a mechanical device that scans sectors ahead or around it by rotating sensors (transmitter and receiver). At each transducer position, a sound pulse will be transmitted into the water, and the echo collected by the receiver will be plotted on the display. Depending on the required resolution, the image may take several tens of seconds to update, during which any movement of the sonar may contaminate and distort the image. Unlike mechanical sonar, Oculus is a multi beam sonar without moving parts. It is a set of receivers that collect echoes from a single transmitted pulse and use a process called "beamforming" to mathematically combine the data into an image. This allows for generating images multiple times per second and viewing them in real-time like the output of a camera.

Some Oculus sonars (with a suffix'd 'at the end of the name) are dual band, with low and high frequency operating modes, allowing operators to choose between longer acoustic ranges or high-resolution images.

Sonar images require some training and practice to interpret, as they appear to the operator as a top-down view covering the area in front of them. Depending on the selected frequency mode, sonar images can illuminate 130 ° horizontally and 20 ° vertically. The brightness of targets and textures on the display indicates how much sound they reflect (gases or dense materials reflect more sound than mud, sand, and silt), while sound shadows can be projected based on the geometric shape of objects or the seabed.

By combining the known speed of sound in water (VOS - "c") with the time to receive the echo ("t"), sonar can calculate the distance of sound propagation ("d").

Since sound must be transmitted from sonar to the target object and then back, the distance ('r ') between sonar and the target is half of the total distance.

In the real world, sonar will see multiple targets ahead. The emitted sound pulses will reflect off each target at different times, but the receiver will record all echoes within a time period equivalent to twice the maximum operating range (for sound traveling back and forth to the target).

Nanjing Juhai Information Technology Co., Ltd

The received echoes are combined into a single received signal, whose time position is directly related to distance, and the strength of each echo depends on the degree of reflection of the target.

Targets with very different densities from water, such as gas/air or rock/concrete, will have strong reflectivity and echoes, while echoes from materials such as mud, silt, sand, and plants will have weaker echoes

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Sound beam mode

When considering how sonar works, imagining sonar as a flashlight used in a dark room may be helpful. Users can only see the part of the room illuminated by the torch, and if the torch's beam is narrow, their field of view will be reduced.

Similarly, sonar has fixed widths and heights for the areas illuminated by sound, which are referred to as horizontal and vertical beam patterns.

Oculus sonars with the suffix "d" (such as M750d and M1200d) are dual band devices that support two operating modes, low frequency and high frequency. The single frequency Oculus sonar (with the suffix's', such as M370s) only supports low-frequency operating mode. E

Nanjing Juhai Information Technology Co., Ltd

Each mode has its own beam mode, as shown in the following figure:

Target visibility

Objects (or targets) located within the sonar beam will be "illuminated" by acoustics and can receive their echoes (targets), while objects located outside of this (targets and ƒ) may not appear on the sonar display:

It should be noted that although the above chart shows the boundaries of sonar beams, this actually represents the "half power" level of sound waves. Vertical targets outside of this area may still be visible on the display, but as they move away from the beam pattern, their echo levels will rapidly decrease.

In the horizontal direction, due to the fixed width of the "top-down" display, images outside of the beam mode will not be displayed.

Sonar cannot determine the vertical arrival angle of echoes, therefore, if two targets are located in front of the sonar at the same vertical distance from each other, the sonar will display these two targets as a single result of their echo combination.

View the seabed

As discussed in the previous sections, sonar can be considered as a handheld flashlight with a horizontally wide and vertically narrow illumination beam - continuing this analogy, the sonar image displayed on the operator monitor can be seen as a "top-down" view of the illuminated area. For users who wish to perform search and location activities or underwater surveys, Oculus can be installed on a display screen to illuminate and see different quantities of the seabed:

If the sonar approaches the seabed and tilts downwards, it will only display a small bar in front of it. By obtaining altitude from the seabed, operators can illuminate a wider wire harness, thereby better utilizing the display

For situations where sonar is needed to search the seabed ahead, the best use of the display is to balance the height above the seabed and the angle of the sonar downwards, in order to maximize the illumination of the seabed ƒ

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As a very common rule, if the downward angle is 15 ° and the height is higher than 10% of the working range, the sonar can achieve the best 70% seabed coverage on the display screen. That is, for a 20m range, the sonar should be installed about 2m above the seabed, and for an 80m range, the height should be increased to about 8m.

Acoustic shadow

The similarity between sonar and torch continues to exist, as the "illumination" of sonar can be used to generate acoustic shadows, which is very helpful for operators to determine the height, shape, and direction of targets ahead of sonar.

As mentioned earlier, the display can be viewed as a top-down (or satellite) view in front of Oculus:

1.1. Understand Echo

Although some have mentioned that sonar displays can be viewed as top-down images of the area in front of them, this analogy has some limitations.

When the sonar illuminates the image from the side, only the edge or surface of the target closest to the sonar will be illuminated.

If the target surface is at a certain angle, some incoming sound waves will be reflected to the sonar, while other sound waves will be dispersed in different directions, and the overall brightness of the target will decrease.

The following diagram illustrates this point, highlighting in red the brightest areas on the display screen for three simple targets, as well as how these areas are displayed in real targets:

According to the distance between sonar and the target, it can also have a significant impact on the image.

Due to the way sound waves propagate from the transmitter, the shadow cast by distant targets will narrow behind them, but as sonar approaches them, the shadow width will increase. In these cases, operators should be aware that these shadows may hide other targets as there is no sound to illuminate them

When the visibility of operators is limited by the shadow of nearby targets, they should strive to increase the sonar altitude above the seabed (as well as the target causing the shadow) and possibly tilt the sonar downwards for compensation.

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Understand Echo

Although some have mentioned that sonar displays can be viewed as top-down images of the area in front of them, this analogy has some limitations. When the sonar illuminates the image from the side, only the edge or surface of the target closest to the sonar will be illuminated.

If the target surface is at a certain angle, some incoming sound waves will be reflected to the sonar, while other sound waves will be dispersed in different directions, and the overall brightness of the target will decrease. The following diagram illustrates this point, highlighting in red the brightest areas on the display screen for three simple targets, as well as how these areas are displayed in real targets:

Range, frequency, and image quality

As mentioned earlier, some Oculus sonars have two working modes:

·Low frequency allows for long-range operations with a wide viewing angle - which is useful for search and measurement tasks.

·High frequency, producing more details in a shorter range, narrow viewing angle -

This is very useful for detailed research on close range targets.

The following figure shows a comparison of the same test site under two operating modes:

Summary of Sonar Operations

Generally speaking, the following points summarize the operation of sonar:

·The sonar image displays the echo received from the leading edge of the target in a "top-down" manner.

·Only targets illuminated by sonar beams can be seen:

Horizontal plane 130 °/80 °, depending on frequency mode

In the vertical direction of 20 °/12 °, although this is the half power point, darker targets may appear outside of it.

·Due to the lack of vertical information available, vertically aligned or overlapping targets in the sonar beam will be merged into a single echo.

·Dense or gaseous targets appear brightest on the display screen, while mud and silt appear very dim.

·The target casts acoustic shadows, which may obscure all or part of the target behind it, especially when the sonar approaches the target.

·Changing the height above the seabed to alter the illumination angle of the targets and the length of the shadows they cast can help explain the features on sonar images.

·In high clutter (rock/boulder) environments, use gain control to enhance weak targets or reduce background noise reflections.

·If possible, use different frequency modes according to the required range and level of detail:

The low-frequency mode can achieve a wide viewing angle (130 °) and the sonar supports the longest range.

The high-frequency mode can provide detailed high-resolution images, but the viewing angle (80 °) and shorter range settings are reduced.

·When navigating or measuring on the seabed, install sonar horizontally, point forward, and tilt slightly downwards (10-15 °).

·A good rule of thumb for optimal seabed coverage on a display while gaining experience using sonar is to maintain the seabed height at approximately 10% of the selected sonar range.

·To accurately calibrate the range, please check if the correct water salinity has been entered into the software at the operating site.