Deep Trekker delves into the essentials of sonar technology, detailing its role in underwater inspections, search and recovery missions, bathymetric mapping, and other applications.
For underwater professionals, sonar is often the preferred tool. Using sonar is an invaluable asset, offering location data, environmental context, and imaging capabilities even in highly turbid waters.
While each technology has a distinct function, this article specifically highlights sonar’s role in underwater inspections and surveys.
What is Sonar and How is it Used?
Since GPS is ineffective underwater and cameras struggle in low-visibility conditions, sonar is an essential tool for subaquatic work. Sonar (sound navigation and ranging) uses sound waves to detect and map objects.
Sound waves are sent out, reflecting off objects and returning to the source. The time taken for these waves to return enables distance measurement.
Sonar provides insights into the seafloor, including:
- Precise ocean depth
- Sediment and seabed types
- Unique topographical features
- Fish species in the area
- Foreign objects on the seafloor
How Does Sonar Work?
An active sonar system consists of a display, transducer, transmitter, and receiver. The transmitter generates an impulse, which the transducer converts into a sound wave. This wave bounces off objects, then returns to the transducer. Depending on the system, sonar can detect objects up to 7,000 meters away.
The returning echo is converted into an electrical signal by the transducer, amplified by the receiver, and displayed on a screen. Multiple hydrophone sensors then measure the sound’s intensity and phase to determine distance.
Sonar performance varies depending on ocean conditions, with scattering from particles in the water affecting clarity similarly to fog scattering light. Regular studies of ocean conditions enhance acoustic range predictions.
Sonar assists in:
- Navigating in turbid water or expansive areas
- Target identification
- Measuring features like sediment layers or defect sizes
- Enhancing situational awareness
Types of Sonar Systems
The simplest sonar is akin to human hearing, but modern systems offer higher resolution and range. Military-grade sonar, for instance, can cover 80% of ocean floors from only four points.
Despite the speed of light and the advantages of RADAR, sonar is unique in its ability to map the ocean floor, create nautical charts, and detect hazards or shipwrecks. The Titanic disaster spurred sonar technology’s advancement, particularly during the World Wars, leading to two main types.
Active Sonar
Active sonar emits sound waves that reflect off objects, returning to the receiver to determine range, bearing, and motion. Submarines employ active sonar to identify nearby objects by measuring time delay between transmission and echo. Advanced tools can also detect an object’s size, shape, and orientation in detail.
Deep Trekker ROVs (remotely operated vehicles) use active sonar to send sound waves that reflect off underwater objects and the seafloor. Multibeam imaging sonar employs multiple beams to create an image of the ROV’s surroundings.
Passive Sonar
Unlike active sonar, passive sonar doesn’t emit sound but instead listens for signals from external sources, like sea life or vessels. Known as Hydrophones, they are commonly used for surveillance and require additional listening devices to locate the sound source precisely, useful for discrete military operations.
CHIRP Sonar
CHIRP (Compressed High-Intensity Radar Pulse) sonar is effective for bottom-tracking and fish-finding. It emits a frequency sweep for detailed imaging, superior to traditional 2D mechanical sonar. With each pulse, the transducer’s frequency rises over time, offering enhanced resolution.
Categories of Sonar Devices
Sonar devices vary based on their applications and capabilities.
Echosounders
Echosounder sonars are fundamental for bathymetric surveys, applied in navigation, charting safe passages, underwater mapping, and assessing potential underwater hazards. There are two primary types of echosounders: single beam and multibeam, providing essential data for navigation safety and understanding underwater topography.
Single Beam Echosounders
Single beam echosounders (SBES) emit a single vertical beam to the seafloor, commonly used for basic depth readings on marine vessels and fish finders. ROVs use echosounders to measure altitude above the seafloor and avoid obstacles, with dual frequency settings that can adjust sonar range in real-time.
Low frequencies allow longer range with lower resolution, while high frequencies are optimal for close-range, high-resolution results.
Due to their simplicity, single beam echosounders are cost-effective and straightforward, ideal for small-scale hydrographic surveys, environmental monitoring, and shallow water research.
However, their limited coverage necessitates multiple passes over larger areas, and factors like temperature and salinity may influence data accuracy.
Multibeam Echosounders
Unlike single beam, multibeam echosounders (MBES) use multiple beams to map larger areas in detail, efficiently creating high-resolution images of the seafloor. These sonars are crucial for hydrographic surveying, oceanographic research, and navigation.
Multibeam sonar provides detailed views of seafloor formations, such as seamounts and trenches, and can locate objects like sunken vessels. However, the increased complexity requires advanced data processing and specific software, adding to the operational costs.
Imaging Sonar
Imaging sonar, unlike echosounders that measure depth, offers detailed images of the underwater environment. This technology is used by researchers, divers, and scientists to study marine life, locate wrecks, and create accurate underwater maps.
The high-resolution images provided by imaging sonar enable detailed examinations of underwater structures, making it invaluable for scientific research, underwater archaeology, and various marine tasks like 2D and 3D modeling.
Scanning Imaging Sonar
Scanning imaging sonar devices use rotating transducers to emit sound pulses in multiple directions, forming a 3D image of underwater surroundings.
These devices are excellent for observing structures, marine life, and intricate terrains, benefiting scientific research, construction, and underwater inspections.
They are especially helpful in low-visibility conditions for navigation, object detection, and high-resolution imaging.
Multibeam Imaging Sonar
Multibeam imaging sonar, also known as “forward looking sonar,” emits multiple beams to cover large areas, producing real-time, high-resolution images essential for hydrographic surveys, oceanography, and search and recovery efforts.
They are compatible with Deep Trekker ROVs or Utility Crawlers for efficient target identification in murky waters. Available models include:
- M370S: Long-range navigation and low-resolution imaging, ideal for open-ocean surveys and shipwreck exploration with up to 200-meter range.
- M750D: Dual-frequency sonar for high-resolution, short-range tasks, also suitable for long-range navigation, making it a best-seller.
- M1200D: High-frequency sonar for close-range inspections, suitable for Explosive Ordnance Disposal (EOD) & Mine Countermeasures (MCM) tasks.
- M3000D: High-frequency model for precise short-range imaging, ideal for tunnel, tank, wall, and hull inspections.
- C550D: Budget-friendly option with a 100-meter range, providing essential imaging for cost-conscious operations.
Side Scan Imaging Sonar
Side scan sonar is designed for detailed imaging along a transect line and can be hull- or ROV-mounted. It emits sound waves perpendicular to the direction of travel, capturing reflections to reveal the seafloor’s shape and texture. This technique is used for seafloor imaging, search and recovery, maritime construction, and archaeology.
Side Scan Imaging Sonar is suited to large-area searches when deployed on an Autonomous Underwater Vehicle (AUV) or surface vessels. On ROVs, side scan sonar is ideal for covering larger areas in confined or hard-to-reach spaces.
Deep Trekker provides side scan sonar options for both the REVOLUTION and PIVOT ROVs.
