Introducing Doppler Motion Tracking on Omniscan

We are very excited to announce this new (patent pending) capability of the Omniscan 450 FS sonar. In addition to long range and high resolution imaging, Omniscan can now do motion tracking and position hold!

Cerulean SonarView works great with Omniscan to “mosaic” the sonar image in real time as your vehicle moves, but of course it needs position information to do this. For a surface vessel with GPS this is no problem, but to accomplish the same result underwater on an ROV additional expensive underwater positioning systems are required.

Introducing Omniscan Doppler Motion Tracking

Cerulean engineers have developed a way to get Doppler information from Omniscan pings by interleaving “imaging pings” and “Doppler pings.” “Imaging pings” are the normal pings Omniscan uses to generate the sonar image. The “Doppler pings” are not suitable for imaging, but with special processing of the return echo, Omniscan is able to produce an estimate of the velocity relative to the ping direction.

Check it out! This window is a live embedded version of SonarView replaying an actual Omniscan log file taken on a BlueROV2 five meters below the surface with no GPS, no USBL, no DVL. Just a pair of Omniscan 450 FS imaging sonars, one mounted forward and one on the port side.

Click here to open this SonarView demo full size in new tab

You can get a lot of the capability even with a single Omiscan 450 FS mounted forward. With this single Omniscan configuration you can rotate to do a scan, then move toward any potential sonar targets and SonarView will render the forward motion so you will see your forward progress toward the target on the sonar image.

Add a second Omniscan 450 FS on either side of the ROV and not only do you now have side-scan imaging, but you also have a second axis of velocity information to enable full 2D tracking in SonarView. In addition, the 2D motion tracking information from Omniscan can be used to enable Position Hold mode.

This new patent pending Doppler Motion Tracking feature works on all Omniscan devices already in the field with just firmware and SonarView updates. Position Hold works out of the box with BlueOS/Ardusub based ROVs. Cerulean is available to work with OEMs to integrate in alternative flight control systems.

Omniscan Doppler Motion Tracking FAQ

Omniscan 450 FS Product Page

Introducing Omniscan

Omniscan is a low-cost, high-resolution, long-range imaging sonar ideally suited for use on small ROVs and surface vessels. Omniscan has a narrow and tall fan beam (<1 deg width) which is scanned by rotating the platform. As the ROV or surface vessel moves, SonarView “paints” the image of the scanned area of the sea floor giving excellent situational awareness in the murkiest conditions.

Animated screen capture of SonarView illustrating how vehicle motion scans the seafloor. To see the Omniscan and SonarView in action check out the web demo at: https://sonarview.ceruleansonar.com/.

In the case of a surface vessel with GPS or an ROV with DVL, scanning can be translational as well as rotational. A key difference between Omniscan and other scanning sonars and side-scan sonars in its class is Omniscan’s built-in IMU and integration with Cerulean’s SonarView application. If SonarView detects that the vehicle supports a MAVLINK connection, the vehicle’s position and attitude information is used to display each ping in its correct absolute orientation and position. Typical side-scan products just display a sequence of pings in a linear array, and require post-processing with high end software tools to achieve correct image rendering. With Omniscan and SonarView, you see the geometrically correct image live in real time. Even without vehicle position information, SonarView displays each ping at the correct compass direction using Omniscan’s built in IMU.

Forward Scanning and Side Scanning Models

There are two Omniscan 450 models. This is the Omniscan 450 FS, ideally suited for forward looking ROV applications. The transducer and electronics are housed in a single enclosure with Ethernet + power interface.

Omniscan 450 FS in 300m depth rated enclosure
Rendering of Omniscan 450 FS with optional mounting bracket on a BlueROV2.

Using Omniscan 450 FS on an ROV, the scanning is under the direct control of the ROV driver so that they can focus on specific areas of interest rather than waiting for a mechanical scanning sonar to slowly come around to sweep the particular sector they want to see. Using the “Heading Up” mode in SonarView makes this manual scanning very intuitive and provides excellent situational awareness.

Omniscan SonarView in Heading Up Mode.

Omniscan 450 SS

The Omniscan 450 SS is tailored for side-scan applications. It has a longer transducer which gives 50% better angular resolution and 150m maximum range. The transducer is rated to 300m operating depth. Two units of the Omniscan 450 SS can be combined in SonarView for the conventional side-scan application in which both sides are scanned simultaneously.

The Omniscan 450 FS and the Omniscan 450 SS use the same electronics module. In the Omniscan 450 FS, the electronics module is mounted in the integrated FS transducer/enclosure. In the Omniscan 450 SS, the transducer is separate, and the electronics module is mounted in the vehicle’s water tight enclosure.

Omniscan 450 SS with transducer, PCB assembly, and cables.

Note that although the model designations indicate Forward Scanning (FS) and Side Scanning (SS), in reality either one can be used for either application. The real difference is in the transducer and the packaging.

Price and Availability

PriceAvailability
Omniscan 450 FS (100m enclosure)$2250March 2023
Omniscan 450 FS (300m enclosure)$2750March 2023
Omniscan 450 SS$2295March 2023

Sounder S500 Testing in Lake Superior

As we approach the last month of summer, Cerulean is gearing up to launch the S500 multipurpose single-beam echosounder in August. The S500 uses a narrow beam-width about 5 degrees that focus the acoustic energy providing 100m range and good angular definition. CHIRP technology also maximizes range and offers excellent range resolution.

Testing is progressing on schedule, and some of our team members got up to Lake Superior over July 4th weekend, where they spent some time on the beautiful schooner Abbey Road and test the Sounder S500 in the deep clear Lake Superior waters and confirm that the 100m range rating is accurate.

The short movie above shows the S500 displaying a depth of 120 meters in Lake Superior. The software being used is an R & D tool — The S500 is fully compatible with the readily available B/R Ping Viewer.

The beautiful schooner Abbey Road was the platform used to test the Sounder S500 in Lake Superior over the 4th of July long weekend.

ROV Locator contributes to the removal of 4 tons of wreckage.

Early in June, an underwater search by Titan Maritime near Mahone Bay Nova Scotia revealed massive quantities of lost or abandoned fishing gear wreckage.

In the seabed, Titan Maritime found three kilometers of plastic fishing lines weighed down by 50 bags filled with sand and gravel, spread over a 600-meter watery grave, and resembling ruins of a sunken ship.

The wreckage had very little monetary value, but its removal is an invaluable contribution to the protection of endangered species such as the North Atlantic right whales and leatherback turtles who are threatened by fishing gear entanglements.

A Blue Robotics BlueROV2 Heavy equipped with Cerulean ROV Locator positioning system was a vital instrument for this “ghost gear” removal operation.
Old fishing lines covered in marine growth resemble the rails on a ship. Many clues pointed to the ghost gear’s being decades-old (photo by Ken deBoer.)
Tony Sampson and Jamie Hiltz were the divers on the ghost gear operation. This image is from the ROV (photo by Ken deBoer.)

Check the News Story by CBC Nova Scotia News.

Coming in August: Multipurpose single-beam echosounder

OVERVIEW

The S500 is a single beam echosounder designed for small ROVs, AUVs, and ASVs. The transducer and control electronics are unbundled to minimize external mechanical profile and maximize flexibility. The transducer (45.7 mm diameter x 33  mm) is rated to 300m depth, and the electronics module is housed inside the vehicle’s pressure enclosure. A narrow beam width about 5 degrees focuses the acoustic energy providing 100m range and good angular definition. CHIRP technology also maximizes range and provides excellent range resolution.

Sounder PCB to be housed in vehicle pressure vessel. 2.7″ x 1.5″ (68.5mm x 37mm)

Product Description

The S500 sonar is a multipurpose single-beam echosounder. It can be used as an altimeter for ROVs and AUVs, for bathymetry work aboard a USV, as an obstacle avoidance sonar, and other underwater distance measurement applications.

The S500 implements CHIRP modulation, which sends a varying frequency ultrasonic pulse. The advantages of CHIRP include better signal to noise ratio, and much higher range resolution than non-CHIRP devices.

The S500 can report a simple distance measurement, or It can also provide the full signal profile for display as a “waterfall” plot like the display of a fishfinder. For that purpose, S500 is compatible with the Blue Robotics Ping Viewer. Raw signal strength data profiles can also be provided for advanced analysis in technical applications.

The S500 uses a high frequency 500 kHz transducer giving about 5 degrees beam width for ROV and AUV altimeter and bathymetry applications. It has a measurement range of over 100 meters. A bottom-tracking algorithm runs on the device to determine the distance to the seafloor.

Three communication interfaces include Ethernet (100Mb/sec), USB (12Mb/sec), and  3.3-5.0V serial (115kbaud).

S500 transducer. Depth rated to 300m. 1.8″ dia x 1.3″ (45.7mm x 33mm)

For those who wish to integrate the S500 to other systems, it communicates with a binary message format. You can find the S500 API documentation here.

Here is what’s in the box:

  • 1 x S500 Sounder Control Board
  • 1 x S550 transducer with one meter cable (1 shield + 2 signal wires)
  • 2 wire power cable with installed JST-GH connector (1 meter)
  • 6 wire serial/sync interface cable with installed JST-GH connector (1 meter)
  • Link and QR code to on line documentation
Control Electronics
Power Supply10-30 Volts, 2.5 Watts idle, 5 Watts max at max ping rate of 10 pings/sec
Dimensions69 x 38 mm. 4 mm below bottom mounting surface, 18 mm above bottom mounting surface. 4 mounting holes spaced at 33mm x 52.8mm (1.3″ x 2.08″)
InterfacesEthernet (RJ45 connector), USB (uUSB connector), 3.3-5.0V Serial (6 pin JST-GH)
External Sync3.3-5.0V digital Sync Input is available to optionally trigger pings timed to avoid interference with other acoustic devices. Sync Out (3.3V) is also available to signal the start and end of each ping emitted by the S500.
Communications ProtocolS500 API documentation here
Minimum Range Resolution3 mm up to 17 meter range
9 mm up to 50 meter range
24 mm over 50 meter range
reduced resolution optional to reduce waterfall data rate
Transducer
Acoustic Frequency500 kHz
Beam Width (2-way, conical)about 5 degrees.
ModulationCHIRP with 20 kHZ bandwidth
monotone ping also supported
Minimum Range0.3 meters
Maximum Range100+ meters 
Depth Rating300 meters

Cerulean Sonar USBL ROV Locator goes into full production

On this past Oct 25th at the second annual Blue Robotics Open House, we introduced the ROV Locator. The product was very well received! with attendees frequently reacting to the ROV Locator, and its $1995 price with disbelief. An underwater positioning system for $1995? Yes, that’s right. 

And now, we are ready to announce that Cerulean Sonar has gone into full production with its underwater position system ROV Locator solution and prepared to take orders!


We are thrilled about the initial market reaction with customers around the world, purchasing and inquiring about the most cost-effective underwater position system solution on the market today!


Probably the most challenging part of operating an ROV or AUV is keeping track of its location. The solution is to fit an underwater positioning system, and the ROV Locator is the best answer and at an unprecedented price range.

With the absence of GPS availability underwater, Ultra Short Baseline (USBL) is a widely used tracking system for ROVs. The ROV Locator is designed for low-cost, medium accuracy localization of underwater objects. The ROV Locator comprises a pinger mounted on the ROV and a USBL receiver module on the surface. Sync them up at the start of the dive and track the ROV location in real-time using a QGroundControl map display.

Cerulean Sonar’s mission is to leverage the latest advances in microelectronics and digital signal processing to bring you sonar products that are Sensibly Priced! We are passionate about making ocean exploration more accessible, and we know that not everyone has the budget of the US Navy and the Big Oil companies. That’s why we do it.

Doppler Velocity Log (DVL)

Have you ever flown a DJI drone? If you have, then you’ll know that if you take your hands off the controls, the drone will stop and hold it’s position exactly where you left it until you again actuate the control to make it move-on. A Doppler Velocity Log (DVL) has the potential to do just that for an underwater ROV.

What is a Doppler Velocity Log (DVL)? 

For those operating beneath the surface, the process of estimating the subsea position has a distinct challenge not found in terrestrial navigation since GPS navigation does not function underwater. 

The Doppler effect (or Doppler shift) is the apparent change in the frequency of a sound, caused by relative motion between the source of the wave and the observer.

An example of a Doppler shift is the pitch difference heard when a car playing its horn passes an observer or a plane or a train passes us by. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by and lower during the recession.

DVL uses Doppler shifting of acoustic signals to compute velocity relative to the seafloor. DVL is a crucial part of subsea navigation by offering an accurate estimate of velocity referenced to the earth.

With a Doppler Velocity Log (DVL), users of remotely operated vehicles (ROVs) can determine velocity in reference to the seafloor.

How does DVL work?

DVL transmits a pulse with a minimum of three acoustic beams, each pointing in a slightly different direction. The reflected pulses are used to produce estimates of velocity in several axes of the DVL platform coordinate system, which are combined with estimates of DVL platform orientation from an internal Inertial Measurement Unit (IMU). The velocity estimates are integrated into position estimates in the IMU’s coordinate system. 

Most Doppler velocity logs use a Janus configuration, named after the Roman god who looks both forward and backward, where a transducer pointing ahead measures speed. A sensor pointing astern is used for checking accuracy, and sensors looking abeam measure athwartship speed. Typically, the beams are only 2 to 30 degrees off vertical referenced from a level DVL platform.

The concept of Doppler Velocity Log and a Janus configuration of the transducers

So with a DVL integrated with the INS and the ROV’s control software, it is now possible to stabilize the platform, e.g. to drift from currents, and hold position relative to the sea floor just like those aerial drones do.

Who else uses DVL?

In recent years, navigation for autonomous underwater vehicles technology has progressed significantly in capability. Navigation has remained one of the main hurdles limiting the full potential of AUVs. Doppler Velocity Logs have become a reliable solution increasingly for tackling AUVs navigation requirements. 

Applications requiring subsea navigation can vary from diver-held guidance systems to larger autonomous undersea vehicles conducting high-accuracy seafloor studies over vast distances.

Coming Soon!

Due to large size and high cost, the use of DVLs have been historically limited to larger and very expensive vehicles where the cost could be justified. The upcoming Cerulean Sonar offering will be small enough to deploy on a low cost commercial grade ROVs like the BlueROV2 and will set a new benchmark for low cost. Watch for Q2 2020 launch!

Prototype Janus Configuration transducer head on a testing pool.

Options to communicate with the ROVL product

Testing has been completed using QGroundControl to communicate with our ROVL product. The Cerulean team has created a sample utility that enables the ROV’s location to be displayed in the map view of QGroundControl. The user can then create a waypoint in QGroundControl and drive to it.

The Cerulean Companion is an open-source program, which allows customers with Python knowledge to customize/add functionality to match their requirements.

The following link ( https://ceruleansonar.github.io/Cerulean-Companion/) provides the steps to getting the ROVL to work with QGroundControl. These instructions currently support the ROVL Rx on the topside connected to a laptop and the ROVL Tx on the ROV. 

If the requirement is to plug the Rx into the ROV and have it forwarded up to a topside computer, the following can be used in Linux:

We have not yet tested an alternative similar to our Linux option under Windows, but it’s probably possible with Windows Subsystem for Linux Installation Guide for Windows 10.

What is CHIRP?

CHIRP stands for “Compressed High-Intensity Radar Pulse.” Instead of sending a single frequency like standard sonars, CHIRP pulses are a continuous sweep of frequencies extending from low to high (or high to low).

CHIRP sonar uses signal processing techniques to precisely identify the center of the received pulse. The signal processing improves both range resolution and signal-to-noise-ratio (SNR), allowing for a lower-power transmitter.

Why is CHIRP useful?

To explain the advantages of using CHIRP acoustic techniques, we must first understand the limitations of using conventional (monotonic) sonar techniques to acquire sonar imaging. A monotone acoustic pulse consists of a single carrier frequency modulated by its amplitude (typically, modulated from off to on to off).

The figure below shows the correlation between the sonar transmitted signal and the receiver circuitry produced output. The receiver will not decode every cycle of the broadcasted pulse. Instead, it generates an envelope of its overall amplitude.

The pulse duration determines the ability of the acoustic system to resolve targets. The shorter the pulse length, the higher the resolution and ability to resolve separate targets. However, this approach has its drawbacks. 

To place sufficient acoustic energy into the water for proper target identification and over a wide variety of ranges, the transmission pulse length has to be relatively long. 

Due to the speed of sound through water (“VOS” – typically around 1500 meters/sec), each pulse occupies an equivalent “distance” related to its pulse duration – this is referred to as “range resolution,” and can be resolved by the following equation.

Range resolution = (pulse-length x velocity of sound) / 2

For instance, in a conventional sonar system at a moderate range, a typical pulse length is 100 microseconds (µs) while the velocity of sound (VOS) in water is 1500 m/s (typically). Consequently, the range resolution would be 75 mm.

The formula adequately predicts the ability to resolve separate targets. Using the example above, if the two targets are less than 75 mm apart, it will not be possible to distinguish them as two different items. The result is that the sonar system will display a single large target, rather than two smaller targets.

How does CHIRP Operates?

Unlike standard monotonic sonars, a CHIRP pulse swept through continuously through the pulse time. 

For example. A CHIRP sonar may send a pulse starting at 125KHz and ending at 150KHz. The difference separating these two frequencies  is known as the “bandwidth” of the transmission. Typically, the center frequency of the broadcast is used to identify the sonar (in this case, it would be a 137.5KHz sonar).

By continuously shifting its frequency over time, the CHIRP signal can be perceived as having a unique acoustic signature. If two pulses overlap due to targets being closer than the range resolution, the CHIRP “frequency versus time information” can be used to discern them as separate images.

CHIRP sonar looks for transmitted CHIRPS echoed back from targets, with the receiver producing a sharp ‘spike’ when a suitable match is found. A monotonic sonar can only generate an output the same duration as its transmit pulse.

With CHIRP, the crucial factor for ascertaining range resolution is not the pulse interval, but rather the CHIRP bandwidth. The following formula can find the range resolution.

Range resolution = Velocity Of Sound /(Bandwidth x 2)

As an example, a chirp sonar with a bandwidth of 50kHZ would have a range resolution of 15mm, assuming a VOS of 1,500 meters/sec. Such a result would provide a theoretical five-fold improvement over the fixed frequency (monotonic) sonar previously discussed.

On the illustration shown above, the two acoustic echoes overlap. However, these CHIRP signals do not merge into a single acoustic return since their frequencies differ from each other at the overlapping points. On a CHIRP sonar environment, the sonar discerns and renders the two targets separately. With CHIRP technology, longer transmissions are feasible, allowing us to see targets further away and without loss in resolution.

Side Scan Sonar

Side scan sonar is a specialized sonar device for finding and identifying objects on the seafloor. Like other sonars, a side scan sonar broadcasts sound energy and interprets the return signal (echo) that reflects from the seabed or other objects. The transmitted energy is projected into the shape of a fan that sweeps the seafloor to either side. As a vessel equipped with side scan sonar moves along in a straight line, an image of the sea floor to either side is developed.

Here is preview of a future Cerulean side scan sonar product we’ve been working on. These are early times in the development cycle, but already the imaging obtained is yielding impressive results. Both of these images were produced using the low cost ($299) Lowrance “3-in-1” sidescan transducer. The image on the right is from the standard Lowrance system, and the image on the left is from the same transducer driven by the prototype Cerulean side scan electronics. The Cerulean result is sharper because of CHIRP technology which provides better signal to noise ratio and improved range resolution.

Cerulean side scan sonar image with CHIRP (left), same target with same transducer but OEM driver and no CHIRP (right).
Cerulean Sonar Side scan sonar images using different processing methods

The Side scan sonar images were taken from a Wayzata Bay wreck in Lake Minnetonka, at a 450khz frequency at about 60 meters range.

A close-up of the Wayzata Bay wreck. 21-HE-401 showing some of the features seen on the Cerulean Sonar SSS imaging.
Side scan image of a mid-50’s car sunk in Lake Minnetonka. Yes, some crazy ice fishermen goes through the ice pretty much every year. You’re not allowed to just leave them there anymore!
Scuba diver checking out same car.

Specific configurations for the Cerulean side scan product are not yet finalized, but our goal is to set a new benchmark for high performance at a very affordable price point.