Buying Guide
Which sonar do you actually need?
Nine products, seven technologies and a lot of decibels. This page explains what each one does in plain language, what it will not do, and what else you have to own before it works — so you can ask us for the right thing the first time.
What are you trying to do?
Sonar is easier to choose backwards — from the job, not from the technology. Find the sentence that sounds like your problem.
I need to find something on the bottom
Side-scan imagingA wreck, lost gear, debris, a dropped tool. You drive a search pattern and the sonar paints a photograph-like strip of the seabed to either side. Objects standing proud throw an acoustic shadow — often that shadow is how you identify what you have found.
I cannot see where I am going
Forward-looking imagingZero visibility, silt-out, night work. A forward-facing sonar gives you obstacle detection out to 120 m and lets you navigate to a target you can see acoustically long before the camera picks it up.
I need to chart the depth of an area
Multibeam echosounderProducing actual bathymetry — a depth model of the seabed, not a picture of it. Many beams across the track means one pass gives you a swath of soundings instead of a single line.
I need to model a structure in 3D
3D imaging sonarQuay walls, dock pilings, scour around a foundation. Structures standing up in the water column come out as a true 3D point cloud rather than a smear on a flat image.
I need to know how far it is to the bottom
Single-beam echosounderAltimetry for an ROV or AUV, simple depth logging from a small boat, or obstacle avoidance. One narrow beam, one number, 0.3 m to over 100 m.
I need to know where my ROV is
USBL acoustic positioningA head at the surface works out the direction and distance to a pinger on the vehicle. Add GPS topside and that becomes a latitude and longitude you can put on a chart.
My ROV will not hold still
Doppler velocity logCurrent pushes the vehicle off the job. A DVL measures how fast the ground is moving past, so the autopilot can hold station the way a camera drone hovers.
I want the ROV to navigate itself
USBL + autopilot integrationWaypoint navigation and position hold need the autopilot to be told where the vehicle is, continuously. Omnitrack is the packaged answer, buoy and topside hub included.
I have run out of ports on the vehicle
Subsea networkingEvery sonar wants an Ethernet port and most small ROVs have exactly one spare. A subsea switch fixes that without another tether penetration.
Seven kinds of sonar, in plain words
What each one measures, what it is good at, and — the part most datasheets skip — what it cannot do.
Forward-looking imaging sonar
Cerulean call it FS. You will also hear "forward-scan" or "obstacle avoidance sonar".
What it does
Sweeps a narrow fan of sound ahead of the vehicle and draws what comes back. Rotate on the spot and it builds a picture of the scene in front of you.
What it is for
Navigating and searching where the camera is useless — silt, night, deep water. Seeing a target from 100 m away and driving to it.
What it is not
It is not a survey instrument and it does not measure depth. And nothing about the hardware limits it to "forward" — see the rigging section.
Side-scan sonar
Cerulean call it SS.
What it does
Fires a fan out sideways at the seabed. As the vehicle travels in a straight line, each ping adds one line to a continuous, photograph-like strip.
What it is for
Search and recovery, wreck hunting, seagrass and habitat mapping, pipeline and cable route checks. Covering ground.
What it is not
It shows you what the bottom looks like, not how deep it is. Most side-scan gives no depth information at all.
3D imaging sonar
Sits between an interferometric side scan and a multibeam.
What it does
Adds a 16-channel receive array that works out the vertical angle of every return. SonarView then builds a real 3D mesh, drapes the high-resolution image on it, and captures everything in the water column as a point cloud.
What it is for
Wide swaths in shallow water, and anywhere the vertical shape matters — pilings, quay walls, scour, weed beds.
What it is not
Not a replacement for a survey-grade multibeam. Cerulean position it between the two, deliberately.
Multibeam echosounder (MBES)
The instrument that makes charts.
What it does
Measures depth across a wide fan under the vessel, many soundings per ping, so one pass produces a swath of the seabed in three dimensions.
What it is for
Bathymetry proper — dredge volumes, berth surveys, channel checks, anything that ends in a depth model rather than a picture.
What it is not
It needs accurate position and heading from the vessel, and it has no logging of its own. This is the one where the supporting kit matters most.
Single-beam echosounder
Also called an altimeter, or a sounder.
What it does
One narrow beam straight down (or straight ahead), returning the distance to whatever it hits. Bottom tracking runs on the device itself.
What it is for
Holding an ROV at a set height off the bottom, simple depth logging, obstacle avoidance, and any underwater distance measurement.
What it is not
One number, one point. It cannot map — that is what the multibeam is for.
USBL acoustic positioning
Ultra-Short BaseLine. Cerulean's are the ROV Locator and Omnitrack.
What it does
A single head at the surface measures the bearing and the distance to a pinger on the vehicle. That gives you the vehicle's position relative to the boat; add topside GPS and it becomes an absolute fix.
What it is for
Knowing where the ROV is. Putting a target on a chart. Geo-referencing a side-scan mosaic so it lands in the right place.
What it is not
Cerulean describe the ROV Locator as medium-accuracy and say so plainly — plan on ±2% of distance at 100 m. It is not a survey-grade positioning system.
Doppler velocity log (DVL)
Cerulean's is the Tracker 650.
What it does
Three angled beams measure how fast the ground is moving past, from the pitch shift in the echo. Feed that to the autopilot and the vehicle knows it is drifting before you do.
What it is for
Position hold, dead reckoning, and steady vehicle behaviour while you work. On a BlueROV2 it is plug-and-play with the flight controller.
What it is not
It measures velocity, not absolute position — over time the reckoning drifts. Pair it with a USBL if you need to stay tied to a chart.
Which imaging sonar?
All four run at 450 kHz and all four are driven by the same free software. Here is what actually separates them.
| Omniscan 450 Compact | Omniscan 450 FS | Omniscan 450 SS | Omniscan 3D 450 SS | |
|---|---|---|---|---|
| Pick it when | Space is tight and you have one spare port | You want the best all-rounder in a sealed housing | You want maximum range and the finest beam | You need the vertical shape, not just the picture |
| Maximum range | 100 m | 120 m | 150 m | 150 m 2D · 100 m 3D per side |
| Beam width | 1.1° | 0.8° | 0.5° | 0.5° |
| Housing | All-in-one | All-in-one | Electronics need your own enclosure | All-in-one, Raspberry Pi 5 inside |
| Depth rating | 300 m | 100 m or 300 m | 300 m | 300 m |
| Weight in air | 934 g | 440 g / 825 g | 300 g | 1057 g |
| Extra Ethernet ports | 2 more devices | None | None | Chainable |
| Produces a 3D point cloud | No | No | No | Yes |
| Price | from €2,811 | from €2,341 | from €2,435 | from €7,511 |
| Full details → | Full details → | Full details → | Full details → |
Every figure is from Cerulean's published specification table. Omniscan 450 specifications · Omniscan 3D specifications
The thing nobody tells you: FS and SS are packaging, not capability
Cerulean say it outright in their own manual — although the model names mean Forward Scanning and Side Scanning, either one can be used for either application. The real difference is the transducer and the box it comes in.
The SS transducer is about 50% longer, which buys a narrower beam (0.5° against 0.8°) and more range (150 m against 120 m). But the FS arrives sealed and ready to bolt on, while the SS electronics module needs a watertight enclosure that you provide. For most buyers that decides it long before the range figure does.
The other frequent surprise: on the FS, “100 m rated” is the depth of water the housing survives, not how far it can see. Both the 100 m and the 300 m FS see out to 120 m.
Four ways to mount an Omniscan — and what each one buys you
FS and SS are packaging, not capability. Both scan forward and both scan sideways — what changes the picture is whether the vehicle is turning or travelling. Cerulean publish four ways to rig it.
One sonar, facing forward
- Motion that builds the image
- Angular — the vehicle rotates
- What you get
- A fan of the scene ahead, built as you turn on the spot. Then drive at whatever you spotted and watch yourself close on it.
- What it needs
- Nothing beyond the sonar.
- What to buy
- One Omniscan 450 FS, SS or Compact.
Two sonars at right angles
- Motion that builds the image
- Angular and translational
- What you get
- Side-scan imaging plus a second axis of velocity — which is what unlocks 2D Doppler motion tracking and position hold with no DVL at all.
- What it needs
- Nothing beyond the two sonars.
- What to buy
- Two Omniscan units — one forward, one on the beam.
One sonar, side-scanning
- Motion that builds the image
- Translational — the vehicle travels in a line
- What you get
- A classic side-scan swath down one side.
- What it needs
- A position source: a DVL or USBL on an ROV, GPS on a surface craft or AUV.
- What to buy
- One Omniscan, plus positioning.
Two sonars, side-scanning
- Motion that builds the image
- Translational
- What you get
- Port and starboard swaths at once — twice the ground per pass.
- What it needs
- A position source, as above.
- What to buy
- Two Omniscan units, port and starboard, plus positioning.
What makes an image a side scan is translation, not which way the sonar points. And the FS-versus-SS choice is driven by packaging first, then by whether you need the SS's 150 m over the FS's 120 m. Cerulean’s configuration guide
Position hold without buying a DVL. Omniscan interleaves ordinary imaging pings with Doppler pings. The Doppler pings make no picture, but the return tells the sonar how fast it is closing on whatever it is pointed at. Two units at right angles give two axes — enough for SonarView to mosaic, and enough for position hold. It works on every Omniscan already in the field, with a firmware and SonarView update. Position hold works out of the box on BlueOS / ArduSub vehicles.
- Does that halve the imaging rate?
Yes. With Doppler motion tracking on, the imaging ping rate drops by half. It is a toggle on the Omniscan device controls panel in SonarView. - Is it as accurate as a DVL?
No. The angle of the reflected signal is ambiguous, so the speed measurement is less accurate than a DVL. It is accurate enough for good situational awareness while SonarView renders the mosaic. - How well does position hold work without a DVL?
It uses two channels where a real DVL has three or four, so expect a slow drift — typically 1–2 m per minute.
Which positioning system?
Two different questions hide in “I need positioning”. Sort out which one you are asking, then pick the Mk.
| Mk II GNSS time sync | Mk III Duplex acoustic sync | Mk V Ethernet network sync | |
|---|---|---|---|
| What is in the bundle | Mk II receiver topside + Mk II transmitter subsea | Mk III transceiver topside + Mk V transmitter subsea | Mk V receiver topside + Mk V transmitter subsea |
| Best for | The least expensive bundle, and it asks almost nothing of the ROV — just power. | Needs the least attention from the operator, and no clock drift at all — the topside interrogates and the subsea unit answers, so it can stay down indefinitely. Can switch to network sync on the fly if a network exists. | The most reliable acoustics around a noisy ROV or a noisy site, no clock drift, and the fastest updates — up to 5 Hz. |
| The catch | Both units must see GPS/GNSS at the start of the job and again roughly once an hour, to beat clock drift. | The most expensive bundle, because both ends carry a full transmit and receive chain. The topside draws more power than Mk II or Mk V. | Needs an Ethernet connection and a network bridge between the topside unit and the subsea unit. |
| Worth knowing | Two selectable channels, so two ROV systems can work the same area. One transmitter can serve several receivers on a channel. | Only one Mk III transceiver can operate in an area at a time. | Only one Mk V system can operate in an area at a time. |
| Maximum range | 500 m | 300 m | 300 m |
| Update rate | 1 Hz | 1 Hz | up to 5 Hz |
| Bundle price | €3,281 | €5,631 | €4,503 |
From Cerulean’s own ROVL system selection guide and system variants pages. All eight ROV Locator configurations →
- Every bundle works with the Omnitrack system.
- Every bundle works with SonarView, and every one can improve how Cerulean's imaging sonars perform.
- All bundles have similar range and angular resolution.
- A minimum complete system is one subsea unit plus one topside unit. Buy a single unit only to pair with one you already own.
How accurate is a USBL, honestly?
The closer the ROV is to the boat, the tighter the fix — with the floor set by your GNSS. Cerulean's own rule of thumb: at 100 m, plan on ±2% of distance.
The acoustics are rarely what limits you. Cerulean break the error down like this:
| Topside GNSS, no RTK corrections | typically 3–5 m CEP |
| Magnetic compass error | typically 3–5°, so ≈ sin(5°) × slant range |
| Angular resolution, topside to deepside | typically 2°, so ≈ sin(2°) × slant range |
| Combined angular error (the two are uncorrelated) | about 5.3° |
| Slant range measurement | usually insignificant next to the others |
Which lands at CEP ≈ √( 5² + ( sin(5.2°) × slant range in metres )² ) — so the closer the vehicle is to the boat, the tighter the fix, with the floor set by your GNSS. Cerulean’s accuracy note
USBL or DVL — or both?
A USBL tells you where you are. A DVL tells you how you are moving. They answer different questions, and plenty of jobs need only one.
Buy the ROV Locator or Omnitrack when the deliverable is a position — a target on a chart, a geo-referenced mosaic, a diver you can direct.
Buy the Tracker 650 when the problem is the vehicle wandering off the job. In position hold, expect it to sit inside about a metre, drifting under a metre a minute.
Run both and they cover each other — pairing the Tracker 650 with an Omnitrack gives USBL and DVL sensor fusion on BlueROV2 systems. And if budget rules out both, two Omniscan 450 FS at right angles give you Doppler position hold with no DVL at all, at the cost of roughly 1–2 m per minute of drift.
A sonar on its own is not a system
The commonest reason a first survey disappoints is not the sonar. It is one of these.
SonarView, on a computer
Every Cerulean sonar is driven and logged by SonarView, and it is free — no licence fee, no per-seat charge. Windows, macOS, Linux, Docker, or as a BlueOS extension running on the vehicle itself. Nothing records without it.
Position and heading, from the vessel
A single ping needs nothing. A map — a side-scan mosaic, a bathymetric surface, a 3D point cloud — needs to know where the sonar was for every ping. SonarView takes this over MAVLink2Rest on BlueOS vehicles, or from NMEA 0183 / NMEA 2000. On the Surveyor this is the single biggest driver of data quality.
A spare Ethernet port
Every sonar wants one, and small vehicles rarely have a second. A BlueBoat has none free as standard. Fix it with a Blue Robotics 5-port switch, a Cerulean Manifold 5L subsea hub, or by choosing the Omniscan 450 Compact, which has a 3-port switch built in.
10–30 V DC
Everything in the range runs on the same 10–30 V rail (the Omniscan 3D wants 12–30 V) and draws very little — 10 W pinging on an Omniscan, 15 W on a Surveyor, 2.5 W on a Tracker 650. Vehicle battery power is fine.
A bracket
Cerulean sell exactly four: an FS bracket, an SS bracket, a Tracker 650 bracket and a BlueBoat bracket for the Omniscan 3D. Everything else mounts on M4 holes you provide. Free 3D-printable mounts exist for the BlueBoat.
Somewhere to put the data
Budget about 5 GB per hour at a 20 Hz ping rate. If you are logging to a Raspberry Pi, fit a 128 GB card.
SonarView drives all of it. One application for Omniscan 450, Omniscan 3D, Surveyor 240-16 MBES, Sounder S500, Tracker 650, ROV Locator, Omnitrack — plus Blue Robotics Ping360 and Blue Robotics Ping Echosounder. Exports CSV and GSF, which most of the bathymetric software community reads. More about SonarView →
Will it fit my vehicle?
What Cerulean document for each platform — including the settings that quietly ruin your data if you skip them.
Blue Robotics — BlueROV2 & BlueBoat
- Cerulean use the Blue Robotics 4-pin JST GH connector standard throughout, so the sonars plug into a Blue Robotics Ethernet switch as they come.
- In QGroundControl, turn on "All Streams Controlled By Vehicle Settings", then set SR0_POSITION and SR0_EXTRA1 to 50 Hz. Skip this and QGroundControl overrides the vehicle's message rates and your data quality drops sharply.
- On a BlueBoat there is no spare Ethernet port as standard — add a 5-port switch. A free 3D-printable Surveyor mount is published on Printables.
- A Surveyor and an Omniscan 450 SS can share mounting holes on a BlueBoat, for imaging and bathymetry on the same pass.
- The SonarView BlueOS extension is the recommended setup: the sonar link never drops packets, raw sonar data stays off the telemetry radio, and settings follow you between computers.
CHASING — M2 Pro / Pro Max
- Connect through the RC3 controller that ships with the M2 Pro Max, or over RJ45 on the WSRC controller.
- CHASING supply the mounting plate and screws, and it can be turned to face the Omniscan forward or sideways.
- With one Omniscan, mount it forward. With two, face one forward and one to the side — that gives you Doppler motion tracking in two dimensions.
- Add the sonar in the CHASING GO1 app under the Accessory dock ("Add manually" → the right Net Port → "Other accessories"). This may need repeating each time the vehicle boots.
- A CHASING M2 Pro Max vehicle model is built into SonarView.
QYSEA — FIFISH E-GO / Master / W6
- Cerulean build factory editions of the Omniscan 450 FS for the E-GO / Master and for the W6, in both 100 m and 300 m ratings, and a Compact edition for the W6.
- These editions exist because the vehicle needs a different connector and cable set — the sonar itself is the same.
Blueye
- The Omniscan 450 Compact is offered in a Blueye edition with the Blue Trail connector.
Something else, or your own build
- Cerulean use the Blue Robotics 4-pin JST GH connector standard across the range, which is the closest thing this corner of the industry has to a common plug.
- Everything speaks 100BaseT Ethernet and runs on 10–30 V DC, so integration is usually a port, a power pair and a mount.
- The Omniscan 450 SS ships as a separate transducer and electronics module precisely so you can put the electronics in your own housing.
- Cerulean publish CAD models and drawings for every product, plus a documented API and a Python library if you want to talk to the device directly rather than through SonarView.
- OEM routes exist — the Tracker 650 and the OS450 board are sold at board level.
Not sure? Tell us what you are integrating and we will check it against the documentation before you order.
Every product, one table
The whole range on one screen, for people who already know what they are looking at.
| Product | Category | What it is | Frequency | Range | Beam | Depth rating | Weight in air | Price |
|---|---|---|---|---|---|---|---|---|
| Omniscan 450 Compact | Imaging | Forward / side scan | 450 kHz | 100 m | 1.1° | 300 m | 934 g | from €2,811 |
| Omniscan 450 FS | Imaging | Forward / side scan | 450 kHz | 120 m | 0.8° | 100 m or 300 m | 440 g / 825 g | from €2,341 |
| Omniscan 450 SS | Imaging | Side / forward scan | 450 kHz | 150 m | 0.5° | 300 m | 300 g | from €2,435 |
| Omniscan 3D 450 SS | Imaging | 3D point cloud + side scan | 450 kHz | 150 m 2D · 100 m 3D | 0.5° | 300 m | 1057 g | from €7,511 |
| Surveyor 240-16 | Bathymetry | Multibeam echosounder | 240 kHz | 100 m suggested | 4° along · 80° across | 300 m | 790 g | from €4,691 |
| Sounder S500 | Bathymetry | Single-beam echosounder | 500 kHz | 0.3 m to 100+ m | about 5° | 300 m | 34 g + 94 g | from €837 |
| Tracker 650 | Positioning | Doppler velocity log | 675 kHz | 0.5 m to 25–50 m altitude | 3 beams at 70° | 300 m | 550 g | from €2,811 |
| ROV Locator | Positioning | USBL | — | 500 m (Mk II) · 300 m | 0.1° resolution | 300 m subsea · 50 m topside | 300–440 g | from €3,281 |
| Omnitrack | Positioning | USBL system with buoy + hub | — | 300 m | 0.1° resolution | 300 m subsea | — | from €7,511 |
Ranges and beam figures are Cerulean's published specifications; prices are our EUR list, ex works. Scroll the table sideways on a narrow screen. Full product list with part numbers →
Jargon decoder
Every term that turns up on a Cerulean datasheet, in one place.
- Sonar
- SOund NAvigation Ranging. Send a pulse of sound, time how long the echo takes to come back, and you know how far away the thing is. How strong the echo is hints at what it is made of.
- Transducer
- The part that turns electricity into sound and sound back into electricity. In small sonars it is a piezoelectric element — it flexes when you apply a voltage, and generates a voltage when something flexes it.
- Frequency, and why it is a trade
- Low frequency travels further but resolves less. High frequency resolves finely but is absorbed by the water sooner. Cerulean's imaging sonars sit at 450 kHz, the Surveyor at 240 kHz, the S500 at 500 kHz.
- Range resolution
- The smallest gap between two targets at which you still see two targets rather than one blob. Quoted as a fraction of the range you have dialled in — 1/1200th on the Omniscan 450.
- Beam width
- How narrow the sound fan is. Narrower means finer detail across the image. The Omniscan 450 SS is 0.5°, the FS 0.8°, the Compact 1.1°.
- Far field
- The distance beyond which the quoted beam width is actually true. Closer than that the beam is wider and the sidelobes bigger. 4 m on the Compact, 5 m on the FS, 9 m on the SS.
- CHIRP
- Instead of one note, the pulse sweeps across a band of frequencies. Because every moment of the pulse has its own pitch, two echoes that overlap can still be told apart. You get better signal-to-noise and finer range resolution from less transmit power. The S500 chirps across 20 kHz.
- Side-scan sonar
- A fan of sound aimed out sideways at the bottom. As the vehicle drives a straight line, the returns build a photograph-like strip. Things standing proud return brightly; the ground behind them returns nothing and reads as a black shadow. That shadow is often how you identify the object.
- Multibeam echosounder (MBES)
- Many beams at once across the track, each measuring depth, so one pass produces a swath of soundings rather than a single line. This is how a chart gets made. The Surveyor 240-16 is Cerulean's.
- Single-beam echosounder
- One narrow beam pointing down. It answers "how far to the bottom" — as an altimeter for an ROV, for simple depth logging, or for obstacle avoidance. That is the S500.
- Point cloud
- A set of individual 3D points rather than a flat picture. The Omniscan 3D builds one as it goes, so structures standing up in the water column — pilings, weed — come out as shapes, not smears.
- USBL
- Ultra-Short BaseLine. One head at the surface works out the direction and distance to a pinger on the ROV, so you know where the ROV is relative to the boat. Add GPS topside and that becomes a latitude and longitude.
- DVL
- Doppler Velocity Log. Several angled beams measure how fast the ground is moving past, using the pitch shift in the echo. Give an ROV that and it can hold station the way a camera drone hovers.
- Slant range
- The straight-line distance between two points — not the horizontal distance. A USBL measures slant range; to get horizontal range you also need depth.
- Mosaic
- Many sonar pings stitched into one continuous image. It only works if the software knows where the vehicle was for each ping — which is why imaging and positioning are sold together more often than people expect.
- CEP
- Circular Error Probable. The radius of the circle your fix lands inside half the time. It is the honest way to state positioning accuracy.
- MAVLink2Rest / NMEA
- The two ways SonarView gets position and heading from your vessel. MAVLink2Rest on BlueOS vehicles; NMEA 0183 or NMEA 2000 from a marine GNSS compass.
- GSF
- Generic Sensor Format — the bathymetry interchange file most hydrographic packages read. SonarView exports it, alongside CSV.
Three ways to get to a quote
However much of the above you read, the last step is the same.
Let the finder do it
Three questions — job, platform, depth — and it names the exact part number, plus what it ruled out and why. Find your system →
Build the list yourself
Every model card across these pages has an Add to Quote button. Collect what you want, then send the lot in one message. All products →
Just describe the job
Tell us the vehicle, the depth and what you need to find. We will come back with a configuration and the reasoning behind it. Ask us →
Tell us the job. We will name the part.
Vehicle, water depth, and what you are trying to see or find. That is enough for us to come back with a configuration — and to say so if Cerulean is the wrong answer.
Ask About Choosing a System
No obligation, and no need to know the terminology. We will explain the reasoning behind whatever we suggest.