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World's smallest DVL

The smallest DVL in the world

From 0.105kg and 25mm x 66mm.

Wide operating altitude

World's shortest blanking distance

Operate virtually at the seabed, as low as at 5cm altitude.

unbeatable price/performance

Unbeatable price/ performance

From less than US$ 7,000.

How it works:

Doppler velocity log - operating concept

The DVL estimates velocity relative to the sea bottom by sending acoustic waves from the four angled transducers and then measures the frequency shift (doppler effect) from the received echo.

By combining the measurements of all four transducers and the time between each acoustic pulse, it is possible to very accurately estimate the speed and direction of movement.

How DVL works

1. Sound wave sent

Acoustic narrow beam wave is sent from each of the four transducers.

2. Sound wave echo

The sound wave will bounce off the bottom and the transducers will receive the echo.

3. Measurements performed

The DVL computer measures the received echo and the IMU:

  • Doppler measurement. The difference in frequency between transmitted and received signal is the “Doppler effect” which is used to calculate the velocity.
  • Time of flight. This gives a measurement of the distance between the transducer and the seabed (altitude).
  • AHRS/IMU. The onboard Attitude and Heading Reference System (AHRS) / Inertial Measurement Unit (IMU) reads its triaxial gyroscope, accelerometer, and compass sensors to determine orientation.

4. Velocity calculated

Estimated distance travelled, time of flight and AHRS headings are all fed into our Kalman filter which in turn will output the velocity of the DVL.

DVL in use:

Use cases of Water Linked DVLs

An onboard computer removes the need for external computers or topside communication, enabling the Water Linked DVL to be used as a navigation sensor on a range of underwater platforms.

ROV using DVL

ROV

By utilizing a Water Linked DVL, the ROV operator will experience a whole new level of stability and control when operating the ROV. Thanks to the increased stability, the quality of the video will improve dramatically as the ROV pilot carries out his works with increased confidence.

Examples:

  • Maintaining stability while operating ROV tools or performing detail inspections.
  • Station keeping in challenging situations like ocean currents or tether pull.
  • Terrain following.
  • General velocity feedback for vehicle control.
AUV using DVL

AUV

Autonomous Underwater Vehicles (AUV) are usually operating without tethers or with any direct input from the surface. While undertaking long range assignments the AUV is typically also unable to relay on an acoustic positioning system for navigation information.

Therefore the most used navigation sensor for an AUV is a DVL in combination with an inertial sensor (IMU/INS).

Examples:

  • Long range assignments.
  • Bathymetry surveys.
  • Military subsea patrolling.
Diving using DVL

Diving

Military, police and commercial divers are examples of divers that often have to follow a very accurate dive path.

This can be achieved with reliable acoustic positioning such as our Underwater GPS, however when very long range is needed, you have to look for a solution that does not require topside support. This is where the DVL comes in.

Examples:

  • Low visibility diving.
  • Long range dives.
  • Diver waypoint navigation.

Why size matters

A lot of effort was put into making sure the Water Linked DVL would be truly unique and provide benefits never seen before in a DVL.

We have used modern computing power, designed our own transducers and removed every millimetre of space that was not absolutely needed. The result has been a DVL design that has disrupted the market by using the latest technology.

 

Competitor comparisons

DVL A50 held by a human hand to show relative size

Image: Water Linked DVL size has set a new standard for high performance DVLs.

Manufacturer

Water Linked

Teledyne

Nortek

Model

A50

A125

Wayfinder

Pathfinder

DVL1000

DVL500

Depth rating

300

3000

200

500

4000

300

Minimum altitude

0.05 

0.05

0.5

0.15

0.2

0.3

Maximum altitude

50

125

60

89

75

200

Diameter

66

125

115

229 x 102

114

186

Height

25

30

70

71

164

203

Weight in air (kg)

0.17

0.98

0.85

1.9

2.7

3.5

Relative volume (litres)

0.1

0.25

0.7

1.6

1.7

2.8

“Teledyne” and “Nortek” are registered trademarks and the property of their respective owners. All company, product and service names used in this article are for identification purposes only. Use of these names, trademarks and brands does not imply endorsement.

Verifying performance

A Water Linked Doppler Velocity Log is a highly accurate instrument. To qualify the DVL we carried out a range of tests to validate the DVL performance.

Test A: How stable is the ROV when operating in a strong current

Benchmark: What level of control is there when performing a task in a strong current

Setup: The DVL was mounted to a ROV which was submerged in a water tank. The water tank dimensions were 210x110cm. A camera was mounted 2 meter above the ROV, filming and documenting any movements of the ROV. Another camera was mounted at the bottom of the water tank. A Blue Robotics T-200 thruster was mounted on the side of the tank pointing directly towards the ROV. The thruster was used to create currents in the water.

Performing the test: The ROV was set in “station keep” mode. Altitude was ~5 cm. The thruster creating current was set to about 40% power.

Results: The ROV was easy to control while approaching the target to be picked up. The critical moment when the gripper connected to the target was performed in a controlled manner.

 

Test B: Station keeping drift

Benchmark: Measurements taken to quantify drift over a set time.

Setup: The DVL was mounted to a ROV which was submerged in a water tank. The water tank dimensions were 210x110cm. A camera was mounted 2 meter above the ROV, filming and documenting any movements of the ROV.

Performing the test: The ROV was set in “station keep” mode. Altitude was ~50 cm. The DVL was left doing station keeping for 5 min 10 sec.

Results: The variation between starting position and end position was measured to be 2 cm. This translates to a drift per sec of 0.0065 cm/sec.

Test C: Station keeping in a strong current

Benchmark: Visual observation of ability to maintain position while in strong current.

Setup: The DVL was mounted to a ROV which was submerged in a water tank. The water tank dimensions were 210x110cm. A camera was mounted 2 meter above the ROV, filming and documenting any movements of the ROV. Another camera was mounted at the bottom of the water tank. A Blue Robotics T-200 thruster was mounted on the side of the tank pointing directly towards the ROV. The thruster was used to create currents in the water.

Performing the test: The ROV was set in “station keep” mode. Altitude was ~5 cm. The thruster creating current was set to about 40% power.

Results: The ROV was easy to control while approaching the target to be picked up. The critical moment when the gripper connected to the target was performed in a controlled manner.

Test D: Reliable navigation

Benchmark: To establish a benchmark for distance covered an RTK enabled GPS system with 7 mm horizontal accuracy was used.

Setup: Setup: The test was carried out on a boat with the DVL mounted on the bottom of a pole and the RTK GPS system mounted on top of the pole.

Performing the test: The boat was driven 295 meters in a straight line at a speed of 2 knots (~1 meter per second). The DVL altitude from the seabed varied between 4 and 9 meters over the 295 meters route.

Results: The distance measured by the RTK GPS system as 29,569.1 cm and the distance measured by the DVL-A50 was 29,530.6 cm. This 38.5cm difference translates to a distance error of 0.13%.

Navigation with DVL Only?

A Water Linked DVL has the ability to operate as a stand-alone navigation system providing Dead Reckoning Navigation of your underwater, or on water, vehicle. This is the process of calculating the vehicle's position by applying speed, time and direction of travel compared to the last known position.

The challenge by doing dead reckoning is that small velocity errors are integrated up and will over time result in a less accurate position estimate. To mitigate this, the DVL can be combined with other navigation sensors which reduce this effect.

Underwater GPS integration (not currently available)

To remove the issue of long-term errors (position drift), it will be possible to integrate the DVL with our Underwater GPS. This will be offered as a software upgrade and will feature auto-discovery between the two systems. By integrating the two systems you will be left with an amazing long-term deployment navigation solution.

DVL vs Underwater GPS

These two systems are both used for underwater navigation. They both however have different strengths and weaknesses although if you combine them on one vehicle, you can more or less eliminate the weaknesses of the stand-alone systems.

  DVL Underwater GPS
Requires initial setup NO YES
Limited range NO YES
Requires topside communication NO YES
High resolution position (millimetre variations) YES NO
Position will drift over time YES NO

Available DVL products

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