Journal of Robotics, Networking and Artificial Life
Vol. 7(3); December (2020), pp. 175–178
DOI: https://doi.org/10.2991/jrnal.k.200909.007; ISSN 2405-9021; eISSN 2352-6386
https://www.atlantis-press.com/journals/jrnal

Resarch Article

Ocean Current Velocity Measuring Device Based on
Acoustic Time Difference Current Meter
Jichao Zhao1, Fengzhi Dai1,2,*, Xin Ma3, Fengkun Wang1
Tianjin University of Science and Technology, College of Electronic Information and Automation, Tianjin, China
Tianjin Tianke Intelligent and Manufacture Technology Co., Ltd., Tianjin, China
3
National Oceanic Administration Beihai Marine Environmental Monitoring Center Station, Behai, China
12ARTICLE INFOABSTRACT

Article History

Ocean current refers to the relatively stable flow of the surface water of the ocean in a certain direction, and is the main regulatorof the thermal environment on the surface of the earth. At present, the ocean current velocity detection at sea is basically a fieldmeasurement by a staff member in a boat, and the adjustment of the detector position during the measurement process is very
inconvenient. This paper designs a new submarine current velocity measuring device that includes the measuring ship, cable,fixed anchor and ocean current velocity detector. The cable on the reel is retracted through the cable retracting room, and theend of the cable is fixedly provided with a fixed anchor. The fixed anchor is fixedly provided with a plurality of ocean current flowrate detectors, which have a built-in control chip, a wireless communication module, and Pressure Sensor. The ocean current
detector adopts the acoustic time difference current meter, which runs stably and is the most widely used current meter atpresent. This device can flexibly adjust the depth of the detector according to actual needs, so as to measure the flow velocity ofdifferent depths.

Received 25 October 2019
Accepted 24 May 2020
Keywords
Ocean current
flow velocity
current meter
acoustic measurement© 2020 The Authors. Published by Atlantis Press B.V.
This is an open access article distributed under the CC BY-NC 4.0 license (http://creativecommons.org/licenses/by-nc/4.0/).

1. INTRODUCTION
In order to develop and utilize the ocean, people have conducted
the long-term observation and research on the ocean. Amongthem, the current velocity is a very important parameter in marinehydrological research. It is very important to grasp the law of seawater flow, which can directly serve national defense, marine transportation, fishery, and port construction.
Ocean currents refer to the relatively stable flow of large-scaleocean surface waters in certain directions throughout the year.
Ocean currents are the main regulators of the thermal environmenton the Earth’s surface, which can be divided into the warm currents
and cold currents. If the temperature of the ocean current is higher
than the water temperature reaching the sea area, it is called warm
current; if the temperature of the ocean current is lower than thewater temperature reaching the sea area, it is called cold current [1].
Generally, the ocean current flowing from the low latitude to highlatitude is the warm current, and the ocean current flowing fromthe high latitude to low latitude is the cold current. Sea vessels sailing along the ocean current can save fuel and speed up. But when
the warm and cold currents meet, sea fog often forms, which is notgood for sea navigation. In addition, ocean currents carry icebergs
south from the Arctic, posing a greater threat to maritime shipping.
The main global currents are shown in Figure 1.

Corresponding author. Email: daifz@tust.edu.cn*

With the continuous development of science and technology andmarine science itself, the methods of observing ocean currents
have also been continuously improved and improved. From
the original drift bottle to modern ocean current meters, alarge variety of current measuring instruments have been
invented.
The current meter is a kind of instrument to measure the velocity and direction of seawater. It is installed on Argo buoys,
anchoring data buoys, submersible buoy, seabed base, autonomous underwater vehicle, underwater glider, survey ship
and other marine current measurement platforms for current
observation.
Recently, with the increasing improvement of the digital signal
processing technology, and the technologies of the optical fiber,laser, graphics and image processing, and computer technology,
the flow velocity measurement technology has also undergone
new developments, and a series of new flow velocity measurement
methods are appeared, such as the flow velocity measurement by
the acoustic Doppler, laser Doppler, radio wave velocity, particle
imaging velocity field measurement, etc. [2].
Particularly, the acoustic flow measurement becomes the mostwidely used solution in ocean velocity measurement with itsunique advantages. At the same time, the study of acoustic current
measurement technology is of great significance for exploring new
approaches to ocean current measurement technology. All kindsof current meters have their own characteristics. In the future, theJ. Zhao et al. / Journal of Robotics, Networking and Artificial Life 7(3) 175–178

176

Figure 3 | Design of ocean current velocity detector.

Figure 1 | The main global currents.

No. 5 indicates the fixed anchor; and No. 6 is the sliding sleeve.
Others are the fixed link No. 7, the sinking plate No. 8, the ocean
current velocity detector No. 9, the rack No. 10, the first motor
No. 11, the second motor No. 12, the gear No. 13 and the transmission belt No. 14.
The structure of ocean current velocity detector is shown in Figure 3.
No. 15 indicates a waterproof case, and others are control chip No. 16,
wireless communication module No. 17, pressure block No. 18, pressure sensor No. 19, connecting rod No. 20 and a suspension No. 21.

2.2. Instructions

Figure 2 | Structure of submarine ocean current speed measurement device.

acoustic current meters will be the main part of the current measurement, and a variety of types of current meters will coexist.
At present, the detection of ocean current velocity at sea is basicallycarried out by staff taking a boat to perform field measurements.
However, it is inconvenient to adjust the position of the detector
during the measurement [3]. It is prone to deviations due to themeasurement of the device, so it is necessary to design a submarine
ocean current speed measurement device to solve these problems.

2. DEVICE DESIGNIn this paper, a new submarine ocean current speed measurement
device is designed in Figure 2, which includes a measuring boat,
cable, fixed anchor, and ocean current velocity detector. The cableon the reel is retracted through the cable storage room. The endof the cable is fixedly provided with a fixed anchor, which is also
fixedly provided with a plurality of ocean current velocity detectors. This device can flexibly be adjusted according to actual needsin order to measure the ocean current velocity at different depths.

The submarine current velocity measuring device includes a survey
ship, cable, fixed anchor and ocean current velocity detector. A
rewinding reel is provided by rotating inside the cable retracting
room, and the reel is wound with a cable. The end of the cable is fixedwith a fixed anchor. Two cables are provided with a sliding sleeve.
The fixing rod is fixedly connected to the sinking plate. Several
ocean current velocity detectors are fixedly arranged below the sinking plate. A rack is fixedly arranged above the sinking plate, and theside of the rack is fixed with a second motor. The output end of thesecond motor is fixed with a gear, and the gear meshes with the rack.
The device is enclosed with a waterproof shell, and a control chip isinstalled inside the shell. A wireless communication module and apressure sensor module are arranged on one side of the control chip[4]. The depth of the detector can be flexibly adjusted according
to the actual needs, so that the ocean current velocity at different
depths can be measured. At the same time, the ocean current velocity detector is provided with at least three sets, and the average ofthree results measured by the detectors is used as the measurement
data, which can further improve the accuracy of the measurement.

3. SPEED MEASUREMENT PRINCIPLE
Acoustic waves are the propagation of energy in medium. Ultrasonicpulse signals generated by piezoelectric ceramic transducers arepropagated in the seawater medium in the form of phase velocity[5]. When the seawater medium itself has velocity, the sound waves
travel downstream at the same distance. It is not the same as thetime of countercurrent propagation [6].

2.1. Structure DesignThe principle is that, under the condition of the same acoustic
propagation distance, the velocity of seawater can be calculated bymeasuring the time difference between the two acoustics propagation in the upstream and downstream.

In Figure 2, No. 1 indicates the measurement ship; No. 2 is thecable storage room; No. 3 indicates the reel; No. 4 is the cable;

The schematic diagram of the propagation plane is shown in
Figure 4, where A and B are the transceiver and replacement

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177

Table 1 | Data of ocean current in Jingu River (China) area
Location

108°37′8.15″E, 21°40′41.02″N

Data

Figure 4 | Speed measurement schematic.

energizer, c is the ocean sound velocity at the measurement point,
v is the velocity of the seawater, and d is the distance (channel axisdistance) between the two transducers.
During the measurement, the transducer pairs are excited by thesame electrical signal, that is, the two transducers transmit ultrasonic waves at the same time, and are ready to receive signals
arriving at each other. Due to the existence of the velocity v, theultrasonic pulse signals that cause the forward and backward propagation will not reach the transducer receiving surface at the sametime [7]. According to the theory of sound wave retransmission ina fluid medium, it is known that the propagation time of the shortultrasonic pulses along the countercurrent and the countercurrent
directions on the biological axis are:Downstream travel time:			 t1 = d /(c + v ) (1)Countercurrent propagation time:			 t 2 = d /(c - v ) (2)Time difference between downstream and upstream:		    Dt = t 2 - t1 »2vd
(3)c2

Flow value:c 2 ∆t		 	 (4)v=(2d )
When c and d are known, as long as Δt is measured, the flow velocity v can be directly obtained. The error coefficient of this approximation is v2/c2.
If the speed of sound and velocity are calculated according to typical values, the error magnitude brought by this approximation is
4 × 10−7. The ocean velocity in the submarine boundary layer isgenerally very low, ranging from about 0.1 cm/s to about 1 m/s.
Assuming that d = 10 cm and c = 1500 m/s, the time difference
range calculated from Eq. (4) is 1.33 to 133 ns. Such small timedifference can be ignored directly [8].
Its principle process is as follows: the ultrasonic signal is transmitted and received by the ultrasonic probe, and a series of processing
processes such as conversion, amplification, operation and compensation of the signal are carried out to finally calculate the flow
value that is measured. For different environment, different parameters need to be set up, the algorithms for these all by automatic
adjustment, and can be set through the function display value ofwhat we need, such as the flow rate of the sea, ocean of instantaneous flow rate and the accumulation of Marine traffic, device
accumulation of running time, etc., which is very convenient todetermine the ocean flow.

2019/11/2–2019/11/3

Time

Sensordepth (m)Velocity 1(cm/s)

Velocity 2(cm/s)

Velocity 3(cm/s)

12:00
14:00
16:00
18:00
20:00
22:00
0:00
2:00
4:00
6:00
8:00
10:00
12:00

4.8
4.0
3.0
2.5
2.1
2.3
3.2
3.5
3.7
3.9
4.1
4.4
4.5

23.0
41.0
28.6
17.7
4.6
25.0
17.8
6.1
13.9
16.1
20.3
6.5
6.2

23.2
41.5
28.0
25.6
4.5
25.2
17.8
6.3
13.8
16.0
20.3
6.4
6.5

23.0
41.0
28.4
17.5
4.6
25.0
17.5
6.0
13.9
16.1
20.8
6.5
6.3

4. EXPERIMENT
We placed the designed ship and measuring equipment into thenearby ocean and measured the current velocity every 2 h. Eachmeasurement records the current time, the depth of the device’sdescent, and the ocean current velocity of the final measurement.
In Table 1, the ocean current velocity 1 is the velocity measured
by the measuring device designed in this paper. In addition, forcross-sectional comparison, we simultaneously used two current
velocity measuring devices made by other companies and sent
them down to the same depth for measurement. Among them, flow
velocity 2 was measured by using the 1 MHz Aquadopp Profiler
current meter produced by Nortek company, and flow velocity 3
was measured by using the SLD stationary doppler current meterproduced by Germany OTT company.
Through data analysis, it can be obtained that the speed measurement method designed in this paper can effectively avoid abnormal
measurement data and make the results more accurate.

5. CONCLUSION
Compared with the prior art, the device can flexibly be adjusted
according to actual needs, so that the ocean current velocity at
different depths can be measured. At the same time, there are atleast three sets of ocean current velocity detectors, and the results
measured by the three detectors are averaged as measurement data,
which further improves the measurement accuracy.

CONFLICTS OF INTEREST
The authors declare they have no conflicts of interest.

ACKNOWLEDGMENTS
The research is partly supported by the Project of Tianjin
Enterprise Science and Technology Commissioner to Tianjin

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J. Zhao et al. / Journal of Robotics, Networking and Artificial Life 7(3) 175–178

Tianke Intelligent and Manufacture Technology Co., Ltd(19JCTPJC53700). It is also supported by the Industry-University
Cooperation and Education Project (201802286009) from
Ministry of Education, China.

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AUTHORS INTRODUCTION
Mr. Jichao Zhao

Mr. Xin Ma
He is a first-year master candidate in Tianjin
University of Science and Technology. His
research is about deep learning, patternrecognition.

Dr. Fengzhi Dai
He received an M.E. and Doctor ofEngineering (PhD) from the Beijing
Institute of Technology, China in 1998
and Oita University, Japan in 2004 respectively. His main research interests areartificial intelligence, pattern recognition and robotics. He worked in National
Institute of Technology, Matsue College,
Japan from 2003 to 2009. Since October
2009, he has been the staff in Tianjin University of Science andTechnology, China, where he is currently an Associate Professorof the College of Electronic Information and Automation.

He received his bachelor’s degree fromHenan Polytechnic University in 2016.
The main research direction is the development and utilization of Marine automation equipment. Currently, he is working
as an Assistant Engineer in the North Sea
Marine environment monitoring center of
the State Oceanic Administration.

Ms. Fengkun Wang
She is a junior at Tianjin University of
Science and Technology. Her research isabout computer vision, deep learning.