ARTICLE IN PRESS

Ocean Engineering 36 (2009) 633–640

Contents lists available at ScienceDirect

Ocean Engineering

0029-80

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/oceaneng

Paving the way for a future underwater omni-directional wireless opticalcommunication systems

Greg Baiden a, Yassiah Bissiri a,b,�, Andrew Masoti a

a Laurentian University, Sudbury, Canadab Penguin Automated Systems Inc., Sudbury, Canada

a r t i c l e i n f o

Article history:

Received 24 November 2007

Accepted 3 March 2009Available online 29 March 2009

Keywords:

Optical communication

Wireless

Scatter

Attenuation

Turbidity

Data rate

Viewing angle

Ocean

Exploration

Underwater construction

18/$ - see front matter Crown Copyright & 20

016/j.oceaneng.2009.03.007

esponding author at: Laurentian University, S

ail address: ybissiri@penguinasi.com (Y. Bissir

a b s t r a c t

To lay down the foundation for an underwater omni-directional optical communication system for tele-

operation, we tested a point-to-point optical communication system, using laser-emitting diodes

(LEDs). The LEDs used in the test emitted light in the green and blue light spectrum and were tested in a

pool and in a tank filled with lake water. The primary objective of these tests was to get profiles of the

behaviors of such communication systems with respect to water characteristics such as turbidity levels,

prior to building the proposed omni-directional optical communication. The results of the tests

indicated that turbidity level, viewing angle and separation distance plays a significant role in the

behavior of blue light in water. Furthermore, it was possible to graph the profile of the behavior of light

with respect to the parameters of interest. The results of the tests and related research are discussed in

this paper.

Crown Copyright & 2009 Published by Elsevier Ltd. All rights reserved.

1. Introduction

This research was inspired by the need to explore differentoptions with respect to the future of the mining industry, but it isalso applicable to other industries such as construction, militaryand underwater inspections. Current mining activities occur ondry surface, where exploration is conducted and mining operationfor extraction follows as soon as it is proven that a given depositcan be economically exploited. Recent technological advances(such as equipment size, automation and better communicationsystems) have made it possible for mining companies to minelarger mineral deposits at a faster rate to respond to an everincreasing worldwide demand. It is clear that at this pace, theworld will soon be faced with severe shortages of criticalresources needed to sustain the world growing economies ifnothing is done in the long run to address this critical issue(Farrell, 2008). Several solutions ranging from responsible con-sumption and sustainability to space exploration for naturalresources have been proposed in the past (Dasgupta and Heal,1979). If the first proposed solution is virtually impossible to take,the second is far from being achieved due to lack of appropriateadvanced technologies (Muff et al., 2004).

09 Published by Elsevier Ltd. All

udbury, Canada.

i).

While these solutions are being investigated, it is urgent thataccessible solutions be implemented to deal with the problem inthe near future. Water covers nearly three quarters of the earth’ssurface in oceans as well as rivers and lakes (Hirvonen, 1993) andtherefore, developing a technology that will allow exploration,construction and mining underwater may be the immediate stepto take while waiting for other solutions to be seriouslyinvestigated. Any underwater communication technology forexploration and mining (which will certainly require a swarm oftele-operated equipment) should take into account the followingfour important factors:

�

righ

real-time remote operation with equipment moving freelyunderwater,

� high data transfer rate for reliable information exchanges, � high bandwidth to handle several video channels and physical

control parameters transmitted simultaneously

� low bit errors rate for data integrity

Early underwater remotely operated vehicle (ROV) requiredumbilical cords to transmit power and relay information betweenan operator and a ROV. However, the length of the cable limitsexcursion distance and the fact that several ROV may be workingin the same area produces the risk of entanglement, therebylimiting the ability of freedom of movement crucial to accom-plishing tasks in exploration, construction or mining. Recent

ts reserved.

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0.1

0.05

0200 300 400 500 600 700 800

Wavelength (nm)

Scat

teri

ng c

oeff

icie

nt (

m^-

1)

Scattering Coefficient of Pure Seawater

Fig. 2. Scatter coefficient of seawater (Bohren and Huffman, 1983).

G. Baiden et al. / Ocean Engineering 36 (2009) 633–640634

efforts have involved in developing networking protocols forwireless underwater acoustic communication (Akyildiz et al.,2004). However, this technology comes with severe limitationssuch as limited bandwidth (critical in operating multiplemachines), high bit error rates due to multipath scenarios,impulse noise and higher latency as excursion distances becomelarger (Stojanovic, 2003). Radio frequency (RF) as a mean ofunderwater information carrier is limited by its high attenuationrate in water (Butler, 1978).

Developed in the 1960s for military and aerospace applica-tions, free space optical (FSO) communications have matured tothe point that installations worldwide are on the rise (Garlingtonand Long, 2005). This growing interest in FSO is justified by theneed for greater bandwidth and the security that the technologyprovides (point-to-point data transfer). FSO technology requiresno spectrum licensing, and installation takes only days tocomplete when compared to fiber systems (Akella et al., 2005).Current FSO systems are capable of transmitting data at rates upto 2.5 Gbps over distances of several kilometers, which is morethan enough for most broadband applications (Wee, 2004). Thesecharacteristics make FSO an attractive technology for underwatercommunication systems provided similar characteristics can beexported to underwater applications. The transmitter and receiverfor an underwater link can be very similar to a FSO link in air, withthe major difference being the wavelength of operation. However,ocean water has widely varying optical properties depending onlocation, time of day, organic and inorganic content, as well astemporal variations such as turbulence. To construct an opticallink it is important to understand these properties. The loss ofoptical energy while traversing the link arises from bothabsorption and scattering. Scattering also adversely impacts thelink by introducing multipath dispersion.

Color and clarity of water, which is generally dependant uponits constituent components, may have a significant impact of thebehavior of light in water (Apel, 1987). Individual trajectories ofphotons in a collimated beam of light passing through a containerof water will result in the disappearance of some photons withinthe water due to absorption. The energy of these photons will beconverted into heat. The trajectories of other photons will changesuddenly due to scatter while maintaining their level of energy(Arst, 2003). Seawater is composed of primarily H2O, whichabsorbs heavily towards the red spectrum. It also containsdissolved salts like NaCl, MgCl2, Na2SO4, CaCl2 and KCl thatabsorb light at specific wavelengths. As shown in Fig. 1, pure

3

2

1

0200 300 400 500 600 700

Wavelength (nm)

Abs

orpt

ion

(m^-

1)

Absorption Coefficient of Seawater

Fig. 1. Absorption coefficient of seawater (Bohren and Huffman, 1983).

seawater is absorptive except around 400–500 nm wavelength,which is the blue-green region of the visible light spectrum. Fig. 2shows that minimum scattering occurs around 560–600 nmwavelength.

FSO communication systems operating in an underwaterenvironment face a number of challenges. Lasers or opticalcommunication can achieve high data rate with limited distancebecause of loss due to photons absorption and scatter in water(Fletcher, 2000). The field of view, a small cross-sectional area of alaser point and an omni-directional light source may represent aserious challenge on its own as it dictates the range of operationfor any future vehicle wanting to communicate with the lightsource and remain within a minimum light power limit for lightdetectors to generate a distinguishable signal. High-power laserscapable of achieving longer distances can consume a large amountof power which can be a problem for underwater remotelycontrolled systems. If FSO technology is to be used underwater, itis critical that the communication profile with respect to thewater characteristic and operational environment be understood.This paper addresses the challenges of FSO technology applied toan underwater environment through tests performed in thelaboratory condition. The tests were limited to three criticalparameters: distance, turbidity and transmitter–receiver orienta-tion (field of view (FOV)). These variables are easy to control in alaboratory conditions and represent the variables that are mostsignificant during operation. Other parameters, such as watertemperature and water chemistry, were not investigated in thispaper.

2. Testing design and procedures

For these experiments a pair of optical transceiver, the model1013C1 High-Bandwidth Underwater Transceiver (as shown inFig. 3), specially designed for underwater use and allows 10megabits per second (Mbps) full duplex communication betweentwo fully submerged platforms, was purchased from AmbaluxCorporation. The device consists of a series of high-intensity laser-emitting diodes (LEDs) operating in the blue light spectrum.Although the device is unidirectional, a fiber optic link closes thecommunication loop to allow full Ethernet capability. Theunidirectionality of the device does not change the objective ofthese tests which is to profile data rate with respect to watercharacteristics.

ARTICLE IN PRESS

Fig. 3. Underwater transmitter and receiver (Ambalux Corporation).

PC (sending) PC (receivingand response))

10 base FL Multimode Fiber

Fiber to copper

converter

Optical transmitter Optical receiver

FSO link

CAT5e

Fig. 4. Description of the communication system.

G. Baiden et al. / Ocean Engineering 36 (2009) 633–640 635

Two categories of tests were performed to determine theprofile of data rate (in Mbps) with respect to distance, field ofview and turbidity: pool and tank tests (controlled environment).

3. Communication system design

The communication design for these tests, illustrated in Fig. 4,consists of a sending and receiving PC. The sending PC isconnected to a fiber-to-copper converter with a CAT5enetworking cable through a typical Ethernet connection. A datapacket from the copper Ethernet network is transmitted to anoptical cable connected to the underwater FSO transmittingdevice which sends light signal to an optical receiver thatcontains a concentrating lens and a photo multiplier tube orPMT. Electronic components sent the received data onto a fibercoming from the underwater FSO receiver. The data packet thentraveled on another fiber-to-copper converter before beingconverted to an electrical signal on the copper Ethernetattached to the receiving PC. If the receiving PC needs torespond to a data packet, it will send a data packet to the fiber-to-copper converter which delivers the data down a fiberconnected to the fiber-to-copper converter at the sending PCend. This fiber closes the communication loop between the twoPCs.

In this experiment, it is important to note that the transmis-sion underwater is done in one direction as the preliminaryobjective of this work is to determine the behavior of LEDs inwater with respect to parameters mentioned previously.

It allows the PCs to send and receive data between each otherwhile tracking the rate at which communication is occurring. Asrequest/response or streaming data rate test is performed, data is

recorded on a spreadsheet that tracks all the variables in theexperiment.

4. Network testing and benchmarking

Two computers, equipped with the network performancetesting software NETPERF (a freeware network benchmarkingutility created by Hewlett-Packard, 1996) are used to run data andtransaction rate tests to benchmark the communications system.NETPERF is used to establish a performance rating with TCP andUDP protocols. These are the most common protocols used for andother network communications, and are also supported by theoptical communication system and its Ethernet backbone.Benchmarking the communication system using data and trans-action rates is an important step to understanding how well thesystem operates in varying underwater conditions. In a potentialtele-operation scenario, a minimum data rate should be obtainedto sustain a digital video feed sufficient for tele-operation. Thismeans that a minimum data rate as well as a minimum time delaymust be met to determine the fitness of the communicationssystem. Since digital video quality data is both time sensitive anddata rate sensitive, the response of these sensitivities to environ-mental conditions is critical knowledge. Streaming data rate testswere conducted for both the UDP and TCP protocols, and therequest and response tests were conducted for the TCP protocolonly. A streaming data rate test works by a client computercreating a connection to a server computer using either the TCP orUDP protocol. The client computer then streams data unidirec-tionally to the server, which responds when the packets arereceived. The number of bits sent by the streamer and received bythe server per second is calculated and reported by the networkbenchmarking utility as megabits per second.

The other important metric adopted in this experiment is themeasure of transactions per second (T/s) for a given request andresponse size. T/s represents the time taken for a request to bemade to the server followed by a response. The number ofrequests and responses that can occur in one second makes up T/s.The size of the request/response packet can be varied to reflect thescenario being analyzed. In this study, the request packet size is1024 bytes and the response packet size is 256 bytes. These sizesrepresent a typical packet size for control data. T/s can be used todetermine the quantity of packets that can be sent and received inone second. If this number proves to be too low, then slowerresponse times may be experienced.

Note that data rate can be derived from transaction rates. Forexample, in the case of the request response test performed, themaximum transaction rate is approximately 512 T/s for a send sizeof 1024 bytes (or 8192 bits). The bitrate to match the transactionrate in this case can be derived as follows:

Bitrate ¼ 8192 bits=T� 512 T=s ¼ 4:2 Mbps (1)

ARTICLE IN PRESS

Fig. 5. View of the pool test. Fig. 6. Description of tank test.

326239

182 102.5

G. Baiden et al. / Ocean Engineering 36 (2009) 633–640636

The transaction rates being displayed in the figures obtainedform the different tests are the TCP request/response transactionrates in transactions per second.

Receiver

Transmitter

Fig. 7. Description of the tank test mechanism.

4.1. Pool tests

Pool tests were conducted by changing the transmitter locationin a manner to define the communication system operating rangethrough offset distances at varying separation distances asdescribed in the procedure below. The same communicationsetup previously described was used for this experiment. In pooltests, control on ambient light levels was possible along withfairly accurate control on separation distance and viewing angle.However, varying turbidity was not an option. Therefore, theresults fell short on defining how the system responded to varyinglevels of suspended particulate.

The test procedure consisted of spacing the transmitter at aninitial distance of one meter in alignment from the receiver (itsposition remained fixed). The transmitter is incrementally offsetfrom the receiver until communication is lost. To find theoptimum offset distance (distance just before communication islost), the offset distance is incrementally decreased until com-munication is regained and the corresponding offset distancerecorded is the threshold offset distance (TOD). The separationdistance between the transmitter and the receiver is increased,and the same offset procedure is repeated to determine the TODfor different separation distances. The procedure is illustrated inFig. 5.

4.2. Tank tests

The tank test consists of a 21-in. inside diameter, 3.65-m longhigh-density polyethylene black plastic pipe. The pipe had threesections cut out one third of its length to allow access to the tankas shown in Fig. 6. Four separation distances between thetransmitter and the receiver were set up. The position of thereceiver was kept constant while that of the transmitter wasvaried.

The viewing angle was determined by incrementally rotatingthe transmitter by five degree until communication was lost. Atthis point, the rotating device is rotated back to its previousposition and a lower increment angle is applied until commu-

nication is lost for an ‘‘accurate’’ determination of the optimumviewing angle. The experiment is illustrated in Fig. 7.

5. Turbidity measurement

Turbidity measurement was limited to the Secchi method(Potsma, 1961), a simple but effective turbidity measurementmethod. The tank was filled with water from Ramsey Lake, a lakelocated in Sudbury, Ontario, Canada. The water in the tank wasmade more turbid by increasing suspended particulate concen-tration consisting of fine silt collected from the bottom of Ramseylake. To increase the significance of the turbidity test, an alternateparticulate composed of iron oxide was also used.

5.1. Notation

To simplify the representation of the results, the followingnotation is adopted:

�

Separation distances: x1 ¼102.5 cm, x2 ¼ 182 cm, x3 ¼ 239 cmand x4 ¼ 326 cm. � Turbidity level: labeled as t0 to t12, with t0 being the turbidity

level for clear water and the remaining turbidity are obtainedfrom adding more silt in the water and, therefore, decreasingthe Secchi depth by approximately 8–10 cm. The particulateswere collected from the bottom of Ramsey Lake (Sudbury,Ontario) to mimic an experiment close to that of Ramsey Lake.

ARTICLE IN PRESS

2.3 Threshold Offset Distances vs.

G. Baiden et al. / Ocean Engineering 36 (2009) 633–640 637

�

Dat

a R

ate

(Mbp

s)

Fig

2

- d0

(m)

Separation Distances

A threshold viewing angle (TVA) is defined as the minimumviewing angle at which communication is lost when one of thecommunication devices is rotated with respect to a virtual axisthat contains the segment represented by the center ofgravities of the two devices when they are aligned.

1.7ce

�

1.4

1.1

0.8hres

hold

Offs

et D

ista

n

Communication data are measured in transactions per second,because it gives a finer resolution for the TCP request response.The transaction rate can be converted to bitrate by multiplyingthe sent data size (in bytes or bits) by the transaction rate.

Note that the TVA is equivalent to the threshold offset distance,since one of them can be derived from the other by the tangent

function or its inverse function.

0.50 2 4 6 8 10 12 14 16 18 20 22

Separation Distance - d (m)

T

Fig. 9. Threshold offset distance as a function of offset distance.

600

500

400

300

200

100

00 10 20 30 40 50 60 70 80 90

Viewing Angle (Degrees)

Tran

sact

ion

Rat

e (T

/s)

Sample Decay Rates ShowingThreshold Viewing Anfgle

t1x0t1x1t1x2t1x3

Fig. 10. Transaction rate as function of viewing angle for turbidity t1.

500

400

300

ion

Rat

e (T

/s)

Request/Response Decay Rates at t0(clear Water Tank)

6. Results and discussion

6.1. Pool tests

The pool test results for separation distances x1 ¼ 3 m,x2 ¼ 3 m, x3 ¼ 5 m and x4 ¼ 21 m are shown in Figs. 6 and 7. Tofine tune the test, variability of offset distances for each separationdistance were, respectively, 5, 11, 14 and finally 30 cm forseparation distance x3. Fig. 8 shows that the data rate profile isalmost identical for all the separation distances. A change of offsetdistance by a few centimeters (relative to the separation distance)causes the data rate to drop from full communication potential(8.2 Mbps) to no communication at all (0 Mbps).

The offset value at which communication suddenly drops tozero is called the threshold offset distance, and it is plotted inFig. 9 against the four separation distances. It indicates that asseparation distance increases, so does the threshold offsetdistance.

In the pool tests, only separation distance was considered thevariable as we did not have permission from Laurentian Universityto add particulate in the pool.

6.2. Tank tests

The experiment in the tank was designed to offset ourlimitation of controlling the parameters of interest in the pool.The results of the tank tests are shown in Figs. 10–14. Fig. 10 showshow the threshold viewing angle for a step t1 turbidity lever atdifferent separation distances x1, x2 and x3. The angle at whichcommunication is the strongest followed by sudden decay whenslightly incremented correspond to the TVA. The profiles of theresponses with respect to the viewing angle parameter are verysimilar for all three separation distances. It shows a sudden decay

8

6

4

2

00 0.5 1 1.5 2 2.5

Offset Distance - d0 (m)

x0 -2mx1 -3mx2-5mx3-21m

TCP Datarate Response to Offset Distance for allseparation distances

. 8. TCP data rate response to offset distance at different separation distances.

200

100

050 60 70 80

Viewing Angle (Degrees)

t0x0t0x1t0x2t0x3Tr

ansa

ct

Fig. 11. Transaction rate as a function of viewing angle for turbidity t0.

of transaction rate from full communication to no communicationat a given viewing angle. For clarity, the request/response decayrates are plotted for turbidity t0 (clear water) and t1, respectively,in Figs. 11 and 12. Although Figs. 11 and 12 show similar graphprofiles, it is clear that increasing the turbidity from t0 to t1

decreases the TVA. The TVA is recorded for the all the turbidities

ARTICLE IN PRESS

500

400

300

200

100

040 50

Viewing Angle (Degrees)60 70 80

t1x0t1x1t1x2t1x3Tr

ansa

ctio

n R

ate

(T/s

)

Request/Response Decay Rates at1st Turbidity Step (t1)

Fig. 12. Transaction rate as a function of viewing angle for turbidity t1.

90

80

70

60

50

40

30

20

10

05 15 25 35 45 55 65 75 85

Secci Depth (cm)1st Testx0

1st Testx2

2nd Testx0

2nd Testx2

2nd Testx1

2nd Testx3

1st Testx1

1st Testx3

Thre

shol

d Vi

ewin

g A

ngle

(deg

rees

)

Ingluence of Turbidity Level on TVA for allthe separation distances

Fig. 13. Influence of turbidity level on TVA for all the separation distances.

100

80

60

40

20

0

10080

6040

20350

300

250200

150

100

Separatio

n Dista

nce (cm

)

Secchi Depth (cm)

TV

A (

degr

ees)

Fig. 14. TVA as a function of separation distances and turbidity levels.

G. Baiden et al. / Ocean Engineering 36 (2009) 633–640638

(t0 to t12) and all separations distances are shown in Fig. 10 whichrepresents the summary of all the experiments performed for thetank test and a replicate to confirm the results. The replication ofdata has shown consistency in our measurements with littlevariation observed that could be attributed to the quality ofmixing particulate in the water (Masoti, 2005). It is however clearthat the trends are consistent. The plot indicates that there existsan angle, the threshold viewing angle, at which communication islost abruptly at given water characteristic. Fig. 12 shows the plotsof the transaction with respect to all the separation distances andthe turbidity levels.

These graphs show similarities in their profile with differentTVA. It is clear from Figs. 11 and 12 that turbidity and viewingangle have a significant impact on transaction rate.

Fig. 13 represents the plots of the TVA with respect to Secchidepth (or turbidity level) at all the different separation distanceswith replication. To show the consistency of the tests, each setwas duplicated. It appears from the graphs that TVA decreases forincreasing turbidity level (increasing Secchi depth value).

For example at a separation distance of x0, the TVA is about 601at a turbidity level of t0 whereas the TVA is about 801 for aturbidity level of t6. The same profile is observed for the remainingseparation distances. The plots show a rapid decay in TVAas turbidity levels increase. Finally, the TVA was plotted as afunction of two variables that are the turbidity level and theseparation distances and the graph is shown in Fig. 14. The plotshown in Fig. 8 indicates a clear pattern of the response of the TVAwith respect to the two variables. This 3-D plot indicates thatan increase in separation distances and turbidity levels decreasesthe TVA.

6.3. Significance of the TVA

For this study, the threshold viewing angle is defined as theminimum angle at which communication is lost when one of thedevices is rotated with respect to their alignment axis. The TVAand/or TOD are very important if LEDs are to be used to transferdata wirelessly under water for UUV. The TVA indicates the regionwhere data transfer is still possible as shown in Fig. 15.

For a given turbidity and separation distance, a vessel has toremain within +TVA and –TVA to receive or send data through anLED.

It is important to point out that the TVA is different from theincidence angle of the transmitter beam. The difference isexplained in the following section.

Tx Rx

Separation distance

CommunicationZone

+ TVA

- TVA

Fig. 15. Illustration of the concept of TVA and communication zone with respect to

viewing angle.

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G. Baiden et al. / Ocean Engineering 36 (2009) 633–640 639

7. Discussion

Light is an ensemble of photons that are absorbed andscattered by water, suspended particles and dissolved matter asthey travel through a sample. The absorption coefficient, a(l), is ameasure of the conversion of radiant energy to heat and chemicalenergy. It is numerically equal to the fraction of energy absorbedfrom a light beam per unit of distance traveled in an absorbingmedium (Smith and Baker, 1981). Light scattering changes thedirection of photon transport, ‘‘dispersing’’ them as they penetratea sample, without changing their wavelength. The scatteringcoefficient, b(l), is equal to the fraction of energy dispersed from alight beam per unit of distance traveled in a scattering medium, incm�1. The attenuation coefficient, c(l) ¼ a(l)+b(l), is a measure ofthe light loss from the combined effects of scattering andabsorption over a unit length of travel in an attenuating medium.The Beer–Lambert law gives a relation between the attenuationcoefficient, separation distances and irradiance for a light beamwith a given wavelength as follows (Killinger, 2002):

IðzÞ ¼ I0 expð�cðlÞ zÞ (2)

where, I0 is the irradiance_at_surface; I(z) the irradiance_at_depth_z; z the depth; c(l) the attenuation_coefficient_for_wave_length_l

The intensity of irradiance is a function of the photons arrivalrate at a given cross section of the medium in which they travel.Eq. (2) shows that as distance increases the intensity, the numberof photon decreases at a given cross section. As photons areabsorbed and scatter, their ‘‘detectability’’ become probabilistic atany given point for a given period of time. The generation ofphoton in an optical transmitter for any given of time follows aPoisson process (Alexander, 1997) as described in Eq. (3)

Pðn=TÞ ¼ðrTÞne�rT

n!r ¼ mean arrival rate in photons=second

Pðn=TÞ ¼ probability of counting n photons in a T seconds

observation time (3)

Fig. 16 illustrates the difference between the angle of incidencewhen the light beam leaves the transmitter due to scatters and theTVA, which represent the minimum angle at whichcommunication is lost or the probability of detecting photons atthe detector (optical receiver) is at its lowest.

Usually an incidence angle is made up of photons that travelingstraight and the ones that are deflected because of particles in the

Tx Rx

Separation distance

CommunicationZone

+ TVA

-TVA

+ i/2

-i/2

Fig. 16. Illustration of the difference between incidence angle and TVA.

water. Scattered photons create a multipath system that injects alot of noise in the communication if not properly filtered.

8. Conclusion and future work

This study has established that turbidity level, viewing angleand separation distance plays a significant role in the behavior ofblue light in water. Further more, it was possible to graph theprofile of the behavior of light with respect to the parameters ofinterest. TVA and TOD have been defined for future application ofunderwater navigation. If a transceiver capable of covering a 3-Denvironment is to be built, TVA values need to be taken intoconsideration with respect to its geometric form. To this date, anomni-directional optical system was built (inspired by this study),tested, and the test results will be published in a futurepublication. A brief description of phase one of the omni-directional transceiver and the testing mechanism are describedin the following sections.

The optical transmitter designed was constructed from multi-LED PCB panels that share the same input signal and powersupply. The optical transmitter system comprises four key designfeatures:

(a)

a geometric form that allows for the omni-directionalpropagation of light while still relying on planar printedcircuit boards;

(b)

a modular design capable of easily repairing inoperative LEDpanels;

(c)

wide angle surface mount bright blue LEDs (468 nm centralwavelength);

(d)

high-speed switching transistors; and (e) TTL compatible signal input for ease of interfacing to various

digital signal sources.

Two geometric forms were modeled to assess their relativemerits against the above design criteria. Although two geome-trical forms (icosahedrons and spherical hexagon) were consid-ered, the icosahedrons was retained because of its simplicity ingeometry and its ability to provide complete free space coverageusing the selected LED as shown in Fig. 17.

Fig. 17. First built underwater omni-directional optical transmitter.

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G. Baiden et al. / Ocean Engineering 36 (2009) 633–640640

The transmitter shown in Fig. 15 has been tested in a lake inNorthern Ontario and the tests results will be published shortly.

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