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P A P E R
Demonstration of Biofouling MitigationMethods for Long-Term
Deploymentsof Optical Cameras
A U T H O R SJames JoslinBrian PolagyeNorthwest National
MarineRenewable Energy Center,University of Washington
88 Marine Technology Society Journa
A B S T R A C T
l
Biofoulingmitigationmeasures for optical ports can extend the
duration of ocean-ographic deployments, but there have been few
quantitative studies of field perfor-mance. Results are presented
from a 4-month field test of a stereo-optical camerasystem intended
for long-term environmental monitoring of tidal turbines. A
com-bination of passive (copper rings and ClearSignal antifouling
coating) and active(mechanical wipers) biofouling mitigation
measures are implemented on the opticalports of the two cameras and
four strobe illuminators. Biofouling on the optical portsis
monitored qualitatively by periodic diver inspections and
quantitatively by metricsdescribing the quality of the images
captured by cameras with different antifoulingtreatments. During
deployment, barnacles colonized almost every surface of thecamera
system, except the optical ports with fouling mitigation measures.
The effec-tiveness of the biofouling mitigation measures suggests
that 4-month deploymentdurations are possible, even during
conditions that would otherwise lead to severefouling and occlusion
of optical ports.Keywords: biofouling, optical cameras,
environmental and remote monitoring,field testing
attenuationmeters (ACmeters), photo-synthetically active
radiation (PAR)
Introduction
Biofouling is often a limiting factorfor long-term deployments
of ocean-ographic optical instrumentation.While this study focuses
on the foulingof camera optical ports, the methodsand outcomes may
be relevant toother instruments that rely on lighttransmission,
such as absorption-
sensors, or fluorometers (Manov et al.,2004). The sensitivity of
each opticalsensor to biofouling can vary greatly,and results from
one instrument shouldnot be extrapolated to another. As bio-logical
growth colonizes a camera’s op-tical port, image quality degrades,
andthe monitoring mission may be com-promised. With the
proliferation ofcabled ocean observatories (Chaveet al., 2009; Howe
& McGinnis, 2004;Woodroffe et al., 2008), long-term
de-ployments of optical instrumentationare becoming more common,
and bio-fouling mitigation methods are receiv-ing more attention.
Research in thisfield is generally focused on
improvingunderstanding of fundamental bio-fouling mechanisms (such
as adhesionand growth) (Phang et al., 2007; Salta
et al., 2013) or development of bio-fouling mitigation measures.
For ex-ample, Manov et al. (2004) discuss theuse of copper to
prolong deploymentsof open, enclosed, or semi-enclosed andshuttered
optical instrumentation, andDebiemme-Chouvy et al. (2011) de-scribe
applications of electrochemistyto produce a biocide on the optical
portsurface. Whelan and Regan (2006) andDelauney et al. (2010)
provide reviewsof existing biofouling mitigation tech-niques and
their implementation ondifferent sensors.
Marine renewable energy, includ-ing wave, tidal and ocean
current,and offshore wind energy, is a growingsector of the
electricity generation in-dustry that requires robust approachesto
biofouling. Energy converters and
their support structures are deployedin the marine environment
for multi-year periods and cannot expect to re-ceive significant
maintenance if theircost of energy is to be competitivewith
conventional forms of electricitygeneration. While biofouling is
possi-ble on any of the converter surfaces,general-purpose
biofouling mitigationmethods may be different from the ap-proach
taken for more sensitive com-ponents, such as sensor
transducers.Optical camera observations havebeen proposed to inform
a numberof critical environmental questions(Polagye et al., 2014),
and the shorecables for the energy converters pro-vide sufficient
power and data band-width to support high-resolutionoptical
measurements over extended
-
periods. This paper discusses the im-plementation of biofouling
mitigationmeasures on the optical ports of a cam-era system
developed for long-termmonitoring of marine energy con-verters
(Joslin et al., 2014a). This sys-tem will be recovered periodically
formaintenance (Joslin et al., 2013), andit is expected that
optical port foulingwill be the limiting factor for the inter-val
between maintenance. Methods toquantitatively evaluate the
effective-ness of these biofouling mitigationmeasures are developed
and applied toa multi-month endurance test of thecamera system.
MethodologyField Deployment Configuration
Figure 1 illustrates the stereo-optical camera system developed
formonitoring marine renewable energyconverters ( Joslin et al.,
2014a). Theintegrated system combines two Allied
Vision Technologies Manta G-201machine vision optical cameras,
fourExcelitas Technologies MVS-5000strobes, and the supporting
powerand communications infrastructure tocable the system to a
shore station. Thesystem is controlled in real time bya computer on
shore that can adjustcamera settings (e.g., frame rate, ex-posure
time, digital gain, and strobetriggering) and archive acquired
stereoimagery. The optical cameras andstrobes are marinized by
enclosingthem in aluminum pressure housingswith planar acrylic
optical ports. Mate-rial selection has been shown to influ-ence the
rate of biofouling on opticalports (Manov et al., 2004), and
al-though not optimal for biofouling,abrasion resistant acrylic is
used heredue to its transparency for optical im-agery and ease of
manufacturing forintegration in the pressure housings.
A multi-month field trial was con-ducted during early 2013 to
evaluate
January/Febru
overall system endurance (hardwareperformance, software
stability, corro-sion, and biofouling). After an initialcalibration
in a tank, the systemwas de-ployed from January 24 to February 8in
freshwater off of a dock on LakeUnion, WA. Subsequently, the
sys-tem was deployed in a saltwater envi-ronment from March 3 to
July 2 offEdmonds, WA.
For the salt-water endurance trial,the camera system was
mountedto the test frame shown in Figure 2.The Applied Physics
Laboratory vesselR/V Jack Robertson lowered the testframe to the
seabed in approximately20 m of water at a point 100 m fromshore.
Mounted to this frame, the cam-era system was suspended 5 m
abovethe seabed in a downward-lookingorientation. The power and
fiber um-bilical was terminated on shore andconnected to a data
logging com-puter. Divers from the Applied Physics
FIGURE 1
Prototype imaging system showing principal components and
scale.
FIGURE 2
Five-meter-tall field test frame on the deck ofthe deployment
vessel R/V Jack Robertson.
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Laboratory at the University of Wash-ington visually inspected
the system forbiofouling and corrosion on March 3,April 11, May 3,
and June 26.
Biofouling Mitigation MeasuresA combination of active and
pas-
sive biofouling mitigation measuresare implemented on the
optical portsof the two cameras and four strobehousings. As shown
in Figure 3, each4-inch optical port has a ring of copper(Cu)
around its perimeter, which is in-tended to suppress biofouling at
theedge of the optical port. Each housingis also equipped with a
mechanicalbrush wiper (Wi) manufactured byZebra-Tech Ltd.
(http://www.zebra-tech.co.nz/Hydro-Wiper). In addition,each of the
camera and strobe ports iscoated with the ClearSignal
foulingrelease coating (CS) produced bySevern Marine Technologies
(http://www.severnmarinetech.com/). Thiscombination of biofouling
mitiga-tion measures is selected based on thedemonstrated
effectiveness of coppershutters (Manov et al., 2004) and
thepotential additional benefit of theClearSignal coating.
Interactions be-
90 Marine Technology Society Journa
tween the copper, wiper, and releasecoating are theorized to
increase theantifouling effectiveness over eachmeasure
individually. A fully shutteredsystem was considered but
deemedundesirable for optical cameras sincefailure in the closed
position would ob-viate any data collection and largeshutters would
be subject to significantstructural loads while open in an
ener-getic environment (wave or current).Ultraviolet lights were
similarly con-sidered but not implemented due tothe uncertainty in
the appropriatewavelengths for preventing foulingand limited
documentation of thisfield in the literature (Manov et
al.,2004).
The wiper, when triggered by thecontrol computer in the shore
station,sweeps a 90° arc across the copper ringand optical port
before reversing di-rection and returning to its “home” po-sition.
This action may transfer traceamounts of copper from the ring
acrossthe optical port over the course ofmany wipe cycles, thus
increasing theeffectiveness of the wiper in isolation.This is,
however, a hypothesis thatwas not part of the test matrix
duringthis field trial (e.g., removing the cop-per ring from one of
the pressurehousings with a wiper). Throughoutthe endurance test,
the wipers actuatedonce per hour during normal systemoperation.
Electrical interference inthe serial communication bus betweenthe
shore computer and camera systemrequired the system to be shut
downon six occasions, during which thewipers were not actuated. For
the finalmonth of the deployment, the systemdid not run
continuously because ofcontinued degradation of the commu-nication
bus. To continue collectingbiofouling data during this period,
thecameras were brought on-line manuallyeach night to capture
images. For this
l
month, the mechanical wipers on thecameras actuated once every
24 h, andthe wipers on the strobes were inactive.During this same
period, the mechan-ical wiper on Camera 2 (Cu and Wi)malfunctioned
and would periodicallystop in front of the optical port aftera wipe
cycle, thereby blocking part ofthe image. This did not affect
thewiper’s ability to remove fouling butdid complicate
quantification of bio-fouling rates (see the following
section).This malfunction was caused by agradual increase in
friction betweenthe wiper and the optical port causedby fouling on
the wiper brush andmay be avoided by decreasing the in-terference
spacing between the wiperbrush and port.
Figure 4 illustrates the arrange-ment of the biofouling
mitigationmeasures on the six optical ports inthe system. Strobe 3
(Cu) was intendedto serve as a control with minimal anti-fouling
protection by disabling thewiper. However, an interruption tothe
bottle’s power supply would cause
FIGURE 3
Biofouling mitigation measures on an opticalcamera port
(preendurance test).
FIGURE 4
Arrangement of antifouling measures on cam-era system optical
ports (S denotes strobe, Cdenotes camera, and MEB denotes the
mainelectronics bottle).
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the wiper to automatically actuate, andsince the system was
power cycled onsix occasions, the results for this opticalport
cannot be considered a controlcase.
Qualitative and QuantitativeEvaluation of BiofoulingMitigation
Measures
Performance of biofouling mitiga-tion measures was monitored
quali-tatively during the endurance trial bydiver inspections and
quantitativelythrough the images captured by thecameras. During the
inspections, thedivers visually checked for the pres-ence or
absence of macrofouling onthe six optical ports and adjacent
sur-faces but did not disturb the surfacesor attempt to quantify
the degree ortype of fouling. More precise methods(ASTM D6990-05,
2011; Dobretsovet al., 2014) to quantify fouling dur-ing
inspections were not attempteddue to diver limitations. A final
quali-tative assessment of the biofoulingon the system and all of
the opticalports was conducted post-recovery onJuly 2.
During testing, the optical cam-eras collected sequences of 10
imagesat 10 frames per second once every15 min to monitor
interactions be-tween marine life and the frame (suchas fish,
crabs, and starfish) and providesome indication of test platform
integ-rity between inspection dives. To mon-itor the biofouling
levels on the cameraoptical ports, a ring of LED lights isinstalled
within the camera housing,at the perimeter of the camera lens.On an
hourly basis, sequences of10 images were captured with theseLEDs
backlighting the optical port,as shown in Figure 5. Biofouling
onthe optical port is illuminated by theLEDs and shows increased
brightnessrelative to clean conditions. This
allows the extent and severity of bio-fouling to be contrasted
for the twocombinations of mitigation treatmentsapplied to the
camera optical ports(Cu, Wi, and CS on Camera 1 versusCu and Wi on
Camera 2).
The brightness, B, of an image col-lected at time t with the LED
illu-mination activated is calculated as a
January/Febru
summation of pixel grayscale values,p(x,y), as
B tð Þ ¼Xnx¼1
Xmy¼1
p x; yð Þ ð1Þ
For this camera configuration, theimage resolution is n = 1624
andm = 1234 with a pixel grayscale rangeof 0–255.
A time-varying biofouling metric,F(t), for each acquired image
is cal-culated as
F tð Þ ¼ B tð Þ � B 0ð Þð ÞBmax � B 0ð Þð Þ : ð2Þ
where B(0) is the baseline value corre-sponding to the
brightness levels onthe first night of the deployment andBmax is
the maximum possible bright-ness value (255 × n × m). This
metrictakes on values between zero (for thebaseline images) and
unity (for a fullyobscured optical port).
Figure 6 demonstrates the effec-tiveness of this method for
quantifying
FIGURE 5
Cross-sectional schematic of camera bottledemonstrating the
photon path from LEDlights to camera lens as a reflection of
biofoul-ing or flocculent.
FIGURE 6
Demonstration images for biofouling metric calculations with LED
backlighting. (a)–(c) show rep-resentative image quality for (a) a
clear optical port with the LEDs inactive, (b) a partially
obscured(F = 0.37) optical port, and (c) a fully obscured (F = 1.0)
optical port. (d)–(f) show the correspond-ing image brightness with
the LEDs active.
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fouling on a camera’s optical port byshowing the quality of
images capturedwith external illumination alongsideimages captured
with the internalLED backlight for a clear (F = 0), blur-ry (F =
0.37), and fully obscured (F =1.0) optical port. The artificial
foulingin these images is simulated in the lab-oratory using a
light coating of siliconegrease as adhesive and fine sand to
ob-scure the image. The maximum ac-ceptable biofouling metric for
opticalimages depends on the monitoringmission intended for the
system. Mis-sions requiring high image resolution(e.g., precise
measurements of targetsize and speed using stereo processing)will
have a lower threshold than sim-pler missions (e.g., fish detection
with-in a few meters of the camera).
The hourly biofouling images werecollected in three sets of 10
imageswith camera exposure times of 10,25, and 50 ms. This range of
exposuretimes is used to evaluate the method’ssensitivity to camera
configuration.For all three exposures, images were ac-quired at a
rate of 1 frame per second,no digital gain was used, and thestrobes
were not triggered. By averag-ing the sets of 10 images
collectedeach hour, the variations in back-scattered light caused
by moving floc-culent in the water are reduced. Adaily mean
biofouling metric is cal-culated as
F tð Þ ¼XNi¼1
Fi tð Þ�
N ð3Þ
where Fi(t) is the fouling metric foreach image and N is the
number ofimages used from each day. Only im-ages collected during
nighttime hours(N = ~80) are used for each camera con-figuration to
avoid the confounding ef-fect of variable external
illumination.
92 Marine Technology Society Journa
ResultsField Deployment
Diving inspections confirmed in-creasing macrofouling on the
testframe throughout the deployment(also observed in camera
imagery),while the optical ports were observedto remain clear of
fouling until thefinal (June 26) inspection. Duringthis final
inspection, the strobe opticalports (which were no longer being
ac-tively wiped) were observed to havevarying degrees of
macrofouling whilethe camera ports remained clear. Fig-ure 7 shows
the increasing level of bio-fouling on the test frame from
cameraimages acquired over the course of thedeployment.
Biofouling Mitigation MeasuresFigure 8 shows the calculated
daily
mean biofouling metric for each cam-era from the images
collected with50-ms exposure times throughout theendurance trial.
Qualitatively similartrends were observed with 10- and25-ms
exposure settings, suggestingan insensitivity to exposure
time.Highlighted periods represent inter-ruptions in system
operation due tosoftware errors, electrical interferencewith serial
communications, and wipermalfunctions. As previously
discussed,during the last month of the deploy-ment, the system
operation was reducedto a short period every night such that
l
the number of images used for thenightly average was reduced to
10 from~80. On three occasions during thissame period, the wiper on
Camera 2(Cu and Wi) malfunctioned and par-tially obscured the
images that werecollected, preventing the calculationof a metric
for that night.
The biofouling metric valuesshown in Figure 8 are
consistentlybelow 0.04, indicating that bothcamera optical ports
remained clearthroughout the deployment, consis-tent with diver
observation and post-recovery inspection. Variation in thecamera
metrics is primarily attributedto changes in the water quality
duringthe deployment because flocculent orturbidity in the water
close to the opti-cal ports is illuminated by the LEDbacklight and
increases the value of F,without actually fouling the port.Days
with F value variations duringthe first 3 months of the
deploymentalso have increased standard devia-tions, indicating that
the variationis within the uncertainty of the mea-surement. During
the last month ofthe deployment, the F values forCamera 1 (Cu, Wi,
and CS) increasewithout an increase in the standarddeviation,
indicating a true change inthe signal. Camera 1 (Cu, Wi, and
CS)images are consistently brighter thanthose from Camera 2 (Cu and
Wi) andhave a larger range of variation. It is hy-pothesized that
the light diffraction
FIGURE 7
Camera 1 (Cu, Wi, and CS) images of biofouling on the field
testing frame from (a) March 19,(b) May 15, and (c) July 2 prior to
recovery.
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through the ClearSignal coating causesa “halo effect,”
increasing the numberof bright pixels and magnifying anyvariation
in brightness. Images ob-tained with external strobe illumina-tion
from the coated camera port arenot of markedly lesser quality than
theuncoated port, so this does not suggestthat the coating degrades
operationaleffectiveness. Counterintuitively, withthe wipers
activated only once per dayat the end of the deployment, the
foul-ing metric increases for Camera 1 (Cu,Wi, and CS), even though
one wouldexpect that the ClearSignal coatingwould mitigate fouling
more effectivelythan the bare acrylic.
Post-recovery inspection of the sys-tem revealed severe
macrofouling of
January/Febru
every surface (including the back ofthe wiper blades) except for
the cameraoptical ports. Figure 9 shows the centerof the camera
frame with a closeupview of the Camera 1 (Cu, Wi, andCS) optical
port. Fouling on the sys-tem generally consisted of barnaclesand
algae and was independent of thesurface orientation. The fouling
releasecoating onCamera 1 (Cu,Wi, andCS)and Strobe 1 (Cu, Wi, and
CS) opticalports was found to be slightly abraded(abrasion grooves
in the arc of thewipers). The degradation of the coat-ing, while
not apparent in review ofimages acquired with strobe illumina-tion,
may have contributed to the foul-ing metric increase on Camera 1
(Cu,Wi, and CS) when illuminated byLED backlighting. As the wiper
abradedthe coating, the diffraction of lightthrough the coating may
have changed,or the surface may have become moresusceptible to
microfouling, both ofwhich could contribute to an increasein the
fouling metric for Camera 1(Cu, Wi, and CS) over time.
FIGURE 8
Averaged nightly biofouling metric values with shaded standard
deviations on (a) Camera 1(Cu, Wi, and CS) and (b) Camera 2 (Cu and
Wi) optical ports throughout the endurance test.
FIGURE 9
Post-recovery biofouling on aluminum frame and camera optical
ports.
ary 2015 Volume 49 Number 1 93
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The strobe optical ports, whichwere notmonitored during the
deploy-ment, other than qualitatively for thepresence of fouling by
the diver in-spections, are shown after recovery inFigure 10. Due
to the wipers being dis-abled over the last month of the
de-ployment for the strobes (whereas thecamera wipers were still
actuated onceeach night), all four optical ports ex-hibit some
barnacle growth. Strobe 1(Cu, Wi, and CS) exhibits the mostgrowth,
though upon recovery, thewiper blade for this bottle was notedto
have rotated out of the plane ofthe optical port, thusmaking it
ineffec-tive for a longer portion of the test thanthe wipers on the
other strobe ports.Coincidentally, the Strobe 1 (Cu, Wi,and CS)
optical port is also coatedwith ClearSignal, suggesting that
the
94 Marine Technology Society Journa
passive fouling mitigation measures(Cu and CS) would not be
sufficientfor multi-month deployments in ad-verse fouling
conditions. Qualitativecomparison of the camera and strobeoptical
ports demonstrates the effec-tiveness of the mechanical wiper
tomitigate fouling (Figures 9 and 10).
Discussion andConclusions
There are expected to be strong sea-sonal and spatial variations
in biofoul-ing within a region the size of PugetSound (Dickey &
Chang, 2001).The dates of this field deploymentwere chosen to span
the spring andsummer seasons, during which foulingis most severe.
Since the endurance
l
trial took place in calm waters withthe camera system entirely
within thephotic zone, the biofouling observedduring the trial was
likely to be moresevere than would occur at the antici-pated
deployment depth of 50 m.
Monitoring biofouling levels oncamera optical ports in a
quantitativemanner is complicated by the variablenature of the
imagery. This method ofbacklighting the optical ports withLEDs in
the absence of external illumi-nation provides a means to
quantifytemporal changes in the optical portclarity. While there
was no apparentdegradation in image quality duringthe deployment,
the biofouling metricwas able to detect more subtle changesthan the
human eye. An upward trendin this metric could, therefore, be
usedto predict the need for system mainte-nance before the optical
port is visiblydegraded, thus affording more time toplan system
recovery (essential in ma-rine renewable energy environments)and
reducing system downtime.
The combination of mechanicaland passive biofouling
mitigationmethods effectively prevented macro-fouling growth that
would have other-wise degraded system performance.The clarity of
the camera optical portsin comparison to adjacent surfaces, asshown
in Figure 9, is intuitively repre-sentative of this effectiveness.
Withno discernible difference between theclarity of the two camera
optical ports,the benefit of the ClearSignal coatingwas minimal
under the test conditions.The abrasion of the coating by thewiper
brush suggests that the combina-tion of these two antifouling
measuresis potentially detrimental with a wiperactuation frequency
shorter than anhour. If a system deployment were tobe power
constrained, and the wiperscould not be run as frequently (aswould
be the case for an autonomous
FIGURE 10
Biofouling on strobe optical ports with (a) Strobe 1 (Cu, Wi,
and CS; though wiper rotated out ofplane during test and was not
effective for unknown period), (b) Strobe 2 (Cu andWi), (c) Strobe
4(Cu and Wi), and (d) Strobe 3 (Cu with six wiper actuations).
Ordering identical to treatment sche-matic in Figure 4.
-
deployment), then a transparent coat-ing may be helpful to
maintain opticalport clarity.
Separating the antifouling con-tributions of the copper rings
fromthe wipers is difficult due to the lackof a true control.
However, evaluationof the surfaces on the outside of thecopper
rings, which were not in con-tact with the wipers, suggests that
thecopper rings directly reduce foulingwithin a proximity of
several milli-meters. Similarly, for the optical porton Strobe 3
(Cu), which had fewerwiper activations, the most severe bio-fouling
was at the center of the opticalport, furthest from the copper
ring.One hypothesis is that the presenceof the ring contributed to
this pattern,but without further testing, it is notpossible to
distinguish causality fromcorrelation.
While the mechanical wipers playan important role in biofouling
miti-gation, they are only effective if theydo not fail themselves.
Integrating thewiper mount into the camera pressurevessel to
control the interference spac-ing between the wiper and optical
portwould reduce the chance of wiperfailures. For the prototype
system de-scribed here, the spacing was set byhand prior to
deployment, whichmay have resulted in inconsistent in-terference
and caused the wiper mal-functions. The modular design of
theZebra-Tech Hydrowiper allows foreasy integration, but caution
shouldbe taken to ensure proper and securealignment. These
modifications havebeen incorporated into the camera sys-tem design
for the next iteration in sys-tem development (Joslin et al.,
2014b;Rush et al., 2014).
For future deployments, measuringturbidity independently from
the cam-eras and overlaying the measurementwith the biofouling
metric may allow
correlations to be identified. This shouldbe possible during
subsequent systemdeployments, since the overall moni-toring package
can support additionalinstrumentation for an optical turbid-ity
measurement. Biofouling of thisturbidity measurement must be
con-sidered similarly to the cameras toavoid confounding the
results.
The clarity of images obtained dur-ing this endurance trial
suggests thatoptical camera deployments of atleast 4 months are
possible evenunder adverse fouling conditions withthese biofouling
mitigation measures.The results for these biofouling mitiga-tion
measures are consistent with theresults for copper shuttered
systemsdescribed in Manov et al. (2004),which have been shown to be
effectivefor multi-month deployments. Whilethe mechanical wiper
does not protectthe optical port by covering it betweencycles like
the shutter, it does not haveto be activated every time data
areacquired. The cleaning effect of thebrush may also be greater
than non-contact shuttered systems. While thisresult is most
applicable to opticalmonitoring in Puget Sound, projectselsewhere
involving long-term deploy-ments of optical cameras may benefitfrom
similar biofouling mitigationmeasures. Future deployments of
thiscamera system for environmentalmonitoring of tidal energy
projectswill provide additional informationabout seasonal
effectiveness of themeasures employed.
AcknowledgmentsThe authors would like to thank
Jeffery Thomas for use of his facilitiesat Sunset Bay Marina,
Jim Thomsonfor coordination of the field deploy-ment and inspection
dives, SandraParker-Stetter and Sharon Kramer for
January/Febru
recommendations on system testing,Capt. Andy Reay-Ellers for
captainingthe R/V Jack Robertson, Alex DeKlerkfor designing and
fabricating the im-aging frame, Joe Talbert and TimMcGinnis for
building the shore cableumbilical, Keith van Thiel for the de-sign
of the pressure housings and op-tical ports, Rick Towler and
KresimirWilliams for insight into componentselection and
stereographic calibration,and last but certainly not least,
RandySindelar for his adaptable custom elec-tronics for power and
communication.
Author Information:James Joslin and Brian PolagyeNorthwest
National MarineRenewable Energy CenterUniversity of Washington,Box
352600, Seattle, WA 98195-2600Email:
[email protected];[email protected]
ReferencesASTMD6990-05. 2011. Standard practice for
evaluating biofouling resistance and physical
performance of marine coating systems. West
Conshohoken, PA, USA: ASTM International.
http://dx.doi.org/10.1520/D6990-05R11.
Chave, A.D., Arrott, M., Farcas, C., &
Farcas, E. 2009. Cyberinfrastructure for
the US ocean observatories initiative: Enabling
interactive observation in the ocean. In:
Proceedings of MTS/IEEE Oceans 2009 –
Europe. Bremen, Germany: MTS/IEEE.
Debiemme-Chouvy, C., Hua, U., Hui, F.,
Duval, J.L., Festy, D., & Cachet, H. 2011.
Electrochemical treatments using tin oxide
anode to prevent biofouling. Electrochem
Acta. 56(28):10364-70. http://dx.doi.org/
10.1016/j.electacta.2011.03.025.
Delauney, L., Compere, C., & Lehaitre, M.
2010. Biofouling protection for marine envi-
ronmental sensors. Ocean Sci. 6(2):503-11.
http://dx.doi.org/10.5194/os-6-503-2010.
ary 2015 Volume 49 Number 1 95
-
Dickey, T.D., & Chang, G.C. 2001. Recent
advances and future visions: Temporal vari-
ability of optical and bio-optical properties
of the ocean. Oceanography. 14(3):15-29.
http://dx.doi.org/10.5670/oceanog.2001.21.
Dobretsov, S.,Williams, D.N.,&Thomason, J.
2014. Biofouling methods. Oxford, UK:
John Wiley & Sons, Ltd. http://dx.doi.org/
10.1002/9781118336144.
Howe, B., & McGinnis, T. 2004. Sensor
networks for cabled ocean observatories. In:
International Symposium on Underwater
Technology. UT: IEEE. pp. 113-20. http://
dx.doi.org/10.1109/UT.2004.1405499.
Joslin, J., Celkis, E., Roper, C., Stewart, A.,
& Polagye, B. 2013. Development of an
adaptable monitoring package for marine re-
newable energy. In: Proceedings of the MTS/
IEEE Oceans 2013 Conference. San Diego,
CA: MTS/IEEE.
Joslin, J., Polagye, B., & Parker-Stetter, S.
2014a. Development of a hybrid optical-
acoustical camera system for monitoring tidal
turbines. J Appl Remote Sens. 8:083633-1-25.
http://dx.doi.org/10.1117/1.JRS.8.083633.
Joslin, J., Polagye, B., Rush, B., & Stewart, A.
2014b. Development of an adaptable moni-
toring package for marine renewable energy
projects: Part II. Hydrodynamic performance.
In: Proceedings of the 2nd Marine Energy
Technology Symposium. Seattle, WA: Global
Marine Renewable Energy Conference.
Manov, D.V., Chang, G.C., & Dickey, T.D.
2004. Methods for reducing biofouling on
moored optical sensors. J Atmos Ocean Tech.
21:958-68. http://dx.doi.org/10.1175/1520-
0426(2004)0212.0.CO;2.
Phang, I.Y., Aldred, N., Clare, A.S., &
Vancso, G.J. 2007. Effective marine antifoul-
ing coatings: Studying barnacle cyprid adhe-
sion with atomic force microscopy. Nano.
1:36-41.
Polagye, B., Copping, A., Suryan, R., Brown-
Saracino, J., & Smith, C. 2014. Instrumentation
for monitoring around marine renewable en-
ergy converters: Workshop final report. Pacific
96 Marine Technology Society Journa
Northwest National Laboratory, Seattle, WA.
Tech. Rep. PNNL-23110.
Rush, B., Joslin, J., Stewart, A., & Polagye, B.
2014. Development of an adaptable monitoring
package for marine renewable energy projects
Part I: Conceptual design and operation. In:
Proceedings of the 2nd Marine Energy Technol-
ogy Symposium. Seattle, WA: Global Marine
Renewable Energy Conference.
Salta, M., Wharton, J.A., Blache, Y., Stokes,
K.R., & Briand, J.F. 2013. Marine biofilms
on artificial surfaces: structure and dynamics.
Environ Microbiol. 15(11):2879-93.
Whelan, A., & Regan, F. 2006. Antifouling
strategies for marine and riverine sensors.
J Environ Monitor. 8(9):880-6. http://dx.doi.
org/10.1039/b603289c.
Woodroffe, A.M., Pridie, S.W., & Druce, G.
2008. The Neptune Canada junction box—
Interfacing science instruments to sub-sea
cabled observatories. In: Proceedings of MTS/
IEEE Kobe Techno-Ocean. Kobe, Japan:
MTS/IEEE.
l