MOVEMENT OF PLASTIC DEBRIS ON BEACHES

~INDICATION OF WEBCAM MONITARINGAND INVESTIGATION IN SITU~

National Institute for Land and Infrastructure Management (NILIM)Coastal, Marine and Disaster Prevention Department

Coastal Zone Systems Division

Tomoya KataokaHirofumi Hinata

Lunchtime Discussion at IPRC 20 February 2013

Kurochio current

Plastic pollution

Risk caused by plastic debris Threats to marine animalsex. Ingestion of plastics, Entangled sea turtles Pollution by toxic chemicals in

plastic debrisex. Lead that leach into beach (Nakashima et al.,

EST, 2012) Transportation of plastic

debris Outflow from sources Washing ashore Returning to ocean Washing ashore

… To Pacific ocean

Jean

JeanJean

Wash ashore

Outflow

Outflow

Outflow

Return offshore

Wash ashore

Return offshore

To Pacific ocean

Outflow

Transportation process in East Asian Seas Monitoring quantity of debris at multiple sites Webcam monitoring (Low cost and Few labor) Simulating drifting debris Ocean circulation model and its quantity at multiple site

Beaching process in nearshore (included returning process offshore) Movement of debris on beach Investigation in situ

Today’s First Topic

Today’s Second Topic

Our focus

(e) Ishigaki

(a)Tsushima (b)Wajima (c)Tobishima ）

(d) Wakkanai

(i) Shiriya(h)Niijima(g)Muroto

(f)Tanegashima

Kuroshio Current

Tsushima Current

East China

Sea

Pacific Ocean

Webcam

JapanSea

OkhotskSea

(b)

(c)

(d)

(a)

(e)

(i)

(h)(g)

(f)

Nine monitoring sites

Tsushima current ： 4 sitesTsushima current: 4 sitesKuroshio current: 4 sitesTsushima current: 4 sitesKuroshio current: 4 sitesOyashio: 1 site

【 Today’s topic】Tsushima Current: 4 sites

Webcam monitoring sites

The webcam monitoring system

Webcam

Control box Storage

batteries

Our laboratory in NILIM

Transmission via

the Internet

Time

Photographs

Solar panels

Operating time every two hours from 7:00 to 15:00 (i.e., five operations every day)Taking photographs five photographs every operating timeDaily number of photographs 25 photographs (i.e., 5 (operations)× 5 (photos)=25)

Saving in a built-inLocal storage

(SDHC card, 32GB)

Webcam monitoring system

Animation of webcam image

Kuroshio Current

Tsushima Current

East China

Sea

Pacific Ocean

Webcam

JapanSea

OkhotskSea

(b)

(c)

(d)

(a)

(e)

(i)

(h)(g)

(f)

Tobishima

December 2010

1. Generation of color referencesColor references for detecting pixels of plastic debris are generated using CIELUV color space.

CIELUV color space:• This space is one of three-dimensional color spaces• Colors are expressed by (L*, u*, v*).

2. Detection of plastic debris pixels using the color referencesPlastic debris pixels are detected using color references and a

composite method.

v*

u*

u*-v* coordinate

v*u*

L*-v* coordinateL*-u* coordinate

L*L*

1) T. Kataoka et al.(2012), MPB, 64, 1829-1836

Technique for detecting plastic debris pixels

,

C

Color distribution of plastic debris “C” in the CIELUV color space.

Color references, which are generated from webcam images at Tobishima.

Three ellipses form the ellipsoid bodyEllipsoid body in the CIELUV color space Color references

GE

AH

D

F

B

Nov./10-Mar./11 Apr./11-Aug./11

white A p1, p2, p3, p4, p5 41755 0.6 0.8

B p2, p3, p4, p5 23491 0.5 0.5C p1 8712 0.6 0.6

D p1, p3, p4, p5 19100 0.5 0.6E p1 5000 0.5 0.5F p1, p2, p3, p4, p5 24000 0.5 0.5

green G p1, p2, p3, p4, p5 62000 0.5 0.5

blue H p1, p3, p4, p5 33200 0.5 0.5

Threshold valuesEllipsoidbody

yellow

red

Typicalcolor Periodsa Number of

selected pixels

aPeriods: p1, November 21-27, 2010; p2, December 14-21, 2010; p3, February 16-22, 2011; p4, April 1-7, 2011; p5, May 18-24, 2011

Generation of color references

, 【 Detection of plastic debris using a single photograph】

Plastic debris with various colors detectione.g., Driftwoods misdetection

Detection using one photograph

misdetected

Composite method:(L*, u*, v*) of the pixel is frequently located in the ellipsoid body of a certain color using photographs for three days.

Plastic debris pixelsNot plastic debris

For 3 days

Plastic debris

Using one photo

Plastic debris white

Using photos for three days

Driftwood Plastic debris

Detection using CRs and composite

154

321

ybxb

bybxbX

154

321

ycxc

cycxcY

Projective transformation1)

1) S. Magome et al.(2007),JO,63,761-773

52,1, icb ii

(X, Y): Geographic coordinate

(x, y): Photographic coordinate

Coefficients

A = N × aN : Number of plastic pixelsa : Area of a single pixel

Covered area A

Beached plastic debris quantity Covered area

GPS

Webcam image

Converted image

Error of computed area: within5.0%

Calculation of debris quantity

m0 5 10

Kuroshio Current

Tsushima Current

East China

Sea

Pacific Ocean

JapanSea

OkhotskSea

Webcam

Wakkanai2010/10/9

Tobishima2010/11/5

Wajima2010/12/5

Tsushima2010/11/22

clean-up

clean-up

Err.: 19%, Corr.: 0.93

Err.: 12%, Corr.: 0.81

Err.: 20%, Corr.: 0.94

Err.: 21%, Corr.: 0.73

Time series of daily covered areas Short-term fluctuations depended on changes in the weather conditions (e.g., amount of sunlight, wind).Removing the short-term fluctuations Time series of 30-day moving averages (bold line).

Time series of plastic debris quantity

Period:1month (April , 2011)Time: 7:00, 9:00, 11:00, 13:00, 15:00Plastic Debris: Three type(Tank (Blue), Cylinder Buoy (White), Cube Buoy (White))

CylinderSide

CylinderTopCube

Top

CubeSide

TankTop

TankSide

Calculate average value and standard deviation of (L, u, v)

Calculate average value and standard deviation of (L, u, v)

What factor causes underestimation?

Blue (Tank) White (Cube)White(Cylinder)

E W

Morning

E W

E WAfternoon

Noon

Monthly variability of debris color (Side)

Wakkanai2010/10/9

Tobishima2010/11/5

Wajima2010/12/5

Tsushima2010/11/22

Webcam sites

Wind obs. sites

Comparison with wind data

Wind

Wind

Wind

Wind

Qin: Quantity of debris washed ashore

Qout: Quantity of debris returned offshore

Factors for variability of debris quantity

Qin > Qout IncreaseQin < Qout decreaseQin = Qout not change

Near shore current

Wave

Wind

【Major conclusion for webcam monitoring】• Sequential monitoring of quantity of debris at multiple sites Succeeded• Debris quantity not only vary by intensification of westerly wind

but also by other factors At Wajima and Tsushima increase according to intensification

westerly wind for Nov. 2010 – Mar. 2011 At Wakkanai and Tobishima Not vary despite intensification of

westerly wind At Tsushima Increase greatly despite no westerly wind

• Factor of the underestimation Strong dependence on sunlight angle• Using only photographs on certain time when variability of debris color is

the lowest Measurement error can be minimized

【Major conclusion for Investigation in situ】• Found seasonal variation of movement and quantity of debris• Established residual function of debris• Estimated residence time on Wadahama beach

152 days (Three type buoys) 98 days (PET bottle)

• Obtained system characteristics on Wadahama beach

Summary