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Lunchtime Discussion at IPRC. 20 February 2013. Movement of plastic debris on beaches ~indication of W EBCAM MONITARING A ND INVESTIGATION in situ~. National Institute for Land and Infrastructure Management (NILIM) Coastal, Marine and Disaster Prevention Department

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movement of plastic debris on beaches indication of w ebcam monitaring a nd investigation in situ

Lunchtime Discussion at IPRC

20February 2013

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

TomoyaKataoka

Hirofumi Hinata

plastic pollution
Plastic pollution
  • Risk caused by plastic debris
    • Threats to marine animals

ex. Ingestion of plastics, Entangled sea turtles

    • Pollution by toxic chemicals in plastic debris

ex. 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

Jean

Jean

Outflow

Outflow

Outflow

Wash ashore

Return offshore

Return offshore

To Pacific ocean

Wash ashore

Kurochio current

Outflow

our focus
Our focus

Today’s First Topic

  • 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 SecondTopic

webcam monitoring sites
Webcam monitoring sites

【Today’s topic】

Tsushima Current: 4 sites

Nine monitoring sites

(a)Tsushima

(b)Wajima

(c)Tobishima)

(d) Wakkanai

(e) Ishigaki

(f)Tanegashima

Tsushima current:4 sites

Tsushima current: 4 sites

Kuroshio current: 4 sites

Tsushima current: 4 sites

Kuroshio current: 4 sites

Oyashio: 1 site

(i) Shiriya

(g)Muroto

(h)Niijima

webcam monitoring system
Webcam monitoring system

The webcam monitoring system

Saving in a built-in

Local storage

(SDHC card, 32GB)

Transmission via the Internet

Our laboratory in NILIM

Webcam

Solar panels

Time

Control box

Storage batteries

Photographs

Operating time  every two hours from 7:00 to 15:00 (i.e., five operations every day)

Taking photographs  five photographs every operating time

Daily number of photographs  25 photographs (i.e., 5 (operations)×5 (photos)=25)

animation of webcam image
Animation of webcam image

Tobishima

December 2010

technique for detecting plastic debri s pixels
Technique for detecting plastic debris pixels
  • 1. Generation of color references
  • Color 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 references
  • Plastic debris pixels are detected using color references and a composite method.

L*-u* coordinate

L*-v* coordinate

u*-v* coordinate

L*

L*

v*

u*

v*

u*

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

generation of color references
Generation of color references

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

,

G

E

B

C

D

H

A

F

Three ellipses form the ellipsoid body

Ellipsoid body in the CIELUV color space  Color references

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

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

detection using crs and composite
Detection using CRs and composite

【Detection of plastic debris using a single photograph】

Plastic debris with various colors  detection

e.g., Driftwoods  misdetection

,

Plastic debris  white

Detection using one photograph

Using one photo

misdetected

Using photos for three days

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 pixels

Plastic debris

Plastic debris

Driftwood

For 3 days

Not plastic debris

calculation of debris quantity
Calculation of debris quantity

Beached plastic debris quantity  Covered area

Projective transformation1)

GPS

(X, Y): Geographic coordinate

(x, y): Photographic coordinate

Coefficients

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

Covered area A

Webcam image

A = N × a

N: Number of plastic pixels

a : Area of a single pixel

Converted image

0 5 10

m

Error of computed area: within5.0%

time series of plastic debris quantity
Time series of plastic debris quantity

Err.: 19%, Corr.: 0.93

Err.: 12%, Corr.: 0.81

clean-up

Err.: 20%, Corr.: 0.94

Err.: 21%, Corr.: 0.73

clean-up

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).

what factor causes underestimation
What factor causes underestimation?

Period:1month (April , 2011)

Time: 7:00, 9:00, 11:00, 13:00, 15:00

Plastic Debris: Three type

(Tank (Blue), Cylinder Buoy (White), Cube Buoy (White))

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

Cylinder

Top

Cube

Top

Tank

Top

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

Cylinder

Side

Cube

Side

Tank

Side

monthly variability of debris color side
Monthly variability of debris color (Side)

Blue (Tank)

White(Cylinder)

White (Cube)

E

W

Morning

E

W

Noon

E

W

Afternoon

comparison with wind data
Comparison with wind data

Factors for variability of debris quantity

Webcam sites

Wind obs. sites

Wind

Wakkanai

2010/10/9

Wind

Qin: Quantity of debris washed ashore

Qout: Quantity of debris returned offshore

Wind

Tobishima

2010/11/5

Wave

Wind

Near shore current

Qin> Qout Increase

Qin < Qout decrease

Qin= Qout not change

Wajima

2010/12/5

Wind

Tsushima

2010/11/22

summary
Summary
  • 【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