Video-derived Navigational and Recreational CSIs at Teignmouth

Mark Davidson – University of Plymouth, UKIsmael Marino-Tapia - University of Plymouth, UK

The CoastView Project

Contents1. Navigation

Frame of reference.Algorithm development• Location of channel marker buoys • Location of navigation channel & hazardous sandbarsAssociated CSI

2. Recreation (Bather safety)Frame of reference Location of bathing hazards• Hydrodynamics (2HD model-aided waves + currents)• Hazardous sand bar locationAssociated CSI

3. Information delivery (Web Page)Week to a pageLast six SpringsMet-Ocean data

The frame of reference

Strategic objective:

3. Intervention procedure

4. Evaluation procedure

CSIs MonitoringSystem knowledgeMeasurementModelling

Operational objective (s)

Reference state

Current state

1. Quantitative state concept

2. Benchmark

Long-term management vision & policy

Describes how part, or all of the strategic objective will be achieved in a four-stage process

“Improve maritime safety and avoid human, economical and ecological disasters”

Video derived buoy positions

1.CSI: Sandbar-Buoy Inter-distance (SBID)

4. Evaluation procedure

SBID < X m / Invade buffer region

Current SBID and channel orientation

3. Move buoys2. Benchmarking exceeded

Frame of reference: Navigation at Teignmouth

“To ensure that the buoys accurately mark the channel perimeter to minimize the possibility of

ships going aground”

Video derived channel location (from intertidal contours and breaking patterns)

“Improve maritime safety and avoid human, economical and ecological

disasters”

Vessels grounding on sandbanks and reefs• Inappropriate position of channel markers and poor signalling of hazards

Buoys drag and move from original position (specially during storms)

Bottom accretes and channel position changes

“Improve maritime safety and avoid human, economical and ecological

disasters”

Vessels grounding on sandbanks and reefs• Consequences

Karachi, Pakistan July 2003 Stranded on channel perimeter at entrance of port

Ship broke, spilling 12,000 – 15,000 tons of crude oil.

Biggest spill on Pakistan history

Where When How Consequences

Santa Fe, Galapagos I., Ecuador

Jan 2001 Ran aground while steering into harbour

3 million litres crude oil spilled.

Back

“To ensure that the buoys accurately mark the channel perimeter to minimize the possibility of ships going

aground”

Navigational problems at Teignmouth• Sanbanks and channel are very dynamic features

Difficult to position buoys adequately relative to channelHence to maintain an effective dredging strategy

• In the past there have been a few cases of ship grounding at the site.• Our aim is to help the manager avoid a potentially catastrophic situation

Back

Video recognition of navigation channel markers

Topics to cover

• Algorithm for extraction of buoy position.

ConceptThe algorithm at work

• Examples of data retrieved and data quality considerations

Buoy 2

Buoy 4

Video recognition of navigation channel markers

Algorithm for extraction of buoy position: The concept• Visual characteristics of buoy vary greatly depending on: Ambient light, tidal stage, poor visibility (rain, fog), obstructions, etc.

Video recognition of navigation channel markers

Algorithm for extraction of buoy position: The concept

1. Reduce the search area

2. Isolate red band

3. Detection of buoy

i=find{max[(Iμ(x) – Imin(x))y]}

4. Transform oblique coordinates to planview (XYZtide to UV)

Video recognition of navigation channel markers

Extraction of buoy position: Algorithm at work

CAMERA 4: Inner buoys CAMERA 5: Outer buoys

Video recognition of navigation channel markers

Extraction of buoy position: Algorithm at work• Method is not infallible • But is simple and robust

Examples of data retrieved: Buoy 2

Jan Feb MarchApril May June July Aug Sep Oct Nov Dec300

325

350

375

400

425

450Cross-shore buoy positions from Jan to November 2003

Months in 2003

Cro

ss-s

ho

re p

osi

tion

fro

m e

stu

ary

mo

uth

(m

) Two methods coincideerrorsTwo methods different

Jan Feb MarchApril May June July Aug Sep Oct Nov Dec310

320

330

340

350

360

370

380

Months in 2003

Cro

ss-s

hore

positio

n fro

m e

stu

ary

(m

) Time series of cross-shore position for buoy 2

Jan Feb MarchApril May June July Aug Sep Oct Nov Dec310

320

330

340

350

360

370

380

Buoy X-shore movementTidesWaves

Time series of cross-shore position for buoy 2

Cro

ss-s

hore

positio

n fro

m e

stu

ary

(m

)

Sep Oct Nov Dec340

345

350

355

360

365

370

375

380

Cro

ss-s

hore

pos

ition

from

est

uary

(m

)

Data quality considerations: Buoy 4• Highly non-stationary time series (variance changes and level

shifts).

• VERY ‘gappy’ structure (only day time, depends on image quality)

• Traditional methods for outlier removal don’t work (differentiation, FFT filtering, moving averages, etc.)

Jan Feb March April May June July Aug Sep Oct Nov Dec Jan200

300

400

500

600

700

800

900Time series of alongshore position (Buoy 4)

Alo

ngsh

ore

posi

tion

from

Nes

s (m

)

Two methods differentTwo methods coincide

Jan Feb March April May June July Aug Sep Oct Nov Dec Jan200

300

400

500

600

700Time series of alongshore position (Buoy 4)

Alo

ng

sho

re p

osi

tion

fro

m N

ess

(m

)

Data quality considerations: Buoy 4

Wavelet analysis

• Specially useful for treating non-stationary time series.

• Analysis in the time-frequency domain (identifies time of variance change at a given frequency.

May June0

200

400

600

800

1000

1200

Ene

rgy

dens

ity /

or

Buo

y po

sitio

n (m

)

Derivative time seriesBuoy positions from video

Interpolated buoy positionsWavelet at 0.16 cycles/hr (6 hrs)

Data quality considerations: Buoy 4

Routine for outlier removal

• Outliers located at energy peaks but use derivative to aid in the identification process.

• Before modification value needs to be compared with a local average to avoid “data erosion”.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan200

300

400

500

600

700Cleaned time series for Buoy 4

Alo

ng

sho

re b

uo

y p

osi

tion

(m

)

Interpolated time seriesIdentified outliersFiltered data

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan200

300

400

500

600

700Cleaned time series for Buoy 4

Alo

ng

sho

re b

uo

y p

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tion

(m

)

A Navigation CSI

An interactive tool that allows:

• Calculation of buoy – sandbank interdistace

• Geographical location (‘in useful coordinates’) of channel entrance

• Could function as a guide for dredging activities

30 January 200423 January 2004

Low -1.48 m ODN

Concluding remarks: Navigation CSI

Finish outlier removal technique (wavelet, derivatives and moving averages)

Make algorithm for buoy detection operational

Create data base for life of the Argus station at Teignmouth

Obtain (IBM?) fixed intertidal contour

Program the interactive tool for CSI calculation/ assessment

Risk maps 4. Evaluation procedure

Frame of reference: Recreation at Teignmouth

“Improve bather safety”

“Maintain awareness of potential dangers for beach users, such as regions of strong currents

or hazardous sandbanks”Numerical model-aided

current patterns

Video derived location of sanbanks

3. Update map 2. Benchmarking exceeded

Risk map no longer valid

(changing morphology)

Current conditions

Bathing Hazards

Flow patterns from numerical model • Siegle, E. 2003 used hydrodynamic model MIKE 21 and video-extracted bathymetries to model flow patterns under different morphological set-ups.

Location of hazardous sandbanks• Using rectified images, hazardous sandbaks where beach users might be cut off as tide rises can be identified.

Bathing Hazards

Risk maps• Use numerical model realizations and rectified images of system at low tide to generate simplified risk maps given a morphological configuration.

Concluding remarks: Recreation CSI

Simple concept easily accomplished – (preliminary?)

Manager has interest of implementing it on summer 2004

Possibility of following the whole frame of reference in practice.