Video-derived Navigational and Recreational CSIs at Teignmouth Mark Davidson – University of...
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Transcript of Video-derived Navigational and Recreational CSIs at Teignmouth Mark Davidson – University of...
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
osi
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.