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Depth estimation using video cameras in the South-West
Erwin Bergsma member of the Coastal Processes Research Group, Plymouth University
Thursday 15 October 2015, Annual partner’s meeting, Newton Abbot
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Contents
Personal background 1. Study site (short)
2. Camera system (short)
3. Depth estimation using cameras (long)
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• MSc. at Delft University of Technology – Environmental Fluid Mechanics
• Turbulence in shallow jet flows – Coastal Engineering:
• Inlet breaching (2010 Xyntia storm) modelling; Pertuis de Maumusson, France
• PhD at Plymouth University – Coastal Oceanography
• Bathymetry estimation using video cameras
• Freelance Coastal Engineer, Hydraulic and morphodynamic modeller and Programming Specialist:
– Modelling: [Delft3D, Xbeach, SWAN, SWASH and Unibest package] – Programming: [MatLAB, Python] – Africa : Gabon, Senegal. Asia : Fujairah (UAE), Abu Dhabi, Bahrain, Iraq.
Personal Background
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Study Site
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Study Site Porthtowan, Cornwall
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Geographical orientation
Camera system
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Camera system
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Camera system
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Camera system
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Why do we want to estimate depths?
Residual coastal strength: first defence against flooding,
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Why do we want to estimate depths?
Residual coastal strength: first defence against flooding, depth estimates between storms to access residual strength
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Why do we want to estimate depths?
Residual coastal strength: first defence against flooding, depth estimates between storms to access residual strength
Calm wave conditions are not required to get an
accurate depth estimation with the video cameras
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Why do we want to estimate depths?
Beach user /Swimmer’s Safety:
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Why do we want to estimate depths?
Beach user /Swimmer’s Safety:
Where those patterns on the left before?
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Why do we want to estimate depths?
Beach user /Swimmer’s Safety:
Where those patterns on the left before?
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How does it works?
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nearshore
offshore
How does it works?
Relation between water waves to get a depth:
𝝈2 = 𝑔𝑔 tanh 𝒌𝒉 ⇔ c = 𝑔𝑘
tanh 𝑔𝒅
c = wave speed. Lower speed = shallower, higher speed = deeper
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Summary
1. Relation between shallow water waves and depth
2. “Tracking” waves with video cameras to find the wave’s speed.
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Results
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Results
SURVEY
ESTIMATE
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Results
SURVEY
ESTIMATE
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Results
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Results Hourly depth estimates:
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Results
Depth estimate – mean cross shore
profile over 1,5 years
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Results
Depth estimate – mean cross shore
profile over 1,5 years
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Results
Depth estimate – mean cross shore
profile over 1,5 years
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Results Pre stormy winter 2014 Post stormy winter 2014
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Results Pre stormy winter 2014 Post stormy winter 2014
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Results Pre stormy winter 2014 Post stormy winter 2014
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Limitations? • Depth estimation in the shallowest parts less accurate:
linear dispersion relation is valid in lesser extend • The more off-shore the harder the waves are
distinguishable by the cameras
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Further work and challenges
• Higher resolution cameras. Leads to more possibilities further offshore
• Mobile cBathy stations, short sampling periods • cBathy applied on X-band radar • cBathy from a UAV / drone • cBathy with satellite imagery • Large scale cBathy deployment over the world
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Thank you
Coastal Processes Research Group: www.coastalprocesses.org [email protected] Erwin W. J. Bergsma: [email protected] or [email protected]
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Extra slides about cBathy
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nearshore
offshore
How does it works?
Relation between water waves to get a depth:
𝝈2 = 𝑔𝑔 tanh 𝒌𝒉 ⇔ c = 𝑔𝑘
tanh 𝑔𝒅
We want to find wave frequency(𝝈) and wave number 𝒌
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How does it works?
• Wave frequency σ = 1𝑤𝑤𝑤𝑤 𝑝𝑤𝑝𝑝𝑝𝑝
has to do with time (t) and period it takes to complete one wave
• Wave number k = 1𝑤𝑤𝑤𝑤 𝑙𝑤𝑙𝑔𝑙𝑙
has to do with space (x,y) and length of one complete wave
one complete wave
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How does it works?
So how do we get the wave frequency and wave number?
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How does it works? 2ND relation: Similarity of pixel intensities to water level elevation:
𝜼 𝒙,𝒚, 𝒕 = �𝐴𝑙 sin 𝝈𝒏𝑡 −𝒌𝒙,𝒏 𝑥 −𝒌𝒚,𝒏 𝑦 + 𝜑𝑁
𝑙=1
1𝑤𝑤𝑤𝑤 𝑝𝑤𝑝𝑝𝑝𝑝
1
𝑤𝑤𝑤𝑤 𝑙𝑤𝑙𝑔𝑡𝑙
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How does it works?
To find the waveWe only have to estimate the distance between (for k) and the speed (𝝈𝒏) of
the waves in time with video cameras;