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PASSIVE AND ACTIVE: REMOTE SURVEY SOLUTIONS FOR THE NEARSHORE

An Integrated Approach Featuring Remote Sensing, ALB and Acoustic Techniques

Don VenturaFugro Pelagos, Inc.Coastal GeoTools 2017, North Charleston, SCFebruary 2017

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Introduction

Photos: http://www.shedexpedition.com/wp-content/uploads/2014/04/Virginia-Beach-sky-view.jpg; http://gpmoorephoto.com/blog/wp-content/uploads/2012/11/Icy-Bay-Mount-Saint-Elias-Alaska-Photo.jpg;

• Emphasis on nearshore surveys and the coastal hinterland has increased over the past few years.

• Generated by concerns over various issues, including:

• sea level rise due to climate change • directly-attributable man-made issues such as

land subsidence through extraction of valuable mineral and water resources;

• growth of, and reliance on, a seaborne Blue Economy delivering goods as efficiently as possible;

• concerns over erosion or damage to nearshore ecosystems necessitating additional focus on habitat mapping and environmental surveys in general

• an increasing percentage of the world’s human population residing in close proximity to the coast which places extra emphasis monitoring of this margin

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Nearshore Mapping

• Where possible, the most cost effective approaches to mapping nearshore, high-impact coastlines – notwithstanding absolute accuracy standards - are:

• Remote sensing from wide-area satellite imagery ($)• Satellite Derived Bathymetry – SDB• Multispectral Imagery• Satellite Altimetry

• Airborne active sensor techniques ($$)• High-resolution RGB Photography• Hyperspectral Imagery• Topographic Lidar• Topo-Bathymetric Lidar• Bathymetric Lidar

• Traditional acoustic hydrographic survey techniques ($$$)• MBES, SBES, SSS etc.

• All of the above are affected in different ways by metocean conditions in the nearshore environment: water clarity, seabed colour and rugosity, platform dynamics and operational parameter windows etc.

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Remote Sensing Techniques (Geospatial)

Low Altitude Corridor LiDAR

(Helicopter)

High Altitude Photogrammetry

Low High

Low

HIg

h

Accuracy

Altit

ude Medium Altitude

LiDAR

Airborne Bathymetric

LiDAR

Satellite Imagery

Mobile / Terrestrial Laser

ScanningSonar

Bathymetric Survey

High Altitude SAR (Radar)

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Satellite Derived Bathymetry (SDB) and Imagery

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Approaches to use optical satellite imagery

Indicative / empirical methods:

Relate brightness and log-ratios to water depth

Photogrammetric / stereo approach:

Find matching points on seafloor

Physics based multispectral approach:

Resolve light-transfer and retrieve optical properties

Source: DigitalGlobe WorldView-2, acquisition date: 2011-10-30

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Physics-Based Approach: Overview

Image courtesy of the Centre for Spatial Environmental Research, University of Queensland

Schema of the light signal measured by optical satellites

Physical realization of the system

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Raw Satellite Imagery: Heron Island WV2

Includes copyrighted material of DigitalGlobe. WorldView-2, acquisition date: 2011-10-30

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Atmospheric Effects Removed

Includes copyrighted material of DigitalGlobe. WorldView-2, acquisition date: 2011-10-30

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Water Column Removed

Includes copyrighted material of DigitalGlobe. WorldView-2, acquisition date: 2011-10-30

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SDB Process Example: Antigua – ‘Raw Image’

Correction applied: Atmosphere andadjacency

Water surface effects

Water column

Provides general information, but typically not well suited for aquatic and benthic analysis

Antigua

Northeast Antigua

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SDB Process Example: Antigua – SubSurface Reflectance

Correction applied: Atmosphere andadjacency

Water surface effects

Water column

Antigua

Provides more detailed information on geomorphologic zoning, spatial and spectral patterns of the seafloor and benthic habitats.

Sat. data used: Moderate res. (15m grid)

Northeast Antigua

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SDB Process Example: Antigua – Seafloor Reflectance

Correction applied: Atmosphere andadjacency

Water surface effects

Water column

Antigua

Sat. data used: Moderate res. (15m grid)

Northeast Antigua

Provides very detailed information on geomorphologic zoning, spatial and spectral patterns of the seafloor and benthic habitats. It represent a clear view to the surface being corrected for water column effects and a perfect baseline for benthic habitat mapping.

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SDB Process Example: Antigua – Satellite Derived Bathymetry

Correction applied: Atmosphere andadjacency

Water surface effects

Water column

Sat. data used: Moderate res. (15m grid)

Provides bathymetric information in a dense grid. Data are mapped using EOMAP’s physics based inversion algorithms, which has been applied in more than 40 areas worldwide.

Antigua

Northeast Antigua

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Can we trust the cheapest option?

We can, if we apply an integrated approach….• SDB can provide very effective cost-effective and initial coverage of a suitable, clear-

water nearshore area• We can take the initial results and do at least three things:

• Use the data to provide reconnaissance information for follow-on, more easily quantifiable survey techniques (put an otherwise poorly charted area in focus)

• Conduct more discrete, higher-resolution surveys of the most critical areas for development or coastal defence/monitoring

• Use the active sensor data to refine the original SDB results to create a better-defined, integrated product which can start to attain accuracies acceptable to a wider stakeholder group

• We can also start to recognize the benefits of well-developed algorithms of satellite imagery to extract even more habitat info from the coastal zone.

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Airborne Lidar Bathymetry (ALB)

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Accurate depth measurement Very cost effective over full operational window Speed Mobility Rapid response Rapid data assessment: storm damage, grounding, seasonal change Completion of surveys in small environmental windows Survey in difficult or impossible areas for vessels Safe in dangerous areas Simultaneously survey water, structures, and land

What’s the overall benefit of ALB?

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Closing the Gap with ALB

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North Jeddah – Chart Comparison

Merged with deeper MBES data in the channels, the overall effect provides a seamless land-water interface

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Point Clouds and Surfaces

• Many of the biggest changes seen during ALB surfaces are often at the coastline itself.

• Wholesale changes in topography and land usage are not uncommon

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RGB Imagery

• Aerial imagery is a hugely useful tool in ALB surveys

• Object detection and classification

• Confirmation of specific high points in the Lidar point cloud

• Source data for ortho-rectified mosaic products

• Good for hydrographic notes – instant proof!

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Bare Earth Surface Elevation Model (DEM)

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Intensity/Backscatter Raster Imagery

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Applications: Eelgrass Mapping

• Boundary maps for eelgrass and aquaculture farms.

• Density counts and maps of aquaculture farming.

• Hydrographic chart data for navigation and aquaculture farming.

• Baseline for change detection.

Image courtesy of Tim Webster, COGS

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Florida PanhandlePost Hurricane Ivan 2004

Applications: Imagery Fusion for Habitat Mapping

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Hi-Res Infrastructure and Coastal Surveys(Integration of Laser and MBES Acoustic Techniques)

Fugro-EOMAP SDB Webinar – 10/11 May 2016

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BOAT-MAP™

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By incorporating mobile laser scanning into our near shore marine surveying services, Fugro brings BOAT-MAP™ a specialized solution for nearshore marine surveys that need to span the waterline.

BOAT-MAP™

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Erosion Zones: Averaged Annual Cliff Retreat (cm/year)

Santa Barbara, California – Annual Retreat (cm) & Estimated Cliff Migration

Applications: Track Changes: Coastal Retreat

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Port of Los Angeles – Integrated MBES and LLS

Piles Beneath Wharf

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Port Infrastructure: Sand Spit Napoleonic Fort, UK

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Summary

• Alternative solutions to the nearshore mapping of many areas are feasible• They will not always attain navigational charting standards• They don’t need to for non-charting agencies• We need to have an open mind as to how we better serve a greater stakeholder group• There are ways and means of improving initial results from SDB with iterative processes

utilizing ALB full waveform algorithms and a GT approach• There are ways and means of improving final coverage and data density which agrees

within a reasonable tolerance for the benefit of many clients• Key is to quantify what we have and apply appropriate risk to the data usage

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Thank You