Coastal Waters Research Synergy Framework

Co-ReSyF RA lecture: Bathymetry SAR Alberto Azevedo, Francisco Sancho and Florent Birrien (LNEC)

Paulo Pinto and Luísa Lamas (IH)

This project has received

funding from the European

Union’s Horizon 2020 Research

and Innovation Programme under

grant agreement no 687289

Lecture outline

Aim of this lecture

Introduction

SAR-Bathymetry estimation

Satellite sensors

Example applications

Take home message

Contact us

2

Why should we develop methodologies based on EO data to determine coastal bathymetry?

How can we use SAR satellite sensors to determine

bathymetry?

How the Co-ReSyF platform can be used to

retrieve bathymetry with SAR satellite images?

Example applications…

3Aim of this lecture

What is bathymetry?

The term "bathymetry" originally referred to the

ocean's depth relative to sea level, although it has

come to mean “submarine topography,” or the

depths and shapes of underwater terrain.

4Introduction

Traditional methods for bathymetry detection

Echo Sounders

5Introduction

Single-Beam

courtesy of the Kongsberg Maritime

Multi-Beam

Who are the users?

Research Institutions

Harbour and Coastal Management Authorities

Military Forces

Consultancy Companies

6Introduction

7SAR-Bathymetry estimation

The SAR-imagery bathymetry application provides the

coastal bathymetry underneath a given coastal area

sensed remotely by a Synthetic Aperture Radar (SAR)

satellite sensor, at a given time of acquisition.

Region of application is the continental shelf, bounded

at the coast by the wave breaking region, and at the

sea by the continental shelf break.

The output of the algorithm consists in a DEM for the

target area.

direct estimate of water depth

linear wave dispersion

relationship

Measurement of the ocean

swell wavelength and wave direction

8SAR-Bathymetry estimation

PRINCIPLE

Algorithms initially developed for TerraSAR-X images1:

1 (Brusch et al., 2011; Lehner et al., 2012)

Step 1. Get SAR satellite images over AOI and

retrieved from platform catalogue.

9Co-ReSyF processing chain

Tilt modulation (Robinson, 2004)

Hydrodynamic modulation (Robinson, 2004)

How are swell signatures

generated in a SAR image?

Step 2. Run Image Selection Protocol

Wind data from ECMWF

Select image if: 4 m/s < wind velocity < 10 m/s

Otherwise: reject image.

Wave data from Buoys and wave models (e.g. WW3)

Select image if a ”good” swell is present (long-crested, narrow-spectra waves)

Reject images with wide-spectra waves, with different directions.

10Co-ReSyF processing chain

Step 1. Get SAR satellite images over AOI and

retrieved from platform catalogue.

Step 2. Run Image Selection Protocol

Step 3. Apply radiometric and geometric

corrections to the selected images (e.g.

georeferencing, sigma0, speckel reduction, etc.).

Step 4. 2D-FFT for each sub-image and

identification of peak wave length and direction

Step 5. Inversion of the dispersion relationship.

Step 6. Create final DEM GeoTiFF file.

11Co-ReSyF processing chain

12SAR-Bathymetry estimationWave

Dispersion𝜔2 = 𝑘 𝑔 𝑡𝑎𝑛ℎ 𝑘 𝑑

Wave number (k) → wavelength (L)

Period (T) → Frequency (⍵)

(e.g. model)

Depth (d): 10m < d < 60m

250m < L

𝑘 = 𝑘𝑥2 + 𝑘𝑦

2𝑘 =

2𝜋

𝐿

𝑑 =𝐿

2𝜋𝑎𝑟𝑐𝑡𝑎𝑛ℎ

𝜔2𝐿

2𝜋𝑔

𝜔 =2𝜋

𝑇

13SAR-Bathymetry estimation

1. Choice of SAR Image

2. Definition of AOI and grid

3. 2D-FFT for each sub-image and

identification of peak wave length

and direction

4. Inversion of the dispersion relationship

14

SAR-Bathymetry flowchartS1/K5/TSXDataset

Land mask

BuoysDatabase

or WW3 model

Pre-processing of the

selected SAR images:

Radiometric, Speckle,

Sigma0, crop

For each image

Output

If image is adequate for the

application of the algorithm

FFT calculation: • Definition of the boxes• Determination of the

wavelength and direction of the swell for each FFT box

For each point of the

grid

Otherwise, STOP processing for this image

Visual check

and definition

of bathymetry

AOI

(SNAP, QGIS)

Inversion of the wave dispersion relation

(Wavelength => Depth)

Final productquality check:

Final annotation (QGIS)

Image selectionprotocol

Winddatabase

Definition of the bathymetric grid

Write output files (shp, netcdf, ascii,

etc.)

Topography or Coastlinedatabase

Parallel cloud

computing

Emodnetdatabase

15Ancillary data

Buoys data URL: http://www.hidrografico.pt/boias-ondografo.php

WaveWatch 3 URL 1: http://polar.ncep.noaa.gov/waves/wavewatch/URL 2: http://ariel.lnec.pt/node/17

EMODnetURL: http://www.emodnet.eu

European Centre for Medium-Range Weather

Forecasts URL: https://www.ecmwf.int

16SAR-Bathymetry estimation

On-going

aproaches: ...

using the original

ray-tracing method

The Co-ReSyF SAR-Bathymetry RA is prepared to work with SAR images from the following satellites:

TerraSAR-X (with 1m and 3 m resolution)URL 1: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10377/565_read-436/#/gallery/350

URL 2: https://centaurus.caf.dlr.de:8443/eoweb-ng/template/default/welcome/entryPage.vm

Sentinel-1 (IW-GRD with 10m resolution)URL 1: https://sentinel.esa.int/web/sentinel/missions/sentinel-1

URL 2: https://scihub.copernicus.eu/dhus/#/home

17Satellite sensors

Numerical modeling:

Hydrodynamic, Wave, Storm-Surges and

Morphodynamic modeling.

Coastal management

Dredging activities

Harbour constructions

Coastal erosion studies

Support to military operations abroad

18Example applications

The Co-ReSyF platform:

will incorporate EO data use into multi-disciplinary

research activities by simplifying the process.

takes advantage of state-of-the-art computational

infrastructures and abstracts the users from their

usage complexity.

will have implemented several applications and

toolboxes focused on coastal research.

EO-data methodologies are low-cost, cover a

wider area and easier to obtain when compared

with the traditional methods.

19Take home message

Presently we are developing a new methodology to improve the determination of the wavelength

with 2D-FFT and spectrum analysis.

20Take home message

Applying a 2D-ellipsoid Butterworth filter

Raw spectrum Filter spectrum Filtered spectrum

Laboratório Nacional de Engenharia Civil - Francisco Sancho (Co-ReSyF LNEC’s Coordinator)Email: fsancho@lnec.pt

- Alberto AzevedoEmail: aazevedo@lnec.pt

- Florent BirrienEmail: fbirrien@lnec.pt

Instituto Hidrográfico- José Paulo PintoEmail: Paulo.Pinto@hidrografico.pt

- Luísa LamasEmail: luisa.lamas@hidrografico.pt

21Contact us