Sylvain Capo,Bertrand Lubac and Driss Bru

A semi‐analytical model for SPOT bathymetric inversion:an historical morphodynamical approach of the Arcachon inlet evolution since 20 years

Sylvain Capo,Vulnerability of coastal ecosystems to global change and extreme events

Biarritz 18-21 October 2011

INFOLITTORAL Project

The aim of the project is to develop and promotes operational remote sensing productsfor coastal users and managers through environmental indicators

In coastal regions, bathymetric data are critical to understand the ecosystem

Use of VHR multispectral remote sensing : most effective and low cost solution

Ocean Color approach: Bathymetric inversion algorithm development adaptation of theQAA to low spectral resolution SPOT

Morphodynamics of the Arcachon Lagoon inlet (Kalideos)

Sylvain Capo,

Ocean Color: characterizing ocean color (satellite reflectance) as a function of the water column constituents and depth Objective : linking AOP to IOP (ligth attenuation by absorption a and scattering b)Remote sensing sensors measure the reflected solar radiation

Bathymetric inversion algorithm

Sylvain Capo,

•3 step process : SPOT model derived from the QAA (Lee et al., 2002)•1 : absorption (a) and backscattering (bb) terms are derived from Rrs•2 : The vertical diffuse attenuation (Kd) is derived from a and bb terms•3 : Depth is derived from Kd , bottom substrate albedo and optically deep water reflectance

•Model interest: All informations are derived from SPOT scene…except the water level

Bathymetric Application for pixels where the bottom substrate contribution is significant Bio optical Models to derive water column constituents concentration [C]

Semi-Analytical Model for coastal systems

Sylvain Capo,

Bathymetric inversion algorithm

In energetic areas, Remote sensing = Very High spatial ResolutionSPOT, FORMOSAT, PLEIADES, IKONOS

VHR (2.510m) frequency (~ 1 to 5-6 days) coverage (~ 10 à 60km)

Model ran on the 2007-09-13 SPOT and soundings data

Bathymetric inversion algorithm

Sylvain Capo,

For measured depth +4 to -6m

Relative error ~ 10%Absolute averaged difference ~ 0,9mRoot Mean Square Error ~ 1,2m

(Capo et al., In prep)

Morphological entities

Northern Channel (NC)•~ 0.8 km

Southern Channel (SC)•~0,8 km

Arguin Sand Bank (ASB)~2,15 km

Bernet Sand Bank (BSB)

Tourlinguet Sand Bank

Sylvain Capo,

Morphodynamic evolutionLarge view

Inlet Focus

Sylvain Capo,

Channels mobility

Tourlinguet Sand BankNorthern Channel

Arguin Sand Bank

Southern Channel

Sylvain Capo,

Measurements performed on a NS transect at the Inlet for the zeros m level

Channels mobility

Sylvain Capo,

~130m averaged ~ 6m/y

~170m averaged ~ 8m/y

Widening of the Tourlinguet Sand Bank>1000 m (~ 60m/year)Sand supply by the littoral driftsouthwards migration and anticlockwise rotation of the channel

South-easternMigration ArguinSB~800 mAveraged ~ 40m/year

Conclusions and perspectives

Sylvain Capo,

Conclusions and perspectives

Channel width stability

Sylvain Capo,

Increasing of the meanderingof the Bernet SBSouthwest migration ~410 m~20m/year

Conclusions and perspectives

Sylvain Capo,

PERSPECTIVES

1. Model improvementAtmospheric correction

Bottom substrate discretisation

Implementation of Bio-optical models for water constituants (TSM, Chloro, CDOM)

2. Morphodynamics

Wave forcing to understang the by-pass process

Sylvain Capo,

Thank you

Sylvain Capo,

SPOT SA inversion model

Sylvain Capo,

1st step: IOP

Synthetic data IOCCG Comparison with QAA model

RMSE divided by 2 compared to Lee et al., 2002 model QAA

SPOT CapoR² = 0.98rmse = 0.03

QAAR² = 0.92rmse = 0.06

SPOT CapoR² = 0.99rmse = 0.04

QAAR² = 0.93rmse = 0.07

Bathymetric inversion algorithm

2nd step: Vertical diffuse attenuation derivationSynthetic database IOCCG+ QAA SA model comparison

Better rmse by 25%

especially for high Kd values

rmse divided by 2 for Kd >0.2(more accurate for coastal environments)

SPOT CapoR² = 0.98rmse = 0.04

QAAR² = 0.96rmse = 0.05

Bathymetric inversion algorithm

Sous évaluation des zones profondes turbides (chenaux et panaches) Bonne reproduction par le modèle de la géomorphologie des zones peuprofondes (+2 à -6m)

profondeurs de sonde de 0 à 20m

Modèle semi‐analytique d’inversion

3eme étape: Depth

4eme étape: Nu données synthétiques de référence IOCCG + comparaison avec modèle QAA

Modèle semi‐analytique d’inversion

Erreur moyenne quadratique divisée par deux par rapport au modèle de Lee et al., 2002

SPOT CapoR² = 0.92rmse = 0.17

QAAR² = 0.87rmse = 0.31

4eme étape: dérivation de l’exposant Nu pour le spectre des bbp (λ) à partir de bbp (λ0)données synthétiques de référence IOCCG + comparaison avec modèle QAA

Modèle semi‐analytique d’inversion

4eme étape: dérivation de l’exposant Nu pour le spectre des bbp (λ) à partir de bbp (λ0)données synthétiques de référence IOCCG + comparaison avec modèle QAA

Modèle semi‐analytique d’inversion

Arcachon Inlet Evolution 1986-2011

Arcachon Inlet Evolution 1986-2011

Northern Channel (NC)• Double and large• ~ 1,7 km

1990-03-17

Southern Channel (SC)• Single• ~0,8 km

1990-03-17

Arguin Sand Bank (ASB)• channel• ~2,15 km

1990-03-17

Flood delta

1990-03-17

Water column

Bottom

Albert and Mobley, 2003 Radiative Transfert Model im:plemented in Hydriloght

SPOT Capo (In prep)

QAA Lee et al., 2002

m0 1+0.005θsun 1+0.005θsun

m1 3.84 4.18

m2 0.256 0.52

m3 10.83 10.8

2eme étape: Paramétrisation du Kdet comparaison avec données synthétiques de référence IOCCG + modèle QAA

Modèle semi‐analytique d’inversion

Rrs 4 bands

λ0 =550nm

rrs

λ0 =490nm

rrs+Kd

λ0 =490nm

Rrs 2 bandes

λ0 =545nm

(IOCCG, 2005)

QAA Lee et al., 2002 et 2005

Loisel Jamet2010Kd derived NN

Loisel JametNew+True Kd

SPOT QAACapo (In Prep.)

a(total) Relative_err 2,79% 10,95% 1,74% 1,86%RMSE 0.0603 0.0554 0.0098 0.0305

bb Relative_err 4,48% 10,41% 1,93% 1,22%RMSE 0.066548 0.0534 0.0117 0.0369

Kd Relative_err 6,30% 16,82% 0,49%RMSE 0.0545 0.148 0.0407

Model Performances compared to synthetic IOCCG dataset

En rouge: meilleur résultatEn Vert : meilleur résultat en n’utilisant que les réflectances

QAA Lee et al., 2010 SPOT Capo (In Prep.)rrs(λ)=Rrs(λ)/(0.52+1.7Rrs(λ)) rrs(λ)=Rrs(λ)/(0.52+1.7Rrs(λ))

u(λ)=

g0= 0.089 g1= 0.125

u(λ)=

g0= 0.088 g1= 0.163