Recovering more and better data from altimetry in the coastal zone:

a community effort

Paolo Cipollini, National Oceanography Centre, UK, cipo@noc.ac.uk

& Coastal Altimetry WS OrgComm: Jérôme Benveniste, Hans Bonekamp,

Laury Miller, Nicolas Picot, P. Ted Strub, Doug Vandemark. Stefano Vignudelli

Pilot ARCOM workshop Lisbon, 1/2 Sept 2015

The Coastal Altimetry Community

• Coastal Altimetry Workshops (CAW) since 2008 – large community: 100+, COASTALT-SWT mailing list

– like a big splinter of OSTST

• A Community Science Review – improving techniques

– refreshing diversity of applications

– recommendations (internal / external)

CAW-5 San Diego, 2011

One of our first recommendations …

• Coastal Altimetry is inherently interdisciplinary and a pretty legitimate

(and very useful) component of coastal observing systems

• Need constant interaction with hydrographers, modellers, in situ

scientists on the application side, engineers on the technical side

RECOMMENDATION: we need to reach out to more (potential) users

CAW-2 Pisa, 2008

…and one of the latest!

• Coastal Altimetry is very relevant to GODAE

OceanView COSS-TT (Coastal and Shelf Seas

Task Team) so…

• …we need COSS-TT/CAW joint meeting to

promote uptake of Coastal Altimetry and expose

issues for SWOT etc.

CAW-8 Konstanz, 2014

Coastal altimetry continues to improve

• Technical Advances

• Continuing improvement in corrections

• Many datasets are now available…

• … and applications are numerous

Technical advances

• Knowledge on how to

handle SAR altimetry is

rapidly expanding

– stacking, improved

waveform models

• CryoSat-2 SARM working

very well and ideal

precursor to Sentinel-3

• AltiKa also extremely good

in coastal zone

• Envisat Individual Echoes

great testbed for new and

future missions

SAR Altimetry Training Course, 21-22 Oct 2014

Technical advances

• Knowledge on how to

handle SAR altimetry is

rapidly expanding

– stacking, improved

waveform models

• CryoSat-2 SARM working

very well and ideal

precursor to Sentinel-3

• AltiKa also extremely good

in coastal zone

• Envisat Individual Echoes

great testbed for new and

future missions

0 5 10 15 20 25 300

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Distance from closest coastline (km)

abs(2

0H

z d

iffe

ren

ce

s)

(m

)

FBR ESRIN SAM R5; Jul12 & Jan13; abs(diff) of 20−Hz TWLE with misfit<4

samples

75th percentile

median

25th percentile

~4.5cm @ 2km

0 5 10 15 20 25 300

0.5

1

Distance from closest coastline (km)fraction

of va

lid p

oin

ts

FBR ESRIN SAM R5; Jul12 & Jan13; fraction of valid points passing misfit<4

~4.0cm @ 5km with ~80% valid

CryoSat-2

UK coasts

CP4O

Team

Technical advances

• Knowledge on how to

handle SAR altimetry is

rapidly expanding

– stacking, improved

waveform models

• CryoSat-2 SARM working

very well and ideal

precursor to Sentinel-3

• AltiKa also extremely good

in coastal zone

• Envisat Individual Echoes

great testbed for new and

future missions

10 km

20 km

AltiKa / Jason-2 West Mediterranean Sea

J2 AltiKa

G. Valladeau

PEACHI

Technical advances

• Knowledge on how to

handle SAR altimetry is

rapidly expanding

– stacking, improved

waveform models

• CryoSat-2 SARM working

very well and ideal

precursor to Sentinel-3

• AltiKa also extremely good

in coastal zone

• Envisat Individual Echoes

great testbed for new and

future missions 1-second of of 1800 Hz echoes in vicinity of

Rio Tigre, Peru; Amplitude in dB re noise

R. Abileah

Technical advances

• Avoiding land effects with

range gate selection

• Improvement in

retrackers/windowing

• Work on inland waters remains

very relevant A. Egido

Technical advances

• Avoiding land effects with

range gate selection

• Improvement in retrackers

– windowing/subwaveforms

• Work on inland waters remains

very relevant and promotes

better understanding

Stack of echos (after migration)

Multilooked echo

Lo

ok N

um

be

r N

orm

aliz

ed

Pow

er

SAR Mode

12 …33 ………………. 115 12 …33 ………..83 12 …33 … 63 12 . 33 . 48 range gates

Window Truncation 12-115 12-83 12-63 12-48

Radius of the WF footprint 7488 m 5848 m 4530 m 3203 m

P. Thibaut

NOC’s ALES retracker

Adaptive Leading-Edge Subwaveform (ALES) retracker

Passaro et al., Rem Sens Env., 2014

radar waveform

Pass 1: identification of leading edge and

initial estimate of SWH

ALES algorithm for width of sub-waveform

window (from Monte Carlo

Simulations)

Pass-2: subwaveform

retracking (Brown Model)

sub-waveform hs(1)

range, σ0, hs

The sub-waveform approach keeps the measurement focused

on the pulse-limited footprint of the instrument prevents any

non-homogeneities in the far-view field from degrading its

accuracy.

very good for coastal zone and fine scales

Examples of Jason-2 retracking by ALES

• Validated for SSH for Envisat, J-1, J-2, AltiKa

• Validated for SWH for Envisat, J-1/2 (Passaro et al 2015)

• J-2 data available now from PODAAC, Envisat coming

see Poster (Passaro et al.)

Open ocean

SWH = 0.75 m

Coastal ocean

SWH = 1.65 m

Open ocean

SWH = 9.5 m

Jason-2 p0044 cycle 252 - 7 May ‘15

44 44.1 44.2 44.3 44.4 44.541

41.5

42

42.5

43

43.5

44

44.5

45

45.5

46

latitude

US

SH

(m

)Uncorrected SSH (orbit minus range)

SGDR

SGDR MLE3

ALES

LAND

Coast

Ships?

ITALY

Ligurian

sea

Continuing improvement in corrections

• DComb Wet Tropo

• High-res MWR on the horizon

• MSS – and tides!!

– in coastal regions data editing for

MSS determination is critical

– SarIN! Example

• Significant differences shown

between the GDR-Global DAC

prediction and local models

within several regions.

– do not apply the global DAC to the

altimeter SSHA, or do so after

evaluation against wind-forced HF

signals along your coastline.

J. Fernandes

18.7 GHz QV

90 GHz

S. Reising

Continuing improvement in corrections

• DComb Wet Tropo

• High-res MWR on the horizon

• MSS – and tides!!

– in coastal regions data editing for

MSS determination is critical

– SARIn useful around fjords

• Significant differences shown

between the GDR-Global DAC

prediction and local models

within several regions.

– do not apply the global DAC to the

altimeter SSHA, or do so after

evaluation against wind-forced HF

signals along your coastline.

None of the global tide

models covers here !

O. Andersen

Continuing improvement in corrections

• DComb Wet Tropo

• High-res MWR on the horizon

• MSS – and tides!!

– in coastal regions data editing for

MSS determination is critical

– SARIn useful around fjords

• Significant differences shown

between the GDR-Global DAC

prediction and local models

within several regions.

– do not apply the global DAC to the

altimeter SSHA, or do so after

evaluation against wind-forced HF

signals along your coastline.

L Ruiz-Etcheverry

Variance HAMSOM

Variance Mog2D

2200 cm2

800 cm

Datasets for coastal altimetry

ID Produced

by

Missions Product

level

Posting

rate

Coverage Download

from

AVISO CLS

CNES

e1,tx,e2, en, j1,

j2, c2

(LRM/PRLM),

sa

L2, L3

also L4

1 Hz Global +

european regions

AVISO+

CMEMS CLS

CNES

e1,tx,e2, en, j1,

j2, c2

(LRM/PRLM),

sa

L3

L3 for assim

1 Hz Global +

european regions

marine.cope

rnicus.eu

PISTACH CLS

CNES

j2 L2 20 Hz Global AVISO+

PEACHI CLS

CNES

sa L2 40 Hz Global AVISO+

XTRACK LEGOS-

CTOH

tx, j1, j2, gfo, en L2, L3 1 Hz

20Hz

(test)

23 regions CTOH

AVISO+

RADS EUMETSAT,

NOAA,

TUDelft

gs, e1, tx, pn,

e2, gfo, j1, n1,

j2, c2, sa

1 Hz Global TUDelft

ALES NOC j2 20 Hz Global, <50 km

from coast

PODAAC

SARvatore ESA-ESRIN c2 (SAR only) 20 Hz SAR mode

regions

ESA GPOD

Cal/Val and Applications

• 30+ contributions at CAW-8

• from broad shelf to the coast

• strong complementarity with models

Mean surface geostrophic

current amplitude (in m/s)

Observations (MDT Rio 2014)

Curvilinear grid

Resolution: 0.6 to 6 km

Symphonie model (regional config in 2014)

F. Birol

Application example 1: coastal dynamics

Example at Ibiza, W Med:

SARAL/AltiKa derived

velocities reveal coherent

mesoscale features with

general good agreement with

HF radar fields

AltiKa

HF radar A. Pascual et al

Application example 2 : storm surges

Surge due to Hurricane Katrina,

29 August 2005

Hurricane Sandy storm surge flooding the World Trade Center construction site

Storm Surges

Predicted

Tides

Measured

Tides

Surge:

Measured - Predicted

Lillibridge et al -

Hurricane Sandy storm surge

HY-2A only altimeter to capture

surge < 12 hr duration

Montauk

HY-2A

Application example 2 : storm surges

Application example 2: storm surges

Present constellation insufficient to reliably capturing all surges, but the time/space information content can be extended using model dynamics (example: statistically altimetry/tide gauge blending by DMI)

ESA due eSurge / eSurge-Venice projects see poster by Bajo et al

Cyclone Xaver seen by Geodetic observations

L. Fenoglio et al

C2 SAR observations of Xaver storm - Dec2013

Friday 6 Dec 23:05

Data were available on eSurge Server by Saturday lunchtime

DMI model

Madsen et al eSurge: ESA DUE

(Data User Element)

Project for 2011-2015

www.storm-surge.info 24

Take home message – “the challenges”

• The quality of coastal altimetry – precision and

resolution – continues to improve, challenging

our understanding of the ocean at short scales

• how do we manage the extra resolution?

• can we use coastal altimetry data to prepare

the community to ingest high-resolution data

from SWOT?

• what applications are possible in Near Real

Time?

18-19 October 2015, Reston (Virginia), United States

www.coastalaltimetry.org

abstracts due Sept 1st, 2015

Extra material

18/10/2011 NOV-3900-SL-11654

© NOVELTIS 2011-This document is the property of Noveltis, no part of it shall be reproduced or transmitted without the express prior written authorisation of Noveltis

28

Comparison of the current anomalies

PISTACH RED3 DUACS

mg/m3

Mean geostrophic

current – HYCOM

model – 30/08/2009

Provided by

M. Le Hénaff,

RSMAS

Cancet et al

CAW-8 Recommendations

• [CAW8-REC1] Unfiltered along-track high-resolution

SSH should be open to public in both delayed and NRT

products

– Best filtering scales may differ regionally and seasonally

• [CAW8-REC2] A Coastal MSS and MDT recomputed

with high-resolution SSH would be a useful thing

– For understanding dynamics

– For cal/val with non-repeating tracks (although less accurate

than in repeating orbits)

• [CAW8-REC3] support R&D in development of more

accurate tidal models in the coast (including merging

regional models with global ones)

To Agencies and data providers

• Data assimilation (via variational methods)

integrates remotely sensed observations and

dynamical constraints to improve ocean state

estimation

• Using all data (SSH, SST, HF-radar) gives

greatest analysis skill; assimilating only one data

type degrades the analysis of unconstrained

variables.

• Adjoint-based methods quantify forecast

uncertainty without computing large ensembles

• Multi-scale hierarchy of models, using altimetry

processed to differing levels, acknowledges the

range of model and data covariance scales.

Coastal Altimetry and Modelling

Coastal Altimetry and Modelling

• Model-based analysis (assimilation; statistical

covariance analysis) are promising approaches

to infer subsurface circulation from surface-only

observations

• Coastal oceanographers need guidance on “best

practise” to match corrections appropriate to

dynamical processes.

• To utilize high sample rate SSH model

development required ~ multi-scale nesting and

data assimilation is recommended.

• Coastal modelers/assimilators need a test-

bed/comparison framework (complementary to

CAW process) to exchange developments in

Relevance to SWOT

US West Coast

80

0 k

m

600 km

*Proposed Mission – Pre-decisional – for planning & discussion purposes only P. Callahan et al