From techniques to applications: NOC's forefront role in coastal altimetry

Paolo Cipolliniwith contributions from Val Byfield, Christine Gommenginger, Graham Quartly, Luke West

Coastal altimetry• Satellite altimetry works well

for open ocean– measures sea surface height,

significant wave height, wind• Near coasts however…

– land contamination, calm water effects on waveform shape, poorer corrections, etc

– data normally flagged as ‘bad’ in the official products - but they can be recovered!

• Coastal region has enormous strategic importance

• 20 years of data over the coastal ocean are waiting to be processed

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We believe so, with dedicated reprocessing and corrections.

For instance - can we recover these?

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• WHY we want coastal altimetry– useful: we’ll see several applications (Sea Level,

currents, Storm Surges)– convenient: 20 years of data to dig in; and new missions

(Cryosat-2) even more promising for the coastal zone.

• But first HOW do we do it? (i.e. the techniques)• and WHAT have we done so far/are we doing now/

are planning to do in the future?

outline

How we recover more valid data

A. Specialized retracking– Use better waveform models,

accounting for change of shape in coastal environment

– Use specialized (2-D or sequential) retracking techniques

B. Improved Corrections– Most crucial is the correction

of path delay due to water vapour (“wet tropospheric” correction)

– Some applications require correction of tidal and high-frequency signals, which are also difficult to model in the coastal zone

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0-10 km 0-50 km

L.J. West, NOC

Example of “wet tropospheric” problems

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Envisat track 343

South Africa

S Africa

J. Maina Mbui for ALTICORE-Africa

Effect of land

• Wet Tropospheric correction:– DLM (Dynamically Linked Model) approach: Use

models to extend radiometer observations implemented in NOC COASTALT processor

– GPD (GNSS-derived Path Delay) - dry and wet tropo from GNSS (GPS/Galileo) measurements (Univ. Porto) computed and available in COASTALT pilot data

– GPD recommended by the ESA Sea Level CCI Consortium as Wet Tropospheric correction of choice in the coastal zone

– GPD included in V2.0r3 COASTALT products

• Tides– COASTALT Investigated local models

(UPorto/CIIMAR, WITM local tidal model for W Iberian shelf)

Corrections: the way forward

The COASTALT Processor for Envisat

• Core deliverable and legacy of COASTALT– Flexible, user-configurable and modular software

• Baseline processor– Reads ENVISAT L2 SGDR files– Retracks all waveforms with different models

• Brown, Specular and Mixed, plus innovative retrackers (see later)

– Generates corrections at 18Hz– Generates Coastal Geophysical Data Records

(CGDRs) output files in NetCDF

• User-defined Geophysical Corrections module (“addcorr”)– Allows addition of any user-generated corrections– used to include GPD correction in CGDRs

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• Innovative retrackers: retrack each waveform not in isolation but using info from adjacent ones

• Two different approaches• The hyperbolic retracker to fit and remove

bright/dark targets is an example • Another example is the Bayes Linear retracker

– Based on the application of Bayesian methods– The idea is to treat the posterior from one waveform as the

prior for the next.

• Both these have been designed within COASTALT and prototyped

Innovative retrackers

Hyperbolic retracker example

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• COASTALT just finished– very good incubator of technical ideas– final results, recommendations presented at 5th Coastal

Altimetry Workshop (San Diego 16-18 October)– processor is a lasting legacy

• ESA CCI Sea level– small contract (35 kEUR) to study effects of coastal

proximity on retracking – complements COASTALT work

• Main development now: ESA eSurge– started in June 2011, 370 K EUR– includes funding for NRT coastal altimetry

Where we are now

eSurge

• ESA DUE (Data User Element) Project for 2011-2013– DUE runs user-driven projects to transfer research to

applications

• eSurge Objectives:• To contribute through Earth Observation to an

integrated approach to storm surge, wave, sea-level and flood forecasting as part of a wider optimal strategy for building an improved forecast and warning capability for coastal inundation.

• To increase the use of the advanced capabilities of ESA and other satellite data for Storm Surge applications

The eSurge consortium

• Then there is “eSurge Venice”: a parallel project on surges in

Northern Adriatic – key area for this kind of application - led by Italian CNR

Coastal and Marine Resources Centre, I RL

Subcontractor

National Oceanography Centre, UK

Subcontractor

Danish Meteorological I nstitute, DK

Subcontractor

Logica, UK

Prime Contractor

Koninklijk NederlandsMeteo I nstituut, NL

Subcontractor

The eSurge System

We aim to prove that by assimilating EO data our hindcasts improve!

SEARS: a database of surge events

Example eSurge Input Data• Altimeter (ERS, Envisat, Geosat,

TOPEX, JASON, CryoSat)• Passive Microwave (SSM/I, AMSRE, TMI,

WindSat)• Scatterometer (ERS, QuickScat, ASCAT,

NSCAT, OceanSat-2 )• SAR (ERS, ENVISAT, RADARSAT,

COSMOSkyMed, TerraSAR-X, RISAT…)• Optical/IR data (MERIS, MODIS, AATSR,

AVHRR, geostationary satellites)• NWP and NOP model outputs• Storm Surge model output and forcing• Flood maps• In situ (Tide Gauges)

• A very important component of eSurge will be the development, validation and provision of dedicated coastal altimetry products

• Coastal altimetry is important as it measures the Total Water Level Envelope (TWLE)– That’s the level you get – inclusive of tide, HF atmospheric effects,

wave setup, etc…– key quantity required by storm surge applications and services

• The wave field in the coastal strip is also relevant– helps development of more realistic wave models

• Of course there is a sampling issue – but altimetry is still useful, in combination with Tide Gauges, to ascertain the modes of variability of the coastal ocean

The role of coastal altimetry

Scharroo et al 2005

JASON ENVISAT CRYOSAT f(x)

RADS -based

Reader

E-Surge Processor: Abstract Input

Extensible design allows for future

missions andother types

of input

E-Surge Processor: RADS-based Reader

• RADS (Radar Altimeter Database System) has already abstracted altimetry missions successfully

• E.g. string mission name standard– ‘tx’ – TOPEX– ‘e1’ – ERS-1

• Identified and codified numerous scalar quantities.

• Wet tropospheric correction• Different kinds of ‘height’• etc..

• We will allow for extending and adapting without reinventing RADS

• which was already used to define the COASTALT products

E-Surge Processor : Input selection and filtering

Mission

LatLon

Time

Scalars &Waveforms f(x)

RADS -based

Reader

Landmask

Cycle/Passnumbers

E-Surge Processor : preprocessing

Save internal

state

Interpolation

Low rate toHigh rate

Scalars &Waveforms

f(x)

Passthruto output without

processing

Averaging

High rate to Lo rate

Processing

Back to input module

output

other filtering

E-surge Processor• Create new scalars from old ones

– Corrections• Create new scalars from waveforms

– Retracker parameters• Create new waveforms from scalars

– Synthetic data• Create new waveforms from old

– Retracking We want to design a system as simple as possible that does everything we want it to do without precluding everything we

might want it to do in the future!

• In a later phase of the eSurge project (mid-2012 onwards) the eSurge coastal altimetry processor will be extended to be able to ingest NRT raw altimetric waveforms– like FDMAR streams from ESA

• (we need ESA, NASA and CNES to make sure we have access to the NRT waveforms)

• this is part of the ‘eSurge-Live’ effort for the provision of NRT data to users during storm surge events

• definitely uncharted waters for coastal altimetry!!!

…and we will venture in NRT territory!

• For the science!– In particular, exploits synergy between NOC-S satellite

work and NOC-L surge research

• Capitalizes on COASTALT investments and allows further development of processor– NOC-S unique capability

• Encompasses whole spread of skills - from technical development through algorithms development to application

• Strengthens the links with BODC (ex Data Group)• Processor can them be redeployed over other areas

– more science!

Why eSurge is good for us

Coastal Altimetry in the Agulhas

Collaboration NOC (K. Rizopoulou) / UMiami / UCT / HartRAO / UPorto

Aim: obtain 20 ys of Agulhas Current transport1) Calibrate Altimeter-derived transports with ACT array (UMiami cruises)2) Then use altimetry to go back to 1992

Needs multi-mission coastal altimetry!(one of the first climate applications)

New GNSS station in Hamburg, SA

• ESA CP4O (Cryosat Plus for oceans), which has a coastal component– Cryosat-2 (Delay-Doppler altimeter) very good in coastal

zone, but needs specialized retracker– Builds heavily on the experience we gained in highly

successful SAMOSA project on Dealy-Doppler altimetry

• FP7 COSMOcean : integration of coastal altimetry with old and new in situ measurements (marine radars, ferrybox, fishing nets) in NW Mediterranean

• FP7 EORCEF, led by Val Byfield, see next slide

Some projects for the future

FP7 Space Call: EORCEF* proposal*Earth Observation for Resilience to Coastal Erosion and Flooding

Mapping coastal hazard exposure: – Tsunamis, storm surges, waves

Partner countries: – UK, France, Norway, S-Africa,

Mozambique, MauritiusNOC contribution: – Extreme waves, sea level, storm surges– Observations and modelling

Part of NOC support for GOOS-Africa capacity development in coastal and marine RS

Started in 2003: – UNESCO-Bilko included in GOOS-Africa

first 5-year plan (ROOFS)– ESA support for NOC-led RS software

and lesson development

Past and ongoing projects: – AltiCoRe-Africa: coastal altimetry

group, 2008 - present – Agulhas Current coastal altimetry

(ongoing PhD project)– DevCoCast (FP7, 2008-2011)– EAMNet (FP7, 2010-2013): Data

dissemination, training, sharing analysis tools, MSc courses, fellowships.

• With COASTALT we have acquired:– understanding of technical issues– analysis and prototyping capability– links to modellers and hydrographers– links to Tide Gauge community– international coordination role (Coastal Altimetry workshops)

• other ongoing studies complement that work (note Agulhas work has profound climate implications)

• eSurge important application (with significant extension to the processor + further links to modelling community)

• more funding requested (ESA/FP7) for R&D and applications• We are at the forefront of coastal altimetry – and we

should make sure we remain there.

Conclusions

www.coastalaltimetry.org