a global coastal altimetry dataset for coastal dynamics ... · - no data available for synergy with...

ALES’ FIRSTS (to our knowledge!)- first global coastal-retracked dataset to include multiple missions - first retracked dataset to be used in a peer-reviewed research on regional sea level variability Thanks to the collaboration with PODAAC, now freely available online

JASON-2 already availableENVISAT under testingJason-1 awaiting GDR version EProcessing tested on AltiKaCoastal GDR Handbook availableLet’s make the ALES community wider!!!

ftp://podaac.jpl.nasa.gov/allData/coastal_alt/L2/ALES

ALES parameter Jason-2 variable ENVISAT variable

Err_ALES wfm_fit_err_20hz_ku_ALES hz18_ku_ALES_wfm_fit_err Epoch_ALES epoch_20hz_ku_ALES hz18_ku_ALES_epoch Range_ALES range_20hz_ku_ALES hz18_ku_ALES SWH_correction_applied net_instr_corr_swh_ku_ALES SWH_ALES swh_20hz_ku_ALES hz18_ku_ALES_swh Sigma0_ALES sig0_20hz_ku_ALES hz18_ku_ALES_bscat SigmaC_ALES width_leading_edge_20hz_ku_ALES hz18_ku_ALES_leading_edge_width

Processed source SGDR data globally within a 55km strip (50km offshore, 5km inland) using ALESCreated Coastal GDR (CGDR) files

Retained source SGDR file-naming conventionsCGDR files contain the full, global dataset of the original SGDR data

But…the ALES variables are set to default values outside the coastal strip.

Essentially unchanged data content from original SGDRs……but with new ALES variables

Users can investigate the transition from open ocean to coastal strip

using data from a single file:

Sea Level Anomaly = Orbit altitude − Range_ALES − Geophysical

Corrections - Mean Sea Surface − Tides – DAC

Geophysical corrections = Dry tropospheric correction + Wet Tropospheric Correction + Sea State Bias + Ionospheric

correction

Part 4: Distribution

Sub-Basin ALES (m) SL_cci ENV (m) SL_cci (m) RADS (m) Kattegat 0.012 0.019 0.006 0.023

Norway Skagerrak 0.014 0.022 0.023 0.028

Denmark Skagerrak 0.008 0.008 0.006 0.012

Sweden Skagerrak 0.008 0.010 0.007 0.013

West Arkona 0.004 0.031 -0.018 0.024

East Arkona 0.005 0.016 0.006 0.773

Belts 0.006 0.008 0.000 0.027

TOTAL SIGNAL (annual sinusoids)

ALES THE ONLY DATASET WITH LESS THAN 1.5 cm

RMS error w.r.t TIDE GAUGES

ALES: reprocessed

coastal dataset-> improves data

quality and quantity

SEA LEVEL AMPLITUDE (squares: tide gauges

Tracks: 1Hz points)

8oE 9oE 10oE 11oE 12oE 13oE 14oE 15oE 54oN

55oN

56oN

57oN

58oN

59oN

Dep

th (m

)

800

600

400

200

100

80

50

2010

Estimation of the annual cycle of sea level: North Sea/Baltic Sea Transition

0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.36 >=0.40

5

10

15

20

25

30

35

%

RMS of SSHA (m)

ALES EnvisatSL_cci EnvisatRADS

ALES=

BETTER DATA

9oE 11oE 13oE 15oE 53oN

54oN

55oN

56oN

57oN

58oN

59oN

SSHA std ALES (m)

SSH

A st

d (m

)

9oE 11oE 13oE 15oE 53oN

54oN

55oN

56oN

57oN

58oN

59oN

SSHA std CCI (m)

SSH

A st

d (m

)

0

0.05

0.1

0.15

0.2

0.25

0.3

Take Home MessageALES Coastal Data (with state of the art geophysical correctionscan be used to estimate sea level variability at a sub-basin scale

*work partially performed at ESA/ESRIN (co-supervised by Jérôme Benveniste)

Part 3: Application

Take Home MessageALES Can get to within ~3km of the coast

Can be used in the open ocean (no additional noise)Can be “added” to open ocean standard data (bias ~1cm at 20Hz!!)

* Absolute validation in NW Adriatic by referring all the sea level values to a common reference (ellipsoid)* Outliers of ALES removed. SGDR evaluated in the same locations for the same points

RMSE NW Adriatic

RMS (closest point) ENV 416 J1 161 J2 296 SGDR - TIDE GAUGE 1.31 m 0.30 m 0.85 m ALES – TIDE GAUGE 0.29 m 0.21 m 0.53 m

Total Water Level Envelope (TWLE)

-> Sea Level including Tides

SGDR - ALES ENV 416 ENV 687 J1 161 J2 198Bias TWLE (m) -0.0093

±0.0223-0.0163±0.0572

-0.0114±0.0409

-0.0057±0.0470

0 0.05 0.1 0.15 0.2 0.250

10

20

30

%

m

J−2 198

0 0.05 0.1 0.15 0.2 0.250

10

20

30

%

m

Env 687

0 0.05 0.1 0.15 0.2 0.250

10

20

30

%

m

J−2 196

0 0.05 0.1 0.15 0.2 0.250

10

20

30

%

m

J−1 161

0 0.05 0.1 0.15 0.2 0.250

10

20

30

%

m

Env 416

SGDRALES

Part 2: Validation

OPEN OCEAN, SWH=0.75 m COASTAL OCEAN, SWH=1.65 m OPEN OCEAN, SWH=9.48 m

1) Leading Edge detection (based on difference of consecutive gates)2) First pass: retracking of subwaveform up to the end of the leading edge3) Adaptation of subwaveform depending on initial estimation of SWH4) Second pass: retracking of new subwaveform and precise estimation of

Epoch, SWH and Sigma0 Estimation:

Least-Square Estimator, convergence found through Nelder-Mead algorithm [(Nelder & Mead, 1965), Halimi (2013)]

0 20 40 60 80 100 120 1400

0.5

1

1.5

Gate number

Nor

mal

ised

pow

er

Nominal Tracking Point

Leading edge rise time - > Significan Wave Height

Tracking Point

Leading edge mid−point

Epoch - > Radar Impulse Travel Time - > Sea SUrface Height

Amplitude -> Backscatter Coefficient -> Wind Speed

RETRACKING:Fitting a model response to the real waveform to retrieve geophysical parameters

Take Home MessageALES Retracks a selected part of the waveforms in order to:

Avoid spurious contributions from bright targetsKeep the same “standard brown” precision in the estimation

Part 1: Design

ALES :a 3-year long effort to overcome the limitations of the

radar measurements in the coastal areas andgenerate a validated and applicable product

Standard practice does not consider data closer than 50 km from the coast, which means:- poor knowledge of coastal circulation- lack of comparability between tide gauges and satellite data

- no data available for synergy with coastal models.

Satellite Altimetry:-Has provided more than twenty years of global measurements of sea level, wave height, wind speed & geostrophic circulation

Marcello Passaro1, Paolo Cipollini2*, Jessica Hausman3, Graham Quartly4, Helen Snaith5

(1) Graduate School of the National Oceanography Centre, Southampton, UK – (2) National Oceanography Centre, UK – (3) JPL/CALTECH, USA – (4) Plymouth Marine Laboratory, UK – (5) British Oceanographic Data Centre, UK* Corresponding author: cipo@noc.ac.uk, +44-(0)23-80596404

A Global Coastal Altimetry Dataset for Coastal Dynamicsand Sea Level Research