a global coastal altimetry dataset for coastal dynamics ... · - no data available for synergy with...
TRANSCRIPT
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: [email protected], +44-(0)23-80596404
A Global Coastal Altimetry Dataset for Coastal Dynamicsand Sea Level Research