1 coss-tt/arcom workshop 31 aug 4 sep 2015 …godae-data/oceanview/events/coss...6 coss-tt/arcom...

COSS-TT/ARCOM Workshop — 31 Aug – 4 Sep 2015 — Lisbon, Portugal 1

PROSPECTS FOR THE USE OF SATELLITE ALTIMETRY IN COASTAL REGIONS

Remko Scharroo,

Hans Bonekamp,

Christelle Ponsard,

Carolina Nogueira-Loddo

EUMETSAT

Darmstadt, Germany

Paolo Cipollini

NOC Southampton, England

3 COSS-TT/ARCOM Workshop — 31 Aug – 4 Sep 2015 — Lisbon, Portugal

Past, current, and future missions

“Reference missions”, to be continued with Jason-3 and Jason-

CS A and B (Sentinel-6)

35-day repeats will likely come to an end

27-day repeats of Sentinel-3

o With SAR and interleaved ground-tracks of S3-A/B

CryoSat-2 still continuing (non-repeat)

SWOT in the planning for 2020.


SAR Altimetry – quantum leap

Sentinel-3 and -6 in SAR mode over the whole ocean!

The improvements w.r.t. conventional (pulse-limited or ‘LRM’

– Low Resolution Mode) altimetry:

o higher along-track resolution

o better signal to noise ratio

o explained with simple energy considerations in the next

slide

More “looks” = improved SSH retrieval accuracy

Finer spatial resolution along track o ~ 300 meters along-track

Less contamination close to land o Very well suited for coastal

altimetry


In SAR mode we split the footprint

along-track, and align multiple

looks over the same resolution cell

This portion of the

waveform contributes very

little information

(even less so in the coastal

zone!)

Range, sigma0, SWH

from the leading edge Waveform:

Illuminated surface:

Po

wer

Doppler isolines (along-track SAR processing)

Flight direction

Po

wer

Multilook Averaging


Closed-burst SAR (CryoSat-2 and Sentinel-3)

In a closed-burst SAR (CryoSat, S-3) transmit and receive are not

interleaved and are not continuous.

o The CryoSat values of N = 64 and PRF = 18 kHz give a burst

duration of ~3.5 ms. But the burst-to-burst interval is ~11.8 ms.

70% of the opportunity to make measurements is not used.

This pulsing scheme cannot be used to make an equivalent LRM

measurement.

CryoSat burst interval 11.8 ms

Two-way time at CryoSat altitude (S-3 is similar):


Interleaved LRM or open-burst SAR (Jason-CS)

PRF ~ 9 kHz and continuously interleaved transmit/receive throughout the

ocean.

All possible statistically independent measurements are made.

SAR and LRM can both be made from the same echoes, under the same

conditions.

LRM from simple sequential averaging of all echoes yields optimal LRM

everywhere, both coastal and open ocean.

Since all individual echoes will be downlinked, SAR products also can be

made.


Coastal zone benefits

Higher SNR — can detect small signals in ‘noisy’ (from

the point of view of altimetry observables) coastal

environment

Much higher along-track resolution

o part of it can be traded off, if not needed, in change

for further noise reduction

Reduced contamination by land and coastal targets

(depending on their position relative to satellite track)

Individual echoes — allows editing out affected echoes

or Doppler bins


Assessing SAR mode performance in the coastal zone

Flight

direction

The difference in height between one along-track resolution cell and the next is essentially only due to instrument noise


Faster …

Requirements

Sentinel LRM and SAR data within 3 hours!

NRT and STC data to be delivered faster

o Get used to the new latency names

Near-Realtime Short Time Critical Non Time Critial

OGDR IGDR GDR

Jason-2 3-5 hours 1-2 days 60 days

Jason-2 and -3 3 hours 48 hours 60 days

FDM (LRM only) LRM and SAR

CryoSat-2 3 hours 30 days

NRT STC NTC

Sentinel-3 3 hours 48 hours 60 days

Sentinel-6/Jason-CS 3 hours 36 hours 60 days


Upcoming SAR missions Upcoming SAR Altimetry Missions

Sentinel-6/Jason-CS (2020)

Sentinel-3 (2015)


Cheaper … (?)

Sentinel-3

Altimetry: LRM and SAR modes. Also: SST and Ocean Colour

Sentinel-3A and -3B (~1 year apart; interleaved tracks)

Part of Copernicus program

o EC responsible for ocean data; ESA for land data

o Coast line is going to be in both datasets

Sentinel-6

Dedicated to altimetry; continuing the reference missions

Jason-CS A and B (~5 years apart; interleaved tracks)

To be part of Copernicus program

o EC operation

o Plus NASA, NOAA and CNES


Cheaper …

Data

Still for free, and more of it …

Level 1

o Calibrated instrument data: waveforms and individual echoes

Level 2

o Geophysical Data Records

Level 2P

o As Level 2, with updated corrections, models

Level 3

o Harmonised with other missions


Sentinel-6 (Jason-CS) Product Baseline

Delivery of L0, L1, L2, L3 data by EUMETSAT

Resolution Service

Name Format

User Data Access

EUMETCast GTS ftp (TBC) Archive

Low

(LRM)

NTC NetCDF - - - L2

STC NetCDF - - L1b L1b, L2, L2P, L3

NRT NetCDF

L2 (std +

red) - - L0, L2

BUFR L2 L2 - L2

High

(SAR)

NTC NetCDF - - - L2

STC NetCDF - - L1a, L1b L1a, L1b, L2, L2P, L3

NRT NetCDF

L2 (std +

red) - - L0, L2

BUFR L2 L2 - L2


Better …

Jason-3

“Carbon copy” of Jason-2

Improved radiometer (more stable)

Sentinel-3

LRM mode (will not be used)

SAR mode (over all terrain)

Sentinel-6

LRM and SAR mode simultaneously


Better …

Orbit

Orbit precision is ever improving

DORIS and GPS for operational/on-board orbit determination

Open-loop tracking

This means that the range is estimated on-board

o based on on-board orbit and DEM model

o not on previous measurement

Improves tracking near coasts

Open burst (interleaved mode) LRM/SAR

To be implemented for Sentinel-6/Jason-CS


Error budgets for sea level

Values in centimeters (1-sigma)

For average conditions (2 m wave height)

SAR reduces noise and overall SSH anomaly error

Envisat Sentinel-3 Jason-2 Jason-CS

Altimeter noise (LRM) 1.8 1.7 1.8 1.7

Altimeter noise (SAR) 1.3 0.8

Ionosphere 0.5 0.5 0.5 0.5

Sea state bias 2.0 2.0 2.0 2.0

Dry troposphere 0.7 0.7 0.7 0.7

Wet troposphere 1.4 1.4 1.0 1.0

Orbit error 1.9 1.9 1.0 1.0

SSHA error (LRM) 3.6 3.6 3.2 3.2

SSHA error (SAR) 3.5 2.8


Cryosat-2 the first SAR altimeter in orbit


Cryosat-2 Mode Mask

SAR mode polygons in green SARin mode in purple Rest in conventional LRM mode


Increased noise with Pseudo-LRM compared to LRM Can be handled with some minor smoothing No apparent jumps or discontinuities at transitions

CryoSat-2 LRM / Pseudo-LRM transition

SAR


Coastal performance: a case study

Envisat p0543

(35-day repeat)

Cryosat

single

passes

20 km



0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

Distance from coast (km)

ab

s(d

iff(T

WLE

20H

z))

Cipollini, Passaro & Vignudelli,

paper in prep.

Envisat p0543 SGDR

(median of 76 passes)



0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25


ab

s(d

iff(T

WLE

20H

z))


paper in prep.

Envisat p0543 SGDR


Envisat p0543 ALES




0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25


ab

s(d

iff(T

WLE

20H

z))

Envisat p0543 SGDR


Envisat p0543 ALES


CryoSat–2 SAMOSA

(single passes)


paper in prep.



0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25


ab

s(d

iff(T

WLE

20H

z))

Envisat p0543 SGDR


Envisat p0543 ALES


CryoSat–2 SAMOSA


CryoSat–2 SAMOSA

(single passes)


paper in prep.


Important application: storm surges

Surge due to Hurricane Katrina,

29 August 2005


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


Conclusions

Jason-3 will soon be launched, and will continue 20+ years of

“reference altimeter missions”

Advantages of SAR altimetry over conventional altimetry (higher

resolution, higher SNR, reduced impact of land/bright targets)

are particularly valuable in the coastal zone

o Demonstrated already with excellent Cryosat-2 data

Sentinel-3 will provide global SAR mode coverage – including

the whole world’s coastline

o First “operational coastal altimetry mission”

Sentinel-6 will introduce SAR on the reference altimeter missions

o “Interleaved mode” will allow LRM/SAR simultaneously, thus

excellent to ensure continuity and a lot of R&D


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

www.coastalaltimetry.org

abstracts due today!

1 coss-tt/arcom workshop 31 aug 4 sep 2015 …godae-data/oceanview/events/coss...6 coss-tt/arcom...

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