https://www.facebook.com/SKIM4EE9 http://tinyurl.com/SKIMonRG

The Sea surface KInematics Multiscale (SKIM) proposal for ESA EE9

http://www.umr-lops.fr/Projets/Projets-actifs/SKIM

the SKIM team :

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 2

… 14 years of Doppler oceanography: When science and technology come together

Envisat SAR data

Drifter data

You may not know, but...

… Doppler oceanography

works,

Even from space!

Image courtesy of A. Mouche & N. Reul

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 3

Outline of this presentation : • Towards a new satellite mission

How ? 1- Context of ESA Earth Explorers

2- The SKIM concept for measuring surface velocity (currents & ice drift) & ocean wave spectra

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 4

Outline of this presentation : • Towards a new satellite mission

How ? 1- Context of ESA Earth Explorers

2- The SKIM concept for measuring surface velocity (currents & ice drift) & ocean wave spectra

Why ? 3- Why a new mission

4- Challenges and opportunities in marginal ice zones & the future Arctic

Performance5- Expected SKIM resolution & accuracy in different current / wind / wave regimes

Summary6- Questions and anwers : find the proposal on ResearchGate

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 5

1. ESA, Earth Explorers and you

ESA has been dedicated to observing Earth from space ever since 1977.

ESA's Living Planet Programme :

- operational : Copernicus Sentinel missions

- science and research element : Earth Explorer (EE) missions.

EEs are research missions designed to address key scientific challenges identified by the science community while demonstrating breakthrough technology in observing techniques.

Involving the science community : - definition of new missions - peer-reviewed selection - data required by the user = science community.

There has been 8 EEs selected so far :

EE1 : GOCE 2009-2013. EE2 : SMOS 2009-... EE3 : Cryosat 2010-...

EE4 : Swarm 2013-… EE5 : ADM-Aeolus 2017 EE6 : EarthCARE 2018

EE7 : Biomass EE8 : FLEX EE9 : ?? → 12 proposals submitted last week

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 6

2. What is SKIM ?

It is a combination of Ka-band

radar altimeter, disco ball, and speed gun …

+ + =

- « altimeter on steroids » : best ever flown (Ka-band, 32 Khz PRF, 200 MHz bandwidth, SAR unfocused) → very low noise for sea level, wave height, ice freeboard … - « disco ball » : a rotating plate with 8 horn feeds : one nadir beam (classic altimeter)

7 other beams at 6 and 12° incidence

- « speed gun » : Doppler analysis → surface currents, ice drift & wave orbital velocities.

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 7

2. What is SKIM ?… and how it works …

Example of horn positions with 8 beams :

And resulting beam patterns :

T_turn = 17.7 s

60 azimuths / beam (6° resolution)

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 8

3. Why a new satellite ?

Primary objective : total surface current - transport of heat, salt, biota, microplastics … - western boundary currents - equatorial currents - marginal ice zones

but accurate currents require…

From Collard et al. (SEASAR 2008)

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 9

3. Why a new satellite ?

Primary objective : total surface current - transport of heat, salt, biota, microplastics … - western boundary currents - equatorial currents - marginal ice zones

but accurate currents require…

Secondary objective : directional ocean wave spectra - wave-current interactions - air-sea fluxes : wind stress & wind work - coastal hazards - marginal ice zones - sources of microseisms

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 10

3. Why we need waves to measure currents

SKIM will resolve much shorter waves (<20 m) than Sentinels (~ 150 m) or CFOSAT (70 m)

fraction of resolved wave energy

Measuring shorter waves → surface Stokes drift U

ss

→ UWB

bias for currents (not in ice):

UWB

= G Uss

Uss

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 11

4. Marginal ice zones & the future Arctic

Polar applications : The Arctic is becoming a giant marginal ice zone

wave & drift data needed by 2025 to observe this regime shift...large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean

features more fragmented thinner sea ice, stronger winds, ocean currents and waves..

(Aksenov et al., Marine Policy 2017)

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 12

4. Marginal ice zones & the future Arctic

Polar applications : The Arctic is becoming a giant marginal ice zone (Aksenov et al., Marine Policy 2017):

wave & drift data needed by 2025 to observe this regime shift

...large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean

features more fragmented thinner sea ice, stronger winds, ocean currents and waves..

→ Excellent revisit : example of 1-day coverage

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 13

4. Marginal ice zones & the future Arctic

Polar applications : - ice drift in marginal ice zone : Today's sensors fail at ice edge, - waves, - currents- freeboard → thickness ?

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 14

5. Expected SKIM resolution & accuracy

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 15

5. Expected SKIM resolution & accuracy

OSSE using TOPAZ ensembles

SKIM is expected to have a larger impacts than today's altimeters(but less than SST)

SLA SKIM

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 16

- SKIM adds new variable for Earth monitoring : total surface velocityfocus : strong currents & marginal ice zones

- leap forward for waves : new applications from nearshore to solid Earth monitoring.

- possibly other uses (warm rain, river flow …)

Questions, Comments ?

https://www.facebook.com/SKIM4EE9

http://tinyurl.com/SKIMonRG

1.5 km

http://www.umr-lops.fr/Projets/Projets-actifs/SKIM

7. Conclusions

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 17

Bonus slides :B3. Measuring waves in ice

No SAR … → only range bunching… should work at 6° incidence (caustic for 10 % slope)

For this type of waves (Hs ~ 2 m, L ~ 160 m) significant slope ~ 8 % .

Sutherland & Gascard (GRL 2016)

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 18

Bonus slides :B1. The wave bias

The current is obtained from the Line-of-Sight (LOS) velocity

Level 1 : ULOS

= UNG

+sin �i U

GD

Level 2 : UR = U

GD - U

WB

The wave bias is UWB

= G Uss,

with Uss the surface Stokes drift (wave effect)

G is a function of : - incidence angle- radar frequency - sea state (via mss_shape see Nouguier et al. 2016,

Hence Mostly wind and Hs ).

For SKIM : - 6° , mss_shape = 0.035 : G ~ 53 - 12° , mss_shape = 0.035 : G ~ 55 → For wind speed ~ 7 m/s, Uss ~ 8 cm / s, G x Uss ~ 4 m/s

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 19

Bonus slides :B1. The wave bias

The wave bias is UWB

= G Uss,

G=-1.*dsig0./sig0./dθi /(2.*tan(θ

i))

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 20

Bonus slides :B1. The wave bias

SKIM 21 June 2017, LEFE-GMMC, Brest, slide 21

Bonus slides :B2. mss_shape

Roughly we need to get UWB

= G Uss, within 4 %

to get an error under 20 cm/s (in the wind direction, for 4 to 7 m/s)