Remote sensing of

oceanic mesoscale processes

Hui Shen, Will Perrie, Catherine Johnson

Bedford Institute of Oceanography

Fisheries and Oceans Canada

Email: Hui.Shen@dfo-mpo.gc.ca2019-05-31OceanPredict'19

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Outline

A brief introduction of mesoscale oceanic processes

Remote sensing techniques for mesoscale processes

observations

Altimeter, Radiometer, HF radar, high resolution

spectrometer, and Synthetic Aperture Radar (SAR)

Mesoscale feature measurements by SAR

Internal waves in Gulf of Maine

Eddies in Labrador Sea

Summary and future perspectives2019-05-31OceanPredict'19

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Oceanic mesoscale processes

Mesoscale:

days to weeks

~100 km

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Oceanic mesoscale processes

Mesoscale:

days to weeks

~100 km

Processes

Eddies

Fronts

Internal waves

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Mesoscale:

days to weeks

~100 km

Importance:

Energy cascade

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Oceanic mesoscale processes

Oceanic mesoscale processes

Mesoscale:

days to weeks

~100 km

Importance:

Energy cascade

Ocean mixing

Vertical mass transport

Driver of local ecology system

Etc. OceanPredict'19

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Faghmous et al., 2011

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Mesoscale:

days to weeks

~100 km

Importance:

Energy cascade

Ocean mixing

Vertical mass transport

Driver of local ecology system

Etc.

Observation of mesoscale processes

Eddy: ship, transect, buoy vs. eddy, isw.

Advantage; most reliable first hand observation,

temporal resolution

Disadvantage: spatial resolution, miss

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Indian Ocean GEOTRACES cruise sections ©

Remote sensing of mesoscale processes

Altimeter

SSHA

Barotropic balance – map

Warm eddy –

Cold eddy –

Operational example:

GlobCurrent®

Drushka et al. SWOT Tseng et al., 2010

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Remote sensing of mesoscale processes

Altimeter

SSHA

Radiometer

SST

Spectrometer

Ocean color

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Remote sensing of mesoscale processes

Altimeter

SSHA

Radiometer

SST <ageostropic >

HF radar

Current vector

IMOS

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High resolution imaging

and its application to mesoscale observations

How high

~Meter resolution

Remote sensing mechanism

Ocean color - optical remote sensing

Surface roughness – SAR + optical

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SAR-Synthetic Aperture Radarmicrowave band (all day, all weather, no clouds)

active monitoring

sensitive to roughness (cm)

SAR sees the capillary waves!

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Optical remote sensing - radiometry

SPIE

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High resolution imaging

and its application to mesoscale observations

Case 1

Internal waves in Gulf of Maine

Sentinel-2 2018/08/102019-05-31OceanPredict'19

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How remote sensing sees ISWs from surface

Alpers theory (Nature

1980)

Coherent modulation

on surface capillary

waves, was sensitive to

the remote sensing

Eyes are blurred /

confused by ocean

color

Ocean surface features

(bubbles, breakings)Field measurement in SCS

2009.05 (Courtesy: P. Hu) 2019-05-31OceanPredict'19

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ISW and Fish school

TerraSAR-X image acquired on 23 June 2008 at 22:25 h

UTC over Cape Cod Bay, showing two large ISW trains

emanating from Race Point Channel with bathymetry

overlaid on the SAR image.

Fig. Internal wave train from acoustic backscatter

on 1 August 2008. Backscatter arising with the

internal wave (16:37 h) was identified as sand

lance. [Pineda et al., 2015 JGR]

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High resolution imaging

and its application to mesoscale processes observations

Internal waves in Gulf of Maine

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High resolution imaging

and its application to mesoscale observations

Internal waves in Gulf of Maine

FVCOM [Chen et al. 2003] Shen, H., W. Perrie, C. Johnson. Predicting internal

solitary waves in Gulf of Maine. In preparation

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Internal wave footprints

Properties of the ISW:

Speed

Wavelength

Amplitude

Mixed Layer Depth

(MLD)

Stratification

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High resolution imaging

and its application to mesoscale observations

2. Labrador Sea Eddies

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High resolution imaging

and its application to mesoscale observations

Labrador Sea Eddies

2010-02-25

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Deep convection within an eddy

Preconditioning

~ large-scale (order of 100 km)

Deep convection

Localized, intense plumes (~1 km)

Lateral exchange

Baroclinic instability, eddies (~10 km)

Re-stratification

OPEN-OCEAN DEEP CONVECTION

Marshall and Scott, 1999

Legg et al., 1998

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Deep convection within an eddy

Preconditioning

~ large-scale (order of 100 km)

Deep convection

Localized, intense plumes (~1 km)

Lateral exchange

Baroclinic instability, eddies (~10 km)

Re-stratification

OPEN-OCEAN DEEP CONVECTION

Marshall and Scott, 1999

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High resolution imaging

and its application to mesoscale observations

Labrador Sea Eddies – Irminger Ring

Kawasaki & Sasumi, 2014

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Summary and future perspectives

Remote Sensing provides unique measurements to

oceanic mesoscale processes

Morden high reolsuiton imaging measurement provide

detailed features of mesoscale processes

High resolution remote sensing data was used to study

the internal waves in Gulf of Maine and eddies in

Labrador Sea

Challenge remains to take the fully advantage of the

high spatial resolution, for bettering understanding of

oceanic processes.

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Thank you for your attention

Comments?

Hui.Shen@dfo-mpo.gc.ca

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St. Laurent & Garret,

2002

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Model validation?

Chanut et al. (2008)

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