“Ice-T”: an autonomous float for real time measurement of ice-thickness and

thermal exchanges at the ocean-ice-atmosphere interface

Frédéric Vivier1 , Antonio Lourenço1,

Antoine Guillot2, Bertrand Alessandrini3, Pascale Bouruet-Aubertot1, Yannis

Cuypers1, Jean-Claude Gascard1, Hervé LeGoff1, Thierry Monglon1

1: CNRS, LOCEAN-IPSL, Université Pierre et Marie Curie, Paris

2:CNRS, INSU Technical Division, Brest

3: LMF, Ecole Centrale Nantes, Nantes

Frederic.Vivier@locean-ipsl.upmc.fr

Antonio.Lourenco@locean-ipsl.upmc.fr

Motivations

The seasonal sea ice zone is getting larger at the expanse of

multiyear ice.

Is it possible to build an instrument, able to sustain thin ice

conditions, to monitor ice-thickness and heat fluxes not only within

the ice but also at both interfaces?

As a step in this direction: developing “Ice-T” (Ice-Thickness )

Intended applications:

document thermal exchanges at the ocean/ice/air interface in different contexts (thick / thin ice, coastal polynia).

validate satellite estimates (eg, upcoming CryoSat-2): ice-thickness, and ideally providing snow load, water density and ice density.

Ice-T prototype Floating instrument. Intended deployment: already formed ice, prior to ice

formation (to be tested), coastal polynia,.. 1 year autonomy. Real time transmission through iridium communication system (duplex

mode: possibility to change sampling rate) Current prototype measures :

ice thickness evolution, thermal profiles within ice and snow, estimate of snow layer thickness, GPS position: ice drift ocean currents at the base of the ice (horizontal heat flux in the OML,

ocean-ice heat flux). No atmospheric fluxes measured yet (except for Pa and Tair) , but developed

with concerns of versatility (electronics engineered to host additional sensors)

Cost effectiveness (deployed in a destructive medium, non recoverable).

A two-body instrument:Surface float trapped in ice: barometer, thermistor string,

inclinometer, GPS, iridium modem, motherboard, batteries

Subsurface float (“fish”), 5m below: sonar altimeter, pressure

sensor, inclinometer+compass.

- Ice draft:

- Ice thickness:

- Thermistors (+inclinometer) used to estimate heat fluxes, heat

content and in the discrimination of snow/ice layers

- Inclinometer+compass in the fish used to estimate surface current

w.r.t. ice. cost-effective currentmeter! Absolute ocean currents

obtained after ice drift correction (GPS data).

ti=ρw H−m s

ρ i

H=Palti− Patm

ρw g−Halti

Hydrodynamics of the “fish”:Measuring ocean currents underneath the ice

• In the presence of current, motions of the fish must be kept under control.

• Why not using embedded sensors to estimate surface ocean current?

– Effect of drag: fish tilting and rising.– Tilt measured accurately (0.2°)

• Numerical simulator of the dynamical response of the system:

to aid the design needed to transpose the velocity/ tilt

relation to in situ T-S conditions.• Developments on shape and mass

repartition to improve response at low velocities.

• Numerical simulations and towing tank experiments indicate accuracy of <2cm/s

Bassin d’essai des carènesEcole Centrale Nantes

In Situ tests

• Project started in 2005 (funding Institut Pierre-Simon Laplace)

• Prototype completed in March 2007

• Deployed in the Storfjord, Svalbard March-April 2007 (“IceDyn” campaign funded by IPEV + DAMOCLES logistics)

• part of a larger experimental setup...

• Ice-T prototype worked fine during the whole experiment (6 weeks)

Vagabond (DAMOCLES)

deployment. weight: 40kg

Atmospheric parameters

Yes we would love to implement the GTS protocol for future deployments! (just tell us how)

Ice thickness

manual soundings

Can we determine snow layer thickness, snow load?

Abrupt snow fall can be detected from underwater pressure, providing directly snow load

Difficult to disentangle changes in ice-thickness and snow load for smoother variations (precipitation, evaporation)

Need to use the information from other sensors onboard.

Thermal measurements

Thermal measurements

In the fjord ...

Surface current measurements: drifting instrument.

Estimate of surface currentsMODIS: March 18, 2007, 10h55

Surface current measurements:

comparison with ADCP

Ongoing and future plans (I) Ocean-ice heat flux can be estimated as a residual of the

heat budget (errors...) Alternatively,direct estimates (McPhee, Kikuchi, Morison,

Stanton, GRL 2003):

Friction velocity determined from ice-ocean velocity Salinity missing (density, freezing point): implementation

of a conductivity sensor in progress... Handling of 16 additional thermistors:

refine sampling, in particular near ice/snow boundary. Alternatively sampling of the ocean mixed layer (short drogue)

Ongoing and future plans (II)

bigger project pending: OPTIMISM (Observing dynamical and thermodynamical Processes involved in The sea Ice Mass balance from In Situ Measurements)!

Scientists from 4 labs (LOCEAN, CETP, LMF, DT-INSU), including meteorologists (A. Weill, L. Eymard, S. Letourneur) and radar altimeter specialist (M. Dechambre)

Development (and deployment) of 9 buoys. Implementation of a short meteo mast equipped to

measure turbulent and radiative fluxes on some floats. Technological challenge given the constraints in terms of payload and energy (lightweight platform!).