SMOS over Antarctica - a short story of massive icebergEwa Slominska, (email:ewa@cbk.waw.pl)W. Marczewski, J. Slominski

Space Research Center PAS

Introduction & Motivation

For nearly a year, the drifting iceberg was tracked on the SMOS data.

An isolated, floating along Antarctica, set of8-10 SMOS DGG pixels is a focal point for thisanalysis. It was characterised by an excess inbrightness temperature of approximately 30K,when compared to surrounding open water.

As part of a natural cycle, ice shelves periodicallycalve icebergs. In March 2000, Antarctica’s RossIce Shelf released a colossal berg, assigned asB-15. The B-15 was the world‘s largest recordediceberg with the area of over 11,000 km2. B-15started to break into smaller pieces in 2002 and2003. One of the pieces from the “B-15 family”(more precisely B-15J) was spotted by theSMOS satellite.

Figure 1: SAR image from ENVISAT taken on

the 25th of August, 2011 at 10:25:04, was used

for the iceberg identification. With a little help

from the CESBIO SMOS Blog followers the

iceberg was identified as the B15J (more de-

tails [1]).

Observation on a massive “natural buoy” could be additional source of information forthe studies on sea - sea-ice - ice interactions.

Goals

Examine the motion of spotted object: trajectory, averaged speed, distance...

Examine the iceberg evolution in terms of brightness temperature measured by SMOS.

Examine polarimetric characteristics for the DGG pixels corresponding to tracked iceberg.

Approach

SMOS Level 1c browse Land and Sea Data were merged in order to produceweekly averaged global maps for the first Stokes parameter. - This provides relevantinsight into dynamics of processes observed by SMOS. Temporal evolution of the firstStokes parameter revealed set of several DGG pixels drifting from the Ross Sea eastwards.Comparison with ENVISAT images confirmed that spotted object is an iceberg (Figure 1).

Figure 2 shows four snapshots with marked iceberg path (from January to December,2011). In order to enhance floating object, the colour scale was modified on purpose. Itis further applied to temporal analysis of I .

For the whole examined dataset, SMOS DGG pixels corresponding to the tracked iceberg,were extracted, in order to examine temporal evolution of brightness temperature. (seeFigure 7)

Figure 2: Set of SMOS L1c browse sea data for ascending passes, illustrating iceberg trajectory. The colour scale has been modified onpurpose, to better distinguish the drifting object. With such an approach areas belonging to the same TB regime are directly shown.

Polarimetric characteristics, iceberg position, drift velocity - Analysis & Results

Polarimetric characteristics for selection of DGG pixels belonging to the iceberg weregrouped into separate sets according to location and time criteria.

Figure 3: Selected set of polarimetric characteristics for the central pixels of the tracked iceberg

Figure 4: Comparison of the first Stokes parameter for the central pixels of the iceberg, and one randomly

picked DGG pixels in the open water, and another one in the closest area of the DOME-C station (reference

and calibration site for SMOS)

Icebergcharacteristics, werecompared with thoseprepared for thefollowing DGG pixels,one located in thevicinity of DOME-C(DGG: 7181359 -123.383 E, 75.272 S)and another one inthe open water (DGG:6221186 - 150.102 W,60.109 S) - Figure 3.

In the same manner,comparison for the 1st

Stokes was done -Figure 4.

I parametercorresponding toiceberg pixels revealsnoticeable change inits shape during theexamined period.

In order to roughly estimate iceberg velocity, the distance betweentwo consecutive locations has been computed with basic haversineformula. Estimated velocities are plotted along the trajectory (seeFigure 5). This result should be compared with the same plot but forthe first Stokes (Figure 6). Results from figures 5 and 6 are combinedin the Figure 7, showing temporal evolution of Vdrift and (I ) . Thegreen line in the Figure 7 marks the averaged velocityV̂drift = 6.22km/day computed with assumption about the great-circledistance (white line in the Figure 5) .

Figure 5: Vdrift along the trajectory, white line marks the great-circle distance used

for estimation of averaged V̂drift.

Figure 6: Values of the I parameter for the central pixel of the iceberg.

Figure 7: Time evolution of Vdrift and (I ).

Discussion & Conclusions

The derived iceberg motion indicated significant change of direction

in the middle of September 2011, when the berg started to move

equatorwards. Straying from Antarctica, was accompanied with

sequential decrease of the brightness temperature. At the end of

December, the signatures of observed iceberg were barely apparent,

making further tracking not feasible.

It seems highly probable that SMOS documented the final stage of

evolution of B-15J.

Estimated velocities depict several cases where dramatic increase of

Vdrift is noted. It is mainly at final days of observations. The

explanation for such an results is highly related to problems of

accurate detection and positioning of the tracked object. Thus all

velocities greater than 40 km/day should be rejected and not

considered as the physical values.

Distance: integrated along the trajectory: Dtraj = 4994.71km,

obtained from great-circle assumption Dg−c−d = 2172.1km

Presented analysis is the initial step for better understanding

various cryospheric processes and is the first approach to the

application of such models as MEMLS (Microwave Emission Model

for Layered Snowpack).

References

[1] CESBIO SMOS blog - http:

//www.cesbio.ups-tlse.fr/SMOS_blog/?tag=iceberg

[2] Full evolution of the drifting B15J -

http://www.cbk.waw.pl/~ewa/SMOS/iceberg

[3] Kerr, Y. H., P. Waldteufel, P. Richaume, P. Ferrazzoli, and

J.-P. Wigneron: SMOS level 2 processor soil moisture

Algorithm Theoretical Basis Document (ATBD), Toulouse,

France: CESBIO, vol. SO-TN-ESL-SM-GS-0001, V3.a, 2008.

Acknowledgements: This work has received fundings in the frame of the PECS program, named SWEX-R, realised between ESA and partners from Poland. SMOS data were provided by the ESA EOPI Cat-1 project SMOS Cal/ Val 3275

http://www.cbk.waw.pl/~ewa/