Gerdes, Rüdiger

Hendricks, Stefan

Hoppmann, Mario

Hunkeler, Priska

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 It is important to account for conductive layers inside or at the top of complex sea-ice features. The existing assumptions of conductive sea water and layered resistive sea ice should no longer be used, especially not for multi-frequency applications.Comprehensive data set from the Atka Bay, Antarctica, November 2013 to January 2013            Porous sea-ice layer is located below the            solid sea iceFrom comparison of calibration data with model data, the sub-ice platelet layer conductivity can be estimated (700-1000 mS/m) for different frequencies and compo-nents (here 5310 Hz, quadrature). With Archie‘s law, the porosity of the platelet-ice layer can be estimated:Pressure ridge ground truth data set from the Weddell Sea, June-August 2013            Sea-ice thickness varies on sub-footprint scale Data from drillings, one cross-sectionRaw GEM-2 data ac-quired over the cross-section1D Inversion EM1DFM from UBC (University of British Columbia)SnowSea IceSea Water0 mS/m~ 20 mS/m20-50 mS/m2200 - 2700 mS/mAirhlh0ZConductiveNon-conductiveRx Tx Rx TxStandard assumptions ...  The sea-ice layer is described as a level plateSea ice and snow are non-conductive, whereas sea water is conductiveObjectivesThese standard assumptions are not valid for platelet ice and pressure ridges. With the processing of mul-ti-frequency GEM-2 data we overcome the limitations of a homogeneous half-space model.... and their limitationsIce thickness variability on sub-footprint scale cannot be resolved (e.g. sea- ice pressure ridges)Non negligible conductivity in the ice layer gives a bias in the 1D ice-thickness estimates. It is not possible to resolve for platelet-ice, floo-ded ice or internal conductive ice structures Upcoming working tasks:Absolute calibration of the in-strument by correction the data for drift and zero-measure-ments and adjusting gain and phase during the post-proces-singProcessing the promising da-taset with a suitable inversion algorithm (2D, inversion for thickness only)The measurements are acquired in a very conductive environ-ment (ocean water: 2700 mS/m)The environmental temperature can reach from -30 up to +10°C           Problems with tempera-           ture dependent drift of           the instrumentEnvironmental conditionsBulk conductivity of sea ice (here 1 S/m)Brine conductivity (here 2.7 S/m)Porosity (relative volume fraction of fluid)Constant (1.55-2.2), depends on the solidphase of porous media (here 1.75)Empirical scaling parameter (here 1)The porosity of the sub-ice platelet layer is an unknown parameter, but important for the sea-ice mass balance of Antarctic landfast sea ice. State of the art single-frequency sea-ice thickness retrieval (Geonics EM-31 / Geophex GEM-2)Exponential repre-sentation of one fre-quency (here quad-rature, 5310 Hz) at one location in diffe-rent heights Atka BayAtka BayGEMMulti-Frequency Electromagnetics for Sea-Ice Thickness RetrievalBREMERHAVENAm Handelshafen 1227570 Bremerhaven Telefon 0471 4831-0www.awi.deReferencesG. S. Dieckmann and H. H. Hellmer. Sea Ice, pages 1-22. Wiley-Blackwell, 2010. The Importan-ce of Sea Ice: An Overview.C. Haas, S. Gerland, H. Eicken, and H. Miller. Comparison of sea-ice thickness measurementsunder summer and winter conditions in the Arctic using a small electromagnetic inductiondevice. Geophysics, 62(3):749-757, 1997.J. Kipfstuhl. On the formation of underwater ice and the growth and energy budget of the seaice in Atka Bay, Antarctica. Reports on Polar Research, Alfred Wegener Institute for Polarand Marine Research, Bremerhaven, (85), 1991.A. A. Pfaffhuber, S. Hendricks, and Y. A. Kvistedal. Progressing from 1D to 2D and 3Dnear-surface airborne electromagnetic mapping with a multisensor, airborne sea-ice explorer,Geophysics, 77(4):109-117, 2012.Priska Hunkeler, Dr. Stefan Hendricks, Mario Hoppmann, Prof. Dr. Rüdiger Gerdes25th Schmucker-Weidelt-Colloquium on deep electromagnetic sounding,Kirchhundem Rahrbach, September 23-27, 2013  MotivationGEM-2 and Sea Ice Data and ResultsConclusion and OutlookDifferent types of sea ice can be found in both Polar Regions depending on the growth history, the season and environmental conditions. In Antarctica, a special sea-ice type is present below the solid sea ice. This porous sub-ice platelet layer contributes significantly to the total sea-ice mass and energy balance of Antarctic landfast sea ice and forms a unique habitat for planktonic organism. Little is known about the platelet-layer thickness and its large-scale distribution in the Antarctic.In general, high resolution sea-ice thickness data are sparse, but important for validation of  high spatial coverage satellite data. One method to measure sea-ice thickness with high resolution is fre-quency domain electromagnetic (FDEM) induction sounding.Arctic summer sea iceAntarctic winter sea iceSub-ice platelet layerDepth [m ]Recovered con- ductvity [S/m]Quadrature [ppm ]Depth [m ]resistive sea iceconductive sea waterconductive surface floodingwater layerDistance [m]SoundingPressure ridgesThis work is the first step to replace traditional homogeneous half-space sea-ice thickness retrieval algorithms, by more de-tailed 1D/2D inversion schemes of multi-frequency FDEM data.Furthermore, the data lays the foundation for future larger scale airborne electromagnetic surveys with the multi-frequency device MAiSIE (Multi-Sensor Airborne Sea-Ice Explorer).internal water layer ???Atka BayWeddell Sea The characterization of the state of the sea-ice cover is of great importance for the evaluation of the polar climate system. Satellite data show a rapid reduction of summer sea-ice extent in the Arctic, which culminated in a new record minimum in September 2012. In the Antarctic re-sults of average September sea-ice extent show a small positive average trend over the last three decades.Sub-ice platelet layerGEM-2sea ice sea icesea ice

Multi-Frequency Electromagnetics for Sea-Ice Thickness Retrieval

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