Investigating Coastal Polynya Thin Sea Ice State in the Laptev Sea Using TerraSAR-X Dual-Pol Stripmap Data

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1 Investigating Coastal Polynya Thin Sea Ice State in the Laptev Sea Using TerraSAR-X Dual-Pol Stripmap Data Thomas Busche (1), Irena Hajnsek (1), Thomas Krumpen (2), Lasse Rabenstein (2), Jens Hoelemann (2), Christian Haas (4), Sascha Willmes (5) (1) German Aerospace Center (DLR) e.v, Germany (2) Alfred Wegener Institute, Bremerhaven, Germany (4) University of Alberta, Edmonton (Alberta), Canada (5) University of Trier, Trier, Germany 28-Jan-2009

2 Project Framework Russian/German project: Laptev Sea System Focus on year-round round integrated system studies of sea ice cover, water column and sea floor across and along the Laptev Sea polynya system. Project duration: Funding: Minobrnauki Russia, BMBF Germany Project leader: H. Kassens,, Kiel Expeditions: 5 expeditions organized by Arctic & Antarctic Research Institute (AARI), St.Petersburg & IFM-GEOMAR, Kiel WP 1 & 4 (Inst. of Marine Science-GEOMAR: Kiel): Oceanography WP 2 (AWI): Polynya dynamics + Remote Sensing WP 3 (Trier): Meteorology Support by: : ESA Proposal AO500 & TerraSAR-X X COA0388 WP3: Atmospheric dataset WP2: Polynya dynamics WP1/4: Ocean model + Isotope Role of polynya for AO water mass modification 2

3 Objectives Polynyas are regions of open water surrounded by sea ice, which remain unfrozen for much of the year. Polynyas are regions of high ice production and sensible to climate change. Are the polarimetric parameters extracted from TerraSAR-X dual-pol data sensitive to thin sea ice thickness? Can those parameters been used for thin sea ice inversion?

4 Transdrift XIII Expedition Activities Satellite Observations: Envisat ASAR Wide Swath Mode (WSM) data in Near Real Time (NRT), C- band, single polarisation (2-3 h after data take available, fully automatic by ), swath width 400km, large scale study, field work & flight planning TerraSAR-X StripMap Mode, dual-pol (HH-VV), 15km swath width Optical data: MODIS, AVHRR Helicopter-Observations: Electromagnetic EM-Bird sea ice thickness measurements (profile flights) Nadir-Looking Digital Camera (GPS connection) Ground Based Methods Sea Floor Mounted Mooring (Acoustic Doppler Current Profiler ADCP, continuously) Ship observations and ground based measurements (oceanography)

5 Polynyas and water mass modification Fast Ice Lena Delta Thin ice Pack ice 5

6 EM induction sea ice thickness sounding

7 EM Bird AWI s EM Bird

8 ENVISAT ASAR WSM time series observations 08/04/ /04/ /04/ /04/ /04/ /04/2008

9 TerraSAR-X Dual Pol HHVV 16 TerraSAR-X X Strip map mode data takes, Dual-Pol HH/VV, between April and May 2008 ENVISAT ASAR WSM Magenta:Overlay of TerraSAR-X Footprints Red: Fast Ice Border

10 Coincident data takes of EM-Bird & TerraSAR-X Profile (3 dates) TerraSAR-X : TerraSAR-X : TerraSAR -X: Blue: TerraSAR-X footprints; Red thickness profiles, overlay on ENVISAT ASAR WSM

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12 Processing Steps Data Processing (TerraSAR-X and EM Bird, ): Correction of sea ice drift for the EM bird thickness profile, due to time difference of 3.5 h between data takes: Initial estimate of drift by feature tracking of 2 TerraSAR-X scene Reconstruction of drift trajectory by means of climatological data (wind direction and speed) First order residual motion compensation for thickness profile (correction of correlation of thickness with flight altitude) Polarimetric processing of TerraSAR-X SLC data (dual-pol HHVV) Polarimetric coherence 2D eigenvector analysis (Entropy, Anisotropy, Alpha Angle etc.) Copol ratio Signature extraction and plot vs. sea ice thickness

13 EM Bird Sea Ice Thickness Profile & Histogram Negative Thickness Values: Only relative thickness values available at the moment! Thicker Sea Ice

14 First Polarimetric Analysis Results: HHVV Coherence HHVV coherence [mean] mean sea ice thickness

15 First Polarimetric Analysis Results: HHVV Coherence Phase HHVV coherence phase [mean] 20 degree mean sea ice thickness

16 First Polarimetric Analysis Results: Polarimetric 2D Entropy 2D Entropy [mean] mean sea ice thickness

17 Summary: Some of the polarimetric parameters seem to be sensitive to thin sea thickness change, Polarimetric TerraSAR-X data may be a useful tool Dual pol X-band data provides informations for thin ice classification of sea ice surfaces Inversion of thin sea ice thickness may be feasible: A combination of several polarimetric parameters is suggested to increase the information content

18 Open Question: Dependency of polarimetric parameters to incidence angle change and upper limit of sea ice thickness sensitivity: Additional experiments are planned Connection to scattering theory (Winebrenner et al. 1995, Radio Science, Vol. 30, No 2) Future work: Fine-tuning of drift correction algorithm Enhanced motion compensation by means of DGPS processing for the thickness profiles to come to absolute thickness values Development of an EM model based inversion algorithm

19 Thank you for your attention! Questions, recommendations?