Spaceborne synthetic aperture radar observations of ocean waves traveling into sea ice

[1] Damping of ocean waves by sea ice is studied using spaceborne synthetic aperture radar (SAR) images of the marginal ice zone (MIZ) acquired by the European Remote sensing satellite ERS-2. SAR imaging of waves damped by sea ice is analyzed theoretically. The impact of sea ice on the azimuthal cutoff is studied by simulation of the azimuthal SAR image autocorrelation function as well as the two- dimensional SAR image spectrum. Typical imaging artifacts like spiky wave crests and wave refraction seen on SAR scenes of the MIZ are reproduced by simulation. Sensitivity studies are performed using models for wind sea and swell systems. It is shown that the degradation of the azimuthal SAR image resolution is dominated by the orbital velocity variance of the waves, while the coherence time of the complex radar reflectivity has a minor impact. A first-order analysis of wave damping observed on SAR scenes is carried out using a technique that was originally developed for wind estimation by Kerbaol et al. [1998]. The method does not require a priori information and is insensitive to real aperture modulation. The azimuthal SAR image cutoff wavelength is estimated and related to the orbital velocity variance of the sea surface by regression. The model is fitted on the basis of a global set of model ocean wave spectra. The technique is applied within the sea ice and in the open water in front of the ice boundary. On the basis of simple models for wind sea and swell, ocean wave attenuation rates are obtained from the observed orbital velocity decrease of waves entering the ice. The required wind information is derived from calibrated SAR data using the CMOD method. Two case studies showing examples from the Greenland and the Weddell Seas are given. It is shown that the estimated wave damping is consistent with damping parameters found in earlier field campaigns carried out in the Weddell Sea and the Bering Sea. An inversion technique providing estimates for the two-dimensional wave spectra behind and in front of the ice boundary as well as a two-dimensional filter function characterizing the sea ice impact is introduced. The technique is based on simultaneous inversion of the two-dimensional image spectra in the open water and within the ice using a priori information from an ocean wave model. It is shown that the technique gives results consistent with the first-order analysis based on the cutoff estimation.

[1]  Harald Johnsen,et al.  SAR-ocean wave inversion using image cross spectra , 1995, IEEE Trans. Geosci. Remote. Sens..

[2]  W. Alpers,et al.  On the Relative Importance of Motion-Related Contributions to the SAR Imaging Mechanism of Ocean Surface Waves , 1986, IEEE Transactions on Geoscience and Remote Sensing.

[3]  J. Apel,et al.  Principles of ocean physics , 1987 .

[4]  Peter Wadhams,et al.  Of Ocean Waves and Sea Ice , 1995 .

[5]  Peter Spellucci,et al.  Numerische Verfahren der nichtlinearen Optimierung , 1993 .

[6]  Richard E. Carande,et al.  Estimating ocean coherence time using dual-baseline interferometric synthetic aperture radar , 1994, IEEE Trans. Geosci. Remote. Sens..

[7]  D. J. Goodman,et al.  The attenuation rates of ocean waves in the marginal ice zone , 1988 .

[8]  Computation of wind vectors over the ocean using spaceborne synthetic aperture radar , 2000 .

[9]  K. Hasselmann,et al.  On the nonlinear mapping of an ocean wave spectrum into a synthetic aperture radar image spectrum and its inversion , 1991 .

[10]  J. Ewing,et al.  Directional Wave Spectra Observed during JONSWAP 1973 , 1980 .

[11]  D. Hartmann.  Global Physical Climatology , 1994 .

[12]  Robert A. Shuchman,et al.  SAR imaging of waves in water and ice: Evidence for velocity bunching , 1985 .

[13]  Paris W. Vachon,et al.  Observation of wave refraction at an ice edge by synthetic aperture radar , 1991 .

[14]  Peter Wadhams,et al.  Waves in frazil and pancake ice and their detection in Seasat synthetic aperture radar imagery , 1991 .

[15]  P. Heimbach,et al.  An improved algorithm for the retrieval of ocean wave spectra from synthetic aperture radar image spectra , 1996 .

[16]  David R. Lyzenga,et al.  An analytic representation of the synthetic aperture radar image spectrum for ocean waves , 1988 .

[17]  P. Vachon,et al.  Ship Detection by the RADARSAT SAR: Validation of Detection Model Predictions , 1997 .

[18]  Paris W. Vachon,et al.  Airborne and spaceborne synthetic aperture radar observations of ocean waves , 1994 .

[19]  Paris W. Vachon,et al.  Wave propagation in the marginal ice zone: Model predictions and comparisons with buoy and synthetic aperture radar data , 1991 .

[20]  C. Mastenbroek,et al.  A semiparametric algorithm to retrieve ocean wave spectra from synthetic aperture radar , 2000 .

[21]  S. Lehner,et al.  Mesoscale wind measurements using recalibrated ERS SAR images , 1998 .

[22]  P. Vachon,et al.  Analysis of ERS-1/2 synthetic aperture radar wave mode imagettes , 1998 .

[23]  D. Ross,et al.  On the detectability of ocean surface waves by real and synthetic aperture radar , 1981 .

[24]  R. Shuchman,et al.  Extraction of marginal ice zone thickness using gravity wave imagery , 1994 .

[25]  Paris W. Vachon,et al.  Airborne synthetic aperture radar observations and simulations for waves in ice , 1993 .

[26]  Omar H. Shemdin,et al.  Models for synthetic aperture radar imaging of the ocean: A comparison , 1990 .

[27]  Ola M. Johannessen,et al.  Analysis of merged SMMR‐SSMI time series of Arctic and Antarctic sea ice parameters 1978–1995 , 1997 .

[28]  R. Raney,et al.  Theory of synthetic aperture radar ocean imaging: A MARSEN view , 1985 .

[29]  Harald E. Krogstad,et al.  A Simple Derivation of Hasselmann's Nonlinear Ocean-Synthetic Aperture Radar Transform , 1992 .

[30]  P. W. Vachon,et al.  Generalizations of the non‐linear ocean‐SAR transform and a simplified SAR inversion algorithm , 1994 .

[31]  Werner Alpers,et al.  Monte-Carlo simulation studies of the nonlinear imaging of a two dimensional surface wave field by a synthetic aperture radar , 1990 .