Ocean Wave Integral Parameter Measurements Using Envisat ASAR Wave Mode Data

An empirical algorithm to retrieve integral ocean wave parameters such as significant wave height (SWH), mean wave period, and wave height of waves with period larger than 12 s (H12) from synthetic aperture radar (SAR) images over sea surface is presented. The algorithm is an extension to the Envisat Advanced SAR (ASAR) wave mode data based on the CWAVE approach developed for ERS-2 SAR wave mode data and is thus called CWAVE_ENV (CWAVE for Envisat). Calibrated ASAR images are used as the only source of input without needing prior information from an ocean wave model (WAM) as the standard algorithms used in weather centers. This algorithm makes SAR an independent instrument measuring integrated wave parameters like SWH and mean wave period to altimeter quality. A global data set of 25 000 pairs of ASAR wave mode images and collocated reanalysis WAM results from the European Centre for Medium-Range Weather Forecasts (ECMWF) is used to tune CWAVE_ENV model coefficients. Validation conducted by comparing the retrieved SWH to in situ buoy measurements shows a scatter index of 0.24 and 0.16 when compared to the ECMWF reanalysis WAM. Two case studies are presented to evaluate the performance of the CWAVE_ENV algorithm for high sea state. A North Atlantic storm during which SWH is above 18 m as observed by SAR and Radar Altimeter simultaneously is analyzed. For an extreme swell case that occurred in the Indian Ocean, the potential of using SWH measurements from ASAR wave mode data derived by the CWAVE_ENV algorithm is demonstrated.

[1]  Johannes Schulz-Stellenfleth,et al.  Validation and intercomparison of ocean wave spectra inversion schemes using ASAR wave mode data , 2010 .

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

[3]  M. Earle,et al.  The Status of Data Produced by NDBO Wave Data Analyzer (WDA) Systems , 1979 .

[4]  P. G. Challenor,et al.  THE JOINT CALIBRATION OF ALTIMETER AND IN SITU WAVE HEIGHTS , 2003 .

[5]  David L. T. Anderson,et al.  Scatterometer data interpretation: Estimation and validation of the transfer function CMOD4 , 1997 .

[6]  Johannes Schulz-Stellenfleth,et al.  Global analysis of a 2 Year ERS-2 wavemode dataset over the oceans , 2007, 2007 IEEE International Geoscience and Remote Sensing Symposium.

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

[8]  S. Caires,et al.  Climatology, variability and extrema of ocean waves: the Web‐based KNMI/ERA‐40 wave atlas , 2005 .

[9]  H. Krogstad,et al.  Satellite wave measurements for coastal engineering applications , 1999 .

[10]  S. Caires,et al.  Validation of ocean wind and wave data using triple collocation , 2003 .

[11]  Xiaoming Li,et al.  Investigation of Ocean Surface Wave Refraction Using TerraSAR-X Data , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[12]  Christine Gommenginger,et al.  Measuring ocean wave period with satellite altimeters: A simple empirical model , 2003 .

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

[14]  Christine Gommenginger,et al.  A parametric model for ocean wave period from Ku band altimeter data , 2008 .

[15]  P. D. Cotton,et al.  Variability and predictability of the North Atlantic wave climate , 2002 .

[16]  Helko Breit,et al.  Wind and wave measurements using complex ERS-2 SAR wave mode data , 2000, IEEE Trans. Geosci. Remote. Sens..

[17]  Johannes Schulz-Stellenfleth,et al.  Measurement of 2-D sea surface elevation fields using complex synthetic aperture radar data , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[18]  Helko Breit,et al.  Wind and Wave measurements using complex ERS-2 wave mode data , 2000 .

[19]  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.

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

[21]  Peter A. E. M. Janssen,et al.  Progress in ocean wave forecasting , 2008, J. Comput. Phys..

[22]  S. Hasselmann,et al.  Statistical analysis and intercomparison of WAM model data with global ERS‐1 SAR wave mode spectral retrievals over 3 years , 1998 .

[23]  Arno Behrens,et al.  Operational wave prediction of extreme storms in Northern Europe , 2009 .

[24]  Bertrand Chapron,et al.  Calibration/Validation of an Altimeter Wave Period Model and Application to TOPEX/Poseidon and Jason-1 Altimeters , 2004 .

[25]  H. Storch,et al.  Statistical Analysis in Climate Research , 2000 .

[26]  Robert C. Beal,et al.  Large‐and small‐scale spatial evolution of digitally processed ocean wave spectra from SEASAT synthetic aperture radar , 1983 .

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

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

[29]  S. Lehner,et al.  A parametric scheme for the retrieval of two-dimensional ocean wave spectra from synthetic aperture radar look cross spectra , 2005 .

[30]  P. Queffeulou.  Long-Term Validation of Wave Height Measurements from Altimeters , 2004 .

[31]  David K. Woolf,et al.  Assessment of the reliability of wave observations from voluntary observing ships: Insights from the validation of a global wind wave climatology based on voluntary observing ship data , 2003 .

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

[33]  Xiaolan L. Wang,et al.  Changes of Extreme Wave Heights in Northern Hemisphere Oceans and Related Atmospheric Circulation Regimes , 2001 .

[34]  S. Lehner,et al.  An empirical approach for the retrieval of integral ocean wave parameters from synthetic aperture radar data , 2007 .