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Ocean Wave Measurements in High and Complex Sea State by SAR Wave Mode Data and Numerical Wave Model

Xiaoming Li(1), Susanne Lehner(1) and Johannes Schulz-Stellenfleth(1)

(1) German Aerospace Center (DLR), Oberpfaffenhofen, 82234, Wessling, Germany

Abstract

In the present paper, ocean wave parameters, such as significant wave height and swell significant wave height, as well 2D spectrum are compared to the empirical algorithm CWAVE, retrieval algorithm PARSA (Partition Rescale and Shift Algorithm) and the numerical wave model WAM and ERA-40 reanalysis results in the high and complex sea state. Part of this work is carried out in the framework of the ESA OSIRIS project.

The research aim is to improve the forecast in numerical wave models in high and complex sea state and better understand the ocean swell propagation on a global scale. The comparison is carried on in some cases studies, which include the North Pacific winter storm, the South Pacific cross seas, the Indian Ocean extreme swell and storms in the North Atlantic.

A severe storm case study in the North Pacific on November 28, 1998 is presented. The reanalysis and hindcast model results show that the highest significant wave height is higher than 10 meters. ERS-2 SAR has an ascending and a descending pass through the storm and provides a good measurement of the real sea state. The significant wave height along the ERS-2 SAR orbits is derived from the two algorithms, and compared with the collocated ERA-40 reanalysis data, WAM model results and ERS-2 Altimeter data. The analysis shows that in low and moderate sea state, the model results agree well with the Altimeter data and SAR measurements, however in the high sea state, the significant wave height is underestimated by the model results.

The WAM model 2D spectra show that the cross sea case in the South Pacific Ocean in August 2000 has two distinct swell peaks originating from different storms. However, the energy of the two individual swell system of the WAM model is different from the PARSA retrieved result. The reason is that the input wind field for WAM model is underestimated compared to Quickscat data.

For the La Reunion Island (Indian Ocean) extreme swell in May 2007, the observed and forecast data show that the extreme swell has a peak wave period near 18 seconds and the generated significant wave height in the coast of Reunion Island is around 10 meters. The swell generated by the storms travelled more than 6000 km to Indonesia islands and west coast of Australia. Based on the observation of Envisat ASAR wave mode data, swell significant wave height derived from CWAVE algorithm is compared with German weather service (DWD) model results, which provides the information that the swell dissipation term in the numerical wave model seems not accurate.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry