Utilization of ASAR wave mode data for shipping safety

Safety of shipping is a growing concern. The causes of shipping casualties are various, while over 30% of the casualties are due to bad weather. Heavy sea state and severe weather conditions have caused the loss of more than 200 large cargo vessels within 20 years between 1981 and 2000. Remote sensing techniques, particularly the active microwave radar provides global sea surface observations for detecting heavy sea state and bad weather independent of clouds and sunlight and therefore it can contribute to shipping safety. A dataset of synthetic aperture radar (SAR) images spans nearly two decades since the launch of ERS-1 in 1991 for operational observations. When no other operations are requested, ERS-1, 2 SAR and ENVISAT ASAR can collect data as small images of 10 km times 5 km size every 200 km or 100 km along the satellite´s orbit. This kind of data is called SAR wave mode data and can be acquired continuously and globally over the sea surface. Using the integral wave parameters derived from SAR wave mode data, global sea state statistics can be carried out. In the present paper, significant wave height and zero upcrossing wave periods derived from ASAR wave mode data using the CWAVEENV empirical algorithm are compiled into a global wave atlas. Wave steepness is a crucial parameter for shipping safety. By using integral wave parameters derived from ASAR wave mode data, wave steepness is calculated and compiled to the global wave atlas as well.