Radar is an actives instrument, an all-weather eye. The radar beams emitted from the satellite illuminate the earth independently of the availability of sunlight, penetrate clouds, and, with the help of special reception and processing methods, produce from the returning radiation especially high resolution images of the rough surface of the ocean.
With high-resolution satellite radars and synthetic aperture radar (SAR) such as the SARs on ERS and ENVISAT or on the German TerraSAR-X satellite, images of the ocean surface can be recorded also under storm clouds or at night, and from their intensity and structure, wind fields and wave heights can be derived. This information can then be used, for example, to improve sea weather forecasts and thereby reduce the number or seriousness of shipping accidents.
The resolution of SAR images of ocean waves is so superior that even individual wave crests can be detected and measured, making it possible also to identify extremely high, so-called rogue waves.
Smooth surfaces such as freshly-frozen ocean ice or oil pollution appear dark on SAR images because they reflect the radar beams away from the recording satellite. This circumstance is useful for detecting surface oil. Radar monitoring from satellites, for example by the European Maritime Safety Agency, EMSA, has also contributed to reducing the oil pollution in European waters to a significant extent. SAR data are also used to provide advice about shipping passages on icy routes.
Because of the high reflectivity of metal and the high resolution of SAR sensors, they are also used to detect ships; this data can then be compared with ship reporting data.
The SAR Oceanography team develops algorithms to identify wind fields, ocean wave parameters, and sea ice cover, to investigate shipping accidents, and to monitor oil pollution. The results are then validated in experiments and ship expeditions, for example with the “Polarstern.”