Clean signals and calm seas

Satellite altimetry is a major tool in the workshop of geophysicists. Over oceans, altimetry provides data on the height of waves and of the sea surface itself, and allows wind information to be deduced. Paradoxically, when the sea is calm and highly reflective to an altimeter’s radar—like during surface-smoothing oil spills or algae blooms—the backscattered waveform is highly distorted and often unusable; about 5% of altimetry data are thus affected. But the distorted data are still rich in structure. Jean Tournadre of the French Research Institute for Exploitation of the Sea, in Plouzané, France, noticed that some features were similar to those seen when a radar pulse is impacted by small atmospheric rain cells within the altimeter’s 8- to 10-km wide “footprint.” He and his colleagues then developed a model to analyze the distorted data in terms of small slick patches and applied the model to several different realistic cases....