Introduction to Microwave Active Techniques and Backscatter Properties

The present article introduces active microwave techniques that are used for remote sensing of the European seas, focusing on RAdio Detection And Ranging (RADAR) and Synthetic Aperture Radar (SAR). In section 1 the ranging principle and associated topics are introduced. As an example of this technique the radar altimeter is described. Radar altimeters employ the ranging technique for one-dimensional sea surface measurements from space. In section 2, two-dimensional imaging systems will be discussed. The addition of resolving power in a second dimension perpendicular to radar ranging leads to imaging devices that exist in many varieties. The major imaging systems that are in use today for remote sensing of the sea will be described, e.g. rotating beam radars, Side looking airborne radar, Synthetic Aperture Radar and polarimetric SAR. Section 3 deals with matters concerning radar backscatter: the basic concepts and definitions, speckle, and backscatter properties of the ocean. Furthermore, Bragg scattering, angular, wind and wave dependences of the backscatter, leading to the main oceanographic applications, are discussed.