ABSTRACT
Radar (RAdio Detection And Ranging) is an active microwave system composed of a transmitter and a receiver. The radar transmits a pulse of electromagnetic energy, and waits for the echo from the target to return. Based upon the echo delay time between the transmitted and received pulse, it is possible to estimate the distance to the object being imaged. By using spaceborne imaging radars, one can image large areas on Earth frequently and independent of daylight and weather conditions. In order to obtain high spatial resolution, the principle of Synthetic Aperture Radar (SAR) has been developed. By the use of an advanced signal processing technique, a large synthetic aperture (synthetic antenna length) is created, allowing a fine resolution and signal phase preservation. The first Earth observing spaceborne SAR was the National Aeronautics and Space Administration (NASA) SEASAT satellite, launched in 1978. Despite its relatively short lifetime, SEASAT proved the SAR instrument’s capability to retrieve geological and geophysical information about the surface of the earth and the oceans. Following SEASAT, a series of spaceborne SAR sensors have been launched. The most successful satellite programme, with respect to SAR applications, has been the European Space Agency (ESA) ERS-1 and ERS-2 satellites followed by Envisat. In Table 9.1 some SAR missions and their important parameters are listed.
