SAR stands for synthetic aperture radar .
Radar sends out a pulse of radio waves which bounces off the object to be depicted.
Then the scattered pulses return to the radar, where they are captured by the receiving antenna. The antenna is the radar's aperture, or its opening on the world. SAR is an active remote sensing system . Active systems transmit their own signal and measure the energy that is reflected or scattered back from the target material. Passive systems measure natural radiation emitted by the target material and energy from other sources reflected from it.