Synthetic Aperture RADAR - SAR

RADAR stand for Radio Detection And Ranging. The basic principle of RADAR imaging is the transmission and reception of electromagnetic signals. A signal with known characteristics is transmitted and the returning echoes are recorded.

The information about the object lies in the change of characteristics such as, magnitude, phase, time interval between pulse transmission and return, polarization and Doppler frequency shift.

SAR stands for Synthetic Aperture RADAR In general the sensor is onboard a satellite or an airplane in motion. The sensor is looking to the side of the vehicle and performing measurements orthogonally to the direction of the sensors line of sight is called range as illustrated in below.

As the sensor passes an object, called a scatterer, many pulse are reflected in sequence. By recording and combining these individual signals a synthetic aperture is created with the same length as the duration of illumination of a target ground, dependent on the acceptable phase error, hence the name.

The advantage of the SAR technology, compared to the Real Aperture Radar, a stationary sensor, is the utilisation of the Doppler shift of an object due to motion to improve the azimuth resolution. SAR image processing is then used to reconstruct the imaged scene from the recorded pulse reflections.


The RADAR sensor is an active sensor meaning that it itself illuminates the scene which it is imaging. The frequency range in which SAR sensors operate is cloud penetrating, due to this they are not dependant of wheater conditions and time of day, one of the technology strong point.