The Back Scattering Alignment (BSA) is a coordinate system used in coherent electromagnetic scattering. The coordinate system is defined from the viewpoint of the wave source, before and after scattering. The BSA is most commonly used in radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

, specifically when working with a Sinclair Matrix because the radar detector and source are physically coaligned. FSA gives rise to conjugate eigenvalue equations. The alternative coordinate system in electromagnetic scattering is the Forward Scattering Alignment

Forward scattering alignment

The Forward Scattering Alignment is a coordinate system used in coherent electromagnetic scattering.The coordinate system is defined from the viewpoint of the electromagnetic wave, before and after scattering...

 (FSA) which is primarily used in optics

Optics

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...

. Both coordinate systems contain essentially the same information and meaning, and thus a scattering matrix can be transformed from one to the other by use of the matrix,