Backscatter

Backscatter is the reflection or scattering of waves or particles in the direction opposite to the incident beam. It is a general phenomenon that occurs across the electromagnetic spectrum, as well as with acoustic waves and particle beams, and is central to many imaging and sensing techniques. In scattering theory, backscattered intensity depends on the properties of the medium, the size and distribution of scatterers, and the geometry of incidence and detection. The differential backscatter cross section and the backscatter coefficient quantify the amount of energy returned toward the source.

In optics and atmospheric science, backscatter occurs when light or solar radiation is reflected by aerosols, clouds, fog, or surfaces like rough terrain. Rayleigh and Mie scattering describe angular distributions that include a backward peak under certain conditions. In radar and lidar remote sensing, backscatter from surfaces or atmospheric constituents provides information on surface roughness, wind, aerosols, and humidity. In oceanography, acoustic backscatter from the seafloor or subsurface features is used to map bathymetry and to infer sediment type or biological scattering layers. In medical ultrasound, backscattered echoes reveal tissue structure and pathology. In electron microscopy, backscattered electrons produced by elastic scattering off atomic nuclei provide compositional contrast.

Backscatter data are often affected by geometry, attenuation, and multiple scattering, and require calibration and correction for reliable interpretation. Backscatter imaging methods are valued for their ability to probe material properties near the surface or within optically or acoustically opaque media, and are widely used in security, remote sensing, geology, medicine, and materials science.