Backscattering is the reflection or "scattering" of acoustic or electromagnetic waves, or particles, or some type of signal, "back" in the same direction as which the wave/particles/signal initially comes from.

This article is written at a definitional level only. Authors wishing to expand this entry are inivited to expand the present treatment, which additions will be peer reviewed prior to publication of any expansion.

Backscattering is applied in many scientific situations where some form of signal, such as sound or electromagnetic radiation, is sent from a device at some object and the returned, or reflected, "backscattered" signal is detected in order to measure some property about the object.

For example, in the image right a radar beam is sent from a satellite toward a mountain and the backscattered signal detected to reveal information amount to dimensions and shape of the mountain.

Backscattering cross–section is the ratio of the acoustic or electromagnetic power scattered at an angle of 180^o from the incident wave to the acoustic intensity incident on a unit volume or area.

The concept of backscatter is also applied in the field of particle high energy physics. This measure, typically referenced to a unit distance, e.g. one meter, is the ratio of the reflected acoustic or electromagnetic power to incident acoustic or electromagnetic power per unit area. The units of this ratio are area, e.g. square meters.

Applications

There are numerous applications of backscatter in the medical, physics research and animal communication fields. Some of the chief applications are:

• Medical ultrasound for acoustical imaging of soft tissue
• High energy physics experimentation
• Echolocation by certain marine mammals and bats
• Photography, where flash methods are used and reflected flash occurs
• Weather radar to differentiate sizes of water droplets in precipitation
• Backscatter X-ray devices for airline security screening
• Bragg scattering in X-ray crystallography

References

• John M. Cowley. 1975. Diffraction physics (North-Holland, Amsterdam) ISBN 0-444-10791-6
• A.C.Upton. 2003. The state of the art in the 1990s: NCRP report No. 136 on the scientific bases for linearity in the dose-response relationship for ionizing radiation. Health Physics 85: 15–22.

See also

• Acoustic signature