Reflectometry is a general term for the use of the reflection of waves or pulses at surfaces and interfaces to detect or characterize objects, sometimes to detect anomalies as in fault detection and medical diagnosis.
There are many different forms of reflectometry. They can be classified in several ways: by the used radiation (electromagnetic, ultrasound, particle beams), by the geometry of wave propagation (unguided versus wave guides or cables), by the involved length scales (wavelength and penetration depth in relation to size of the investigated object), by the method of measurement (continuous versus pulsed, polarization resolved, ...), and by the application domain.
Electromagnetic radiation of widely varying wavelength is used in many different forms of reflectometry:
Radar: Reflections of radiofrequency pulses are used to detect the presence and to measure the location and speed of objects such as aircraft, missiles, ships, vehicles.
Lidar: Reflections of light pulses are used typically to penetrate ground cover by vegetation in aerial archaeological surveys.
Characterization of semiconductor and dielectric thin films: Analysis of reflectance data utilizing the Forouhi Bloomer dispersion equations can determine the thickness, refractive index, and extinction coefficient of thin films utilized in the semiconductor industry.
X-ray reflectometry: is a surface-sensitive analytical technique used in chemistry, physics, and materials science to characterize surfaces, thin films and multilayers.
Propagation of electric pulses and reflection at discontinuities in cables is used in time domain reflectometry (TDR) to detect and localize defects in electric wiring.
Skin reflectance: In anthropology, reflectometry devices are often used to gauge human skin color through the measurement of skin reflectance. These devices are typically pointed at the upper arm or forehead, with the emitted waves then interpreted at various percentages.
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