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.
[1] 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.
Many techniques are based on the principle of reflectometry and are distinguished by the type of waves used and the analysis of the reflected signal.
Among all these techniques, we can classify the main but not limited to: