The longer version of the power reflection factor formula suggests liquid-liquid interfaces should
be detectable using radar, and indeed they are. All that is needed is a sufficiently large difference in
permittivity between the two liquids to create a strong enough echo to reliably detect. Liquid-liquid
interface level measurement with radar works best when the upper liquid has a substantially lesser
permittivity value than the lower liquid28. A layer of hydrocarbon oil on top of water (or any aqueous
solution such as an acid or a caustic) is a good candidate for guided-wave radar level measurement.