Abstract: There is provided a method and associated apparatus for measurement. Specifically, a method for determining a distance travelled by a signal in a medium, or the time of flight of a signal travelled. The method comprises considering an unambiguous range wherein the unambiguous range greater than a distance to be travelled by a signal. A signal is then transmitted across the distance to be determined, the signal comprising at least two frequency components, the frequency components based on the unambiguous range and the speed of the signal in the medium. The distance travelled (or the time of flight) is determined by using the variance of the received phase characteristics, such as phase angle) of one frequency component of the received signal with the received phase characteristics of another frequency component of the received signal.

Abstract: Methods and apparatus for determining the speed of a signal species, such as an acoustic signal, in a multilayered medium is described. The multilayer medium, generally, has a first and second layer (e.g. oil and water), whereby first and second signals are transmitted across particular distances in the medium such that a second distance differs from a first distance, and whereby the time of flight of each signal can be used in order to determine the speed of the signals species in one or both of the first and second layer. In other words, in some cases, the speed of sound can be determined in oil and/or water, or the like.