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.

Abstract: Methods and apparatus for providing for determining the time of receipt of a received signal are described. In particular, there is described method and apparatus for receiving a signal, and using a phase characteristic, such as the received phase angle at which a received signal is initially sampled, together with the frequency of the received signal in order to determine a receive time error. The receive time error can then subsequently be used to determine the actual time of receipt 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.

Abstract: Apparatus and methods for determining flow characteristics (e.g. flow rate, direction of flow, mass flow rate, etc.) of a multi-layered medium are described, such as a multi-layered medium in a pipeline. Such a multi-layered medium may be considered to have a first layer and second layer and an interface region, wherein the interface region is defined between the first and second layers. In some examples, a flow characteristic can be determined by using the time of flight of advanced signal communicated in a particular manner across the medium with the time of flight of a retarded signal communicated in a different manner across the medium, such that it is possible to use the time of flights together with a static speed of the advanced and retarded signal in both the first and second layers and the location of the interface region in order to determine the flow characteristics of the medium.

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.