Measurement method and apparatus

A computer implemented method for determining a distance travelled by a received signal having been transmitted between a transmitter and a receiver in a medium, the received signal having at least three frequency components, the method comprising:

• determining, using the computer, a first estimate of a distance travelled by a received signal by using a variance of received phase characteristics of a first frequency component together with received phase characteristics of a second frequency component, wherein the first and second frequency components have been based on an unambiguous range, that unambiguous range being greater than the distance travelled by the received signal, such that the number of cycles of the first and second frequency components accommodated in the distance travelled by the received signal vary by no more than one, and
• determining, using the computer, the distance travelled by the received signal by using a variance of received phase characteristics of the first frequency component together with received phase characteristics of a third frequency component, as well as the first estimate of the distance travelled by the received signal, the third frequency component having been selected such that the number of cycles of the first and third frequency components vary by more than one in the distance travelled by the signal between the transmitter and a receiver.

Apparatus for determining a distance travelled by a signal in a medium, the apparatus comprising:

• a transmitter configured to transmit a signal comprising at least three frequency components, wherein at least first and second frequency components are based on an unambiguous range, which is greater than the distance travelled by the received signal, and the speed of the signal in a medium, such that the number of cycles of the first and second frequency component that can be accommodated in the distance travelled by the signal between the transmitter and a receiver varies by no more than one, and
• wherein at least a third frequency component is provided such that the number of cycles of the first and third frequency components vary by more than one in the distance travelled by the signal between the transmitter and a receiver;
• a receiver configured to receive a transmitted signal comprising the at least three frequency components;
• wherein the apparatus is configured to determine, using a controller in communication with the receiver, a first estimate of a distance travelled by a signal by using the variance in received phase characteristics of the first frequency component of received signal with received phase characteristics of the second frequency component of received signal, and configured to determine, using the controller, the distance travelled by the signal between transmitter and receiver by using a variance of the received phase characteristics of the first frequency component with the received phase characteristics of the third frequency component, as well as the first estimate of the distance travelled by the signal.

Means for determining a distance travelled by a signal in a medium, the means for determining a distance comprising:

• a means for transmitting a signal, the means for transmitting configured to transmit a signal comprising at least three frequency components,
• wherein at least first and second frequency components are based on an unambiguous range, which is greater than the distance travelled by the received signal, and the speed of the signal in a medium such that the number of cycles of the first and second frequency components that can be accommodated in the distance travelled by the signal between the transmitter and a receiver varies by no more than one, and
• wherein at least a third frequency component is provided such that the number of cycles of the first and third frequency components vary by more than one in the distance travelled by the signal between the transmitter and a receiver;
• a means for receiving a signal, the means for receiving configured to receive a transmitted signal comprising the at least three frequency components, and
• means for determining a first estimate of a distance travelled by a signal by using the variance in a received phase characteristics of the first frequency component of a received signal with a received phase characteristics of the second frequency component of a received signal, and means for determining the distance travelled by the signal between transmitter and receiver by using a variance of the received phase characteristics of the first frequency component with the received phase characteristics of the third frequency component, as well as the first estimate of the distance travelled by the signal.