A method and apparatus for determining at least one property of a target material is disclosed. The method is constituted of: providing a time varying signal at comprising frequency content over a range of frequencies; transducing the provided signal so as to interact with the target material; receiving the provided time varying signal after interaction with the target material; mixing the received time varying signal with a portion of the provided time varying signal; determining the propagation delay associated with the target material of the received provided time varying signal at each of a plurality of frequencies within the range of frequencies; and determining at least one property of the target material responsive to the determined propagation delay at each of the plurality of frequencies.