The invention provides for generating a set of signature signals that correspond to a range of depths within a target. These signature signals can include multiple individual reference signals and be can modified to compensate for specific characteristics of the target. In the preferred embodiment the members of the set of signature signals are correlated with data sets by phase rotating individual reference signals to determine maximum and minimum correlation and thereby enabling determination of the scattering characteristic of the target at each depth. Also a pilot signal is monitored to dynamically determine the phase relationship between individual reference signals and thereby avail of phase sensitive detection techniques to enhance SNR at deeper regions where multiple individual reference signals exist.