Self-referencing microdoppler ladar receiver and associated detection method

A microdoppler ladar system comprising:

• a transmitter for producing signals to illuminate a target;
• and
• a self-referencing receiver for receiving a backscattered signal from the target, said self-referencing receiver comprising:
• a frequency shifter for controllably shifting the frequency of the backscattered signal;
• an unequal path length interferometer for receiving the frequency shifted signal and for producing first and second output signals;
• and
• a signal processor for providing a feedback signal to control said frequency shifter based upon differences in the respective power levels of the first and second output signals such that said interferometer is driven towards quadrature, wherein the feedback signal is proportional to an instantaneous frequency of the backscattered signal including frequency contributors due to a vibrational velocity of the target such that the vibration of the target is detectable without a local reference derived from said transmitter.

A method of detecting vibration of a target without a local reference derived from a transmitter that illuminates the target, the method comprising:

• controllably shifting the frequency of a signal backscattered from the target;
• directing portions of the frequency shifted signal along first and second paths defined by an interferometer, wherein the first and second paths are of unequal length;
• combining the portions of the frequency shifted signal to produce first and second output signals;
• and
• providing a feedback signal to control the frequency shift imparted upon the backscattered signal, wherein the feedback signal is based upon differences in the respective power levels of the first and second output signals such that the interferometer is driven towards quadrature,
• wherein the feedback signal is proportional to an instantaneous frequency of the backscattered signal including frequency contributions due to a vibrational velocity of the target such that the vibration of the target is detectable without a local reference derived from the transmitter.