Systems and methods for distance independent differential signature detection

A differential signature detection system is provided. The system comprises: a target sensor, wherein the target sensor is configured to measure acoustical signals within a first narrow band around a target frequency; an offset sensor, wherein the offset sensor is configured to measure acoustical signals within a second narrow band around an offset frequency; and a controller coupled to the target sensor and the offset sensor, wherein the controller is configured to: compare a signal output of the target sensor with an output of the signal output of the offset sensor to calculate a differential measurement that comprises a difference in signal peak intensity; compare the differential measurement to a reference signal, wherein the reference signal comprises a threshold indicative of a presence of a characteristic signature peak associated with a target object; and produce an output based on the comparison between the differential measurement and the reference signal.