A method for detecting hardened bunkers within a target, the method including: producing a first output from a sensor fired to travel through the hardened bunkers, the first output being different from a second output when the sensor travels in a void between the hardened bunkers or encounters other objects outside of the hardened bunkers; and determining one or more of the number of hardened bunkers, a thickness of the hardened bunkers and a strength of the hardened bunkers based on the first and second outputs of the sensor over time. The sensor can include one of a piezoelectric generator for producing a voltage output and a circuit input by the voltage output or an accelerometer having a locking member for locking a proof mass during periods of impact with the one or more hardened bunkers.