1. A signal processing method for providing passive target tracking information as cues to initiate active target tracking comprising the steps of: taking target bearing measurements over predetermined time intervals hereafter called epochs, wherein the step of taking a target bearing measurement includes receiving target signals upon a linear array of signal sensors; measuring the received target signals to generate measured target signals; deriving a single target bearing measurement from the target signals measured during a single said epoch; taking the target bearing measurements for a plurality of epochs to generate at least three target bearing measurements; calculating initial target track parameters using the at least three target bearing measurements; using nonlinear optimization to calculate optimized target track parameters using the calculated initial target track parameters as a starting point for the optimization; estimating target positions and target velocities in normalized coordinates from the optimized target track parameters; determining a normalized area of uncertainty value for each estimated target position; smoothing the normalized area of uncertainty values to arrive at smoothed area of uncertainty values; determining if the optimized target track parameters meet passive cueing criterion by comparing each of the smoothed area of uncertainty values to a user-defined threshold 1 and comparing the absolute value of the difference between two of the smoothed area of uncertainty values to a user-defined threshold 2; and providing the estimated target positions and target velocities to initiate an active target tracker when the smoothed area of uncertainty value is less than the threshold 1 and the absolute value of the time difference between two consecutive values of the smoothed area of uncertainty is less than the user-defined threshold 2.