Abstract: A method for enhancing lofargram data images utilizing a rule base. The system takes a plurality of sequentially occurring vertical frequency strips of a lofargram data image and computes an estimate for the mean and variance of each vertical frequency strip. A linear transformation utilizing a rule base is then applied to each pixel of the vertical frequency strip to improve the visual clarity of the lofargram data image.

Abstract: The present invention describes a method and apparatus for determining the noise power ratio (NPR) of a unit under test (UUT). According to the method, a frequency domain representation of a desired test spectrum is generated by prompting an operator to input selected parameters to a general purpose digital computer. The desired test spectrum includes a notch of predetermined depth. The frequency domain representation is transformed into an input signal sequence by an inverse Fast Fourier Transform algorithm, the sequence defining a time domain representation thereof. The input signal sequence is then applied to the unit under test. An output signal sequence defining a time domain representation of a measured test spectrum is received from the unit under test and transformed back into a frequency domain representation. This frequency domain representation includes a notch whose depth is normalized in dB to determine the noise power ratio of the unit under test.