Abstract: This paper deals with analysis procedures of periodically locally stationary random process which is a specific class of locally stationary process. A method of local sta-tionariness test and a practical measurement procedure are diseussed. Double frequency spectra are applied to description of this kind of processes. In the end of this paper some examples of measuring double frequency spectra of radiative noise of merchant ship and fisher boat are listed. Various kinds of physical characteristics of ships, e.g. rotative velocity of propeller, number of blades, can be easily seen from their double frequency spectra. This method supplies a useful tool for recognition of ship objects.