An effective utilization of spectral spread in holographic passive imaging systems

Holographic passive imaging systems are examined from the viewpoint of an effective utilization of thsep ectral spread of an object emitting random waves, and two effective methodsf or improving images are proposed. One is the smoothing of sample spectra by a spectral window at the stage of hologram signal estimation by taking into account thep rocess of wave propagation in order to obtain precise hologram signals with reduced noise. The other is the synthesis of complex valued imageso ver a wide frequency range to get a highly resolved image in the range direction. These processings are discussed theoretically and examined experimentally by using a bispectral passive imaging system which had been designed and constructed for machine system diagnosis in the audio frequency region. The results show thek effectiveness.