Apparatus for detecting molecular vapors in an atmospheric region includes an interferometer which monitors light parameter data signals received and provides an interferometer light parameter signal corresponding to the light parameter data signals at a plurality of frequencies. The apparatus further includes an interferogram detector/converter which records and digitizes the interferometer light parameter signal to generate a plurality of discrete data points wherein each discrete data point corresponds to the interferometer light parameter signal at a specific frequency. The apparatus also includes a Fourier transform circuit for receiving the discrete interferometer light parameter signal and providing a Fourier transformed molecular parameter data signal. The apparatus further includes a probabilistic neural network for receiving and sorting the Fourier transformed molecular parameter data signals without the use of a priori training data.