Image Number 5 for United States Patent #5444441.
An electro-optical detection system for detecting objects 12 embedded within a partially transmitting medium comprises means 20 to receive electro-magnetic radiation in two close spectral channels 28, 212: a signal channel 212 where the wavelength and bandwidth of the signal channel are optimized to correspond to the peak of transmission of the medium and a reference channel 28 where the wavelength and bandwidth are selected to correspond to a spectral region where attenuation in the medium is high. The signal and reference channels are then subtracted (213) so as to remove the effect of reflected radiation from the signal channel 212. The signal is processed digitally (218) to provide an enhanced image of the field of view. In a particular arrangement for detecting objects underwater a CCD TV camera 20 is used with three separate CCD detector arrays providing concurrent red (R), green (G), blue (B) output signals. The green and blue signals are combined in an adjustable ratio to provide the image signal to match the prevailing conditions of the partially transmitting sea. A notch filter is employed to cut out light in a spectral band between the signal and reference channels.