Communications: electrical – Underwater
Patent
1994-05-18
1995-08-22
Eldred, J. Woodrow
Communications: electrical
Underwater
342 22, 359141, 356300, 356303, 356307, H04B 1302, G01S 1300, G01J 300
Patent
active
054444411
DESCRIPTION:
BRIEF SUMMARY
The invention relates to electro-optical detectors which can be applied to a wide range of remote sensing applications.
Many electro-optical remote sensing problems involving sensing from the air of structure on or just below the sea surface are complicated by the effects of solar glare from the sea surface. For example, simply using a television camera fitted to a helicopter to observe marine life (fish, dolphins etc) is often ineffective because the contrast of the image of the marine animals is significantly reduced by the reflection of the background sky from the sea. Similar problems can arise whenever reflections occuring at the interface between two media interfere with the reception of light transmitting through the interface.
Polarisation processing is not a significantly useful image processing technique for removing sea surface glare because light is only significantly linearly polarised when the illuminating source and the observer form the Brewster angle with the reflecting surface normal. Since the source (the sky) is spatially extended and the reflecting surface is highly structural because of waves, sea reflections are poorly polarised.
The object of the invention is to provide an electro-optical detection system capable of improved detection of submerged objects and of surface structure displaying a particular spectral reflectance, scattering or emission.
The invention provides:
an electro-optical detection systems for detecting objects embedded within a partially transmitting medium comprising: channels; in the respective channels; and processor comprising: channel are optimised to correspond to the peak of transmission of the medium and to give a high signal to noise ratio; to correspond to a spectral region where attenuation in the medium is high but which is close to the signal wavelengths thereby ensuring that reflected radiation at both signal and reference wavelengths are of similar intensity and geometric distribution; and so as to remove the effect of reflected radiation.
For a system capable of detecting objects underwater the signal channel preferably is in the waveband 400 nm to 570 nm and the reference channel is in the waveband 570 nm to 700 nm. Electro-magnetic radiation reflected from the sea surface is spectrally broadband, covering the signal and reference wavelength range from 400 nm to 700 nm. By contrast, radiation scattered or reflected from objects below the surface is mainly blue-green (400 nm 570 mm) because water attenuated red (570 nm-700 nm) very strongly. Thus the signal processor is advantageously arranged such that the signal and reference channels are combined by analogue subtraction to remove sea surface effects. Preferably the analogue subtracted signal is connected to a variable offset DC control so that a positive going signal results from the subtraction. The resulting signal is then connected to an adder where the necessary sync pulses are added to produce a video signal for operation of a video monitor.
Advantageously the video signal is processed digitally using, for example, contrast stretch to provide an enhanced image of the field of view. Digital processing options may also include edge enhancement, frame to frame integration, pseudo-colour coding and invert video. After digital processing the signal is digital to analogue converted and then connected to a TV monitor. After digital processing the digital signal may be connected to an automatic detection system using standard image processing technique (noise reduction, segmentation, edge mapping, spatial filtering and track formation) to give an automatic visual and audio cue through the monitor.
In one form means to receive the radiation from the field of view comprises a single chromatically corrected lens; radiation transmitted by the lens being spectrally divided to provide at least two separate images, a two dimensional detector array being placed to receive each image to thereby form at least one signal image and one reference image of the field of view. In a particularly advantageous arran
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Eldred J. Woodrow
The Secretary of State for Defence in Her Britannic Majesty's Go
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