Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1997-10-14
2001-04-24
Hellner, Mark (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C250S339150, C250S342000
Reexamination Certificate
active
06222618
ABSTRACT:
BACKGROUND OF THE INVENTION
Various objects, such as the plume of a rocket or other fire, or a hot filament or gas discharge of a lamp, are known to act as sources of radiation having characteristic spectra. There are situations in which it is desirable to determine the location of such a source from a viewing site distant from the source, the location, data including range, elevation and azimuth of the target source from the viewing site. However, a problem arises in that the usual apparatuses for determination of target location, such as active radar, are not operative with the foregoing type of radiant energy signal for a passive determination of the ranging of the source.
Therefore, the need exists for a means of passively determining the range to sources of thermal radiation.
SUMMARY OF THE INVENTION
The aforementioned problem is overcome and other advantages are provided by a system and method of passive ranging, in accordance with the invention, wherein a distant source of radiation is observed and then at least a portion of the source's emission spectrum is analyzed to determine the range to the source.
This invention relates to a measurement of the range of a source of electromagnetic radiation and, more particularly, to the use of passive ranging by examination of relative attenuation among a plurality of spectral lines wherein differences in attenuation among various portions of the radiation spectrum arise from selective atmospheric absorption of radiation at various frequencies as a function of propagation distance of the radiation through the atmosphere. The foregoing attenuation is in addition to the attenuation arising from the spreading of the waves of radiation through increasing regions of space, the latter attenuation following the well-known relationship of intensity varying as the inverse square of the range from a point source of the radiation.
The invention is particularly useful in the situation
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wherein a source of radiation, on or near the ground, illuminates a cloud above the source, and a distant observer obtains range of the source by observation of radiation scattered from the cloud.
A typical spectrum includes both a continuous distribution of spectral energies in an emission band or in each of a plurality of emission bands, as well as a line spectrum wherein individual ones of the lines are characteristic of certain constituent substances in a source of the radiation, such as the various gasses in a rocket plume.
In accordance with a feature of the invention, a continuous portion of the received spectrum can be employed to determine range of a target, such as the plume of a rocket, independently of whether or not there be any Doppler frequency shift. Operation of the invention to obtain the range may be explained as follows. As the radiation propagates through the atmosphere from the source to optical receiving apparatus employed by the invention, there may be interaction between the radiation and various substances dependent on the frequency of the radiation. The interaction results in a relative attenuation of various spectral components by the atmosphere as a function of frequency and a function of distance of propagation of the radiation through the atmosphere. Thus, the attenuation is indicative of target range.
The present invention relates to a system and method of passive ranging for a luminous target which employs a prior knowledge of atmospheric attenuation of spectral frequencies to determine range by comparing the intensities of a frequency component, that is attenuated by propagation through the atmosphere, with a frequency component that is not.
REFERENCES:
patent: 3576371 (1971-04-01), Ulicki
patent: 4296324 (1981-10-01), Kern et al.
patent: 4355894 (1982-10-01), Maeda
patent: 4694172 (1987-09-01), Powell et al.
patent: 5282013 (1994-01-01), Gregoris
patent: 5677761 (1997-10-01), Hasson
patent: 5804825 (1998-09-01), Schuler
Bloom, S.A., et al., “Helicopter Plume Detection by Using an Ultranarrow-Band Noncoherent Laser Doppler Velocimeter”,Optical Letters, 18: 244-246; Jan. 1, 1993.
Hamilton Brook Smith & Reynolds P.C.
Hellner Mark
Textron Systems Corporation
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