US4371946A — Servomechanism for doppler shift compensation in …

Claim 1

Independent Claim 168 words

In an optical correlator for synthetic aperture radar data compression having a means for directing a laser beam at a signal film having radar return pulse intensity and phase information recorded thereon, a resultant modulated laser beam then passing through a range telescope, an azimuth telescope, and a Fourier transform filter located between said range and azimuth telescopes, thereby forming an image for recordation on an image film, a compensation means for a doppler shift compensation in said radar return pulse intensity information comprising: first means optically coupled to monitor the Fourier transform of said modulated laser beam at the output of said range telescope for continuously detecting doppler shift in said radar return and generating a control signal indicative of the sign and magnitude of said doppler shift; and second means responsive to said control signal for continuously controlling the angle of incidence between said laser beam and said signal film whereby said doppler shift is reduced to below a predetermined minimum shift, thereby minimizing image ambiguities.

Claim 2

Dependent Claim 168 words

In an optical correlator for synthetic aperture radar data compression having a means for directing a laser beam at a signal film having radar return pulse intensity and phase information recorded thereon, a resultant modulated laser beam then passing through a range telescope, an azimuth telescope, and a Fourier transform filter located between said range and azimuth telescopes, thereby forming an image for recordation on an image film, a compensation means for a doppler shift compensation in said radar return pulse intensity information comprising: first means optically coupled to monitor the Fourier transform of said modulated laser beam at the output of said range telescope for continuously detecting doppler shift in said radar return and generating a control signal indicative of the sign and magnitude of said doppler shift; and second means responsive to said control signal for continuously controlling the angle of incidence between said laser beam and said signal film whereby said doppler shift is reduced to below a predetermined minimum shift, thereby minimizing image ambiguities.

Claim 3

Dependent Claim 60 words

The compensation means of claim 1 wherein said first means comprises: a beam splitter located between said Fourier transform filter and said azimuth telescope for reflecting a portion of said modulated laser beam; and means for detecting light intensity differentials between two portions of said reflected modulated laser light beam, said light intensity differentials being related to said doppler shift.

Claim 4

Dependent Claim 46 words

The compensation means of claim 2 wherein said means for detecting comprises first and second photodetectors positioned on either side of a centered lobe of said reflected modulated laser light beam, said first and second photodetectors providing first and second light intensity related output signals, respectively.

Claim 5

Dependent Claim 102 words

The compensation means of claim 3 wherein said optical correlator further includes a reflective surface for reflecting said laser beam to said signal film and a motor means responsive to a control signal for controlling the angle of said reflective surface relative to said laser beam, said second means comprising: third means for generating a difference signal related to a difference between said first and second photodetector output signals: fourth means for generating a sum signal related to the sum of said first and second photodetector output signals; and means responsive to said third and fourth means for generating said control signal.

Claim 6

Dependent Claim 91 words

The compensation means of claim 4 wherein said means responsive to said third and fourth means comprises: means for developing a ratio signal related to the ratio of said difference signal to said sum signal; and means for developing a signal having a first voltage state when said ratio signal is positive and a second voltage state when said ratio signal is negative, said first and second voltage states indicating a direction of change of said reflective surface angle relative to said laser beam to be effected by said control signal.

Claim 7

Dependent Claim 33 words

The compensation means of claim 5 wherein said means responsive to said third and fourth means further comprises means for thresholding said control signal until said ratio signal exceeds a predetermined absolute value.

Claim 8

Dependent Claim 38 words

The compensation means of claim 6 wherein said means responsive to said third and fourth means further comprises timing means for inhibiting said control signal for a predetermined time after said ratio signal exceeds said predetermined absolute value.

Claim 9

Dependent Claim 162 words

A synthetic aperture radar data optical correlator having means for detecting and tracking doppler shifts in said radar data comprising: a reflective surface for directing a laser beam at a signal film containing said radar data; a range telescope positioned to receive said laser beam after being modulated by said radar data; a Fourier transform filter for removing a DC component and a virtual image component from said modulated laser beam; an azimuth telescope for focusing said modulated laser beam, after having passed through said Fourier transform filter, on an image film; first means for determining first and second light level intensities at two cross-sectional portions of said modulated laser beam after having passed through said Fourier transform filter; and second means responsive to said first means for altering the angle of said reflective surface with respect to said laser beam reflected therefrom until the light level intensities at said two cross-sectional portions have a predetermined relationship with respect to each other.

Claim 10

Dependent Claim 162 words

A synthetic aperture radar data optical correlator having means for detecting and tracking doppler shifts in said radar data comprising: a reflective surface for directing a laser beam at a signal film containing said radar data; a range telescope positioned to receive said laser beam after being modulated by said radar data; a Fourier transform filter for removing a DC component and a virtual image component from said modulated laser beam; an azimuth telescope for focusing said modulated laser beam, after having passed through said Fourier transform filter, on an image film; first means for determining first and second light level intensities at two cross-sectional portions of said modulated laser beam after having passed through said Fourier transform filter; and second means responsive to said first means for altering the angle of said reflective surface with respect to said laser beam reflected therefrom until the light level intensities at said two cross-sectional portions have a predetermined relationship with respect to each other.

Claim 11

Dependent Claim 64 words

The optical correlator of claim 8 wherein said first means comprises; a beam splitter located in the path of said modulated laser beam after having passed through said Fourier transform filter for reflecting a portion of said modulated laser beam; and first and second light level detecting means located in said reflected modulated laser beam for determining said first and second light level intensities.

Claim 12

Dependent Claim 39 words

The optical correlator of claim 9 wherein said first and second light detecting means comprise first and second photodetectors symetrically located with respect to each other on opposite sides of a DC spot portion of said modulated laser beam.

Claim 13

Dependent Claim 72 words

The optical correlator of claim 9 wherein said second means comprises: electronic processing means responsive to said first and second light level intensities for generating a motor control signal related to intensity differences therebetween; and motor means connected to said reflective surface and responsive to said motor control signal for altering the angle of said reflective surface until said cross-sectional portion light intensities have said predetermined relationship with respect to each other.

Claim 14

Dependent Claim 119 words

The optical correlator of claim 11 wherein said electronic processing means comprises: difference means for generating a signal related to the difference between said first and second light level intensities; sum means for generating a signal related to the sum of said first and second light level intensities; sign means responsive to said difference means for determining the direction of alteration of the angle of said reflective surface; and threshold means responsive to said difference means and said sum means for determining when said motor signal should be applied to said motor, said motor control signal being applied to said motor when the ratio between said difference means signal and said sum means signal exceeds a predetermined absolute ratio.

Claim 15

Dependent Claim 41 words

The optical correlator of claim 12 further comprising means for inhibiting said motor control signal from said motor until the ratio between said difference means signal and said sum means signal exceeds said predetermined absolute ratio for a predetermined time interval.

Claim 16

Dependent Claim 22 words

The optical correlator of claim 8 wherein said predetermined ratio between said light level intensities at said two cross-sectional portions is one.

Claim 17

Dependent Claim 16 words

The optical correlator of claim 9 wherein said laser beam is generated by a helium-neon laser.

Claim 18

Dependent Claim 159 words

In an optical correlator for synthetic aperture radar data having a means for directing a laser beam at a signal film having radar return pulse information recorded thereon, a resultant modulated laser beam then passing through a range telescope, an azimuth telescope, and a Fourier transform filter located between said range and azimuth telescopes, thereby forming an image for recordation on an image film, a method for compensating for a doppler shift in said radar return pulse intensity information comprising the steps of: determining first and second light level intensities at two portions of said modulated laser beam after passing through said range telescope; and altering in response to said determining step the angle of incidence between said laser beam and said signal film until the light level intensities at said two cross-sectional portions have a predetermined relationship with respect to each other, said predetermined relationship being chosen to define zero doppler in said radar return pulse intensity information.

Claim 19

Dependent Claim 159 words

In an optical correlator for synthetic aperture radar data having a means for directing a laser beam at a signal film having radar return pulse information recorded thereon, a resultant modulated laser beam then passing through a range telescope, an azimuth telescope, and a Fourier transform filter located between said range and azimuth telescopes, thereby forming an image for recordation on an image film, a method for compensating for a doppler shift in said radar return pulse intensity information comprising the steps of: determining first and second light level intensities at two portions of said modulated laser beam after passing through said range telescope; and altering in response to said determining step the angle of incidence between said laser beam and said signal film until the light level intensities at said two cross-sectional portions have a predetermined relationship with respect to each other, said predetermined relationship being chosen to define zero doppler in said radar return pulse intensity information.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1986-01-31	1986-08-02	1987-02-01	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1990-01-31	1990-08-02	1991-02-01	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1994-01-31	1994-08-02	1995-02-01	$7700.00	Window Closed / Lapsed

Servomechanism for doppler shift compensation in optical correlator for synthetic aperture radar

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