Synthetic aperture ladar system and method using real-time holography
First Claim
1. An imaging system comprising:
- first means mounted on a mobile platform for receiving a beam of electromagnetic energy;
second means for recording an image provided by said beam; and
third means for compensating said image for motion of said platform relative to an external reference.
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Abstract
This invention uses a real-time holographic medium to record the amplitude and phase information collected from a moving platform at the aperture plane of a side-looking optical sensor over the collection time. A back-scan mirror is used to compensate platform motion during the synthetic aperture integration time. Phase errors caused by a nonlinear platform motion are compensated by controlling the phase offset between the illumination beam and the reference beam used to write the hologram based on inertial measurements of the flight path and the sensor line-of-sight pointing angles. In the illustrative embodiment, a synthetic aperture ladar (SAL) imaging system is mounted on a mobile platform. The system is adapted to receive a beam of electromagnetic energy; record the intensity and phase pattern carried by the beam; and store the pattern to compensate for motion of the platform relative to an external reference. In the illustrative embodiment, the image is stored as a holographic image. The system includes a back-scan mirror, which compensates the stored holographic pattern for motion of the platform. The medium and back-scan mirror may be replaced with a digital camera and one-dimensional and two-dimensional arrays may be used. In a specific embodiment, a two-dimensional array is used with a time delay and integration (TDI) scheme, which compensates for motion of the platform in the storage of the optical signals. In an alternative embodiment, a back-scanning mirror is used to compensate for motion of the platform. Consequently, the interference pattern between a relayed image of the aperture plane and a reference beam is continuously stored. In this embodiment, the instantaneous location of the received beam on the recording medium is controlled to compensate for motion of the platform.
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Citations
31 Claims
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1. An imaging system comprising:
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first means mounted on a mobile platform for receiving a beam of electromagnetic energy;
second means for recording an image provided by said beam; and
third means for compensating said image for motion of said platform relative to an external reference.
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- 2. The invention of claim 2 wherein said second means includes means for digitally storing a holographic image.
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10. An imaging system comprising:
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first means mounted on a moving platform for receiving a beam of electromagnetic energy at physical aperture of said imaging system;
second means for recording an intensity and phase pattern provided by said beam; and
third means mounted on said platform for redirecting said beam to said means for recording whereby the instantaneous location of said beam on said recording medium is controlled to compensate for motion of said platform relative to an external reference over a predetermined time interval.. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A holographic synthetic aperture ladar system comprising:
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a laser, mounted on a mobile platform and adapted to output a beam of coherent energy;
an optical arrangement mounted on said platform for directing said beam to a target and receiving a reflection therefrom;
a scan mirror in optical alignment with said optical arrangement;
a holographic optical storage medium; and
a controller for directing said scan mirror to adjust a position of said reflection on said medium in response to motion of said platform relative to said target.
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31. An imaging method comprising the steps of:
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receiving a beam of electromagnetic energy on a moving platform;
recording an image provided by said beam; and
compensating said recorded image for motion of said platform relative to an external reference.
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Specification