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.