System and method for remote image sensing and autocalibration
AssigneeHughes Electronics Corporation
InventorPeter V. Messina
Life of this patent
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Abstract
An autocalibration system is provided for a back-scanning, gimbal-mounted step and stare imaging system. The step and stare imaging system effects step and stare performance even though the gimbal mounted platform upon which the system telescope is mounted rotates at a constant rate. The autocalibration system calibrates the system's static line of sight positioning and the system's rotational, or angular rate line of sight positioning.
Claims22
An airborne gimbal mounted step and stare imaging system, the gimbal supported from an aircraft by a gimbal support, comprising:
- a rotatable gimbal platform attached to the gimbal support to provide an axis of isolation from angular disturbances,
- imaging optics comprising a telescope, scanning mirror and imager which are affixed to the gimbal's platform and rotate along with the platform,
- a positioning system which positions the imaging optics in relation to an inertial reference frame,
- an imager positioned to receive images from the imaging optics, and
- an autocalibration system, comprising reference mirror, IMU, and beam aligner, distributed between the gimbal platform and the gimbal support for calibration of the imaging system's inertial position.
An autocalibration system for a gimbal-mounted, step and stare back-scanning imaging system, comprising:
- a controller,
- a beam aligner,
- calibration optics which, subject to control by the controller, alter the optical path of a test signal emitted by the beam aligner and
- an inertial positioning system which provides position information to and is controlled by the controller.
A back-scanning step and stare imager comprising:
- a rotatable planar gimbal platform suspended from a gimbal support which provides at least one axis of isolation from mechanical or other disturbances,
- a scanning mirror positioned upon the platform with a scanning axis orthogonal to the plane of the platform,
- a telescope positioned upon the platform to receive electromagnetic radiation from a target scene,
- an image processor positioned to receive radiation transmitted through the telescope and connected to effect movement of the platform,
- a scanning mirror positioned in the optical path between the telescope and the image processor,
- a reference mirror positioned along an optical path between the scanning mirror and the image processor,
- a beam aligner positioned along the periphery of the platform so that an electromagnetic signal transmitted from the beam aligner travels along an optical path through the telescope to the scanning mirror, is reflected from the reference mirror to the scanning mirror and back to the beam aligner,
- an inertial measurement unit, and
- a controller connected to receive measurements from the beam aligner, the inertial measurement unit, the reference mirror and the scanning mirror and to transmit position control signals to the reference mirror and to the scanning mirror.
A method of automatically calibrating the imager line of sight position of a back-scanning step and stare imaging system using the system's reference optics, beam aligner, inertial measurement unit, imager and controller, comprising:
- A. moving reference optics and imager into a calibration position
- B. initializing the system's beam aligner and inertial measurement unit and injecting a known disturbance into the imaging system,
- C. transmitting a test signal from the beam aligner through the imaging system to the reference optics and back to the beam aligner,
- D. reading the outputs of the beam aligner and the inertial measurement unit,
- E. computing the imager line of sight position based upon the measurements obtained in steps D,
- F. moving the reference optics and the imager out of the calibration position and quitting the calibration process if the position computed in step E is within an acceptable range,
- G. adjusting the position of an imaging system component if the position computed in step E is outside an acceptable range, and
- H. returning to step B.
A method of automatically calibrating the imager line of sight angular rate of a back-scanning step and stare imaging system using the system's reference optics, scanning mirror, beam aligner, inertial measurement unit, gimbal-platformmounted imager and controller, comprising:
- A. moving reference optics and imager into a calibration position,
- B. rotating the gimbal platform at a predetermined rate,
- C. counter-rotating the scanning mirror at a rate chosen to counteract the platform's rotation, thereby creating a stationary imager line of sight,
- D. transmitting a series of signals from the beam aligner through the imaging system to the reference optics and back from the reference optics to the beam aligner during a calibration period,
- E. reading the output of the beam aligner during the calibration period,
- F. reading the output of the inertial measurement unit during the calibration period,
- G. computing the inertial line of sight rate of the imager based upon the measurements obtained in steps E and F,
- H. moving the reference optics out of the calibration position and quitting the calibration process if the rate computed in step G is within an acceptable range,
- I. adjusting the rate of the scanning mirror if the rate computed in step G is outside an acceptable range, and
- J. returning to step A.
Dependencies are inferred from the claim text.