Imaging system

• US 4,952,809 A
• Filed: 07/06/1988
• Issued: 08/28/1990
• Est. Priority Date: 07/08/1987
• Status: Expired due to Fees

• Current Assignee: BAE Systems Electronics Limited (BAE Systems Plc)
• Original Assignee: GEC Marconi Limited (Gooding Consumer Electronics Ltd.)
• Inventors: McEwen, Robert K.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/215,507
• Time in Patent Office: 783 Days
• Field of Search: 250/203 CT, 250/332, 250/334, 250/342, 358/113, 358/213.24
• US Class Current: 250/342
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An infra-red imaging system is operable selectively in wide and narrow field of view modes. Radiation from the object is imaged onto an infra-red CCD staring focal plane array (SFPA) which provides an output representing the image. In the narrow field of view mode, operative on detection of a particular target by target detection electronics, the image is not scanned but is made to follow any movement of the target, and the SFPA stares at the target to build up an image. In the wide field of view mode, the same SFPA is used to provide the image, but the image is scanned along a swath. Smearing of the image is minimized by driving the IRCCD array such that the image-bearing charge is passed down the array from element to element at a speed equal to the scanning speed, so that the output signal from the end element represents the intensity of radiation from a given portion of the object time-integrated by all the elements of the array in succession.

Claims

1. A method of imaging with selectively a wide or a narrow field of view, using the same two-dimensional array of detector elements for both, each element storing an electrical signal representative of the time-integrated intensity of the light incident on it, wherein, in a wide field of view mode of operation, the array is made to scan swathes of an object along respective columns of the array and periodically the stored electrical signals are shifted simultaneously in the direction of the scan from each element to its neighbour for continued time-integration, the stored electrical signal from the end element of each column of the array being provided as an output signal, the average speed at which the signals progress along the array being equal to the speed of the image scan whereby smearing of the image is minimised, each successive output signal of a column being representative of the intensity of radiation from a different portion of the object time-integrated by all the elements in succession, and wherein, in a narrow field of view mode, the array is held stationary relative to the image, the elements are made to perform a time integration over a stare period substantially greater than the period between successive simultaneous shifts in the wide field of view mode, and the stored signals are then read out from all the elements.

2. A method according to claim 1, wherein the two-dimensional array is a staring focal plane array.

3. A method according to claim 1, further including the detection of a particular target when in the wide field of view mode, and consequently switching to the narrow field of view mode during which the target is tracked by continuous adjustment of the position of the image on the array so that the target image is not lost.

4. A method according to claim 3, wherein the tracking of the target is carried out by the same apparatus which causes the scanning movement in the wide field of view mode.

5. Imaging apparatus comprising a two dimensional array of elements operable selectively in a wide or a narrow field of view mode, each element storing an electrical signal representative of the time-integrated intensity of the light incident on it, scanning means for causing the array to scan swaths of an object along respective columns of the array, drive means for the array, and means responsive to the output of the array to provide an image of the scanned object, wherein, in the wide field of view mode of operation, the scanning means causes the array to scan the object, and the drive means periodically shifts the stored electrical signals simultaneously in the direction of the scan from each element to its neighbour for continued time-integration, and provides, at the output of the array, the stored electrical signal from the end element of each column of the array, the average speed at which the signals progress along the array being equal to the speed of the image scan whereby smearing of the image is minimised, and each successive output signal of a column being representative of the intensity of radiation from a different portion of the object time-integrated by all the elements in succession, and wherein, in the narrow field of view mode, the scanning means ceases the regular scan of the image and the drive means causes the elements to perform a time-integration over a stare period substantially greater than the period between successive simultaneous shifts in the wide field of view mode, and causes the stored signals then to be read-out from all the elements.

6. Imaging apparatus according to claim 5, comprising:

target detection means responsive to the output of the array to determine the presence or absence of a target and to set the mode of operation of the array to the wide or the narrow field of view mode in accordance with that determination.

7. Imaging apparatus according to claim 5, comprising:

target tracking means operable in the narrow field of view mode to provide target co-ordinates to the scanning means to cause the scanning means to follow the target if the target moves relative to the remainder of the object, the scanning means otherwise holding the image stationary relative to the array.

8. Imaging apparatus according to claim 7, wherein the two-dimensional array is a staring focal plane array.

9. Imaging apparatus according to claim 5, wherein the array is a CCD array.

10. Imaging apparatus according to claim 9, in which the array is an IRCCD array.

11. Imaging apparatus according to claim 5, in which the scanning means comprises a mirror driven by a motor.

12. Imaging apparatus according to claim 11, wherein the scanning means operates in the wide field of view mode to rotate the mirror such as to cause the regular scanning of the image, and alternatively in the narrow field of view mode to move the same mirror intermittently such as to follow the target.