IL143731A - Scanning system with a staring detector - Google Patents

Description

143731/2 iiw fl iwn ¾>a N > ov np> « naive Scanning system with a staring detector Israel Aircraft Industries Ltd, i>Niy flvmwii τι>¾>)>ιΐίΐ Tamam Division The inventors: Zeev LISSAK Tal MAZOR -mo o Asher LOTTAN Izhack ZUBALSKY pNtri? .l ^ C.131363.4 SCANNING SYSTEM WITH A STARING DETECTOR FIELD OF THE INVENTION This invention relates to a scanning system with a staring array detector, for scanning a broad field of regard with the detector having a small field of view. In such scanning system, the field of view is temporarily held in a certain direction to permit the detector enough exposure time to obtain a unsmeared image of a corresponding portion of the field of regard.

BACKGROUND OF THE INVENTION Problems solved by, and advantages of, staring scanning systems are described, for example, in US Patent No. 5,663,825. This patent discloses a scanning system comprising two rotating scanning elements and a fixed sensor. One scanning element is a focal optical assembly that rotates continuously and smoothly to provide azimuth and/or elevation scan. Thus, the line of sight of the assembly rotates during the scan, and so does an image provided thereby. To stabilize this image relative to the sensor, the other scanning element is used which is in the form of a fast scanning mirror spaced from the optical system at a distance kept constant throughout the scan, and which is rotated in the direction opposite to that of the optical system. This mirror holds the line of sight re-directing it to the detector, thereby 'de-scanning' the image and, consequently, enabling the sensor to integrate it and to form a sufficient image signal.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a novel scanning system for scanning a field of regard (FOR) by dividing it into a plurality of fields of view (FOVs ) having different space orientations, said system having a central axis and a reference plane perpendicular thereto and comprising: a fixed optical system having a line of sight directed along said axis; a plurality of flat mirrors having different orientations relative to said reference plane and facing in different directions of sight to define said FOVs; each mirror having an operative state when its FOV is viewed by said optical system and a corresponding inoperative state, and being radially spaced from said central axis at least in the inoperative state; a switching mechanism for switching between said mirrors to successively bring them into their operative state while keeping unchanged their said orientation and said space orientation of the FOV.

The switching mechanism may be adapted to successively bring each flat mirror onto said central axis by its movement in a direction parallel or perpendicular to the plane of the mirror. Alternatively, each of said flat mirrors may be fixed, being spaced from said central axis, and the switching mechanism may comprise a folding member movable to successively establish a folded optical path between each flat mirror and said optical system. Such folding member may, for example, comprise a central mirror disposed on the central axis and a lateral mirror spaced from the central axis and having a fixed orientation relative to the central mirror. The switching in this case may be performed by rotating the folding member about the central axis to successively bring the lateral mirror into optical alignment with the flat mirrors, thereby putting them in their operative state.

In the present description and claims, the term "optical alignment" means such mutual disposition of two reflective surfaces that at least a part of light reflected by one of the surfaces is admitted by the other.

In both above cases, it is preferable that the flat mirrors constitute facets of a polygonal member, which is movable in the former case and fixed in the latter case. By virtue of this design, the switching between two adjacent facets may be performed, in both the above cases, by the movement of only one member of the system, which may simplify the system and make it compact, In the former case, this member is the polygonal member and in the latter case it is the folding member.

The optical system preferably comprises an imaging optics and a detector, such as a staring array detector, or a projection screen, for imaging each FOV in its original space orientation.

It should be appreciated that, since the switching arrangement of the present invention does not change the space orientation of the FOVs of the facets in their operative states, the image of each FOV formed by the imaging optics on the detector or the projection screen, will always be stable, i.e. unsmeared. Due to this, the l o scanning process may be continuous and, therefore, fast.

The facets of the polygonal member and the lateral mirror of the folding member may be equidistant from the central axis or rather may be disposed at different distances therefrom. In the former case, the facets are preferably designed to reflect light incident thereon from their substantially radial directions of sight, in substantially axial direction, and the lateral mirror is designed to admit substantially axialfy incident light and to reflect it in substantially radial direction. In the latter case, the reflective may be located closer to or further from the central axis than the lateral mirror and, consequently, reflect light towards the lateral mirror along an optical path defining an angle with the central axis.

The system of the present invention may be used for both panoramic scanning and also for scanning fields of regard in a certain direction, thus increasing the resolution of an image obtained thereby. For this purpose, in addition to the panoramic polygonal member, the system may be provided with a unidirectional polygonal member having the same number of reflecting sides as the panoramic polygonal member. Such unidirectional member should preferably be so disposed in the system as to enable each of its reflective sides to admit incident light from a direction defining a sharp acute angle with said central axis, and to reflect this light in a substantially radial direction to its associated reflective facet of the panoramic polygonal mirror.

The folding member is capable of reflecting light in the direction parallel to that of the incident light This folding member may be either a retroreflector such as a corner cube, or a reflector, such as periscope. The folding member may also have additional mirrors or other optical elements.

The panoramic polygonal member, the folding member and, optionally, the unidirectional polygonal member constitute a scanning unit, which is also subject of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, specific embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of the optical setup of a scanning system in accordance with one embodiment of the present invention; Figs. 2 and 3 are schematic illustrations of the optical setup of a scanning system in accordance with alternative embodiments of the present invention; Figs. 4A and 4B are, respectively, isometric and plan views of a panoramic polygonal member used in the scanning system illustrated in Figs. 1, 2 and 3; Figs.5 A and 5B are, respectively, isometric and plan views of a unidirectional polygonal member used in the scanning system illustrated in Figs. 1, 2 and 3; Fig. 6 is a schematic plan view of a scanning unit used in the scanning system of Fig. 1, and comprising the polygonal members shown in Figs. 4A, 4B and 5 A, 5B; and Fig. 7 is an optical scheme illustrating the scanning system illustrated in Fig. 1, in operation.

DETAILED DESCRIPTION OF THE INVENTION A schematic illustration of a scanning system 1 according to the present invention is shown in Fig. 1. The scanning system 1 is designed for scanning a field of regard (FOR) in a certain direction G, by dividing it into a plurality of field of views (FOVs). The scanning system 1 has a central axis Z and a reference plane XY perpendicular thereto (not shown), and it comprises a scanning unit generally designated as 10, and a stationary optical system 12. The optical system 12 is fixedly mounted so that its line of sight coincides with the central axis Z.

The scanning unit 10 comprises a folding member 20 rotatable about the axis Z by a drive (not shown) and stationary panoramic and unidirectional polygonal members 30 and 40. The folding member 20 is located axially between the optical system 12 and the polygonal members 30 and 40. Altemative mutual disposition of the folding member 20 and the polygonal members 30 and 40 is shown in Fig. 3. It should be noted that the unidirectional polygonal member 40 is optional and the scanning unit 10 may be used without it The folding member 20 has a rigid construction extending generally parallel to the plane XY and it is designed to admit incident light travelling in a generally axis direction, at a location spaced from the central axis Z and to direct it along the central axis Z towards the optical system 12. For this purpose, the folding member 20 comprises a central mirror 22 disposed on the central axis Z and a lateral mirror 24 spaced radially from the central mirror 22 and having a fixed orientation relative thereto. In the scanning unit shown in Fig. 1, the folding member 20 is in the form of a periscope, but it may also be a retroreflector such as a corner cube 20' shown in Fig. 3. The folding member may also be of any other appropriate design and may have additional mirrors or other optical elements.

The panoramic polygonal member 30 is shown separately in Figs. 4A and 4B. It has six flat reflective facets 32 facing in different generally radial directions of sight A to F that define respective fields of view FOVA to FOVF (not shown) having different space orientation. The directions of sight A to F of the reflective facets 32 do not need to be strictly radial but rather may form an angle with the plane XY. Also, the number of reflective facets 32 does not need to be six, but may be any other appropriate number. Reverting to Fig. 1, each reflective facet 32 of the polygonal member 30 is spaced from the central axis Z to the same distance as the lateral mirror 24 of the folding member 20, and is inclined relative to the plane XY so as to admit incident light from its direction of sight (designated as A) and to reflect it in generally axial direction towards the lateral mirror 24 of the folding member 20.

As seen in Figs. 5A and 5B, the unidirectional polygonal member 40 has the same number of reflective sides 42 as the panoramic polygonal member 30. The reflective sides 42 have directions of sight Gl to G6 all facing generally in the same direction G, diverging in accordance with the desired FOR of the system, and defining respective fields of view FOVi to FOVe (now shown) that have different space orientations. Reverting to Fig. 1, each reflective side 42 is so inclined relative to the plane XY as to reflect light incident from its direction of sight (designated as Gl) along the direction of sight of its associated reflective facet 32 of the panoramic polygonal member 30.

Fig. 6 schematically shows a plan view of the scanning unit 10, when assembled from the panoramic and unidirectional polygonal members 30 and 40, and the folding member 20. In the embodiment illustrated in Figs. 1 and 6, the unidirectional polygonal member 40 surrounds the panoramic polygonal member 30. However, this does not necessarily have to be the case, as, for example, is shown in Fig. 2.

In the embodiments of Figs. 1 and 2, the panoramic and unidirectional polygonal members 30 and 40 are disposed so that the reflecting sides 42 of the unidirectional polygonal member 40 are generally parallel to the reflective facets 32 of the panoramic polygonal member 30. However, as shown in Fig. 3, they may be inclined relative to the plane XY in different senses.

With reference to Figs. 1 to 3, and also to Fig. 7, in operation of the scanning unit 10, the light incident on the reflective sides 42 of the unidirectional polygonal member 40 is redirected thereby to the associated reflective facets 32 of the panoramic polygonal member 30 and is reflected thereby towards the folding member 20. The folding member 20 is continuously rotated about the axis Z, preferably with a constant rotational speed, to switch between the reflective facets 32. Thereby, these facets are successively brought into their operative position in which their FOVs, and consequently the FOVs of the respective reflective sides 42 of the unidirectional member 40, are viewed by the optical system 12. During the scanning process, the lateral mirror 24 of the folding member 20 is continuously brought into optical alignment with one after another portion of each reflective facet 32 of the panoramic polygonal member 30, moving f om one reflective facet 32 to another, neighboring reflective facet. During such optical alignment, the lateral mirror 24 admits light from the reflective facet 32 which it is passing by, and reflects this light to the central mirror 22 which in turn re-directs the light into the optical system 12. With the folding member 20 being rotated continuously, the lateral mirror 24 is continuously brought into the alignment with all the facets 32 of the panoramic polygonal mirror 30, thereby switching successively between the fields of view FOVi to FOVi of the reflective sides 42 of the umdirectional polygonal member 40, and consequently scanning the entire FOR- Since during the scanning process, each reflective facet 32, its corresponding reflective side 42 and the lateral and central mirrors 22 and 24 are in fixed disposition relative to each other, to the detector and to the associated FOV, the FOV is viewed by the optical system in its original space orientation during the entire scanning of this FOV.

The system 1 may be used without the umdirectional member 40, in which case panoramic scanning with the 360° -field of regard will be provided by switching between the fields of view FOVA to FOVF of the panoramic polygonal member 30. With reference to Fig. 7, the optical system 12 may be any suitably designed camera for day or night vision. The optical system 12 comprises an imaging optics 50 having a relatively small field of view and adapted to operate in collimated light designated as R, and an array detector 52 located in the focal plane of the imaging optics. The field of view of the imaging optics may, for example, be 20°xl6°. To mimaturize the system of the present invention, a front lens 54 of the imaging optics 50 has a very small entrance pupil and each reflective facet 32 of the panoramic polygonal member 30, when in its operative position, is located in the vicinity of this entrance pupil. Alternatively, the lateral member 24 of the folding member may be disposed in the vicinity of the entrance pupil. Clearly, the optical system may be designed to operate in any desired spectral range, and it may, accordingly, comprise such optical elements as filters 56.

When the folding member 30 is rotated, one or more image is obtained by the optical system 12 of every field of view FOV1 to FOV6 (or FOVA to FOVF. when the system is used without the unidirectional member 40). Each such image is obtained when the lateral mirror 24 of the folding member 20 is in the optical alignment with at least a portion of each reflective facet 32 of the panoramic polygonal member 30 for a 'staring' time which corresponds to the integration time of several frames of the detector 52. Also, at least one exposure time is spent when the lateral mirror 24 passes from its alignment with one reflective facet 32 into alignment with another, neighboring facet Images obtained during each scanning cycle are then combined in a full image. This full image has a resolution much higher than that obtained with the same detector without the division of the FOR into a plurality of the FOVs corresponding to the number of reflective sides in the polygonal members of the scanning unit 10 according to the present invention.

The scanning system and the scanning unit of the present invention have been described above based on specific examples thereof, and their different features may clearly be modified in various manners obvious to a person skilled in the art.

Claims (24)

CLAIMS:

1. A scanning system for scanning a field of regard (FOR) by dividing it into a plurality of fields of view (FOVs> having different space orientations, said system having a central axis and a reference plane perpendicular thereto and comprising: - a fixed optical system having a line of sight directed along said axis; a plurality of flat mirrors having different orientations relative to said reference plane and facing in different directions of sight to define said FOVs; each mirror having an operative state when its FOV is viewed by said optical system and a corresponding inoperative state, and being radially spaced from said central axis at least in the inoperative state; a switching mechanism for switching between said mirrors to successively bring them into their operative state while keeping unchanged their said orientation and said space orientation of the FOV.

2. A scanning system according to Claim 1 , wherein each of said flat mirrors are fixed, being spaced from said central axis, and the switching mechanism comprises a folding member to perform said switching by the movement of the folding member to successively establish a folded optical path between each flat mirror and said optical system.

3. A scanning system according to Claim 2, wherein said movement is continuous.

4. A scanning system according to Claim 2, wherein said folding member comprises a central mirror disposed on the central axis and a lateral mirror spaced from the central axis and having a fixed orientation relative to the central mirror.

5. A scanning system according to Claim 4, wherein said folding member is rotatable about the central axis to successively bring the lateral mirror into optical alignment with each flat mirror, thereby putting said flat mirror in its operative state.

6. A scanning system according to Claim 2, wherein said folding member is a member reflecting light in a direction parallel to that of the incident light.

7. A scanning system according to Claim 1, wherein the switching mechanism is adapted to successively bring each flat mirror onto said central axis by its movement in a direction parallel and/or perpendicular to the plane of the mirror.

8. A scanning system according to any one of the preceding claims, comprising a panoramic polygonal member, wherein said flat mirrors constitute facets of said polygonal member.

9. A scanning system according to anyone of the preceding claims, wherein said optical system comprises an imaging optics with a front lens, which is designed to have an entrance pupil at a distance from said front lens, and each said flat mirror, when in its operative state, is located in the vicinity of said entrance pupil.

10. A scanning system according to any one of Claims 5 to 8, wherein said optical system comprises an imaging optics with a front lens, which is designed to have an entrance pupil at a distance from said front lens, and lateral mirror of the folding member is located in the vicinity of said entrance pupil

11. A scanning system according to anyone of the preceding claims, wherein said optical system comprises an array detector or a projection screen.

12. A scanning system according to anyone of the preceding claims, further comprising a unidirectional polygonal member having the same number of reflective sides as the panoramic polygonal member, which reflective sides have axially diverging directions of sight

13. A scanning system for scanning a field of regard (FOR) by dividing it into a plurality of fields of view (FOVs), said system having a central axis and a reference plane perpendicular thereto and comprising: an optical system fixedly mounted so as to have its line of sight directed along said axis; a panoramic polygonal member having a plurality of reflective facets radially spaced from said central axis and facing in different directions of sight to define said FOVs, a folding member comprising a central mirror disposed on the central axis and a lateral mirror spaced from said central axis, said folding member being capable of switching between said facets by successively bringing said lateral mirror into optical alignment with said facets, and thereby establishing a folded optical path between each facet and the optical system to put each facet into its operative state in which its FOV is viewed by the optical system. 5

14. A scanning system according to Claim 13, further comprising a drive adapted for the continuous movement of said folding member relative to said polygonal member.

15. A scanning system according to Claim 14, wherein the drive is adapted to rotate the folding member about said central axis, with said polygonal member being 10 stationary.

16. A scanning system according to Claim 13, 14 or 15, wherein said folding member is a member reflecting light in a direction parallel to that of the incident light.

17. A scanning system according to any one of Claims 13 to 17, wherein said 15 optical system comprises an imaging optics with a front lens, which is designed to have an entrance pupil at a distance from said front lens, and each said facet, when in its operative state, or said lateral mirror, is located in the vicinity of said entrance pupil.

18. A scanning system according to anyone of the preceding claims, wherein said 20 optical system comprises an array detector or a projection screen.

19. A scanning system according to anyone of the preceding claims, further comprising a unidirectional polygonal member having the same number of reflective sides as the panoramic polygonal member, which reflective sides have axially diverging directions of sight. 25

20. A scanning unit having central axis and a reference plane perpendicular thereto, and comprising: a panoramic polygonal member having a plurality of reflective facets radially spaced from said central axis and facing in different directions of sight to define dfferent FOVs, a folding member comprising a central mirror disposed on the central axis and a lateral mirror spaced from said central axis, said folding member being capable of switching between said facets by successively bringing said lateral mirror into optical alignment with said facets.

21. A scanning unit according to Claim 18, further comprising a drive for the continuous movement of said folding member relative to said polygonal member to successively bring said lateral mirror into said optical alignment with each of said reflective facets.

22. A scanning unit according to Claim 19, wherein said continuous movement is a rotation of me folding member about said central axis, with said polygonal member being stationary.

23. A scanning unit according to Claim 19 or 20, wherein said folding member is a member reflecting light in a direction parallel to that of the incident light

24. A scanning unit according to any one of the preceding claims, further comprising a unidirectional polygonal member having the same number of reflective sides as the panoramic polygonal member, which reflective sides have axially diverging directions of sight. For the Applicants, J:\01313634\0131363