AIRBORNE RECONNAISSANCE SYSTEM

• US 20080211912A1
• Filed: 10/29/2007
• Published: 09/04/2008
• Est. Priority Date: 01/23/2004
• Status: Active Grant

• Current Assignee: Rafael - Armament Development Authority Ltd.
• Original Assignee: Rafael - Armament Development Authority Ltd.
• Inventors: Yavin, Zvi, Greenfeld, Israel, Uhl, Bernd
• Granted Patent: US 8,527,115 B2
• Time in Patent Office: Days
• US Class Current: 348/144
• CPC Class Codes: G01C 11/02 Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures

Abstract

An airborne reconnaissance system comprising: (1) Gimbals having at least two degrees of freedom; (2) At least one array of light sensors positioned on the gimbals, for being directed by the same within at least two degrees of freedom; (3) Map storage means for storing at least one Digital Elevation Map of an area of interest, divided into portions; (4) Inertial Navigation System for real-time providing to a gimbals control unit navigation and orientation data of the aircraft with respect to a predefined global axes system; (5) Portion selection unit for selecting, one at a time, another area portion from the area of interest; and (6) servo means for directing the gimbals. The system uses data from the inertial navigation system and from the digital elevation map for real-time calculating direction to selected area portions, and for maintaining the direction during integration of light from the terrain, and for producing corresponding images of area portions.

Claims

1. An airborne reconnaissance system comprising:

Gimbals having at least two degrees of freedom;

At least one array of light sensors positioned on the gimbals, for being directed by the same within at least two degrees of freedom;

Inertial Navigation System for real-time providing to a gimbals control unit navigation and orientation data of the aircraft with respect to a predefined global axes system;

Portion selection unit for selecting, one at a time, another area portion from the area of interest;

Servo control unit for;

A. Receiving one at a time, a coordinates set of the selective area portion, said set comprising the x;

y coordinates of said area portion, and the elevation z of the center of that portion;

B. Receiving continuously from said inertial navigation system present location and orientation data of the aircraft;

C. Repeatedly calculating and conveying into a gimbals servo unit in real time and at a high rate signals for;

a. during a direction period, signals for directing accordingly the gimbals including said at least one array of light-sensing units towards said x;

y;

z coordinates of the selected area portion, and;

b. during an integration period, in which the array sensors integrates light coming from the area portion, providing to the gimbals unit signals for compensating for the change in direction towards the x;

y;

z coordinates of the selected portion evolving from the aircraft motion;

Gimbals servo for effecting direction of the gimbals in at least two degrees of freedom according to the signals provided from said Servo Control Unit;

Sampling means for simultaneously sampling at the end of the integration period pixel levels from each of said array sensors, a set of all of said sampled pixel levels forms an image of said area portion; and

Storage means for storing a plurality of area portion images.

2. System according to claim 1, wherein said one or more arrays are selected from at least a visual light-sensitive array, a UV light sensitive-array, an infrared light-sensitive array, a multi/hyper-spectral array, and an active illumination array.

3. System according to claim 1, wherein said navigation data of the aircraft comprises data relating to the 3D location of the aircraft, and its velocity and acceleration vectors with respect to a predefined coordinates system, and its orientation data relating to the orientation of the aircraft with respect to said predefined coordinates system.

4. System according to claim 1, wherein said Inertial Navigation System comprises velocity, acceleration, and orientation sensors, at least some of said sensors being positioned on the gimbals.

5. System according to claim 1, wherein at least some of said arrays of sensors being positioned on the gimbals.

6. System according to claim 1, comprising two Inertial Navigation Systems, the first inertial navigation system being the main Inertial Navigation System of the aircraft and its sensors being positioned within the aircraft, and the second Inertial Navigation System being a system dedicated to the reconnaissance system, at least some of the sensors of said second Inertial Navigation System being positioned on the gimbals unit, measuring navigation and orientation data of the gimbals with respect to the said predefined axes system, for better eliminating misalignments occurring between the gimbals and LOS and the said main Inertial Navigation System of the aircraft due to aero-elastic deflections and vibrations of the aircraft, by using a process of transfer alignment from the said first INS to the said second INS.

7. System according to claim 1, wherein the portion selecting unit is used for calculating and determining a center of a next area portion that provides a predefined overlap between the said imaged area portion and the adjacent previously imaged area portion.

8. System according to claim 1, wherein in an automatic mode of operation the gimbals are activated to cover in a sequential, step-wise manner, the area of interest, said coverage is made from a predefined starting portion and according to a stored mission plan, thereby sequentially scanning one after the other area portions of the area of interest, and sampling images from each of said portions.

9. System according to claim 1, wherein in a manual mode of the system the pilot of the aircraft defines an area of interest during the flight, said area of interest being automatically divided into at least one area portion, all the area portions being automatically scanned one after the other by means of correspondingly directing to them the on-gimbals array, for capturing images of each of said scanned portions.

10. System according to claim 1, wherein the gimbals comprise two gimbals mechanisms, an external gimbals mechanism and an internal gimbals mechanism.

11. System according to claim 10, wherein the external gimbals mechanism is used for coarse directing the on-gimbals array to the center of a selected area portion.

12. System according to claim 10, wherein the external gimbals mechanism has two degrees of freedom, elevation and roll.

13. System according to claim 10, wherein the internal gimbals mechanism is used for fine directing the on-gimbals array to the center of a selected area portion, particularly for compensating the gimbals direction for the aircraft motion and orientation change during the integration period.

14. System according to claim 10, wherein the internal gimbals mechanism has two degrees of freedom, yaw and pitch.

15. System according to claim 10, wherein the external gimbals mechanism is slaved to the internal gimbals mechanism.

16. System according to claim 1, wherein during the integration period each of the array sensors simultaneously senses light from a corresponding section of the area portion, and at the end of the integration period the data from all the array sensors is read simultaneously, and stored as an image of the area portion.

17. System according to claim 1, wherein the array light sensors are sensitive to light in the range of visual light, IR, UV, multi/hyper-spectral, and/or an active illumination.

18. System according to claim 1, wherein the arrays are focal plane arrays.

19. System according to claim 1, wherein the predefined axes system is a global axes system.

20. System according to claim 1, assembled within a pod attached to the aircraft.

21. System according to claim 1, assembled within a payload installed inside the aircraft with only its windows protruding for obtaining a clear, unobstructed Line of Sight.

22. System according to claim 21, wherein the gimbals are located at the front of the pod, behind a transparent window.

23. System according to claim 1, further comprising a back-scanning mechanism comprising a mirror or prism, positioned on the gimbals and rotatable with respect thereto, light coming from the area portion first passing through said mirror which deflects the same towards the array, and,

a. the servo control unit applies to the gimbals a continuous row and/or column scanning movement without stopping;

and

b. while the direction towards an area portion is being established, applying to said back-scanning mirror during the integration period an opposite direction movement with respect to said row and/or column scanning continuous movement, thereby compensating for that continuous movement and ensuring a fixed orientation relationship of the array with respect to the area portion imaged.

24. A method for carrying out airborne reconnaissance, comprising:

a. Providing at least one array of light-sensitive pixels;

b. Mounting the at least one array on gimbals having at least two degrees of freedom so that the gimbals can direct the array to a selected Line of Sight;

c. Providing an Inertial Navigation System for obtaining at any time during the flight the updated x_a;

y_a;

z_a coordinates of the center of the array with respect to a predefined coordinates system;

d. Providing a calculation unit for, given x_p;

y_p location coordinates of a center of specific area portion within the area of interest, and the z_p elevation coordinate at said portion center, and the said x_a;

y_a;

z_a coordinates of the array center at same specific time, determining the exact angles for establishing a line of sight direction connecting between the center of the array and the said x_p;

y_p;

z_p coordinates;

e. Given the calculation of step d, directing accordingly the center of the array'"'"'s Line of Sight to the center of the area portion;

f. During an integration period, effecting accumulation of light separately by any of the array light sensors;

g. During the integration period, repeating at a high rate the calculation of step d with updated array x_a;

y_a;

z_a coordinates, and repeatedly, following each said calculation, correcting the direction as in step e;

h. At the end of the integration period, sampling all the array sensors, and saving in a storage as images of the array portion;

i. Selecting new portion coordinates x_p;

z_p within the area of interest, and repeating steps d to i for these new coordinates;

j. When the coverage of all the area of interest is complete, terminating the process, or beginning coverage of a new area of interest.

25. Method according to claim 24, wherein the selection of x_p:

y_p coordinates of a new area portion is performed to assure overlap between adjacent area portions within a predefined range, by calculating the 3-dimensional footprint of the new area portion on the ground, and then projecting it on the footprint of a previous area portion.

26. Method according to claim 25, wherein the overlap assurance is obtained by a trial and error selection, overlap calculation, and correction when necessary, or by an exact analytical calculation.

27. Method according to claim 24, wherein at least some of the sensors of the Inertial Navigation System are positioned on the gimbals, for improving the measuring of the orientation of the array with respect to the selective area portion.

28. Method according to claim 24, wherein at least some of the light sensitive sensors are positioned on the gimbals, for improving the measuring of the orientation of the Line of Sight with respect to the selective area portion.

29. Method according to claim 24, wherein the Inertial Navigation System comprises a dedicated Inertial Navigation System of the reconnaissance system and the main Inertial Navigation System of the aircraft, to improve the measuring of the orientation of the array with respect to the selective area portion, by using a process of transfer alignment from the aircraft Inertial Navigation System to the dedicated reconnaissance system'"'"'s Inertial Navigation System.

31. Method according to claim 24, for further carrying out airborne targeting, comprising:

a. Providing said gimbals having at least two degrees of freedom so that the gimbals can be directed to a selected Line of Sight;

b. Providing said Inertial Navigation System for obtaining at any time during the flight the updated x_a;

y_a;

z_a coordinates of the center of the gimbals with respect to a predefined coordinates system;

c. Providing said calculation unit for, given x_p;

y_p location coordinates of a center of a specific target within the area of interest, and the z_p elevation coordinate at said target center and the said x_a;

y_a;

z_a coordinates of the gimbals center at same specific time, determining the exact angles for establishing a Line of Sight direction connecting between the center of the gimbals and said x_p;

y_p;

z_p coordinates;

d. Given the calculation of step c, directing accordingly the center of the gimbals Line of Sight to the center of a selected target;

e. During the effective targeting period, motion compensating for the motion of the aircraft by repeating at a high rate the calculation of step d with updated target x_a;

y_a;

z_a coordinates, and repeatedly, following each said calculation, correcting the direction as in step d.

30. A method for providing motion compensation during airborne photographing comprising:

a. Providing at least one array of light-sensitive pixels;

b. Mounting the at least one array on gimbals having at least two degrees of freedom so that the gimbals can direct its Line of Sight towards a selective area portion;

c. Providing an Inertial Navigation System for obtaining at any instant during flight the updated x_a;

y_a;

z_a coordinates of the center of the array with respect to a predefined coordinates system;

d. Providing a calculation unit for, given x_p;

y_p location coordinates of a center of specific area portion within the area of interest, and the z_p elevation coordinate at said portion center, and the said x_a;

y_a;

z_a coordinates of the array center at same specific time, determining the exact angles for establishing a line of sight direction connecting between the center of the array and the said x_p;

y_p;

z_p coordinates;

e. During an integration period, when the center of the array'"'"'s Line of Sight is directed to a center of an area portion, effecting accumulation of light separately by any of the array light sensors;

f. During the integration period, repeating at a high rate the calculation of step d with updated array x_a;

y_a;

z_a coordinates, and repeatedly, following each said calculation, correcting the direction by keeping the center of the array directed to the center of the selected area portion, therefore compensating for aircraft movement; and

g. At the end of the integration period, sampling all the array sensors, and saving in a storage as images of the array portion.