Wide-area aerial camera systems
A system for capturing aerial images, the system comprising at least one steerable camera module, the steerable camera module comprising a camera and a beam-steering mechanism in the optical path of the camera module whereby the pointing direction of the camera is time-multiplexed to provide a wider effective field of view, the beam-steering mechanism comprising a steerable mirror tilted with respect to an optical axis of the camera module, the steerable mirror adapted to spin about the optical axis to effect beam steering.
1. A system for capturing aerial images, the system comprising:
two steerable detail camera modules, each steerable detail camera module comprising a detail camera and a first beam-steering mechanism, a pointing direction of the detail camera being time-multiplexed by the first beam-steering mechanism to sweep out a wider effective field of view along a steering axis, the first beam-steering mechanism comprising a first steerable mirror tilted with respect to an optical axis of the detail camera module, the first steerable mirror being configured to spin about the optical axis of the detail camera module to effect beam steering, the steering axes of every detail camera module being angularly distributed substantially 90 degrees apart from each other and angled at substantially 45 degrees to a direction of flight, each detail camera module being configured to sweep out a field of view between an extreme right oblique angle and an extreme left oblique angle.
2. The system of claim 1 , wherein the system is attachable, above a camera hole, to at least one of: a floor of an aircraft or a floor of a pod carried by an aircraft, to provide the detail cameras with a view of the ground below the aircraft through the camera hole.
3. The system of claim 1 , the system comprising at least one overview camera, a focal length of the overview camera being shorter than a focal length of each detail camera.
4. The system of claim 1 , wherein, within each detail camera module, the detail camera has a lens selected from the group comprising: a dioptric lens, a catoptric lens, or a catadioptric lens.
5. The system of claim 1 , wherein, within each detail camera module, the first steerable mirror is stationary during an exposure period of the detail camera.
6. The system of claim 1 , wherein, within each detail camera module, the first steerable mirror has anon-zero angular velocity during an exposure period of the detail camera, and each steerable camera module comprises a second steerable mirror configured to correct an effect, on the detail camera, of the angular velocity of the first steerable mirror during the exposure period, to ensure the detail camera points in a consistent direction during the exposure period.
7. The system of claim 6 , wherein an angular velocity of the second steerable mirror is sinusoidal, and an average angular velocity of the second steerable mirror is equal to an average angular velocity of the first steerable mirror during the exposure period.
8. The system of claim 7 , wherein the angular velocity of the first steerable mirror is constant during the exposure period, and the angular velocity of the second steerable mirror is at a maximum during the exposure period.
9. The system of claim 6 , wherein an angular velocity of the second steerable mirror is constant during the exposure period.
10. The system of claim 6 , wherein the angular velocity of the first steerable mirror is a constant modulated by a sinusoid, to reduce an average angular velocity of the first steerable mirror during the exposure period.
11. The system of claim 1 further comprising at least one angular motion compensation (AMC) mechanism, the at least one AMC mechanism being configured to correct an effect, on each detail camera, of angular motion of the aircraft, to ensure the detail cameras point in a consistent direction over time.
12. The system of claim 11 , wherein AMC is provided via a steerable mirror.
13. The system of claim 1 further comprising at least one forward motion compensation (FMC) mechanism, the at least one FMC mechanism being configured to correct an effect, on each detail camera, of forward motion of the aircraft, to reduce motion blur in photos captured by the detail cameras.
14. The system of claim 13 , wherein FMC is provided via a steerable mirror.
15. The system of claim 1 , wherein the direction of flight is angled at substantially 45 degrees to a cardinal direction.
16. A method for capturing aerial images, comprising:
time-multiplexing pointing directions of two steerable detail camera modules to sweep out a wider effective field of view along a steering axis, each steerable detail camera module comprising a detail camera and a first beam-steering mechanism, the first beam-steering mechanism comprising a first steerable mirror tilted with respect to an optical axis of the detail camera module, the time-multiplexing including
spinning the first steerable mirror spin about the optical axis of the detail camera module to effect beam steering, the steering axes of the detail camera modules being angularly distributed substantially 90 degrees apart from each other and angled at substantially 45 degrees to a direction of flight, each detail camera module being configured to sweep out a field of view between an extreme right oblique angle and an extreme left oblique angle,
wherein the direction of flight is angled at substantially 45 degrees to a cardinal direction.