Method and system for scanning a focal plane array during earth observation imaging

Abstract

An imaging system includes a body, a stage coupled to the body, and an actuator coupled to the body and the stage. The actuator is configured to move the stage in one or more directions relative to the body. The imaging system also includes a focal plane array including one or more detectors and coupled to the stage, and a controller coupled to the actuator. The controller is configured to determine a velocity of the body and cause the actuator to back scan the stage in the one or more directions at a drive velocity corresponding to the velocity of the body. Further, the controller is communicatively coupled to the one or more detectors and causes the one or more detectors to capture image data during the back scan.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 650,978, filed March 30, 2018, entitled “Method and System for Scanning Focal Plane Arrays During Earth Observation Imaging,” the disclosure of which is incorporated herein by reference in its entirety for all purposes. Background of the Invention

[0004] Satellite imaging has been developed. However, near-Earth orbit imaging applications utilizing staring sensors will experience image smear due to satellite ground velocity. Therefore, there is a need in the art for improved methods and systems related to satellite imaging. Summary of the Invention

[0005] Embodiments of the present invention generally relate to systems and methods for image stabilization, and more particularly, to utilizing a focal plane array positioning system to reduce image blur or image tailing. This focal plane array positioning system can perform a backscan of the focal plane array to reduce or eliminate image tailing, improve relative edge response, and increase the integration time associated with the image. Increasing the integration time can improve the signal-to-noise ratio of the sensor and enhance the ability to detect features in the observed scene. Backscanning the focal plane array reduces or eliminates the need for additional scanning mirrors and complex mechanical systems to move lenses or manipulate the field of view in front of the lenses to stabilize the image.

[0006] According to an embodiment of the present invention, an imaging system includes a subject, a stage, and an actuator. In some embodiments, the actuator may be coupled to the subject and the stage and configured to move the stage relative to the subject in one or more directions. An image sensor may be coupled to the stage. A focal plane array including one or more detectors may be coupled to the stage. A controller may be coupled to the actuator and configured to determine the velocity of the subject and cause the actuator to move the stage in one or more directions, thereby performing a back scan of the stage in said one or more directions at a drive speed corresponding to the velocity of the subject. The controller may be communicatively coupled to the one or more detectors and cause the one or more detectors to capture image data during the back scan.

[0007] In some embodiments, the actuator may be a piezoelectric actuator. In some embodiments, the imaging system includes a lens coupled to the subject. In some embodiments, the drive velocity may be characterized by a sawtooth curve. In other embodiments, the velocity of the subject may correspond to the forward velocity of at least one of an aircraft or a satellite. In some embodiments, the one or more detectors include one or more focal plane arrays. The one or more focal plane arrays may include one or more spectral filters. In some embodiments, the imaging system may include an I / O module configured to transmit and receive at least one or more of the subject's velocity, drive velocity, or image data.

[0008] According to embodiments of the present invention, a method is provided. The method provides a subject. The method provides an actuator coupled to the subject. The method also provides a stage coupled to the actuator. The method provides an imaging plane coupled to the stage. The method determines a subject velocity corresponding to movement of the subject. In some cases, determining the subject velocity includes reading the subject velocity from a memory. In some cases, determining the subject velocity includes receiving the subject velocity from an I / O subsystem. The method determines a drive velocity associated with the subject velocity. The method uses the actuator to perform a back scan of the stage at a drive velocity relative to the subject velocity. In some cases, the back scan includes sending a control signal to the actuator. In some cases, the back scan includes determining one or more gain coefficients and updating the drive velocity in response to the one or more gain coefficients. The method captures one or more frames during the back scan of the stage via an image sensor.

[0009] In some embodiments, the method further includes using drive speed and a timer to determine the position of the stage. In some embodiments, the method provides one or more stage position sensors, receives position sensor data from the one or more stage position sensors, and uses the position sensor data to determine the stage position. In some embodiments, determining the body speed further includes receiving the body speed from the I / O subsystem.

[0010] According to another embodiment of the present invention, a method is provided. The method includes sending a control signal to an actuator to initiate a back scan of a stage at a drive speed. The method further includes determining a body speed. The method further includes determining a position of the stage. The method further includes updating the drive speed in response to the body speed and the position of the stage. Additionally, the method includes determining that the stage has reached a cutoff amplitude. The method further includes sending a second control signal to reset the stage to an initial position.

[0011] In some embodiments, the method includes sending a control signal and resetting a timer. The method can utilize the body speed and a timer to determine the stage position. In some embodiments, determining the body speed includes at least one of: reading the body speed from memory, receiving the body speed from an I / O subsystem, and receiving the body speed from a sensor. In some embodiments, the method can update the drive speed by determining one or more gain coefficients and updating the drive speed in response to the one or more gain coefficients. In some embodiments, determining that the stage has reached a cutoff amplitude includes: receiving position sensor data and determining that the position sensor data exceeds a value associated with the cutoff amplitude. Many benefits can be obtained by this invention compared to conventional techniques. Attached Figure Description

[0012] Exemplary embodiments of the present invention will now be described in detail with reference to the following accompanying drawings.

[0013] Figure 1 The illustration shows three consecutive frames captured using an imaging system with a focal plane array according to an embodiment of the invention, the focal plane array being unadjusted for movement of the camera body.

[0014] Figure 2 An imaging system configured to perform a back scan of a focal plane array during movement of the imaging system, according to an embodiment of the invention, is shown.

[0015] Figure 3 The illustration shows three consecutive frames captured by an imaging system with a focal plane array according to an embodiment of the invention, used to form a "snapshot", wherein the focal plane array is scanned back at a speed that matches and cancels out the speed of the camera subject relative to the scene.

[0016] Figure 4A The illustration shows two complete loops of capturing consecutive image frames using a focal plane array according to an embodiment of the invention, wherein the focal plane array moves at a speed equal to the speed of the images on the focal plane array.

[0017] Figure 4B An overlay of snapshots according to an embodiment of the present invention is shown.

[0018] Figure 5A A focal plane array consisting of five staggered focal plane arrays on a stage is shown according to an embodiment of the present invention.

[0019] Figure 5B The ground swath width of a scan associated with five staggered focal plane arrays is shown according to an embodiment of the invention.

[0020] Figure 6 This is a simplified flowchart illustrating a method for translating a focal plane array of a sensor according to an embodiment of the present invention.

[0021] Figure 7 This is a simplified flowchart illustrating a method for retrace scanning of a focal plane array according to an embodiment of the present invention.

[0022] Figure 8 The illustration shows a comparison of the relative edge responses of various focal plane array configurations according to embodiments of the present invention.

[0023] Figure 9 This is a simplified flowchart illustrating yet another method for retracement of a focal plane array according to an embodiment of the present invention. Detailed Implementation

[0024] Numerous sources of interference exist in satellite imaging technology. Conventional techniques for stabilizing images during the integration time of a focal plane array (FLA) use fast steering mirrors in the optical chain or physically manipulate the optical system to control the pointing of the image on the FLA. Fast steering mirrors are large and occupy significant space, especially when located at the entrance aperture of the optical system. Due to the size of the fast steering mirror, large moving mirrors require more time to move and more time to stabilize before the integration time can begin, leaving less time for signal integration and / or frame stacking. This invention performs a backscan of the FLA by moving the FLA to match image movement, rather than manipulating the image. The embodiments described herein are more compact and more reliable compared to conventional techniques used in spacecraft and airborne applications.

[0025] To improve the signal-to-noise ratio of ground-based scene images, individual frames of the ground scene captured by the image sensor can be co-added. Co-addition simplifies this process if the images do not move relative to the sensor and image registration is not required. Large staring focal plane arrays used in modern satellite and aerial cameras suffer from image blurring or image trailing due to stage movement during exposure time. Image blurring or image trailing reduces the useful integration time for the large staring focal plane array and thus degrades image quality. Existing technologies, in order to address image blurring caused by movement of the focal plane array on a moving platform (e.g., a satellite), incorporate complex mechanical systems for moving the lens barrel or combine additional scanning mirrors. Therefore, there is a need in the art for improved methods and systems related to reducing image blur in cameras located on moving platforms.

[0026] Embodiments of the present invention provide a method for reducing image blur or image trailing in scans performed using high-altitude imaging systems (e.g., satellite-based imaging systems). More specifically, embodiments of the invention utilize a piezoelectrically driven stage to translate a focal plane array of a sensor. In some embodiments, the focal plane array of the sensor is a staring focal plane array. In some embodiments, the sensor may be part of a satellite space platform moving relative to the Earth. The focal plane array of the sensor may be translated along the same axis as the sensor's motion relative to the Earth. The speed of the piezoelectrically driven stage may be matched to the speed of the satellite, thereby forming a backscan of the focal plane array such that the image appears static during the integration time period of the focal plane array. In some embodiments, the integration time period may be continuous during the duration of the backscan of the focal plane array. In other embodiments, multiple consecutive frames may be stacked together to form a single snapshot. The backscan of the focal plane array ensures that the target image does not move relative to the focal plane array during the backscan. The piezoelectrically driven stage may return to its starting position while the rear edge of the field of view moves over the scene on the ground that has already been captured. In some embodiments, the focal plane array may include a focal plane array that captures images from multiple spectral bands. Embodiments of the present invention provide a stable staring imager. Each individual two-dimensional staring image can be stitched together to create a larger two-dimensional image. This technique enables the use of staring focal plane arrays in applications with scanning motion, which historically used linear scanning sensors.

[0027] Figure 1 The illustration shows three consecutive frames captured using an imaging system with a focal plane array according to an embodiment of the present invention, wherein the focal plane array is not adjusted for movement of the camera body. The imaging system 100 includes one or more of a detector module 102, a fixed stage 104, a focal plane array 106, and a lens 108. In some embodiments, the imaging system 100 may be mounted in a moving vehicle, such as a satellite, aircraft, vehicle, etc. Figure 1 Ray 110 associated with an object on ground 112 is also shown.

[0028] exist Figure 1In the first frame 116, the imaging system 100 moves above an object on the ground 112 at a speed of 114. In the first frame 116, the ray 110 associated with the object on the ground 112 is centered on the focal plane array 106, and the first image 117 on the focal plane array 106 shows the object on the ground 112. The movement of the system causes the imaging plane formed by the lens 108 to move. For the second frame 120, due to the speed 114 of the imaging system 100, the imaging system 100 has moved relative to the object on the ground 112. In the second frame 120, the ray 110 associated with the object on the ground 112 is no longer centered on the focal plane array 106, but has moved a first distance 122. Therefore, the second image 121 on the focal plane array 106 is different from the first image 117.

[0029] For the third frame 124, due to the velocity 114 of the imaging system 100, the imaging system 100 has moved further relative to the object on the ground 112. In the third frame 124, the ray 110 associated with the object on the ground 112 has currently moved by a first distance 122 and a second distance 126. Therefore, the third image 125 on the focal plane array 106 differs from the first image 117 and the second image 121. If an image of the object on the ground 112 is generated without image registration based on the integration of the first image 117, the second image 121, and the third image 125, the integrated image of the object on the ground 112 will include significant blur. To prevent image blurring in the first image 117, the second image 121, or the third image 125, the integration time of the sensor must be significantly less than the time it takes for a single pixel on the sensor to move one pixel length. Otherwise, significant image blurring will occur in each of the first image 117, the second image 121, or the third image 125.

[0030] Figure 2An imaging system according to an embodiment of the invention is illustrated, configured to perform a back scan of a focal plane array during movement of the imaging system. The back scan of the focal plane array allows for a sufficiently long dwell time during image capture to achieve a reasonable signal-to-noise ratio (SNR). The back scan also allows for frame stacking of consecutively captured frames, thereby reducing image blur. If the noise is inherently “white,” frame stacking is beneficial to SNR by the square root of the number of stacked frames. An image composed of four stacked frames has twice the SNR of an image formed from a single frame. The imaging system 200 may include a camera body 202, a lens 204, a detector module 206, a controller 208, and an I / O module 210. In some embodiments, the camera body 202 of the imaging system 200 is located in a vehicle, such as a satellite or aircraft. In some embodiments, the camera body 202 may be configured to provide structural support and alignment for the detector module 206 and the lens 204. In some embodiments, the camera body may include anchor points for the controller 208 and I / O module 210, and may be configured to manage heat transfer and isothermal performance. In other embodiments, the camera body 202 may be replaced by two separate partitions. The lens 204 may be mounted on the first partition, and the detector module 206, controller 208, and I / O module 210 may be mounted on the second partition.

[0031] In some embodiments, lens 204 may be optimized for transmitting specific wavelengths, such as visible light, near-infrared light, short-wavelength infrared light, mid-wavelength infrared light, long-wavelength infrared light, and far-infrared light. In some embodiments, lens 204 may be an optical system having one or more optical elements, such as lenses, filters, beam splitters, collimators, diffraction gratings, etc.

[0032] Detector module 206 may include a body 212, an actuator 214, a stage 216, and a focal plane array 218. The body 212 of detector module 206 may be coupled to camera body 202 and / or controller 208. In some embodiments, detector module 206 is communicatively coupled to controller 208 and / or I / O module 210. In some embodiments, controller 208 may be located external to camera body 202.

[0033] Actuator 214 may be coupled to body 212 and stage 216 and configured to move stage 216 relative to body 212 in one or more directions. In some embodiments, actuator 214 may include a piezoelectric actuator configured to move stage 216 having a focal plane array 218, such as a focal plane array, to reverse the movement of a satellite platform or aircraft. The piezoelectric actuator may be configured to move along a single axis or multiple axes. In some embodiments, the magnitude of movement of the piezoelectric actuator along a single axis may be 1200 μm. The magnitude of movement of the actuator may range from 50 μm to 1800 μm. In some embodiments, actuator 214 may provide a scan resolution of approximately 0.1 nm. In other embodiments, the actuator may provide a scan resolution of approximately 2 nm. In some embodiments, the piezoelectric actuator may utilize a flexure guide to control the movement of stage 216. The flexure guide may provide frictionless movement without rolling or sliding components.

[0034] Although some embodiments have been discussed with respect to piezoelectric actuators, it should be understood that actuators can be implemented using mechanical actuators, electromechanical actuators, hydraulic actuators, pneumatic actuators, etc. Therefore, actuator 214 is not intended to represent a piezoelectric actuator, but rather encompasses a machine for moving or controlling the stage 216 to perform a back scan of the focal plane array 218. Many variations, modifications, and substitutions will be recognized by those skilled in the art.

[0035] In some embodiments, actuator 214 may include one or more sensors that monitor the movement and position of stage 216. The one or more sensors may measure in-plane performance (e.g., position, velocity, acceleration, etc.) that affects image trailing. The one or more sensors may also measure out-of-plane performance (e.g., motion along the z-axis) that affects image focusing. In some embodiments, the one or more sensors are capacitive sensors. In other embodiments, the one or more sensors may include laser displacement sensors. The position of the stage may be sent to controller 208 and / or I / O module 210 for image processing and control loop calculations.

[0036] The stage 216 coupled to the actuator may include a focal plane array 218. The focal plane array 218 may be configured with one or more focal plane arrays operable to collect image data. In some embodiments, the focal plane array 218 may include a microbolometer. The microbolometer may consist of an array of pixels, with each pixel composed of several layers. In some embodiments, the focal plane array 218 may be a passive infrared (IR) detector that does not require supplemental illumination or light. In some embodiments, the focal plane array 218 may operate without cooling the detector material. In other embodiments, the detector module 206 may include thermal strapping between the focal plane array 218 and the body 212. An uncooled microbolometer array can reduce size, weight, and power requirements compared to a cooled thermal camera. In some embodiments, the focal plane array 218 may include one or more spectral filters. In some embodiments, the focal plane array 218 may be a multispectral band imager. In other embodiments, the focal plane array may include: a complementary metal-oxide-semiconductor (CMOS) sensor, a charge-coupled device (CCD) sensor, etc.

[0037] In some embodiments, the unit cell (pixel cell) may have a size of less than 20 micrometers (sub-20 μm). In some embodiments, the focal plane array 218 may include a plurality of individual pixel cells arranged in an array (e.g., a focal plane array) that defines, for example, a detector format and image resolution. Common 4:3 aspect ratio video formats include: 160×120, 320×240, 640×480, 1024×768, and 1280×960. In some embodiments, the focal plane array 106 may include, for example, Figure 5A and Figure 5B The plurality of focal plane arrays are further described herein. In some embodiments, the detector module may include a bias plate that provides power to the focal plane arrays and signal conditioning. In some embodiments, the detector module 206 may include a shutter.

[0038] Controller 208 may include one or more processors 220 and memory 222 to control focal plane array 218 and actuator 214. Controller 208 may be communicatively coupled to focal plane array 218 to provide sensor clocking and to perform image processing on sensor data collected by focal plane array 218. Controller 208 may also be communicatively coupled to actuator 214. Controller 208 may provide positioning signals to actuator 214 to perform retrace of stage 216 and focal plane array 218 coupled to stage 216. The positioning signals may be proportional to the drive speed associated with the retrace.

[0039] In some embodiments, controller 208 may determine a drive speed proportional to the aircraft or satellite ground speed and match the backscan to image movement during image acquisition. Controller 208 may include one or more sensors for determining the speed of camera body 202. The speed of camera body 202 may be correlated with the aircraft or satellite ground speed. The one or more sensors may include, for example, a position sensor, an accelerometer, a magnetometer, etc. In some embodiments, controller 208 may be communicatively coupled to I / O module 210 and determine the speed of camera body 202 based on data received from I / O module 210. In other embodiments, the drive speed may be pre-programmed based on a predetermined orbital speed (e.g., low Earth orbit speed).

[0040] After determining the speed of the camera body 202, a method can be used to determine the drive speed that reduces or eliminates image trailing caused by image sensors with long time constants. This method can use the speed of the camera body 202 to determine the forward platform speed associated with the motion of an aircraft or satellite. The method can determine a drive speed that, when applied to the stage 216 and focal plane array 218, will cause it to scan back to compensate for the forward stage speed.

[0041] As used herein, controller 208 may include one or more processors, which may be implemented as one or more integrated circuits (e.g., microprocessors or microcontrollers) to control the operation of actuator 214 and / or focal plane array 218. The one or more processors may be implemented as dedicated processors, such as application-specific integrated circuits (ASICs), which may be customized for a specific purpose and not for general use. In some embodiments, ASICs may be used to increase the speed of image processing. In some embodiments, controller 208 may include one or more graphics processing units (GPUs). The GPU may be configured to process sensor data collected by focal plane array 218. Controller 208 may include one or more processors, including single-core and / or multi-core processors. In some embodiments, controller 208 may be external to camera body 202. In these embodiments, focal plane array 218 and actuators may be communicatively coupled to I / O module 210.

[0042] I / O module 210 can be configured to send and receive data using an external system communicatively coupled to imaging system 200. Imaging system 200 may be located in a vehicle, such as an aircraft, satellite, etc. Data sent to and received from external systems may include speed, position, temperature, etc. In some embodiments, the I / O module can transmit sensor data collected by focal plane array 218 and / or controller 208 to one or more systems on the vehicle. I / O module 210 may include a device controller for sending and receiving data, one or more modems, a universal serial bus. Interfaces, RF transceiver components, serial buses, etc.

[0043] Figure 3 The illustration shows three consecutive frames captured by an imaging system with a focal plane array, according to an embodiment of the invention, to form a "snapshot," wherein the focal plane array is scanned back at a speed that matches and cancels out the speed of the camera subject relative to the scene. The imaging system 300 includes a detector module 302, an actuator 304, a stage 305, a focal plane array 306, and a lens 308. In some embodiments, the imaging system 300 may be mounted in a moving vehicle, such as a satellite, aircraft, vehicle, etc. Figure 3 Ray 310 associated with an object on ground 312 is also shown.

[0044] exist Figure 3 In the first frame 316, the imaging system 300 moves above an object on the ground 312 at a speed of 314. In the second frame 320, the ray 310 associated with the object on the ground 312 is centered on the focal plane array 306, and the first image 317 on the focal plane array 306 shows the object on the ground 312. For the second frame 320, due to the speed 314 of the imaging system 300, the imaging system 300 has moved relative to the object on the ground 312. In the second frame 320, the ray 310 associated with the object on the ground 312 is no longer at the first position on the detector module 302, but has moved a first distance 322. Figure 3 In the illustrated embodiment, the controller (e.g. Figure 2 The controller 208 described herein causes the actuator 304 to perform a back scan of the stage 305 at a drive speed corresponding to speed 314. The drive speed causes the stage 305 and the focal plane array 306 to translate a first distance 322. Therefore, the second image 321 on the focal plane array 306 is located at the same position as the first image 317 on the focal plane array 306.

[0045] For the third frame 324, the imaging system 300 has moved further relative to the object on the ground 312 due to the velocity 314 of the imaging system 300. In the third frame 324, the ray 310 associated with the object on the ground 312 has currently moved a first distance 322 and a second distance 326. The controller causes the actuator 304 to scan the stage 305 and the focal plane array 306 back to the second distance 326. Therefore, the third image 325 on the focal plane array 306 is located in the same position as the first image 317 and the second image 321 on the focal plane array 306. As shown in the first image 317, the second image 321, and the third image 325, the drive speed can be configured to scan the stage and the focal plane array 306 back to stabilize the image on the focal plane array 306. As a result, no image trailing is produced. If the integral image of the object on ground 312 is generated from the integration of the first image 317, the second image 321, and the third image 325, then the integral image of the object on ground 312 will have an improved signal-to-noise ratio and improved other quality metrics compared to a single image or integral image generated from an image that has not been re-scanned.

[0046] Figure 4A Two complete cycles of capturing consecutive image frames using a focal plane array according to an embodiment of the invention are illustrated, wherein the focal plane array moves at a constant speed relative to the camera body speed. Plot 400 shows a sawtooth-shaped movement curve of the stage generated by this method. In some embodiments, the method automatically adjusts the scan speed to match the speed of the image sensor relative to the Earth's surface. Plot 400 shows the stage position 402 along the y-axis and time 404 along the x-axis. The starting position 406 is at zero, while the final position 408 is at a position based on the physical extent of the stage and the snapshot time period length. In some embodiments, the final position of the stage is determined by the shorter of the physical extent and the snapshot time period length.

[0047] Figure 4AThe system includes three snapshot periods: a first snapshot period 410, a second snapshot period 440, and a third snapshot period 460. The first snapshot period 410 includes the capture of a first frame 413 as the focal plane array moves from position 412 to position 414, the capture of a second frame 415 as the focal plane array moves from position 414 to position 416, and the capture of a third frame 417 as the focal plane array moves from position 416 to position 418. The frames are captured within the total exposure time. For example, a second time segment 424 is associated with the first snapshot period 410, which has a total movement period 420. The exposure duration for each frame depends on the saturation time of the image sensor. In an exemplary embodiment, frames can be captured at a rate of 30 frames per second. The resulting maximum exposure time is 33.3 ms per frame, or a total exposure time of 100 ms for three frames. The velocity of the focal plane array during the first snapshot period 410 can be divided into three time segments. The first time segment 422 is associated with the period of time during which the actuator accelerates and causes the focal plane array to reach a constant speed. The second time segment 424 is associated with a period in which the actuator moves the focal plane array at a constant speed corresponding to the speed of the camera body, and this constant speed is opposite to the movement of the imaging plane caused by the speed of the camera body. The speed of the camera body may correspond to the movement of the platform in which the camera body is placed or mounted. The platform may include, for example, a satellite, an aircraft, etc.

[0048] During the second time segment 424, the image is stabilized on the focal plane array, and multiple frames can be stacked together without image trailing or blurring. In some embodiments, a single continuous frame can be captured during the duration of the second time segment 424 if the image sensor does not saturate. In some embodiments, the sensor can operate at a higher frame rate, and more than three frames can be stacked during the same time segment 424. The third time segment 426 is associated with the time period required for the actuator to move the focal plane array from the final position 408 to the starting position 406. In some embodiments, the third time segment can be considered as a reset time.

[0049] The second snapshot period 440 includes: capturing a first frame 443 when the focal plane array moves from 442 to 444, capturing a second frame 445 when the focal plane array moves from 444 to 446, and capturing a third frame 447 when the focal plane array moves from 446 to 448. The frames are captured during a total exposure time 450 associated with the second snapshot period 440, which has a total movement period 450. The speed of the focal plane array during the second snapshot period 440 can be divided into three time segments. A first time segment 452 is associated with a period during which the actuator accelerates and causes the focal plane array to reach a constant speed. A second time segment 454 is associated with a constant period during which the actuator causes the focal plane array to move at a constant speed. During the second time segment 454, the image is stabilized on the focal plane array, and multiple frames can be stacked together, reducing or eliminating image trailing or blur. The third time segment 456 is associated with the time period required for the actuator to move the focal plane array from the final position 408 to the starting position 406. For simplicity, the third snapshot period is shortened, but it still comprises three stacked frames similar to the first snapshot period 410 and the second snapshot period 440. The stage speed during the second time segments 424 and 454 can correspond to... Figure 2 The controller 208 described herein is associated with a drive speed. In some embodiments, a stable period may be inserted between a third time segment 426 of the first snapshot period 410 and a first time segment 452 of the second snapshot period 440.

[0050] Figure 4B The overlay of snapshots according to an embodiment of the present invention is illustrated. Snapshot 1, Snapshot 2, and Snapshot 3 are shown along the travel direction of ground 470. A first snapshot overlay 472 and a second snapshot overlay 474 provide a continuous strip image associated with one or more focal plane arrays on a focal plane array. The field of view of the imaging system captures an image of size 476,d, which corresponds to a distance parallel to the travel direction along ground 470. The time it takes for the trailing edge 478 of snapshot 1 to travel across the scene captured by snapshot 1 and reach the first edge 480 of the first snapshot overlay 472 corresponds to the available time for the actuator to reset the stage and focal plane array to the starting position 406. Each snapshot comprises three frames, and frame stacking can be used to improve the signal-to-noise ratio (SNR) of the resulting snapshots. White noise from the detector array is improved when multiple frames are added together; the SNR benefit corresponds to the square root of the number of stacked frames. Longer duration retracements of the image sensor or operation of the sensor at a higher frame rate result in more frames per snapshot and improve the SNR of the resulting snapshot image.

[0051] Figure 5A A focal plane array comprising five staggered focal plane arrays on a piezoelectric stage is illustrated according to an embodiment of the present invention. Imaging system 500 includes: focal plane array 502, a first staring focal plane array 504, a second staring focal plane array 506, a third staring focal plane array 508, a fourth staring focal plane array 510, a fifth staring focal plane array 512, and a tropical zone 514. Each focal plane array may include one or more spectral filters. In some embodiments, focal plane array 502 may be coupled to, for example,... Figure 2 The stage described herein. In some embodiments, each focal plane array can be based on... Figure 4A and Figure 4B The period shown is used to capture images.

[0052] Figure 5B A ground scan swath 550 associated with five staggered focal plane arrays is shown according to an embodiment of the invention. In some embodiments, reference is made to... Figure 5A and Figure 5B The focal plane arrays can be staggered and aligned to eliminate dead zones in the scan generated by focal plane array 502. For example, the first staring focal plane array 504 and the second staring focal plane array 506 are aligned together and staggered with the third staring focal plane array 508, the fourth staring focal plane array 510, and the fifth staring focal plane array 512. The direction of satellite motion 516 will capture image strips corresponding to each focal plane array. For example, the first starting focal plane array 504 may correspond to the first strip 524, the second starting focal plane array 506 may correspond to the second strip 526, the third starting focal plane array 508 may correspond to the third strip 528, the fourth starting focal plane array 510 may correspond to the fourth strip 530, and the fifth starting focal plane array 512 may correspond to the fifth strip 532. Figure 4A and Figure 4B As shown, each strip can consist of multiple snapshots, and each snapshot can correspond to multiple frames. The snapshot size perpendicular to the direction of motion forms a terrestrial scan swath width of 550.

[0053] although Figure 5A and Figure 5B An imaging system 500 with five focal plane arrays is shown; however, according to some embodiments of the invention, the imaging system may include one to ten focal plane arrays having up to 12 spectral filters. Other embodiments may include many focal plane arrays with a number of spectral filters. The benefit of increasing the number of focal plane arrays is that it supports multispectral imaging. Many variations, modifications, and substitutions will be recognized by those skilled in the art.

[0054] like Figure 5A and Figure 5B As shown, the imaging system 500 is arranged in a staggered layout. However, staggering is not mandatory. For example, focal plane arrays 504, 506, 508, 510, and 512 can be arranged side by side. In any case, the layout can be adjusted so that it has a different width or height than shown. For example, focal plane arrays 504, 506, 508, 510, and 512 can be spread out, uniformly distributed, or otherwise distributed, thereby increasing the ground scan swath 550. In another example, focal plane arrays 504 and 506 can be further spread out in the vertical dimension from focal plane arrays 508, 510, and 512.

[0055] Additionally or alternatively, the amount of overlap between adjacent arrays can be adjusted. For example, as shown, focal plane arrays 504 and 508 are slightly overlapped. However, focal plane arrays, such as 504, 506, 508, 510, and 512, can be further spaced apart or brought closer together with any degree of overlap.

[0056] Figure 6 This is a simplified flowchart illustrating a method 600 for translating a focal plane array of a sensor according to an embodiment of the present invention. At 610, the method provides a body. In some embodiments, the body is in motion. At 612, the method provides an actuator coupled to the body. In some embodiments, the actuator may be a piezoelectric actuator. At 614, the method provides a stage coupled to the actuator. In some embodiments, the actuator and the stage may include a piezoelectric stage. At 616, the method provides a focal plane array coupled to the stage. The focal plane array may include one or more focal plane arrays. At 618, the method determines a body velocity corresponding to the motion of the body. At 620, the method determines a drive velocity proportional to the body velocity. At 622, the method performs a back scan of the stage at the drive velocity relative to the motion of the body. In some embodiments, the actuator translates the stage to perform a back scan of the stage and the focal plane array at the drive velocity. At 624, the method captures one or more frames during the back scan of the stage. In some embodiments, the one or more focal plane arrays may capture the one or more frames.

[0057] It should be understood that Figure 6 The method shown provides a specific approach for scanning a focal plane array during Earth observation imaging according to embodiments of the present invention. Other operations may also be performed according to alternative embodiments. Furthermore, Figure 6The various operations shown may include multiple sub-operations, which can be executed in various orders suitable for each operation. Furthermore, depending on the specific application, additional operations may be added, or existing operations may be removed. Those skilled in the art will recognize many variations, modifications, and substitutions.

[0058] Figure 7 This is a simplified flowchart illustrating a method 700 for retracement of a focal plane array according to an embodiment of the present invention. At 710, the method initiates movement of a camera body. In some embodiments, the movement of the camera body may be associated with a path along the Earth's surface. The camera body may include one or more of the following: a lens, an actuator, a stage having a focal plane array (or imaging plane), and a controller. In some embodiments, the camera body may include an I / O module. At 712, the method sends a control signal to the actuator to initiate retracement of the focal plane array at a drive speed. In some embodiments, the control signal may include an instruction to begin capturing images. In some embodiments, the control signal may start / restart a timer associated with the retracement of the stage. At 714, the method reads the body speed. The body speed may be determined and / or received by a processor in the controller. The body speed may be read by a processor in the controller. In some embodiments, the body speed may indicate that a constant drive speed has been reached, and the controller will send an instruction to the focal plane array to begin capturing one or more images.

[0059] At 716, the method updates the drive speed based on the body speed and a gain coefficient. In some embodiments, the gain coefficient may be a vector or matrix with multiple terms. The gain coefficient may adjust the drive speed based on image sensor properties (e.g., image sensor size, actuator characteristics, and focal plane array characteristics). In some embodiments, the gain coefficient may be applied at a specific stage position during retrace. In some embodiments, the gain coefficient may compensate for hysteresis effects in the piezoelectric actuator to improve the linearity of the retrace slope. In some embodiments, an additional speed scaling factor may be added to handle variables specific to the particular implementation.

[0060] At 718, the method determines the stage position. In some embodiments, the processor in the controller may read data from one or more stage position sensors to determine the stage position. In other embodiments, the drive speed may be used to estimate the stage position. In other embodiments, the stage position may be inferred based on a predetermined time period. At 720, the method determines that the stage has reached a cutoff amplitude. This cutoff amplitude may be associated with the maximum position of the stage and actuator relative to the body. In some embodiments, the inferred stage position may be used to determine that the stage will reach the cutoff amplitude within a predetermined time period. At 722, after reaching the cutoff amplitude, the method returns the stage and actuator to their initial position or state.

[0061] It should be understood that Figure 7 The specific operations illustrated provide a method for performing a back scan of a focal plane array during Earth observation imaging according to an embodiment of the present invention. Other operational sequences may also be performed according to alternative embodiments. Furthermore, Figure 7 The various operations shown may include multiple sub-operations, which can be executed in various orders suitable for each operation. Furthermore, depending on the specific application, additional operations may be added, or existing operations may be removed. Those skilled in the art will recognize many variations, modifications, and substitutions.

[0062] Figure 8 A comparison of the relative edge response (RER) for various focal plane array configurations according to embodiments of the present invention is shown. Relationship diagram 800 illustrates the RER of the image as a function of distance to the edge. The x-axis 810 shows the distance to the edge in pixels at the zero point on the x-axis 810. The y-axis 812 shows the RER magnitude. The first focal plane array configuration is a static focal plane array, shown by trace 816, capturing a single frame. The static focal plane array has an RER of 0.52759 at zero pixels.

[0063] The second focal plane array configuration is a non-retrograde focal plane array shown by trace 814. This second focal plane array configuration is mounted on a test vehicle that simulates the movement of the non-retrograde focal plane array at a ground speed of 280 kts. The RER of the non-retrograde focal plane array traveling at a ground speed of 280 kts at zero pixels is 0.34141. The third focal plane array configuration is a retrograde focal plane array shown by trace 818, which is mounted on a test vehicle that simulates the movement of the focal plane array at a ground speed of 280 kts. The RER of the retrograde focal plane array at zero pixels is 0.52953. Relationship diagram 800 shows that the RER of the non-retrograde focal plane array is reduced by approximately 35% compared to the static focal plane array. 820 The reduced RER is due to the trailing caused by the movement of the focal plane array during the focal plane array integration time. Relationship diagram 800 shows that the RER of the retrograde focal plane array is almost equal to the RER of the static focal plane array.

[0064] Based on the discussion, some embodiments can be implemented in a satellite system that can be relatively stable, allowing the stage speed to match the platform speed. Alternatively, embodiments can be implemented on an aircraft that will have a slight deviation in terms of stage speed. Therefore, a feedback loop can be implemented so that the stage speed is periodically updated on a real-time basis. Different techniques are possible, such as correlating pixels between images or performing operations related to... Figure 7 and Figure 9 The process described.

[0065] Figure 9 This is a simplified flowchart illustrating another method 900 for retracement of a focal plane array according to an embodiment of the present invention. At 912, the method sends a control signal to the actuator to initiate retracement of the stage at a drive speed. The focal plane array may be attached to the stage. At 914, the method reads the subject speed. The subject speed can be determined and / or received by a processor in the controller. The subject speed can be received from the I / O subsystem. In some embodiments, the subject speed may indicate a constant drive speed reached, and the controller sends instructions to the focal plane array to begin capturing one or more images.

[0066] In 916, the method updates the drive speed based on the subject speed. In some cases, one or more gain coefficients may be used. For example, a single gain coefficient may be used. In another example, multiple gain coefficients may be used, such as a vector or matrix with multiple terms. The one or more gain coefficients may adjust the drive speed based on image sensor properties (e.g., image sensor size, actuator characteristics, and focal plane array characteristics). In some embodiments, the one or more gain coefficients may be applied at a specific stage position during retrace. In some embodiments, the one or more gain coefficients may compensate for hysteresis effects in the piezoelectric actuator to improve the linearity of the retrace slope. In some embodiments, additional speed scaling factors may be added to handle variables specific to the particular implementation.

[0067] In 918, the method determines the stage position. In some embodiments, the processor in the controller can read data from one or more stage position sensors to determine the stage position. In other embodiments, the drive speed can be used to estimate the stage position. In other embodiments, the stage position can be inferred based on a predetermined time period.

[0068] At 920, the method determines that the stage has reached a cutoff amplitude. This cutoff amplitude may be associated with the maximum position of the stage and / or actuator relative to the body. In some embodiments, a presumed stage position may be used to determine that the stage will reach the cutoff amplitude within a predetermined time period.

[0069] In step 922, after determining that the stage has reached the cutoff amplitude, the method resets the stage to its initial position. Consequently, the focal plane array is also reset to its initial position.

[0070] It should be understood that Figure 9 The specific operations illustrated provide a particular method for performing a back scan of a focal plane array during Earth observation imaging according to an embodiment of the present invention. According to alternative embodiments, other sequences of operations may also be performed. Furthermore, Figure 9 The various operations shown may include multiple sub-operations, which can be executed in various orders suitable for each operation. Furthermore, depending on the specific application, additional operations may be added, or existing operations may be removed. Those skilled in the art will recognize many variations, modifications, and substitutions.

[0071] It should also be understood that the examples and embodiments described herein are for illustrative purposes only and will inspire those skilled in the art to make various modifications or alterations based on the examples and embodiments, and such modifications or alterations will be included within the spirit and scope of this application and within the scope of the appended claims.

Claims

1. An imaging system, comprising: main body; A stage coupled to the main body; An actuator coupled to the body and the stage, wherein the actuator is configured to move the stage relative to the body in one or more directions; A focal plane array comprising one or more detectors and coupled to the stage; and A controller coupled to the actuator, wherein the controller is configured to determine the speed of the body, wherein the controller is configured to cause the actuator to perform a back scan of the stage from an initial position in one or more directions at a drive speed corresponding to the speed of the body, wherein performing a back scan of the stage includes determining one or more gain coefficients and updating the drive speed in response to the one or more gain coefficients, wherein the controller is communicatively coupled to the one or more detectors and causes the one or more detectors to capture image data during the back scan, and wherein the controller is configured to reset the stage to the initial position.

2. The imaging system as claimed in claim 1, wherein, The actuator is a piezoelectric actuator.

3. The imaging system of claim 1, further comprising: A lens coupled to the main body.

4. The imaging system as claimed in claim 1, wherein, The driving speed is characterized by a sawtooth curve.

5. The imaging system as claimed in claim 1, wherein, The velocity of the subject corresponds to the forward velocity of at least one of the aircraft or satellite.

6. The imaging system of claim 1, wherein, The focal plane array also includes one or more spectral filters.

7. The imaging system of claim 1, further comprising an I / O module configured to transmit and receive at least one or more of the speed of the subject, the drive speed, or the image data.

8. A method comprising: Provider; Provide an actuator coupled to the body; A stage is provided that is coupled to the actuator; An image sensor is provided that is coupled to the stage; Determine the body speed corresponding to the movement of the body; Determine the drive speed associated with the speed of the main body; The stage is scanned back using the actuator at the drive speed relative to the speed of the main body, wherein the scan back includes: Determine one or more gain coefficients; and The drive speed is updated in response to the one or more gain coefficients; During the retrace of the stage, one or more frames are captured by the image sensor, and the stage is reset to its initial position using the actuator.

9. The method of claim 8, wherein, The process of scanning back the stage also includes sending a control signal to the actuator.

10. The method of claim 8, further comprising: The position of the stage is determined using a timer and the drive speed.

11. The method of claim 8, wherein, Determining the subject speed also includes reading the subject speed from the memory.

12. The method according to claim 8, further comprising: Provide one or more stage position sensors; Receive position sensor data from the one or more stage position sensors; as well as The position of the stage is determined using the position sensor data.

13. A method comprising: A focal plane array coupled to a stage is provided, the focal plane array comprising one or more detectors; Send a control signal to the actuator to drive the speed to start scanning back on the stage; Data loading speed; In response to the main body speed, the drive speed is updated, wherein updating the drive speed further includes: Determine one or more gain coefficients; and The drive speed is updated in response to the one or more gain coefficients; Determine the position of the stage; Determine that the stage has reached the cutoff range; and After determining that the stage has reached the cutoff range, a second control signal is sent to reset the stage to its initial position.

14. The method of claim 13, wherein, Sending the control signal also includes resetting the timer.

15. The method of claim 14, further comprising: The position of the stage is determined using the speed of the main body and the timer.

16. The method of claim 13, wherein, Determining the subject speed also includes reading the subject speed from the memory.

17. The method of claim 13, wherein, Determining the main body speed also includes receiving the main body speed from the I / O subsystem.

18. The method of claim 13, wherein, Determining that the stage has reached the cutoff range also includes: Receive position sensor data; and The position sensor data is determined to exceed a value associated with the cutoff range.

Images