Patent Description:
Document <CIT> discloses inter-frame stabilization based on the velocity of a vehicle on which the video camera is mounted and the pan rate of a line-of-sight controller of the video camera. The inter-frame stabilization is performed by a software component by moving a display area (or viewport) within a larger image area. The inter-frame stabilization removes small-amplitude jitter while accounting for vehicle velocity and orientation, pan rate and orientation of the line-of-sight controller, distance to an object within the image, and field of view of the camera. The stabilization system converts an inter-frame stabilization adjustment into a pan rate adjustment so the line-of-sight controller will keep the desired object within the image area of the camera. In this way, the stabilization system uses an electronic stabilization to remove small-amplitude jitters and feeds those adjustments to a mechanical stabilization to account for large-amplitude jitter.

Document <CIT> relates to capturing images while in motion, including at least one CCD camera housed within an aircraft traveling along a flight path. The document teaches to take multiple pictures in a first direction while the aircraft's path is in a second direction perpendicular to the first direction. This approach allows the system to stitch together a patchwork of images to form a complete view of a larger area.

Document <CIT> discloses a multi-spectral sensor system mountable to a mobile platform. The system comprises an image capturing system, a first translation stage affixed to the image capturing system and a stationary optics assembly. The system further comprises a motion controller configured to move the first translation stage and image capturing system across the stationary optics along a traveling direction opposite of a traveling direction of the mobile platform and at substantially the same rate as the mobile platform is moving during a stare operation. Document <CIT> discloses a disturbance compensation system for a camera on board a spacecraft and having an imaging device and condensing means for condensing light onto the imaging device. Linear actuators adjust the position of the imaging device by moving it with multifreedom. A control circuit computes, in response to position information associated with the imaging device, an amount in which the position of the imaging device should be corrected, and controls the linear actuators on the basis of the computed amount.

Document <CIT> discloses an imaging system for satellite platforms comprising a linear actuator coupled to the body supporting a camera such as to move the camera on a tracking rail in a direction relative to the motion of the satellite platform; a controller coupled to the actuator is configured to determine a velocity of the platform and cause the actuator to backscan the stage from an initial position in a direction and at a drive velocity corresponding with the apparent motion of the platform.

The invention is defined by the combination of features of the independent claims.

Embodiments of the present invention relate generally to systems and methods for image stabilization and, in particular, to reduction of image blur or smear using a focal plane array positioning system. The focal plane array positioning system can backscan a focal plane array to reduce or remove image smear, improve relative edge response, and allow an increased integration time associated with an image. Increasing the integration time can improve the signal to noise ratio of the sensor and improve the ability to detect features in the observed scene. Backscanning the focal plane array reduces or eliminates the need to incorporate additional scan mirrors and complex mechanical systems to move a lens or steer the field of view in front of the lens to stabilize the image.

According to the invention, an imaging system includes a body, a stage, and an actuator. The actuator is coupled to the body and the stage and configured to move the stage in one or more directions relative to the body. An image sensor can be coupled to the stage. A focal plane array including one or more detectors is coupled to the stage. A controller is coupled to the actuator and configured to determine a velocity of the body and cause the actuator to move the stage in one or more directions to backscan the stage from an initial position in a direction and in at a drive velocity corresponding the velocity of the body, wherein backscanning the stage comprises determining one or more gain coefficients and updating the drive velocity in response to the one or more gain coefficients. The controller is communicatively coupled to the one or more detectors and cause the one or more detectors to capture image data during the backscan.

The actuator is a piezoelectric actuator, and wherein updating the drive velocity in response to the one or more gain coefficients is performed such that hysteresis effects in the piezoelectric actuator are compensated to improve backscan slope linearity. In some embodiments, the imaging system includes a lens coupled to the body. In some embodiments, the drive velocity can be characterized by a sawtooth profile. In other embodiments, the velocity of the body can correspond to a forward velocity of at least one of an aircraft or a satellite. In some embodiments, the one or more detectors comprises one or more focal plane arrays. The one or more focal plane arrays can include one or more spectral filters. In some embodiments, the imaging system can include an I/O module configured to transmit and receive at least one or more of the velocity of the body, the drive velocity, or the image data.

According to an embodiment of the invention, a method is provided. The method provides a body. The method provides a piezoelectric actuator coupled to the body. The method further provides a stage coupled to the actuator. The method provides an image plane coupled to the stage. The method determines a body velocity corresponding to motion of the body by reading body velocity from a memory. In some cases, determining the body velocity includes receiving the body velocity from an I/O subsystem. The method determines a drive velocity associated with the body velocity. The method backscans the stage at the drive velocity relative to the body velocity using the actuator. The In backscanning includes sending a control signal to the actuator. The method includes determining one or more gain coefficients and updating the drive velocity in response to the body velocity and in response to the one or more gain coefficients, and wherein updating the drive velocity in response to the one or more gain coefficients is performed such that hysteresis effects in the piezoelectric actuator are compensated to improve backscan slope linearity. The method captures one or more frames during backscanning of the stage by the image sensor.

In some embodiments, the method further includes determining a position of the stage using the drive velocity and a timer. 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 determines stage position using the position sensor data. In some embodiments, determining the body velocity further comprises receiving the body velocity from an I/O subsystem.

According to another embodiment of the invention, a method is provided. The method includes sending a control signal to an actuator to start a backscan of a stage at a drive velocity. The method further includes determining a body velocity. The method further includes determining a position of the stage. The method further includes updating the drive velocity in response to the body velocity and the position of the stage. Additionally, the method includes determining that the stage reaches a cutoff amplitude. The method further includes sending a second control signal to reset the stage to an initial position.

In some embodiments, the method includes sending the control signal and resetting a timer. The method can determine the position of the stage using the body velocity and the timer. In some embodiments, determining the body velocity includes at least one of reading body velocity from a memory, receiving the body velocity from an I/O subsystem, and receiving the body velocity from a sensor. In some embodiments, the method can update the drive velocity by determining one or more gain coefficients and updating the drive velocity in response to the one or more gain coefficients. In some embodiments, determining the stage reaches the cutoff amplitude includes receiving position sensor data and determining the position sensor data exceeds a value associated with the cutoff amplitude. Numerous benefits are achieved by way of the present invention over conventional techniques.

Illustrative embodiments of the present disclosure are described in detail below with reference to the following drawing figures.

Unless explicitly indicated as "embodiment(s) according to the claimed invention", the terms embodiments/examples/aspects mentioned as such in the following description may include some but not all features as literally defined in the claims, these shall be apprehended only for illustration purposes.

Numerous sources of interference exist in satellite imaging technologies. Conventional techniques to stabilize an image during a Focal Plane Array integration time use a fast steering mirror in the optical chain or physically steer the optical system to control the pointing of the image on the focal plane array. Fast steering mirrors are large and can take up a significant amount of space, especially when located at the entrance aperture of the optical system. Because of their size, large moving mirrors require more time to move and time to settle before the integration time can commence, leaving less time for integration of signal and/or frame stacking. The present invention can backscan a focal plane array by moving the focal plane array to match the image motion instead of steering the image. Embodiments described herein are more compact and improve reliability over conventional techniques used for spaceborne and airborne applications.

To improve the signal to noise ratio of an image of a scene on the ground, individual frames of the scene on the ground captured by an image sensor can be co-added. Co-adding is simplified if the image has not moved relative to the sensor and no image registration is required. Large staring focal plane arrays used in modern satellites and aerial cameras are subject to image blur or smear due to the motion of the stage during the exposure time. The image blur or smear reduces the useful integration time for a large staring focal plane array and as a result, image quality. Existing technologies to address image blur caused by the motion of a focal plane array in a moving platform, such as a satellite, include complex mechanical systems to move the lens barrel or incorporate additional scan mirrors. Accordingly, there is a need in the art for improved methods and systems related to reducing image blur in cameras positioned in a moving platform.

Embodiments of the present invention provide a method for reducing image blur or smear present in scans taken using high altitude imaging systems, for example, satellite-based imaging systems. More specifically, embodiments of the present invention utilize a piezo driven stage to translate the 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 can be part of a satellite space platform that is moving relative to the earth. The focal plane array of the sensor can be translated in the same axis as the sensor's motion relative to the earth. The piezo driven stage velocity can be matched to the velocity of the satellite resulting in a backscan of the focal plane array so that the image appears static during a focal plane array integration period. In some embodiments, the integration period can be continuous during the duration of the backscan of the focal plane array. In other embodiments, multiple consecutive frames can be stacked together to form a single snap. The backscan of the focal plane array results in the target image not moving relative to the focal plane array during the backscan. The piezo driven stage can return to a starting position while the trailing edge of the field of view moves across a scene on the ground that has already been captured. In some embodiments, the focal plane array can include a focal plane array that captures images from multiple spectral bands. Embodiments of the present invention provide a stabilized staring imager. Each individual two-dimensional staring image can be stitched together to create a larger two dimensional image. The use of this technology enables the use of staring focal plane arrays in applications that have a scan motion that historically used linear scan sensors.

<FIG> illustrates three successive frames captured using an imaging system with a focal plane array that is not adjusted for the motion of the camera body according to an embodiment of the present invention. The imaging system <NUM> includes one or more of a detector module <NUM>, a stationary stage <NUM>, a focal plane array <NUM>, and a lens <NUM>. In some embodiments, the imaging system <NUM> can be mounted in a moving vehicle such as a satellite, an aircraft, an automobile, and the like. <FIG> also illustrates the rays <NUM> associated with an object on the ground <NUM>.

In <FIG>, the imaging system <NUM> is moving at a velocity <NUM> over the object on the ground <NUM>. In a first frame <NUM>, the rays <NUM> associated with the object on the ground <NUM> are centered on the focal plane array <NUM> and a first image <NUM> on the focal plane array <NUM> shows the object on the ground <NUM>. The motion of the system causes the image plane formed by the lens <NUM> to move. For a second frame <NUM>, imaging system <NUM> has moved relative to the object on the ground <NUM> due to the velocity <NUM> of the imaging system <NUM>. In the second frame <NUM>, the rays <NUM> associated with the object on the ground <NUM> are no longer centered on the focal plane array <NUM> but have moved a first distance <NUM>. Accordingly, a second image <NUM> on the focal plane array <NUM> is different from the first image <NUM>.

For a third frame <NUM>, the imaging system <NUM> has moved further relative to the object on the ground <NUM> due to the velocity <NUM> of the imaging system <NUM>. In the third frame <NUM>, the rays <NUM> associated with the object on the ground <NUM> have now moved the first distance <NUM> and a second distance <NUM>. Accordingly, a third image <NUM> on the focal plane array <NUM> is different from the first image <NUM> and the second image <NUM>. If an image of the object on the ground <NUM> was produced without image registration from the integration of the first image <NUM>, the second image <NUM>, and the third image <NUM>, the integrated image of the object on the ground <NUM> would include significant blur. To prevent image blur from within the first image <NUM>, the second image <NUM> or the third image <NUM>, 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 blur occurs within each of the first image <NUM>, the second image <NUM> or the third image <NUM>.

<FIG> illustrates an imaging system configured to backscan a focal plane array during motion of the imaging system according to an embodiment of the present invention. Backscanning the focal plane array makes it possible to dwell long enough during a capture of an image to obtain a reasonable Signal to Noise Ratio (SNR). Backscanning also allows fame stacking of successively captured frames, reducing blurring the image. If the noise is "white" in nature, frame stacking benefits the SNR by the square root of the number of frames stacked. An image made up of <NUM> frames stacked has two-times higher SNR than an image taken with one frame. The imaging system <NUM> can include a camera body <NUM>, a lens <NUM>, a detector module <NUM>, a controller <NUM>, and an I/O module <NUM>. In some embodiments, the camera body <NUM> of the imaging system <NUM> is positioned in a vehicle such as satellite or an aircraft. In some embodiments, the camera body <NUM> can be configured to provide structural support and alignment for the detector module <NUM> and lens <NUM>. In some embodiments, the camera body can include anchor points for the controller <NUM> and the I/O module <NUM> and can be configured to manage heat transfer and isothermal performance. In other embodiments, the camera body <NUM> can be replaced by two separate bulkheads. The lens <NUM> can be mounted on a first bulkhead and the detector module <NUM>, controller <NUM>, and I/O module <NUM> can be mounted on a second bulkhead.

In some embodiments, the lens <NUM> can be optimized for the transmission of a specific wavelength such as visible, near-infrared, short-wavelength infrared, mid-wavelength infrared, long-wavelength infrared, and far infrared. In some embodiments, lens <NUM> can be an optical system with one or more optical elements such as a lens, a filter, a beam splitter, a collimator, a diffraction grating, and the like.

The detector module <NUM> can include a body <NUM>, an actuator <NUM>, a stage <NUM>, and a focal plane array <NUM>. The body <NUM> of the detector module <NUM> can be coupled to the camera body <NUM> and/or the controller <NUM>. In some embodiments, the detector module <NUM> is communicatively coupled to the controller <NUM> and/or the I/O module <NUM>. In some embodiments, the controller <NUM> may be positioned outside the camera body <NUM>.

The actuator <NUM> is coupled to the body <NUM> and the stage <NUM> and is configured to move the stage <NUM> in one or more directions relative to the body <NUM>. The actuator <NUM> includes a piezoelectric actuator configured to move the stage <NUM> with a focal plane array <NUM>, such as a focal plane array, to counter the motion of a satellite platform or aircraft. The piezoelectric actuator can be configured to move along a single axis or multiple axes. In some embodiments, the amplitude of the piezoelectric actuator along a single axis can be <NUM>. The amplitude of the movement of the actuator can range from <NUM> to <NUM>. In some embodiments, the actuator <NUM> can provide a backscan resolution on the order of <NUM>. In other embodiments, the actuator can provide a backscan resolution on the order of <NUM>. In some embodiments, the piezoelectric actuator can control the motion of the stage <NUM> using flexure guides. The flexure guides can provide frictionless motion with no rolling or sliding parts.

In some embodiments, the actuator <NUM> can include one or more sensors to monitor the motion and position of the stage <NUM>. The one or more sensors can measure in-plane performance such as position, velocity, acceleration, and the like which affect image smearing. The one or more sensors can also measure out of plane performance such as motion along the z-axis which affects image focus. In some embodiments the one or more sensors are capacitive sensors. In other embodiments, the one or more sensors can include a laser displacement sensor. The position of the stage can be transmitted to the controller <NUM> and/or the I/O module <NUM> for use in image processing and control loop calculations.

The stage <NUM> coupled to the actuator can include the focal plane array <NUM>. The focal plane array <NUM> can be configured with one or more focal plane arrays operable to collect image data. In some embodiments, the focal plane array <NUM> can include a microbolometer. The microbolometer can consist of an array of pixels, each pixel being made up of several layers. In some embodiments, the focal plane array <NUM> can be a passive Infrared (IR) detector that does not require supplemental illumination or light. In some embodiments, the focal plane array <NUM> can operate without cooling of a detector material. In other embodiments, the detector module <NUM> can include thermal strapping between the focal plane array <NUM> and the body <NUM>. An uncooled microbolometer array can enable reductions in size, weight, and power requirements relative to cooled thermal cameras. In some embodiments, the focal plane array <NUM> can include one or more spectral filters. In some embodiments, the focal plane array <NUM> can be a multi-spectral band imager. In other embodiments, the focal plane array can include a Complementary Metal Oxide Semiconductor (CMOS) sensor, a Charge-Coupled Device (CCD) sensor, or the like.

In some embodiments, unit cells (pixel elements) can include sub-<NUM> dimensions. In some embodiments, the focal plane array <NUM> can include individual pixel elements arranged into an array such as a focal plane array that defines the detector format and image resolution. Common <NUM>:<NUM> aspect ratio video formats include: 160x120, 320x240, 640x480, 1024x768 and 1280x960. In some embodiments, the focal plane array <NUM> can include a plurality of focal plane arrays as described further in <FIG>. In some embodiments, the detector module can include a bias board to provide power for the focal plane array as well as signal conditioning. In some embodiments, the detector module <NUM> can include a shutter.

Controller <NUM> can include one or more processors <NUM> and memory <NUM> to control the focal plane array <NUM> and the actuator <NUM>. The controller <NUM> can be communicatively coupled to the focal plane array <NUM> to provide sensor clocking and image processing of sensor data collected by the focal plane array <NUM>. The controller <NUM> can also be communicatively coupled to the actuator <NUM>. The controller <NUM> can provide positioning signals to the actuator <NUM> to backscan the stage <NUM> and the focal plane array <NUM> coupled thereto. The positioning signals can be proportional to a drive velocity associated with the backscan.

In some embodiments, the controller <NUM> can determine a drive velocity that is proportional to the aircraft or satellite ground velocity and causes the backscan to match the motion of an image during image collection. The controller <NUM> can include one or more sensors to determine a velocity of the camera body <NUM>. The velocity of the camera body <NUM> can be associated with the aircraft or satellite ground velocity. The one or more sensors can include, for example, positioning sensors, accelerometers, magnetometers, and the like. In some embodiments, the controller <NUM> can be communicatively coupled to the I/O module <NUM> and determine the velocity of the camera body <NUM> based on data received from the I/O Module <NUM>. In other embodiments, the drive velocity can be pre-programmed based on a predetermined orbit velocity, such as a low earth orbit velocity.

After determining the velocity of the camera body <NUM>, the drive velocity can be determined using a method such that the image smear caused by an image sensor with a long time constant can be reduced or eliminated. The method can use the velocity of the camera body <NUM> to determine a forward platform velocity associated with the motion of an aircraft or satellite. The method can determine a drive velocity that when applied to the stage <NUM> and focal plane array <NUM>, will backscan to compensate for the forward platform velocity.

As used herein, controller <NUM> can include one or more processors, which can be implemented as one or more integrated circuits (e.g., a microprocessor or microcontroller), to control the operation of the actuator <NUM> and/or the focal plane array <NUM>. The one or more processors can be implemented as a special purpose processor, such an application-specific integrated circuit (ASIC), which may be customized for a particular use and not usable for general-purpose use. In some implementations, an ASIC may be used to increase the speed of image processing. In some embodiments, the controller <NUM> can include one or more graphics processing units (GPUs). The GPUs can be configured to process sensor data collected by the focal plane array <NUM>. One or more processors, including single core and/or multicore processors, can be included in controller <NUM>. In some embodiments, the controller <NUM> can be outside the camera body <NUM>. In these embodiments, the focal plane array <NUM> and the actuator can be communicatively coupled to the I/O module <NUM>.

The I/O module <NUM> can be configured to send and receive data with external systems communicatively coupled to the imaging system <NUM>. The imaging system <NUM> can be positioned in a vehicle such as an airplane, satellite, and the like. The data sent and received to and from external systems can include velocity, position, temperature, and the like. In some embodiments, the I/O module can transmit sensor data collected by the focal plane array <NUM> and/or the controller <NUM> to one or more systems on the vehicle. I/O module <NUM> can include device controllers, one or more modems, Universal Serial Bus (USB)® interfaces, radio frequency transceiver components, a serial bus, and the like to send and receive data.

<FIG> illustrates three successive frames captured to make a "snap" using an imaging system with a focal plane array that is backscanned at a velocity that matches and cancels the velocity of the camera body relative to the scene according to an embodiment of the present invention. The imaging system <NUM> includes a detector module <NUM>, an actuator <NUM>, a stage <NUM>, a focal plane array <NUM>, and a lens <NUM>. In some embodiments, the imaging system <NUM> can be mounted in a moving vehicle such as a satellite, an aircraft, an automobile and the like. <FIG> also illustrates the rays <NUM> associated with an object on the ground <NUM>.

In <FIG>, the imaging system <NUM> is moving at a velocity <NUM> over the object on the ground <NUM>. In a first frame <NUM>, the rays <NUM> associated with the object on the ground <NUM> are centered on the focal plane array <NUM> and a first image <NUM> on the focal plane array <NUM> shows the object on the ground <NUM>. For a second frame <NUM>, imaging system <NUM> has moved relative to the object on the ground <NUM> due to the velocity <NUM> of the imaging system <NUM>. In the second frame <NUM>, the rays <NUM> associated with the object on the ground <NUM> are no longer in a first position on the detector module <NUM> but have moved a first distance <NUM>. In the embodiment illustrated in <FIG>, a controller, such as controller <NUM> described in <FIG>, causes the actuator <NUM> to backscan the stage <NUM> at a drive velocity corresponding to the velocity <NUM>. The drive velocity causes the stage <NUM> and the focal plane array <NUM> to translate the first distance <NUM>. Accordingly, a second image <NUM> on the focal plane array <NUM> is in the same position as the first image <NUM> on the focal plane array <NUM>.

For a third frame <NUM>, the imaging system <NUM> has moved further relative to the object on the ground <NUM> due to the velocity <NUM> of the imaging system <NUM>. In the third frame <NUM> the rays <NUM> associated with the object on the ground <NUM> have now moved the first distance <NUM> and a second distance <NUM>. The controller causes the actuator <NUM> to backscan the stage <NUM> and the focal plane array <NUM> the second distance <NUM>. Accordingly, a third image <NUM> on the focal plane array <NUM> is in the same position as the first image <NUM> and the second image <NUM> on the focal plane array <NUM>. As illustrated in the first image <NUM>, the second image <NUM>, and the third image <NUM>, the drive velocity can be configured to backscan the stage and focal plane array <NUM> to stabilize the image on the focal plane array <NUM>. As a result, no image smearing occurs. If an integrated image of the object on the ground <NUM> was produced from the integration of the first image <NUM>, the second image <NUM>, and the third image <NUM> with backscanning, the integrated image of the object on the ground <NUM> will have an improved signal to noise ratio and other quality metrics in comparison to a single image or an integrated image produced from images without backscanning.

<FIG> illustrates two full cycles of capturing consecutive image frames with a focal plane array moving at a constant velocity relative to the velocity of the camera body according to an embodiment of the present invention. The plot <NUM> illustrates a sawtooth motion profile of the stage generated by the method. In some embodiments, the method automatically adjusts scan velocity to match the velocity of the image sensor relative to the earth's surface. The plot <NUM> shows the stage position <NUM> along the y-axis and the time <NUM> along the x-axis. A starting position <NUM> is at zero and a final position <NUM> is in a position based on a physical range of the stage and a length of the snap period. In some embodiments, the final stage position is determined by the shorter of the physical range and the length of the snap period.

<FIG> includes three snap periods, a first snap period <NUM>, a second snap period <NUM>, and a third snap period <NUM>. The first snap period <NUM> includes capture of a first frame <NUM> when the focal plane array is moving from position <NUM> to position <NUM>, a second frame <NUM> when the focal plane array is moving from position <NUM> to position <NUM>, and a third frame <NUM> when the focal plane array is moving from position <NUM> to position <NUM>. The frames are captured during a total exposure time. For example, the second time segment <NUM> associated with the first snap period <NUM>, which has a total movement cycle period of <NUM>. The exposure duration for each frame depends on the saturation time of the image sensor. In an example embodiment, the frames can be captured at a rate of <NUM> frames per second. The resulting maximum exposure time is <NUM> per frame, or <NUM> for the three frame total exposure time. The velocity of the focal plane array during the first snap period <NUM> can be divided into three time segments. The first time segment <NUM> is associated with a period of time for the actuator to accelerate and cause the focal plane array to reach a constant velocity. The second time segment <NUM> is associated with a period of time where the actuator is causing the focal plane array to move at a constant velocity corresponding to the velocity of the camera body and the constant velocity opposes the motion of the image plane caused by the velocity of the camera body. The velocity of the camera body can correspond to motion of a platform in which the camera body is placed or mounted. A platform can include, for example, a satellite, an airplane, and the like.

During the second time segment <NUM>, an image is stabilized on the focal plane array and frames can be stacked together with no image smear or blur. In some embodiments, if the image sensor will not be saturated, a single, continuous frame can be captured for the duration of the second time segment <NUM>. In some embodiments the sensor can operate at a higher frame rate and more than <NUM> frames can be stacked during the same <NUM> time segment. The third time segment <NUM> is associated with a period of time required for the actuator to move the focal plane array from the final position <NUM> to the starting position <NUM>. In some embodiments, the third time segment can be considered the reset time.

The second snap period <NUM> includes capture of a first frame <NUM> when the focal plane array is moving from <NUM> to <NUM>, a second frame <NUM> when the focal plane array is moving from <NUM> to <NUM>, and a third frame <NUM> when the focal plane array is moving from <NUM> to <NUM>. The frames are captured during an total exposure time <NUM> associated with the second snap period <NUM>, which has a total movement cycle period of <NUM>. The velocity of the focal plane array during the second snap period <NUM> can be divided into three time segments. The first time segment <NUM> is associated with a period of time for the actuator to accelerate and cause the focal plane array to reach a constant velocity. The second time segment <NUM> is associated with a period of constant time where the actuator is causing the focal plane array to move at a constant velocity. During the second time segment <NUM>, an image is stabilized on the focal plane array and frames can be stacked together with reduced or no image smear or blur. The third time segment <NUM> is associated with a period of time required for the actuator to move the focal plane array from the final position <NUM> to the starting position <NUM>. For simplicity, the third snap period is shortened but includes three stacked frames similar to the first snap period <NUM> and the second snap period <NUM>. The velocity of the stage during the second time segments <NUM> and <NUM> can correspond to the drive velocity associated with the controller <NUM> described in <FIG>. In some embodiments, a stabilization period can be inserted between the third time segment <NUM> of first snap period <NUM> and the first time segment <NUM> of the second snap period <NUM>.

<FIG> illustrates the overlap between snaps according to an embodiment of the present invention. Snap <NUM>, snap <NUM>, and snap <NUM> are shown along the direction of travel along the ground <NUM>. The first snap overlap <NUM> and the second snap overlap <NUM> provide for a continuous strip image associated with one or more focal plane arrays on a focal plane array. A field of view of the imaging system captures an image with a dimension <NUM>, d, that corresponds to a distance parallel to the direction of travel along the ground <NUM>. The time for a trailing edge <NUM> of snap <NUM> to travel a across a scene captured by snap <NUM> and reach a first edge <NUM> of the first snap overlap <NUM> corresponds to the time available for the actuator to reset the stage and focal plane array to the starting position <NUM>. Each snap includes three frames and can use frame stacking to improve the signal to noise ratio of the resulting snap. White noise from the detector array improves with multiple frames added together; the SNR benefit corresponds to the square root of the number of frames stacked. Longer duration backscanning of the image sensor or operating the sensor with a higher frame rate results in a greater number of frames per snap and improved SNR of the resulting snap image.

<FIG> illustrates a focal plane array consisting of five stagger butted focal plane arrays on a piezo stage according to an embodiment of the present invention. The imaging system <NUM> includes a focal plane array <NUM>, a first staring focal plane array <NUM>, a second staring focal plane array <NUM>, a third staring focal plane array <NUM>, a fourth staring focal plane array <NUM>, and a fifth staring focal plane array <NUM>, and thermal strapping <NUM>. Each focal plane array can include one or more spectral filters. In some embodiments, the focal plane array <NUM> can be coupled to a stage as described in <FIG>. In some embodiments, each focal plane array can capture images according to the cycles illustrated in <FIG>.

<FIG> illustrates the ground swath width <NUM> of a scan associated with five stagger butted focal plane arrays according to an embodiment of the present invention. In some embodiments, referring to <FIG>, the focal plane arrays can be staggered and butted to eliminate dead areas in a scan generated by focal plane array <NUM>. For example, the first staring focal plane array <NUM> and the second staring focal plane array <NUM> are aligned together and staggered from the third staring focal plane array <NUM>, the fourth staring focal plane array <NUM>, and the fifth staring focal plane array <NUM>. The direction of satellite motion <NUM> will capture a strip of images corresponding to each focal plane array. For example, the first staring focal plane array <NUM> can correspond to a first strip <NUM>, the second staring focal plane array <NUM> can correspond to a second strip <NUM>, the third staring focal plane array <NUM> can correspond to a third strip <NUM>, the fourth staring focal plane array <NUM> can correspond to a fourth strip <NUM>, and the fifth staring focal plane array <NUM> can correspond to a fifth strip <NUM>. Each strip can consist of a plurality of snaps and each snap can correspond to a plurality of frames as illustrated in <FIG>. The snap dimensions perpendicular to the direction of motion form the ground swath width <NUM>.

While <FIG> illustrate an imaging system <NUM> with <NUM> focal plane arrays, according to some embodiments of the present invention, an imaging system can include from <NUM> to <NUM> focal plane arrays, with up to <NUM> spectral filters. Other embodiments can include many focal plane arrays with many spectral filters. Benefits of increasing the number of focal plane arrays is support for multi-spectral imaging. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

As depicted in <FIG>, imaging system <NUM> is arranged in a staggered layout. But staggering is not required. For example, focal plane arrays <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be arranged side by side. In either case, the layout can be adjusted such that the layout has a different width or height than as depicted. For example, focal plane arrays <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be spread out, evenly distributed or otherwise, thereby increasing ground swath width <NUM>. In another example, focal plane arrays <NUM> and <NUM> can be spread further out in a vertical dimension from focal plane arrays <NUM>, <NUM>, and <NUM>.

Additionally or alternatively, an amount of overlap between adjacent arrays can also be adjusted. For example, as depicted, for example, focal plane array <NUM> and focal plane array <NUM> overlap slightly. But the focal plane arrays, e.g., <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be spaced further apart or closer together with any degree of overlap.

<FIG> is a simplified flowchart illustrating a method <NUM> of translating a focal plane array of a sensor according to an embodiment of the present invention. At <NUM>, the method provides a body. In some embodiments the body is in motion. At <NUM>, the method provides an actuator coupled to the body. The actuator is a piezoelectric actuator. At <NUM>, the method provides a stage coupled to the actuator. At <NUM>, the method provides a focal plane array coupled to the stage. The focal plane array can include one or more focal plane arrays. At <NUM>, the method determines a body velocity corresponding to motion of the body. At <NUM>, the method determines a drive velocity proportional to the body velocity. At <NUM>, the method backscans the stage at the drive velocity relative to the motion of the body. In some embodiments, the actuator translates the stage to backscan the stage and focal plane array at the drive velocity. At <NUM> the method, captures one or more frames during backscanning of the stage. In some embodiments, the one or more focal plane arrays can capture the one or more frames.

It should be appreciated that the method illustrated in <FIG> provide a particular method of scanning a focal plane array during earth observation imaging according to an embodiment of the present invention. Other operations may also be performed according to alternative embodiments. Moreover, the individual operations illustrated in <FIG> may include multiple sub-operations that may be performed in various sequences as appropriate to the individual operation. Furthermore, additional operations may be added or existing operations may be removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

<FIG> is a simplified flowchart illustrating a method <NUM> for backscanning a focal plane array according to an embodiment of the present invention. At <NUM>, the method initiates motion of a camera body. In some embodiments, the motion of the camera body can be associated with a path along the surface of the earth. The camera body can include one or more of: a lens, an actuator, a stage with a focal plane array (or an image plane), and a controller. In some embodiments, the camera body can include an I/O module. At <NUM>, the method sends a control signal to the actuator to start a backscan of the focal plane array at a drive velocity. In some embodiments, the control signal can include a command to begin capturing images. In some embodiments, the control signal can start/restart a timer associated with the backscan of the stage. At <NUM>, the method reads body velocity. Body velocity can be determined and or received by a processor in the controller. The body velocity can be read by the processor in the controller. In some embodiments, the body velocity can indicate that a constant drive velocity has been reached and the controller will send a command to the focal plane array to begin capturing one or more images.

At <NUM>, the method updates the drive velocity according to the body velocity and a gain coefficient. In some embodiments the gain coefficient can be a vector or matrix with multiple terms. The gain coefficient can adjust the drive velocity based on the properties of the image sensor such as image sensor dimensions, actuator characteristics, and focal plane array characteristics. In some embodiments, the gain coefficients can be applied at specific stage positions during a backscan. The gain coefficients compensate for hysteresis effects in a piezoelectric actuator to improve backscan slope linearity. In some embodiments, additional velocity scale factors can be added to address variables specific to a particular implementation.

At <NUM>, the method determines the stage position. In some embodiments, a processor in the controller can read data from one or more stage position sensors to determine the stage position. In other embodiments, the stage position can be estimated using the drive velocity. In other embodiments, the stage position can be extrapolated based on a predetermined time period. At <NUM>, the method determines the stage reaches a cutoff amplitude. The cutoff amplitude can be associated with a maximum position of the stage and actuator relative to the body. In some embodiments, an extrapolated stage position can be used to determine the stage will reach the cutoff amplitude within the predetermined time period. At <NUM>, the method, after reaching the cutoff amplitude, returns the stage and actuator to an initial position or state.

It should be appreciated that the specific operations illustrated in <FIG> provide a particular method of backscanning a focal plane array during earth observation imaging according to an embodiment of the present invention. Other sequences of operations may also be performed according to alternative embodiments. Moreover, the individual operations illustrated in <FIG> may include multiple sub- operations that may be performed in various sequences as appropriate to the individual operation. Furthermore, additional operations may be added or existing operations may be removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

<FIG> shows a comparison of relative edge response (RER) for various focal plane array configurations according to embodiments of the present invention. The plot <NUM> illustrates the RER for an image as a function of the distance from the edge. The x-axis <NUM> illustrates the distance in pixels from an edge at zero on the x-axis <NUM>. The y-axis <NUM> illustrates the RER amplitude. A first focal plane array configuration is a static focal plane array illustrated by trace <NUM> that captures a single frame. The RER of the static focal plane array at the zero pixel is <NUM>.

A second focal plane array configuration is a non-backscanning focal plane array illustrated by trace <NUM>. The second focal plane array configuration is mounted on a test vehicle that simulates motion of the non-backscanning focal plane array at a ground speed of <NUM> kts. The RER of the non-backscanning focal plane array travelling at a ground speed of <NUM> kts at the zero pixel is <NUM>. A third focal plane array configuration is a backscanning focal plane array illustrated by trace <NUM> mounted on a test vehicle that simulates motion of the focal plane array at a ground speed of <NUM> kts. The RER of the backscanning focal plane array at the zero pixel is <NUM>. The plot <NUM> illustrates that the RER of the non-backscanning focal plane array is degraded <NUM> by ~<NUM>% from the static focal plane array. The degraded RER is due to smearing caused by the motion of the focal plane array during the focal plane array integration time. The plot <NUM> shows the RER of the backscanning focal plane array nearly equals the RER of the static focal plane array.

As discussed, certain embodiments can be implemented in a satellite system, which can be relatively stable such that the stage velocity matches the platform velocity. Alternatively, embodiments can be implemented on aircraft, which may have slight deviations in stage velocity. Accordingly, a feedback loop can be implemented such that the stage velocity is periodically updated on a real-time basis. Different techniques are possible such as correlating pixels between images or performing the process described with respect to <FIG> and <FIG>.

<FIG> is a simplified flowchart illustrating an additional method <NUM> for backscanning a focal plane array according to an embodiment of the present invention. At <NUM>, the method sends a control signal to the actuator to start a backscan of a stage at a drive velocity. A focal plane array can be attached to the stage. At <NUM>, the method reads the body velocity. Body velocity can be determined and or received by a processor in the controller. The body velocity can be received from an I/O subsystem. In some embodiments, the body velocity can indicate that a constant drive velocity has been reached and the controller will send a command to the focal plane array to begin capturing one or more images.

At <NUM>, the method updates the drive velocity according to the body velocity. In some cases, one or more gain coefficients can be used. For example, a single gain coefficient can be used. In another example, multiple gain coefficients, such as a vector or matrix with multiple terms, can be used. The gain coefficient(s) can adjust the drive velocity based on the properties of the image sensor such as image sensor dimensions, actuator characteristics, and focal plane array characteristics. In some embodiments, the gain coefficient(s) can be applied at specific stage positions during a backscan. The gain coefficient(s) compensate for hysteresis effects in a piezoelectric actuator to improve backscan slope linearity. In some embodiments, additional velocity scale factors can be added to address variables specific to a particular implementation.

At <NUM>, the method determines the stage position. In some embodiments, a processor in the controller can read data from one or more stage position sensors to determine the stage position. In other embodiments, the stage position can be estimated using the drive velocity. In other embodiments, the stage position can be extrapolated based on a predetermined time period.

At <NUM>, the method determines the stage reaches a cutoff amplitude. The cutoff amplitude can be associated with a maximum position of the stage and/or actuator relative to the body. In some embodiments, an extrapolated stage position can be used to determine the stage will reach the cutoff amplitude within the predetermined time period.

At <NUM>, after determining that the stage reaches the cutoff amplitude, the method resets the stage to an initial position. The focal plane array is also thereby reset to an initial position.

It should be appreciated that the specific operations illustrated in <FIG> provide a particular method of backscanning a focal plane array during earth observation imaging according to an embodiment of the present invention. Other sequences of operations may also be performed according to alternative embodiments. Moreover, the individual operations illustrated in <FIG> may include multiple sub-operations that may be performed in various sequences as appropriate to the individual operation. Furthermore, additional operations may be added or existing operations may be removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

Claim 1:
An imaging system (<NUM>) mounted on a moving platform, comprising:
a body (<NUM>);
a stage (<NUM>) coupled to the body (<NUM>);
an actuator (<NUM>) coupled to the body (<NUM>) and the stage (<NUM>), wherein the actuator is configured to move the stage in a direction relative to the body, wherein the actuator is a piezoelectric actuator;
a focal plane array (<NUM>) that comprises one or more detectors and coupled to the stage; and
a controller (<NUM>) coupled to the actuator (<NUM>), wherein the controller is configured to determine a velocity of the body corresponding to motion of the moving platform, wherein the controller is configured to cause the actuator to backscan the stage from an initial position in the direction at a drive velocity proportional to the velocity of the body, wherein backscanning the stage comprises determining one or more gain coefficients and updating the drive velocity in response to the one or more gain coefficients, wherein updating the drive velocity in response to the one or more gain coefficients is performed such that hysteresis effects in the piezoelectric actuator are compensated to improve backscan slope linearity, and 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 backscan, and the controller is configured to reset the stage to the initial position.