Satellite with spotlight mode for long duration target imaging

Abstract

A satellite (140) for operation in an orbit around the Earth includes an ADCS (131, Fig. 1) configured to mechanically steer the satellite in an azimuth direction to extend a dwell time (1105) during which a target is visible from the satellite when the satellite is orbiting above the target of choice. A processor at a ground station can be configured to process raw SAR data from any of the satellites described herein. The raw SAR data can be processed in a variety of ways to provide image information, including but not limited to forming multi-view images, compiling video sequences, and color coding images.

Description

[0001] The present invention relates to the field of satellites and satellite systems with SAR imaging capabilities. BACKGROUND

[0002] Synthetic aperture radar (SAR) systems can obtain range resolution through the nature of its pulsed waveform. Azimuth (along track) resolution is built by looking at a ground site or target area on earth over a range of angles. Typically, SAR obtains a finer azimuth resolution than range (edge-to-edge) resolution. This finer resolution is averaged together to make a pixel with the same size as the range resolution but with better signal-to-noise ratio. This is called multiple looks.

[0003] Operators of SAR systems have been working to improve the accuracy and range of information that satellite imagery can provide.

[0004] Some embodiments of the invention described below address some of these problems. However, the invention is not limited to solutions of these problems and some embodiments of the invention address other problems. SUMMARY

[0005] This summary is provided to introduce some concepts of the present invention in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features of the claimed subject matter, nor is it meant to be used in determining the scope of the claimed subject matter.

[0006] Some embodiments of the invention provide a satellite, a ground station, a satellite system or a method of processing raw SAR data, wherein the raw data is obtained using an extended dwell time. In the case of a satellite, the extended dwell time can be achieved by mechanical steering of the satellite.

[0007] In a first aspect, there is provided herein below a satellite for operation in an orbit around the earth, comprising: a propulsion system, an attitude determination and control system "ADCS", one or more radar antennas or antenna arrays, a synthetic aperture radar "SAR" image acquisition device, and a communication system configured to transmit signals to and receive signals from one or more ground stations on earth, wherein the ADCS is configured for mechanically steering the satellite in azimuth direction to extend a dwell time during which a target is visible from the satellite when the satellite is orbiting over the target of choice.

[0008] The ADCS can achieve a larger range of viewing angles than might be achieved, for example, by manipulation with an electron beam. This capability can be enhanced by using a small, agile satellite, as described further below. In some embodiments, the angular range is at least from -0.75 degrees to +0.75 degrees, the angular range can be from -10 degrees to +10 degrees, or from -23 degrees to +23 degrees, or from -30 degrees to +30 degrees, or from -40 degrees to +40 degrees.

[0009] In some embodiments, the ADCS can be configured to use mechanical manipulation to slew the satellite in the azimuth direction up to 1 degree per second back and forth.

[0010] In another aspect, a ground station for receiving SAR data from a satellite in an orbit around the Earth and processing the data to form one or more images of a target on the Earth is provided herein below, the ground station comprising at least one processor configured to: receive raw SAR data from the satellite, the raw data comprising pulse records resulting from reflections of radio energy pulses emitted from the satellite from a target on the Earth; wherein the radio energy pulses correspond to an angular range in the azimuth direction achieved by manipulating the satellite in the azimuth direction to extend the dwell time over the target.

[0011] The processor at the ground station can be configured to process raw SAR data from any of the satellites described herein. The raw SAR data can be processed in a variety of ways to provide image information, including but not limited to forming multi-view images, compiling video sequences, and color coding images, as will be described further below.

[0012] In another aspect, a method of processing raw SAR data, for example received from any of the satellites described herein, is provided, which can be performed at a ground station. Thus, the computing equipment at the ground station can be configured to implement any of the methods described herein.

[0013] Embodiments of the invention also provide a computer readable medium comprising instructions, for example in the form of an algorithm, which when implemented in a computing system forming part of a satellite operating system, cause the system to perform any of the methods described herein.

[0014] As will be apparent to the skilled person, the different aspects of embodiments of the invention and features of embodiments can be combined as appropriate, and can be combined with any of the aspects of the invention. BRIEF DESCRIPTION OF DRAWINGS

[0015] Embodiments of the invention will be described, by way of example only, with reference to the following drawings, in which:

[0016] Figure 1is a schematic representation of components of a satellite according to some embodiments of the application.

[0017] Figure 2 , Figure 3 and Figure 4 show different perspective views of a satellite according to some embodiments of the application.

[0018] Figure 5 schematically illustrates a satellite operating in spotlight mode.

[0019] Figure 6 is a flowchart showing a possible configuration of a ground station according to some embodiments of the application;

[0020] Figure 7 shows an example of a multi-view image obtained according to some embodiments of the application.

[0021] Figure 8 (a) and Figure 8 (b) show examples of patch single-view and multi-view images using dwell times of 2 seconds and 14 seconds, respectively.

[0022] Figure 9 (a) and Figure 9 (b) show examples of patch multi-view images using a dwell time of 25 seconds.

[0023] Figure 10 is another example of a multi-view image generated from azimuthal multi- viewing to reduce speckle.

[0024] Figure 11 schematically illustrates the generation of multi-view and overlay images according to some embodiments of the application.

[0025] Figure 12 shows a synthesis of long-dwell acquisition video frames obtained according to some embodiments of the application.

[0026] Figure 13 schematically illustrates time-based color coding of images according to some embodiments of the application.

[0027] Figure 14 is an example of a synthesis of time-color images obtained according to some embodiments of the application.

[0028] Figure 15 is an annotated time-color image obtained according to some embodiments of the application.

[0029] All figures use the same reference numerals to denote similar features. DETAILED DESCRIPTION

[0030] Embodiments of the application are described below by way of example only. These examples represent the best ways of putting the application into practice currently known to the Applicant although these examples are not the only ways in which the application can be practiced.

[0031] Embodiments of the application provide a satellite and a method of operating a satellite. Embodiments of the application are particularly suitable for a class of satellites known as micro-satellites. These are designed to have a mass in the range 50kg to 250kg.

[0032] A satellite according to some embodiments of the application will be described first.

[0033] Figure 1 is a schematic representation of components of a satellite (e.g. a micro-satellite) according to some embodiments of the application. The single-headed solid arrows between components are used to indicate electrical power connections, the double-headed solid arrows are used to indicate RF signal connections, and the dashed lines are used to indicate data connections.

[0034] Some components are located at the satellite body indicated by rectangle 120 and some components are located at the wings indicated by rectangle 130. Figure 1 The illustrated satellite includes a power supply 101 and a power distribution system 102. The power supply 101 and power distribution system 102 power the propulsion system 190, the propulsion controller 109, the attitude determination and control system “ADCS” 131, the computing system 103, the buffer 135 and the communications system 104. The buffer 135, although shown as a separate item, can be included in the computing system 103. The propulsion controller 109 is shown herein as a separate item, but in practice it can form part of the computing system 103. The propulsion controller can be configured to implement methods according to some embodiments of the application by using control software implemented in one or more processors included in the propulsion controller 109 or in response to instructions received, for example, from the computing system. In the case where instructions are transmitted from the computing system 103, the computing system can be considered to include the propulsion controller. One of the functions of the propulsion controller 109 can be to output control signals to the ion and electron sources of thrusters in the propulsion system 190.

[0035] The power supply 101, power distribution system 102, computing system 103 and communications system 104 are collectively referred to in the art as the satellite “bus”. The communications system 104 can include one or more antennas located on the satellite body, for example. Alternatively, the communications system 104 can transmit and receive signals via one or more antennas on the wings 130.

[0036] Figure 1The power supply 101 and power distribution system 102 shown can also supply power to one or more sensors (not shown) that may be located at the main body 120. The sensors form part of what is referred to in the art as the satellite's "payload." The number and type of sensors can vary depending on the intended use of the satellite.

[0037] In the case of an Earth observation satellite, the payload may include one or more radar antennas 106 or antenna arrays that may be located at one or more wings 130. Each antenna 106 or antenna array may have an associated amplifier 107, which is powered from a power source 101 (e.g., via a power distribution system 102) via a power distribution system 108. Both power distribution systems 102 and 108 may include control logic known in the art.

[0038] As those skilled in the art will know, antenna 106, together with amplifier 107 and power distribution system 108, forms a satellite image acquisition device. They can perform functions other than acquiring image data.

[0039] In a typical satellite, each antenna may include a phased array antenna. The effective radar aperture depends on the area of ​​one or more antennas; in other words, the larger the total antenna area, the larger the aperture. This aperture is also referred to in the art as the satellite receiving window.

[0040] In the illustrated example, amplifier 107 has a bidirectional data communication link with computing system 103 via power distribution system 108 and can be configured to send data, such as data related to received radar signals, to computing system 103. This data can be processed by communication system 103, for example, to generate an image as described elsewhere herein, which can then be output to communication system 104 for forward transmission. Figure 1 In the system shown, raw data is output from computing system 103 to communication system 104 for processing by a remote computing system. Figure 1 In this context, for example, the SAR processor 133 may be located at, for example, a ground station, or at another processing location. The computing system 103 may send data, such as operating instructions, data requests, and other signals familiar to those skilled in the art, to the amplifier 107, for example, via the power distribution system 108.

[0041] Raw SAR data is stored in the satellite's memory (e.g., buffer 135). In this example, 30 seconds of imagery can be stored at full resolution (bandwidth). More can be stored at a lower resolution (e.g., 60 seconds at half resolution). In this example, the microsatellite has a 150MB download link. At this data rate, downloading 30 seconds of full-resolution imagery data takes approximately 3 minutes.

[0042] During operation, such as in spotlight mode, approximately 5,000 pulses can be emitted per second. This means that at any given time, there could be 27 pulses in the air.

[0043] The communication system 104 can communicate with earth stations or other satellites using radio frequency communication, optical (e.g., laser communication) or any other form of communication known in the art.

[0044] Figure 2 and Figure 3 This is a perspective view of Satellite 140, which may be a microsatellite and may include... Figure 1 The components, in Figure 3 The diagram shows it orbiting in space. Figure 2 The satellite includes a main body 110, which can accommodate Figure 1 Some of the components in the main body 120, or components on which can be mounted. Figure 1 Some of the components. The body 110 is also referred to in the art as a "bus" because it can house or support bus components. The body 110 may additionally house one or more batteries. The body 110 may be partially enclosed, for example, to house and protect components. A housing may provide a surface on which components can be mounted. Figure 2 In one example, a solar panel 150 is mounted on a rectangular surface of the body 110, and an additional solar panel 155 is attached to the panel 150 via a support post 115.

[0045] Satellite 140 includes a generally planar structure extending from body 110 in two opposite directions to provide two "wings" 160. The structure including the wings 160 is shown mounted on or adjacent to a rectangular surface of body 110. Figure 4 As most clearly shown, it is formed into multiple sections so that it can be folded for transport and unfolded upon deployment. The body 110 and wing 160 are collectively referred to herein as the spacecraft frame and have electrical properties further described below.

[0046] One or more antennas, as described above, can be mounted on a satellite "wing". For illustrative purposes, an antenna array 180 is shown as... Figure 4 The satellite can be removed from the wing and may include patch antennas as known in the art. Other components, including power distribution components and amplifiers, examples of which are described in the earlier patent application GB-A-2598793, may be mounted on the wing as known in the art.

[0047] Satellite 140 is equipped with a propulsion system 190 for maneuvering the satellite with generated thrust. The propulsion system 190 is... Figure 3 The most clearly visible part is the solar panel 150, which is mounted on the surface of the body 110 opposite to the solar panel 150 in this embodiment.

[0048] like Figure 3 As shown, the propulsion system 190 includes multiple thrusters 205, 210, 215, and 220, which generate thrust for maneuvering the satellite 140 when needed. Figure 3 The plurality of thrusters 205, 210, 215, and 220 shown are positioned at a corner on one side of the main body 110 and may be spaced equally apart. However, in some embodiments of the invention, the propulsion system may have different configurations.

[0049] Thrusters 205, 210, 215, and 220 are typically operated to maintain a satellite in a specific orbit. For example, thrusters can be used to propel a satellite in a specific direction relative to the Earth's surface.

[0050] ADCS131 is typically located within the satellite body 120 and is used to control the satellite's orientation. ADCS can be implemented in several ways. The ADCS131 shown in the figure includes a set of reaction wheels, one of which... Figure 3 The diagram illustrates this. The reaction wheel is usually, but not necessarily, located in the main body 120 of the satellite. Figure 4 A set of three reaction wheels 41, 42, and 43 located in the satellite body 120 is shown. Reaction wheels are sometimes also referred to as momentum wheels.

[0051] In the satellites described herein, ADCS is used to mechanically manipulate the satellite to keep a target on the Earth's surface within the radar aperture (in other words, within the satellite's field of view) for a longer period than would be visible without mechanical manipulation while the satellite is traveling in its orbit. This "spotlight mode" is used, for example, to hover over a specific target. Traditionally, this is achieved using electron beam manipulation, and only for much shorter durations (e.g., less than 10 seconds). The hovering of a satellite acquisition device over a target is also referred to in the art as "staring."

[0052] The reaction wheels 41, 42, and 43 function by using an electric motor to rotate wheels inside the spacecraft body 120. Due to the conservation of angular momentum and the absence of external forces in space, rotating the wheels in one direction causes the spacecraft to rotate in the opposite direction. Using reaction wheels is a well-known method for orienting spacecraft such as satellites.

[0053] In this example, three reaction wheels are positioned inside the spacecraft body, one for orienting the satellite on each axis. Therefore, reaction wheels 41, 42, and 43 are shown with orthogonal axes.

[0054] In another instance, four or more reaction wheels can be used to allow for better control over various aspects of satellite dynamics, such as gyration rate (how fast the satellite can rotate) and fine positioning control, especially for satellites with high moments of inertia. This technique can contribute to the ability to remain stationary at specific points on the Earth's surface, which is discussed further elsewhere in this paper but is not essential.

[0055] Various categories of satellites are currently in orbit around the Earth, typically defined by weight ranges, although the boundaries between categories are somewhat fluid and arbitrary:

[0056] CubeSats: 1kg to 10kg

[0057] Microsatellites: 50kg to 250kg

[0058] Small satellite: 500kg

[0059] Conventional satellite: 800kg to 1200kg.

[0060] Reaction wheels are rated according to their "momentum capability," which is measured in nms (Newton-meter-second). The rotational rate is related to the wheel's speed and the satellite system's inertia. Satellites with particularly low mass have much lower moments of inertia than conventional, larger SAR satellites. Appropriately low mass can be below 1000 kg, for example, below 500 kg, below 250 kg, between 50 kg and 250 kg, or below 100 kg.

[0061] Very small CubeSats currently lack the capability to carry current SAR payloads. Heavier satellites are generally less flexible due to their higher inertia. Embodiments of the satellites and operational methods described herein have been successfully implemented in microsatellites.

[0062] Some of the methods described further in this paper benefit from reaction wheels within a specific range of magnitudes. For example, a suitable range for microsatellites could be 0.5 nms to 2.5 nms. Reaction wheels with a magnitude of 1 nms have been successfully tested. This allows for rotation within a range of 1° / s, sufficient to track points on the ground and achieve any of the methods described herein without consuming excessive power. Therefore, in any of the satellites described herein, the ADCS can be configured to use mechanical maneuvers to rotate the satellite in the azimuth direction at up to 1 degree / s. Alternatively or additionally, the ADCS can be configured for dwell times up to 60 seconds.

[0063] Larger satellites are known to use reaction wheels of about 10 nms, but due to the large mass of the satellites and the resulting high rotational inertia, they cannot currently achieve a sufficient rotational rate for the dwell time discussed further in this paper, and they also consume much more power than smaller reaction wheels.

[0064] In this example, the satellite orbits the Earth in a low Earth orbit. A low Earth orbit can be between 160 km and 1000 km above the Earth's surface. Therefore, examples of SAR-based Earth observation satellites can have orbits between 450 km and 650 km above the Earth. In an example according to the invention, the satellite has an orbit 550 km above the Earth's surface. For example, at an orbit 550 km above the Earth, the satellite effectively crosses the Earth at approximately 7.5 km / s or 27,000 km / h. Most satellites in this orbit will cross the Earth at speeds in the range of 7 km / s to 8 km / s.

[0065] In some embodiments, to keep the SAR antenna stationary on a point on Earth and pointing at that point, a microsatellite can be designed to rotate at a rate of approximately 1 second. This is something that conventional satellites cannot mechanically achieve. However, according to some embodiments of the invention, a satellite such as a microsatellite can rotate from horizon to horizon for approximately 10 minutes at the speed required to maintain its pointing at a point on Earth. However, in extreme cases within this range, the distance to the imaged point or target is too great to obtain a good SAR image, thus resulting in a relatively short practical dwell time. In one example, a satellite can generate 12 images of a 6 km × 6 km area with a dwell time of 25 seconds. In another example, a satellite can point at a single point on Earth and achieve a good image with a dwell time of up to 60 seconds.

[0066] Figure 5 This is a schematic diagram of a satellite operating in spotlight mode. Curve 501 indicates the change in satellite angle in an exaggerated manner in order to prolong the time the satellite spends above target 502, in this case, a region on Earth.

[0067] Figure 6 This is a flowchart illustrating a method for processing raw satellite data according to some embodiments of the present invention, which may be performed at a ground station. The method can be performed using one or more processors, as known in the field of SAR image data processing. In some embodiments, a single processor may be used. Figure 6 The operations are illustrated. In other embodiments, individual processes can be executed in a separate processor.

[0068] Raw image data, or data to be processed to form an image, includes records of pulses received at a satellite, as a result of the reflection of radio energy pulses emitted from the satellite from a target (e.g., an area on the ground). Data from multiple pulse records is processed to form a series of images or “images.” In other words, an “image” comprises images formed from more than one pulse.

[0069] The challenge in forming a view is ensuring that data relating to the same point on the ground is used to form pixels in the image or view. According to some embodiments of the invention, this can be achieved through a technique known as back-projection SAR processing, where data from different pulses are coherently summed, for example, summing amplitude and phase information. One reason for performing coherent summation is to improve resolution in the final image.

[0070] The coherently summed data can be further processed in several different ways, three of which are... Figure 6 As shown in the image.

[0071] In some embodiments of the invention, mechanical antenna manipulation in the azimuth direction is used to increase illumination time, resulting in an increased synthetic aperture and thus an increased azimuth resolution. In other words, multiple views, for example, generated as a result of back-projection SAR processing, can be combined to form a single image. For this purpose, data from consecutive views or coherent summation can be incoherently summed. In incoherent summation, amplitude information is summed, and the mean is used to form a multiview image. Phase information is not summed.

[0072] Figure 7 An example of a multi-view image with 12 views and ground-range detection images is shown, with a resolution of 0.5 m azimuth and 0.5 m tilt range. Specifically, the image was acquired over the urban area of ​​Tokyo, Japan (approximately 6 km × 6 km) from a microsatellite SAR constellation using a long-dwell staring spotlight mode. With the increased dwell time achieved through staring spotlight acquisition via mechanical maneuvering of the satellite in its orbit, more views of the ultra-high resolution image can be generated and incoherently summed, resulting in an increase in SCR (signal-to-clutter ratio) and suppression of speckle noise. This is in Figure 8 (a) and Figure 8 (b) and Figure 9 (a) and Figure 9 As shown in (b).

[0073] Figure 10 This is another example of a multiview image generated by taking multiple views in orientation to reduce speckle. It is a small subset of a much larger scene shown on the right, where a lot of detail and very little speckle can be seen, which greatly simplifies interpretability in complex scenes.

[0074] Return to referenceFigure 6 In some embodiments of the invention, different images can be used as frames in a video to query the ground based on time. This is in Figure 11 The image is shown schematically. The resulting SAR video provides a unique way to observe movement and other dynamic activities on the Earth's surface, such as the movement of ships and other vehicles.

[0075] Figure 11 The figure below shows the satellite's angular variation in a magnified form to achieve extended dwell time on the target. The range of a conventional synthetic aperture without mechanical manipulation is indicated by 1101, with the vertical line 1102 indicating the center of the aperture. The possible extended dwell time (and associated extended angular range) is indicated at 1105. A conventional synthetic aperture corresponds to a dwell time of approximately 10 seconds. Extended-duration spotlight SAR, according to some embodiments of the invention, has been demonstrated to be up to 25 seconds. In principle, the satellite can maintain a pointing point for up to 60 seconds or more. However, the processing of additional data will correspondingly require more onboard storage.

[0076] To provide a concrete example for illustrative purposes only, for a satellite traveling at 7.5 km / s at an altitude of 550 km above the Earth, neglecting the Earth's curvature, this means that in 30 seconds the satellite would travel 225 km directly above the target. To remain directly pointed at the same point on Earth throughout this 30-second period, an angle range of approximately 23 degrees is required. Different embodiments of the invention may use different angle ranges. This may depend on factors such as, but not limited to, the capability of mechanical manipulation and the capacity of the satellite's onboard memory, as data is typically downloaded in batches as it passes ground stations.

[0077] At 1107, a set of non-overlapping movie frames is indicated, from which it can be seen that successive views can be compiled to form a video sequence. Figure 1109 demonstrates the creation of a movie from overlapping frames. It is worth noting that the aperture centers of the successive views are continuous, and therefore overlapping frames can be presented as consecutive images in a video sequence.

[0078] Overlapping images can be generated using appropriate image formation algorithms that can create temporally overlapping frames. Each frame can have an observation time corresponding to the center of its synthetic aperture. By overlapping frames, the observation times of the center aperture of each frame can be made closer together. This means that any number of frames can be formed in a video, and a user-defined resolution can be specified for each frame.

[0079] Figure 12An example of combining multiple images (video frames) captured during a long dwell time is shown, which can be presented as a color composite. Frames can also be played back at an appropriate frame rate for better observation of movement within them. Very long dwell time staring spotlight imaging not only enables ultra-high resolution imaging but also allows the use of images as video frames, thus permitting the observation of dynamic phenomena.

[0080] Return to reference Figure 6 In some embodiments of the invention, successive views at a target location can be color-coded using "time-color" to distinguish images corresponding to different time periods. In other words, different frames (or views) are colored differently based on the time they were captured (and by implying the angle at which they were captured). They can then be superimposed on each other, for example, to form a composite image. This is a multi-view image. The superposition of color-coded images, in other words, combining frames into a single image, makes it possible to use color coding to distinguish features on the ground. For the composite image, features that reflect more or less uniformly across the viewing angle range appear gray because the contributions of different colors are equal, while objects that reflect more at one or more given angles will appear colored. In some embodiments, frames (or views or images) are color-coded based on the time spent rather than individual pixels. Individual pixels will then appear as different colors in the superimposed image based on the correlation of reflectivity with angle, or if there is movement. Moving objects are unlikely to appear gray because they will shift their position during the process of the spotlight "staring," and therefore, during the superposition of images, pixels will be unlikely to have an equal color contribution from all views. If the earlier image is colored red and the later image is colored blue, then an object at its starting position during the "gaze" will appear red and then blue at its final image position.

[0081] In some embodiments, this color encoding can be implemented by weighting the red / blue / green colors and assigning them to successive views based on the time the corresponding data was acquired. This is in Figure 13 It is shown schematically in the diagram.

[0082] Frames can be color-coded so that each frame has a color value different from the color spectrum. This can be called "time-color". Colors are carefully selected so that the equal quality of each color adds up to a grayscale value (e.g., 3 frames tinted red, green, and blue). When each frame is then combined by adding their color contributions together, stationary items appear gray, and items that move in one direction or are brighter in the scene will have the dominant color. This makes it easy for the observer to identify one or more objects that have varying degrees of radar reflectivity when imaged from different angles. Typically, non-overlapping frames are used for this type of "time-color" image.

[0083] Alternatively, the Python OpenCV optical flow library (https: / / opencv-python-tutroalsreadthedocs.io / en / latest / py_kinetics / py_video / py_lucas_kanade / py_lucas_kanade.html) can be used to compare each frame to detect moving targets by subtracting regions within the scene that do not "flow" from one frame to the next. This provides a technique for moving target detection from space-based SAR systems.

[0084] Figure 14 An example of a synthetic image based on a long dwell time acquisition view, color-coded according to the time spent, is shown. In this image, buildings in the upper left quadrant of the image have a different color than others due to the anisotropic radar cross-section "RCS" of the objects. Buildings that are usually close to each other will share the same color due to the regular arrangement (orientation) of the buildings. The area of ​​the image is approximately 5 km × 5 km.

[0085] Figure 15 Another example of time-chromatic imagery is shown. This image specifically illustrates how motion can be highlighted using color. For example, a moving boat can be seen to exhibit a significant change in (instantaneous) radial velocity during the collection duration. Below, one can see how man-made structures (in this case, the support cables of a bridge) are highlighted using time-chromatic techniques. In conventional imagery, these cables might be difficult to see because they are very thin. This technique can also be advantageously applied to things such as detecting and monitoring transmission lines. At the top of the image, one can see a curved up / down ramp indicating a moving reflection point.

[0086] It should be noted that the same successive images can also be used as video frames to form a video. In other words, the same image sequence can be processed using "time-color" to color-encode it based on time and form a composite image, or it can be used as a frame in a video to dynamically show movement.

[0087] From the foregoing, it will be understood that, referring to Figure 6 All the methods described benefit from the use of flexible microsatellites. Until now, using traditional satellites, it was possible to obtain only a few views without reducing the resolution of each view. Appropriately sized microsatellites can rotate to observe targets over extended time periods (up to 60 seconds). This provides them with an unprecedented ability to acquire many image frames at the same resolution as range resolution over a given time period.

[0088] Some embodiments of the present invention have been implemented by the following:

[0089] A satellite with an antenna can point to an area of ​​observation and maintain that pointing position for an extended period of time (60 seconds). This is typically much longer than what larger satellites can achieve (nominal 2 seconds, because the ICEYE satellite has low mass and low moment of inertia, allowing antenna and beam pointing to be achieved without consuming fuel and using only internal momentum wheels).

[0090] Spotlight imaging mode, which keeps the target scene within its receiving window, even if the range of the target scene varies significantly.

[0091] A spotlight-mode SAR processor that can process SAR images into frames with any number of pulses per frame and a user-defined center point.

[0092] The spotlight mode SAR processor can combine individual SAR frames into frames for a movie and export them as well.

[0093] In any embodiment of the present invention, the satellite may travel in low Earth orbit, or be configured to travel in low Earth orbit.

[0094] As is known in the art, a satellite according to any embodiment of the present invention can be configured for side-looking. It can have both left-looking and right-looking capabilities.

[0095] Satellites in any embodiment of the present invention may use X-band radar.

[0096] Any of the computing systems described in this paper can be combined into a single computing system with multiple functions. Similarly, the functions of any of the computing systems described in this paper can be distributed across multiple computing systems.

[0097] Some operations described herein can be performed by software in a machine-readable form (e.g., in the form of a computer program including computer program code). Therefore, some aspects of the invention provide a computer-readable medium that, when implemented in a computing system, causes the system to perform some or all of the operations of any of the methods described herein. The computer-readable medium can be in a transient or tangible (or non-transient) form, such as a storage medium including a disk, thumb drive, memory card, etc. The software can be adapted to execute on a parallel or serial processor, such that the method steps can be performed in any suitable order or simultaneously.

[0098] This application acknowledges that firmware and software can be valuable, separately tradable goods. It is intended to cover software that runs on or controls “dumb” or standard hardware to achieve desired functionality. It is also intended to cover software that “describes” or defines the configuration of hardware, such as HDL (Hardware Description Language) software, as used for designing silicon chips or configuring general-purpose configurable chips to achieve desired functionality.

[0099] The embodiments described above are largely automated. In some instances, the user or operator of the system may manually guide the execution of some steps of the method.

[0100] In the embodiments described in this invention, the system can be implemented as any form of computing and / or electronic system as described elsewhere herein. For example, a ground station may include such a computing and / or electronic system. Such a system may include one or more processors, which may be microprocessors, controllers, or any other suitable type of processor for processing computer-executable instructions to control the operation of the device to acquire and record routing information. In some instances, such as when using a system-on-a-chip architecture, the processor may include one or more fixed functional blocks (also referred to as accelerators) that implement part of the method in hardware (rather than software or firmware). Platform software, including an operating system or any other suitable platform software, may be provided at the computing-based device to enable application software to execute on the device.

[0101] The term "computer" is used herein to refer to any device that has processing power that enables it to execute instructions. Those skilled in the art will recognize that such processing power is incorporated into many different devices, and therefore the term "computer" includes PCs, servers, mobile phones, personal digital assistants, and many other devices.

[0102] It should be understood that the benefits and advantages described above may apply to one embodiment or several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or have any or all of the stated benefits and advantages.

[0103] Any reference to “a” means one or more of those items. The term “comprising” is used herein to mean including identified method steps or elements, but such steps or elements are not included in an exclusive list and the method or apparatus may contain additional steps or elements.

[0104] Furthermore, with respect to the use of the term "comprising" in the detailed description or claims, this term is intended to be open-ended in a similar manner to the term "including," since "comprising" is interpreted as a transitional word in the claims when used.

[0105] The accompanying figures illustrate an exemplary method. While the method is shown and described as a series of actions performed in a specific sequence, it should be understood and appreciated that the method is not limited by the order of the sequence. For example, some actions may occur in a different order than that described herein. Additionally, one action may occur simultaneously with another. Furthermore, in some cases, it may not be necessary to complete all actions to implement the method described herein.

[0106] The order of steps in the methods described herein is exemplary, but these steps may be performed in any suitable order or simultaneously, where appropriate. Furthermore, steps may be added or substituted, or individual steps may be deleted from any method, without departing from the scope of the subject matter described herein. Aspects of any instance in the examples described above may be combined with aspects of any other instance in the other examples described to form further instances.

[0107] It should be understood that the above description of the preferred embodiments is given by way of example only and that various modifications can be made by those skilled in the art. The content described above includes examples of one or more embodiments. Of course, it is not possible to describe every conceivable modification and alteration to the above-mentioned apparatus or method for the purpose of describing the aspects mentioned above, but those skilled in the art will recognize that many other modifications and arrangements of the aspects are possible. Therefore, the described aspects are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims.

Claims

1. A satellite for operation in orbit around the Earth, said satellite comprising: Propulsion system An attitude determination and control system (ADCS) is configured to mechanically maneuver the satellite in the azimuth direction to extend its dwell time during extended spotlight mode operation, during which time, while the satellite orbits over a selected target, it performs extended-duration target imaging by keeping the target within the radar aperture, the target being visible from the satellite during the extended spotlight mode operation. One or more radar antennas or antenna arrays Synthetic Aperture Radar (SAR) image acquisition equipment, and A communication system configured to transmit signals to and receive signals from one or more ground stations on Earth.

2. The satellite of claim 1, wherein the ADCS comprises one or more reaction wheels.

3. The satellite according to claim 1 or claim 2, wherein the ADCS is configured to mechanically maneuver the satellite in the azimuth direction within at least one of the following angular ranges: from -0.75 degrees to +0.75 degrees, or from -10 degrees to +10 degrees, or from -23 degrees to +23 degrees, or from -30 degrees to +30 degrees, or from -40 degrees to +40 degrees.

4. The satellite according to claim 1 or claim 2, wherein the ADCS is configured to use mechanical manipulation to rotate the satellite in the azimuth direction at a rate of up to 1 degree / second.

5. The satellite according to claim 1 or claim 2, wherein the satellite has a total mass of less than 1000 kg, or less than 500 kg, or less than 250 kg, or less than 100 kg.

6. The satellite of claim 1 or claim 2, wherein the ADCS is configured for a dwell time of up to 60 seconds.

7. A ground station for receiving SAR data from a satellite in orbit according to any of the preceding claims and processing the data to form one or more images of targets on Earth, the ground station comprising at least one processor configured to: Raw SAR data is received from the satellite, which includes pulse records generated by the reflection of radio energy pulses emitted from the satellite from targets on Earth; The radio energy pulses refer to an angular range in the azimuth direction achieved by manipulating the satellite in the azimuth direction during extended spotlight mode operation of the satellite to extend the dwell time, during which the target is kept within the radar aperture for extended duration target imaging by the satellite as it orbits the target, and the target is visible from the satellite during the extended spotlight mode operation of the satellite.

8. The ground station according to claim 7, wherein the angle range is from -0.75 degrees to +0.75 degrees, or from -10 degrees to +10 degrees, or from -23 degrees to +23 degrees, or from -30 degrees to +30 degrees, or from -40 degrees to +40 degrees.

9. The ground station according to claim 7 or claim 8, wherein the processor is further configured to form successive views at the target, wherein data from a series of pulses is used to form each view.

10. The ground station of claim 9, wherein the processor is further configured to perform coherent summation of data from a series of pulses to form successive views at the target.

11. The ground station according to claim 7 or claim 8, wherein the processor is further configured to perform incoherent summation of data to form a multi-view image.

12. The ground station of claim 9, wherein the processor is further configured to form one or more video sequences from the successive views at the target.

13. The ground station of claim 12, wherein the successive views correspond to overlapping time periods during the dwell time.

14. The ground station of claim 12, wherein the processor is further configured to receive one or both of a user selection of an overlapping time period between successive images and a user selection of the number of images to be generated during a predetermined time period, and to generate the successive images in response to the user selection.

15. The ground station according to claim 7 or claim 8, wherein the processor is further configured to color-encode successive views at the target to distinguish images corresponding to different time periods, and to combine them into a single image by summing the color contributions.

16. The ground station of claim 15, wherein the different colors span the visible spectrum, thereby giving the uniformly reflected features within the target a gray hue.

17. A satellite imaging system comprising a satellite according to any one of claims 1 to 6 and at least one ground station according to any one of claims 7 to 16.

18. A method for processing raw SAR data, said raw SAR data comprising pulse records generated from the reflection of radio energy pulses emitted from a satellite according to any one of claims 1-6 from a target on Earth, said method comprising: Data from a series of pulses is used to form successive views of the target location. The radio energy pulses therein correspond to an angular range in the azimuth direction achieved by manipulating the satellite in the azimuth direction during the extended spotlight mode operation of the satellite to extend the dwell time, during which the target is kept within the radar aperture for extended duration target imaging while the satellite is orbiting the target, and the target is visible from the satellite.

19. The method of claim 18, wherein the angle range is one of the following: from -0.75 degrees to +0.75 degrees, or from -10 degrees to +10 degrees, or from -23 degrees to +23 degrees, or from -30 degrees to +30 degrees, or from -40 degrees to +40 degrees.

20. The method of claim 18 or claim 19, the method comprising coherently summing data from a series of pulses to form a successive view at the target.

21. The method of claim 18 or claim 19, the method comprising performing incoherent summation on the data to form a multiview image.

22. The method of claim 18 or claim 19, the method comprising forming one or more video sequences from the successive views at the target.

23. The method of claim 22, wherein the successive views correspond to overlapping time periods within the dwell time.

24. The method of claim 22, the method comprising receiving one or both of a user selection of an overlapping time period between successive images and a user selection of the number of images to be generated during a predetermined time period, or generating the successive images in response to the user selection.

25. The method of claim 18 or claim 19, the method comprising color-coding successive views at the target location to distinguish images corresponding to different time periods, and combining them into a single image by summing the color contributions.

26. The method of claim 25, wherein different colors span the visible spectrum, thereby giving the uniformly reflected features within the target a gray hue.

27. A computer-readable medium comprising instructions which, when implemented in a satellite image processing system, cause the system to perform the method of any one of claims 18 to 26.

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