Classification of objects from space

Abstract

Multiple synthetic aperture radar (SAR) images of a target area on Earth are acquired using a satellite orbiting above the Earth in a single pass over the target area. In some methods, the data for each image is acquired from a different angle of incidence relative to the target area. The variation in the amount of backscatter versus angle of incidence is then analyzed and used to identify the object imaged in the pixel or group of pixels. In other methods, the data for each image is acquired from a different angle of incidence relative to the target area, which is determined based on the specular reflectance curve for each object. The amount of backscatter is then analyzed to determine whether a particular object is present based on the amount of backscatter. An "extended dwell spotlight acquisition" geometry can be used, in which the image data acquisition device can be fixed to illuminate the same target as the satellite passes over it for, for example, 20 seconds.

Description

[Technical Field]

[0001] The present invention relates to Earth observation. The present invention can be implemented by communications satellites and other types of spacecraft. [Background technology]

[0002] Communication satellites orbiting the Earth are increasingly being used for a variety of purposes, such as tracking the location of objects, conducting field surveys, and observing changing weather patterns.

[0003] Many modern satellites are equipped with synthetic aperture radar (SAR). These types of radars can be used to create 2D and 3D area images of the Earth's surface. Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, there has been growing interest in using satellites to detect water on Earth, such as flooding in urban or other areas. However, this is an example of a problem where traditional SAR detection / classification methods (such as polarization, thresholding, change detection, statistical analysis, etc.) are inadequate. This is due to the fact that large differences in reflectivity, complex multipath reflections, and the lack of large open areas make statistical or textural analysis very difficult to achieve. [Means for solving the problem]

[0005] In one aspect of the present invention, a method of Earth observation is presented in which a satellite orbiting above the Earth is used to acquire multiple Synthetic Aperture Radar (SAR) images of a target area on the Earth.

[0006] In some methods, the data for each image is acquired using different angles of incidence relative to the target area. The variation in the amount of backscattered radiation with respect to the angle of incidence for at least one pixel or group of pixels in the image is then analyzed and used to identify the object imaged by the pixel or group of pixels. Objects that can be identified include, for example, features of the Earth's surface, whether built (such as towns and cities), cultivated, or natural, as well as specific objects such as water, crops, roads, and forests, and other objects that will occur to those skilled in the art.

[0007] Alternatively, data for each image is acquired from different angles of incidence relative to the target area, the different angles of incidence being determined based on the specular reflection curve for a particular object, such as a particular material, and the amount of backscatter for at least one pixel or group of pixels in the image is analyzed, and the presence or absence of a particular object is determined based on the amount of backscatter.

[0008] While the above method can be accomplished over successive passes of the satellite, the orientation of the image capture device on the satellite relative to the target area can be controlled to remain pointed at the target area for a specific period as the satellite passes over the target area, thereby allowing multiple images to be captured in a single pass of the satellite over the target area.

[0009] Some embodiments of the present invention can be implemented by appropriately controlling a satellite already in orbit, and thus can be achieved using appropriate algorithms executed in a processor on an existing satellite. Thus, in some embodiments, the present invention provides instructions that, when executed on one or more processors on a satellite, result in the implementation of any of the methods described herein. The instructions can be provided on a computer-readable medium, such as a signal transmitted from Earth to the satellite.

[0010] It will be understood that this Summary is provided to introduce a selection of concepts in a simplified form that are described in more detail below in the Detailed Description section.

[0011] This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.

[0012] Some embodiments of the present invention will now be described, by way of example only, with reference to the following drawings in which: [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating the difference in the variation of backscattering intensity with angle of incidence for water and forest, according to some embodiments of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating a method implemented by acquiring image data in successive passes of a satellite over a target area, according to some embodiments of the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating a method implemented by acquiring image data in a single pass of a satellite over a target area, according to some embodiments of the present invention. [Figure 4] FIG. 4 shows an example of an image obtained by one method according to some embodiments of the present invention. [Figure 5] FIG. 5 is a flow chart illustrating a method of Earth observation according to some embodiments of the present invention. [Figure 6] FIG. 6 is a schematic diagram of components of a satellite 140 in communication with a ground station, according to some embodiments of the present invention. [Figure 7] FIG. 7 is a perspective view of a satellite in orbit above the Earth, according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be understood from the following detailed description of the embodiments, which is given by way of example only and is not intended to be limiting. For the sake of brevity, the details of some well-known aspects, methods, systems, processes, components, circuits, etc., which are believed to be familiar to those skilled in the art, are not described.

[0015] Some embodiments of the present invention provide a method of Earth observation using information obtained from satellites to identify or classify objects, such as materials, the term "material" being used broadly herein to refer to anything that covers the Earth's surface, including but not limited to water, forests, grasslands, cultivated crops, construction materials, or other objects.

[0016] The reflection of radar-like radiation from a surface may be due to a combination of normal or "specular" reflection and backscatter or diffuse reflection. Some materials are known to have different "specular reflection curves" than others, indicating a dependence of the radiation or backscatter brightness on the angle of incidence of the radiation. The same is true for other types of objects. For example, water has a specific specular reflection curve that is very different from forest. At small angles of incidence, the water surface reflects most of the energy like a mirror; in other words, most of the reflection is specular. At larger angles of incidence, the surface reflects energy forward, resulting in very low backscatter measurements. In contrast, forests or grasslands, for example, return more diffuse scattering, and the dependence of backscatter energy on the angle of incidence is much smaller. Figure 1 shows a schematic diagram of backscatter intensity versus angle of incidence for water and forest, illustrating the contrasting properties of these two different materials. Differences in specular reflection can be used to identify a wide range of objects, including but not limited to those mentioned above. For example, agricultural fields at various stages of growth will have particular "specular reflection curves." Where precise identification is not possible, methods according to some embodiments may be used to classify objects, e.g., to identify their general type. Thus, in all described embodiments, "classification" of a material or object could be used in place of "identification."

[0017] Other bright reflector targets, such as buildings, may have a strong dependence on the angle of incidence, but often the bright dispersion is at various corners and the cutoff angle for bright reflection is very different from that of water. Furthermore, building walls are vertical and therefore have a very different dependence.

[0018] According to some embodiments of the present invention, objects can be identified using SAR image data, using information obtained from satellites in orbit around the Earth. For example, a satellite can be used to acquire multiple images of a target area on the Earth, with data for each image acquired from a different angle of incidence or angular position relative to the target area. The image data can then be analyzed, for example, pixel by pixel or group of pixels, for changes in the amount of backscatter with respect to angular position. The analysis can be used to identify the object imaged in that pixel or group of pixels.

[0019] For example, in the case of a satellite with a predetermined "flight path," such as a fixed orbit above the Earth, the possibilities for acquiring image data from different angular positions relative to a target are limited. Many of the possibilities for specific embodiments of the present invention are described in more detail below.

[0020] By using an appropriate range of different angles of incidence, multiple different types of objects can be identified in a target area. Using angles of incidence based on known backscattering properties of a particular material, methods according to some embodiments can also be used to identify a single material in a target area. Thus, different angles of incidence for acquiring image data can be determined based on known properties of individual materials, and the amount of backscattering can be used to determine whether that individual material is present on Earth, for example, compared to other parts of the target area. Water is an example of a material that is particularly suited to this type of process. For example, a similar process can be used to distinguish built-up areas from other areas of the Earth's surface.

[0021] It should be noted that it is not necessary to have a visible image to practice embodiments of the present invention, and thus the term "image" as used herein can be taken to mean pixels with pixel intensity readout unless otherwise specified.

[0022] [Image Acquisition] The satellite is typically equipped with image acquisition devices known in the art, as further described with reference to FIGS. 6 and 7. Methods according to some embodiments of the present invention can, in principle, be implemented by acquiring image data on successive passes of the satellite over a target area, often without the need to reorient the image acquisition device relative to the target, for example, using a technique known as "cross-track" mode, in which image data is acquired at different positions on successive passes. This is illustrated generally in FIG. 2. It can be seen that the satellite is "looking sideways." In other words, image data is not collected from the area directly below the satellite. Without reorienting the image acquisition device between passes, target T is imaged from pass 1 at time t1 from position 1 at an angle of 10°, pass 2 at time t2 from an angle of 15°, and pass 3 at time t3 from position 3 at an angle of 30°. While different angles are given as examples, other angles and pass numbers can be used.

[0023] Experiments using successive images obtained in this manner have demonstrated that water can be reliably identified in relatively complex environments due to the known dependence of backscatter on incidence angle. Furthermore, this has been demonstrated to be achievable within the limited incidence angle range achievable using profile-looking satellites, typically exceeding 10° in magnitude, either positive or negative, and often with an upper limit of 30°. However, where faster object identification is important, image data can be acquired in a single satellite pass in accordance with some embodiments of the present invention.

[0024] For example, it is known to operate SAR radar in a "spotlight" mode from a satellite to obtain higher resolution images of a particular target. In this mode, any change in the angle of incidence of the image capture device or radar source relative to the target is insignificant. According to some embodiments of the present invention, the orientation of the image capture device relative to the target can be controlled by keeping it pointed at the target area for a predetermined period while the satellite passes over the target area, thereby acquiring image data from multiple different angles in a single pass of the satellite over the target area. This can be referred to as an "extended dwell spotlight acquisition" geometry, which differs from what is known as a "cross-track" geometry. In one example of an extended dwell, the image data acquisition device is fixed and illuminates the same target for, e.g., 20 seconds, as the satellite passes over it. However, it should be noted that embodiments of the present invention are not limited to implementing a pure spotlight mode, but may employ other modes that allow for data acquisition from multiple different angles, such as those described below.

[0025] The image capture device may "see" the same target for a longer period of time than normal, thereby reducing the frequency of image data capture. Methods according to some embodiments of the present invention may, for example, sacrifice image quality in the process of identifying objects on Earth in order to save processing time and associated power.

[0026] 3 is a diagram that schematically illustrates a method implemented by acquiring image data during a single satellite leg over a target area, according to some embodiments of the present invention. Here, the target may be imaged at position 1, angle 10°, which is closest to the "cross-track" position in FIG. 2. Additionally, by pointing the image acquisition device toward the target, one image may be acquired during the same satellite leg at position 2, angle 30°. Similarly, one image may be acquired at -30° and at some angle in between. In other words, during one satellite leg, there may be several data acquisitions corresponding to several images.

[0027] This method can be used to acquire image data to identify or classify objects in real time, virtually instantaneously, rather than over multiple passes, and can prove very important in flood detection, for example, since conditions such as water spread can change dramatically between satellite passes. The method shown in Figure 3 allows for the creation of meaningful variations in incidence angles within a single satellite pass.

[0028] As mentioned above, in a practical situation using satellites, as further described below, the same target may be illuminated for up to 20 seconds as the satellite passes over it (as opposed to the typical 2 to 3 seconds for known "spotlight" images).

[0029] In most cases, the instantaneous incidence angle is generated forward, but sometimes it can occur backward along the flight path (contrary to the traditional definition of cross-track incidence angle, but which is a perfectly valid incidence angle from the perspective of reflection), or both forward and backward. An added advantage of using small incidence angles, e.g., 10-20 degrees, and / or both forward and backward, for flood detection in urban areas is that it can generate a more effective inter-building situation picture than traditional SAR acquisitions with large incidence angles, typically 35-50 degrees.

[0030] It can be seen from Figure 3 that the distance between the satellite and the target area varies between positions 1, 2, and 3, with position 2 being the closest possible position to the target area and resulting in a zero degree incident angle (straight above). At large incident angles, the reflected or backscattered power received is reduced due to the large distance between the satellite and the target, which may limit the range of possible incident angles and may require adjustment of the reflected power to compensate for this.

[0031] Image data obtained from a satellite using either a multi-pass or single-pass approach can be used to analyze the variation of backscatter with angular position in order to identify the object imaged in a pixel or group of pixels. Analysis of the image data obtained from the satellite can be performed on board the satellite or at one or more ground stations.

[0032] Thus, according to some embodiments of the present invention, multiple images of a target can be acquired using different angles of incidence, and objects observed in the images, such as water, in urban areas or other relatively complex areas or environments, can be classified based on the known dependence of backscatter or reflection on angle of incidence.

[0033] As mentioned above, for the purposes of identifying objects in a single image, lower resolution image data may be sufficient compared to that required for other Earth observation tasks, thus reducing the frequency of data acquisition and thereby reducing the power and processing required.

[0034] According to some embodiments of the present invention that use a single path to acquire the image data, the image data can be acquired at specific or discrete intervals, thereby intentionally ignoring gaps between acquisition periods while pointing at the same target. For example, as a satellite flies over a target such as a city, the spotlight can be pointed at the target 50 seconds before and 50 seconds after its closest approach (directly above the target) (a total of 100 seconds), with a 5-second acquisition period every 20 seconds, resulting in five times the 5-second total "looks" without expending image-making energy for the full 100 seconds, while allowing for large variations in the angle of incidence. During each interval, the orientation of the image capture device relative to the target area can be controlled relative to the target, and the image acquisition process is paused while images are acquired over a continuous range of angles. In other words, for continuous or regular image data acquisition, the orientation of the image capture device is controlled as the satellite passes over the target, compensating for the satellite's movement along its orbit and keeping the image capture device pointed at the target. To allow for spaced image acquisition, the steering is further controlled to allow for acquisition of images over a continuous range of angles while interrupting image data acquisition.

[0035] Some embodiments of the present invention may be implemented using small, agile satellites, such as those operated by ICEYE OY. Using such satellites, the orientation of the image capture device relative to the target can be controlled by controlling the orientation of the satellite relative to the target area. In other words, the orientation of the image capture device relative to the target area can be changed by moving the entire satellite. Therefore, the orientation of the image capture device does not need to be changed relative to the satellite body. On the other hand, for larger satellites, for example, controlling the orientation of the image capture device may require reorienting the image capture device relative to the satellite body, for example, using one or more motors on the satellite.

[0036] [Image data analysis] The following is an example of how image data can be acquired, analyzed, and displayed according to some embodiments of the present invention.

[0037] In this example, the task was to generate an image of a city in a single satellite pass to identify water, particularly water between buildings caused by flooding. The process began by setting the image acquisition mode to what is known in the art as a "spotlight," i.e., to continuously illuminate a target area. In this example, the period was set to 40 seconds. This will generally depend on a variety of factors, including, but not limited to, the angular range(s) involved and the satellite's flight speed.

[0038] The smallest angle of incidence for the target was determined to be 10° in this example, where backscattering from water is high. It should be noted that satellites rarely fly directly overhead at the target point. The minimum angle of incidence is determined by the closest angle of incidence. Only in the special case where the satellite passes directly overhead at the target point does the minimum angle of incidence become zero (however, SAR imaging requires a side-looking geometry, meaning that an image at a 0° angle does not result in a single image). According to some embodiments of the present invention, the different angles of incidence at which image data are acquired are predetermined based on known characteristics, such as the angle of incidence or the specular curve dependence of the object, e.g., the material being identified.

[0039] The "edges" in this example, i.e., the furthest locations where useful data would be obtained, were determined to be + / - 20 seconds of flight time from the center or overhead position, where the incidence angle was approximately 20° (backscattering from water is low). Therefore, the incidence angle range was determined to be 10° to 20°.

[0040] Next, multiple high-resolution "looks" at the target area were processed at an incidence angle range of up to (edge) 20° and a minimum (center) 10°.

[0041] Each "look" or image corresponds to a different angle of incidence. It is therefore possible to analyze the reflected radiant power for dependence on the angle of incidence and use this to identify objects on a pixel-by-pixel or group of pixels basis. This analysis can be used to identify objects in the image.

[0042] The analysis may be performed by a computing system onboard the satellite, or the image data may be transmitted to a ground station for analysis by any method known in the art, and the display of the data may be performed at one or more ground stations.

[0043] According to some embodiments of the present invention, to identify ground objects from image data, lookup tables or other reference data can be used and correlated with image data obtained by the process described in this example. It will be appreciated that such a process can be augmented using machine learning to increase the reliability of object identification.

[0044] According to some embodiments of the present invention, a multi-channel raster can be generated from "looks," e.g., respective image data for each angle of incidence, allowing objects to be classified according to their response and, optionally, presented as an image on a display. In some embodiments, a subset of different angles of incidence can be assigned to each primary color to create a visually appealing display, and the summed intensity values ​​can be used to generate a color representation of the target area. To generate an image, red, green, and blue (RGB) channels can be specified, where R is the sum of looks for angles of incidence greater than 15°, G is the sum of looks for angles of incidence between 15° and 10°, and G is the look for an angle of incidence of 10°. In such an image (bright in the B channel and dark in the others), water should appear "blue" and diffuse targets should appear "white" (equally bright in all channels).

[0045] Figure 4 shows an example of a two-channel image resulting from two acquisitions, with the difference between large and small angles of incidence colored. Here, the river R can be identified, along with other patches of water W.

[0046] Figure 5 illustrates a method for Earth observation according to some embodiments of the present invention, and is an example of the method used to produce the image of Figure 4. Although Figure 5 uses a specific material example, the method can be used for objects in general, as described elsewhere herein.

[0047] In methods according to some embodiments of the present invention, the first step may be target identification. This can be achieved in many ways. In some examples, the target area may be communicated to the satellite from a ground station, for example, following observation by a human on the ground or following automatic detection of an area requiring observation. Alternatively, a target area may be identified by one or more algorithms executed on the satellite. Any other method may be used to identify the target area.

[0048] In operation 502, image data is acquired. This acquired data may be in the form of a set of image data, i.e., one data set corresponding to each different angle of incidence on the same target area. As described above, each pixel or group of pixels represented in the image data may be analyzed for variations in the amount of backscatter, typically represented by pixel intensity values, in order to identify the material imaged in that pixel or group of pixels.

[0049] In one example, the analysis may consist of operations 504-508 of FIG.

[0050] Operation 504 comprises assigning at least two subsets of angles of incidence to each channel. In the example shown in FIG. 4, two subsets of angles, above and below a predetermined threshold, were used. When the data is displayed, the channels can display colors. This assignment can be made before acquiring the image data, for example, based on known specular properties of the material of interest. Typically, a subset will represent a subrange of the full range of angles of incidence, although this is not necessarily the case for a particular material.

[0051] Operation 506 consists of summing the pixel intensity values ​​from each set of image data for each angle in each subset. An exemplary set of results, e.g., above and below an angle threshold, would be one intensity value for each channel. This can be done for groups of pixels, rather than for each pixel.

[0052] Operation 508 comprises using said analysis, e.g., analysis of the channel intensity values, to identify one material in a pixel or group of pixels. In the example of Figure 4, this was used to distinguish water from other materials on the Earth's surface.

[0053] The combined intensity values ​​can be displayed on a visual display, for example, in the form of an image of the target area, with each channel assigned a color, as shown in the two-color example of Figure 4. It will be appreciated that there is not necessarily a one-to-one correspondence between substances and channels, as some substances may give rise to an intensity value in more than one channel.

[0054] In the three-channel example described above, RGB values ​​can be used to generate a visual representation of the distribution of one or more substances in a target area. It will be understood that embodiments of the present invention are not limited to the use of RGB as primary colors, or to the use of only three primary colors.

[0055] As can be seen from the above, methods according to some embodiments of the present invention can be devised to identify individual materials. For example, while two- and three-channel processing is described above, "single-channel" processing is also possible, in which different angular positions or ranges of incident angles are predetermined based on known properties of the target material, such as the specular reflectance curve of water. The presence or absence of a material can then be determined based on the amount of backscattered radiation in that range of incident angles. For example, pixel intensity values ​​in that range of incident angles can be summed and visually presented in grayscale, with darker areas representing a higher probability of the material being present. The same can be done for more general object identification.

[0056] The method may include displaying the image at operation 510 .

[0057] Above, some specific embodiments of the present invention are described. Other application of the method according to the present invention include:

[0058] Embodiments of the present invention can be used to classify things other than water, such as, for example, agricultural land in various stages of growth that will have a particular "specular curve."

[0059] As previously mentioned, embodiments of the present invention are not limited to what is understood as a pure “staring spotlight” imaging mode. As known to those skilled in the art, various modes of SAR operation are known and under development, including, but not limited to, staring spotlight, sliding spotlight, and “along-track ScanSAR,” as described in detail in “TerraSAR-X Staring Spotlight Optimization and Global Performance Predictions,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol. 93, March 2016. For application to a wider area, for example, “along-track ScanSAR” type imaging can be used, sacrificing resolution but not the total number of angles of incidence (whereas a “sliding spotlight” geometry would also allow imaging of a wider area, but would limit the angles available).

[0060] [Image acquisition device] Apparatus suitable for carrying out methods according to some embodiments of the present invention is now described with reference to Figures 6 and 7, which respectively show a schematic diagram and a perspective view of components of a satellite 140 in communication with a target location and / or a ground station 120 on Earth. A more detailed description of an example satellite design is provided in WO2020094872 (A1).

[0061] In FIG. 6, single-headed solid arrows between components are used to indicate power connections, double-headed solid arrows are used to indicate RF signal connections, and dotted lines are used to indicate data connections.

[0062] Several components are mounted on the satellite body, represented by box 120 in FIG. 6 , with some mounted on wings, represented by box 130 in FIG. 6 . The satellite components shown in FIG. 6 comprise a power supply 101 and a power distribution system 102. The power supply 101 and power distribution system 102 provide power to a propulsion system 190, a propulsion controller 109, a computing system 103, and a communications system 104. While shown here as a separate item, the propulsion controller 109 may in practice form part of the computing system 103. The propulsion controller may be configured to control the orientation of image capture devices on the satellite 140, according to some embodiments of the invention, either through the use of control software implemented on one or more processors included in the propulsion controller 109, or in response to commands received from a computing system, for example. If commands are transmitted from the computing system 103, the computing system may be considered to comprise the propulsion controller.

[0063] The power source 101, power distribution system 102, computing system 103, and communication system 104 are collectively referred to in the art as the satellite "bus." The communication system 104 may include, for example, one or more antennas mounted on the satellite body. Alternatively, the communication system 104 may transmit and receive signals via one or more antennas on the wings 130.

[0064] In the case of an Earth observation satellite, one or more radar antennas 106 or antenna arrays may be mounted on one or more wings 160. Each antenna 106 or antenna array may have an associated amplifier 107. The amplifier 107 is powered by a power source 101 via a power distribution system 108, e.g., via power distribution system 102. As known to those skilled in the art, the antenna 106, along with the amplifier 107 and power distribution system 108, collectively form an image capture device, referred to elsewhere herein, which may perform functions other than capturing image data. As known in the art, both power distribution systems 102 and 108 may contain control logic.

[0065] As is well known to those skilled in the art, the amplifier 107 has a two-way data communication link with the computing system 103, in the illustrated example via the power distribution system 108, and may be configured to transmit data to the computing system 103, such as data related to received radar signals, optionally via a transceiver (not shown). Such data may include image acquisition data according to some embodiments of the present invention. The acquired image data may be processed by the communication system 103, e.g., to form an image and identify objects on Earth as described elsewhere, and then output to the communication system 104 for onward transmission. Alternatively, raw data may be output by the computing system 103 to the communication system 104 for processing by a remote computing system, e.g., at a ground station or another satellite. As is well known to those skilled in the art, the computing system 103 may transmit operational instructions, data requests, and other signals to the amplifier 107, e.g., via the power distribution system 108.

[0066] The communication system 104 may communicate with an earth station, such as ground station 200, or another satellite using radio frequency communication, optical, e.g., laser communication, or other forms of communication known in the art.

[0067] FIG. 7 is a perspective view of a satellite 140 orbiting in space that can include the components of FIG. 6. The satellite of FIG. 7 comprises a body 110 within which some of the components of body 120 of FIG. 6 can be housed, or in which some of the components of FIG. 6 can be mounted. Body 110 can also house one or more batteries. For example, body 110 can be partially enclosed to house and protect the components. The housing provides a surface upon which the components can be mounted. In the example of FIG. 7, solar panel 150 is mounted on one rectangular face of body 110, and an additional solar panel 155 is attached to panel 150 by struts 115.

[0068] The satellite 140 comprises a generally planar structure extending in two opposite directions from the body 110, resulting in two "wings" 160. The structure comprising the wings 160 is shown mounted on or near a rectangular face of the body 110. The body 110 and wings 160 are collectively referred to as the spacecraft frame. One or more antennas, as described above, may be mounted on the satellite "wings." The satellite 140 is provided with a propulsion system 190 for generating thrust to steer the satellite.

[0069] In embodiments of the present invention, the orbit or orbital path of the satellite is not limited and may include, for example, any geostationary orbit (GEO), low earth orbit (LEO), medium earth orbit (MEO), polar orbit and sun synchronous orbit (SSO), transfer orbit and geostationary transfer orbit (GTO), Lagrange point (L-point), etc. However, in some embodiments of the present invention, those skilled in the art will readily understand that laboratory testing of the satellite (e.g., in a ground-based testing facility) may be required prior to launch into space.

[0070] Satellites according to some embodiments of the present invention may also comprise systems not detailed herein, such as, but not limited to, thermal control systems and attitude control systems to ensure that the satellite is pointed in the correct direction.

[0071] The term "computing system" is used herein to refer to a device or group of devices that have processing capability such that instructions can be executed. Those skilled in the art will recognize that such processing capability is incorporated into many different devices, and therefore the term "computing system" as used herein can include PCs, servers, and many other devices.

[0072] The components described herein are not necessarily physically separated from one another unless otherwise specified, and the functionality of the components shown in the figures may be distributed or shared among different or the same physical device, for example, some of the functionality of a communication system may be performed by a computing system and vice versa.

[0073] It will be understood that the benefits and advantages described above may relate to one embodiment or to several embodiments, and such embodiments are not limited to those that solve some or all of the stated problems or that have some or all of the stated benefits and advantages.

[0074] A reference to "an" or "an" item refers to one or more of that item. As used herein, the term "comprising" is used to mean including identified method steps or elements, but such steps or elements do not comprise an exclusive list and a method or apparatus may include additional steps or elements.

[0075] As used herein, the terms "component" and "system" may include computer-readable data storage that is comprised of computer-executable instructions that, when executed by a processor, cause a particular function to be performed. Such computer-executable instructions may include routines, functions, etc. It should also be understood that a component or system may be provided on a single device or distributed across several devices.

[0076] Furthermore, to the extent the term "include" is used in either the detailed description or the claims, such term is intended to be as inclusive as the term "including" is interpreted when "comprises" is used as a transitional term in the claims.

[0077] Each figure depicts an exemplary method. While the method is shown and described as a series of acts performed in a particular sequence, it should be understood and appreciated that the order of the sequence is not a limitation of the method unless otherwise specified. For example, some acts may occur in a different order than described herein. Additionally, one act may occur simultaneously with other acts. Furthermore, in some cases, not all acts may be required to implement the method described herein.

[0078] It will be understood that the above description of the embodiments is by way of example only, and that various modifications may be made by those skilled in the art. The above description includes one or more example embodiments. Of course, it is not possible to describe every conceivable variation of the above-described apparatus or method for purposes of describing the foregoing aspects, but one skilled in the art will recognize that many further variations and permutations of the various aspects are possible. Accordingly, the described aspects are intended to encompass all such variations, modifications, and variations that fall within the scope of the appended claims.

Claims

1. 1. A method of observing Earth, comprising: using a satellite moving in low Earth orbit above the Earth to acquire multiple synthetic aperture radar (SAR) images of a target area on the Earth, each image acquired from a different angle of incidence relative to the target area, the different angles of incidence having a magnitude of 10 degrees or greater; said acquiring comprising controlling the orientation of an image acquisition device on said satellite relative to said target area to remain pointed at said target area for a predetermined period of time as said satellite passes over said target area, and acquiring multiple images in a single pass of said satellite over said target area; controlling the orientation of the image capture device relative to the target area is accomplished by controlling the orientation of the satellite relative to the target area; At least one of the different angles of incidence is generated forward and / or aft along the flight path of the satellite; analyzing the variation of backscatter dose with respect to angle of incidence for at least one pixel or group of pixels in the image, the backscatter dose for the at least one pixel or group of pixels being represented by a pixel or group of pixels intensity value; using said analysis to identify an object imaged at a pixel or group of pixels; The method of analyzing the variation of backscatter dose with respect to incidence angle includes assigning at least two subsets of different incidence angles to different channels, each channel corresponding to a different subset of different incidence angles, and summing the intensity values ​​of the pixel or group of pixels for each channel to calculate one intensity value for each channel.

2. The method of claim 1 , wherein the different angles of incidence are determined based on the specular reflection curve of a particular object.

3. The method of claim 2 , wherein the particular object is water.

4. A method according to any one of claims 1 to 3, wherein each image is acquired during a discrete interval within the predetermined period of time as the satellite passes over the target area.

5. 5. The method of claim 4, wherein the orientation of the image capture device is controlled to enable capture of images from a continuous range of different angular positions relative to the target area during the discrete intervals within the predetermined time period as the satellite passes over the target area.

6. The method of claim 1 , further comprising representing the summed pixel or pixel group intensity value on a visual display.

7. 10. The method of claim 1 or 6, further comprising: assigning different subsets of the different angles of incidence to different channels, each channel representing a different primary color for visual display; and summing the pixel or pixel group intensity values ​​for each channel representing a different primary color to generate a color representation of the target area.

8. The method of any one of claims 1 to 7, wherein at least some of the different angles of incidence are generated backwards along the satellite's flight trajectory.

9. A computer readable medium comprising instructions which, when executed on one or more processors in a satellite, cause the performance of the method of any one of claims 1 to 8.

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