Digital beamforming interferometry

A method according to an illustrative embodiment includes generating first, second, third, and fourth signals. The method also includes transmitting from an antenna, the first signal, and transmitting the antenna, the second signal. The first and second signals are configured such that when the signals are transmitted simultaneously the signals constructively interact to form a first beam signal. The first beam signal has a first look angle. The method also includes transmitting from the antenna the third signal and from the antenna the fourth signal. The third and fourth signals are configured such that when the signals are transmitted simultaneously the signals constructively interact to form a second beam signal. The second beam signal has a second look angle. The method also includes receiving a first and second reflected signals and generating an interferogram utilizing information in the first and second reflected signals.

BACKGROUND

Airborne or spaceborne Syntheic Aperture Radar (SAR) can be used in a variety of ways, and is often used to generate two dimensional images of a surface. SAR involves the use of radio waves to determine presence, properties, and features of extended areas. Specifically, radio waves are transmitted in the presence of a ground surface. A portion of the radio wave's energy is reflected back to the radar system, which allows the radar system to detect and image the surface. Such radar systems may be used in science applications, military contexts, and other commercial applications.

SUMMARY

A method according to an illustrative embodiment includes generating, by a processor of a computing device, a first signal, a second signal, a third signal, and a fourth signal. Each of the first, second, third, and fourth signals have a frequency, a phase, and an amplitude. The method also includes transmitting, by the processor, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal. The method also includes transmitting, by the processor, from a second sub-array of the antenna, the second signal. The first signal amplitude, frequency, and phase, as well as the second signal amplitude, frequency, and phase, are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal. The first beam signal is configured to have a first look angle. The method also includes transmitting, by the processor, from a third sub-array of the antenna, the third signal. The method further includes transmitting, by the processor, from a fourth sub-array of the antenna, the fourth signal. The third signal amplitude, frequency, and phase, as well as the fourth signal amplitude, frequency, and phase, are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal. The second beam signal is configured to have a second look angle. The method also includes receiving a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The first reflected signal includes a reflected portion of the first beam signal, and the reflected portion of the first beam signal has been reflected off of a first region within the first look angle. The method further includes receiving a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The second reflected signal includes a reflected portion of the second beam signal, and the reflected portion of the second beam signal has been reflected off of a second region within the second look angle. The method further includes generating, by the processor, an interferogram utilizing information in the first reflected signal and the second reflected signal.

An apparatus according to an illustrative embodiment includes a memory, a processor coupled to the memory, and a set of instructions stored on the memory and configured to be executed by a processor. The instructions include instructions to generate a first signal, a second signal, a third signal, and a fourth signal. Each of the first, second, third, and fourth signals have a frequency, a phase, and an amplitude. The instructions also include instructions to transmit, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal. The instructions also include instructions to transmit, from a second sub-array of the antenna, the second signal. The first signal amplitude, frequency, and phase, as well as the second signal amplitude, frequency, and phase are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal. The first beam signal is configured to have a first look angle. The instructions also include instructions to transmit, from a third sub-array of the antenna, the third signal. The instructions also include instructions to transmit, from a fourth sub-array of the antenna, the fourth signal. The third signal amplitude, frequency, and phase, as well as the fourth signal amplitude, frequency, and phase are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal. The second beam signal is configured to have a second look angle. The instructions also include instructions to receive a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The first reflected signal includes a reflected portion of the first beam signal, and the reflected portion of the first beam signal has been reflected off of a first region within the first look angle. The instructions also include instructions to receive a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The second reflected signal includes a reflected portion of the second beam signal, and the reflected portion of the second beam signal has been reflected off of a second region within the second look angle. The instructions also include instructions to generate an interferogram utilizing information in the first reflected signal and the second reflected signal.

An illustrative non-transitory computer readable medium has instructions stored thereon that, upon execution by a computing device, cause the computing device to perform the operations including generating a first signal, a second signal, a third signal, and a fourth signal. Each of the first, second, third, and fourth signals have a frequency, a phase, and an amplitude. The operations also include transmitting, from a first sub-array of a plurality of sub-arrays of an antenna, the first signal. The operations also include transmitting, from a second sub-array of the antenna, the second signal. The first signal amplitude, frequency, and phase, as well as the second signal amplitude, frequency, and phase are configured such that when the first signal and the second signal are transmitted simultaneously the first signal and the second signal constructively interact to form a first beam signal. The first beam signal is configured to have a first look angle. The operations also include transmitting, from a third sub-array of the antenna, the third signal. The operations also include transmitting, from a fourth sub-array of the antenna, the fourth signal. The third signal amplitude, frequency, and phase, as well as the fourth signal amplitude, frequency, and phase are configured such that when the third signal and the fourth signal are transmitted simultaneously the third signal and the fourth signal constructively interact to form a second beam signal. The second beam signal is configured to have a second look angle. The operations also include receiving a first reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The first reflected signal includes a reflected portion of the first beam signal, and the reflected portion of the first beam signal has been reflected off of a first region within the first look angle. The operations also include receiving a second reflected signal by at least one sub-array of the plurality of sub-arrays of the antenna. The second reflected signal includes a reflected portion of the second beam signal, and the reflected portion of the second beam signal has been reflected off of a second region within the second look angle. The operations also include generating an interferogram utilizing information in the first reflected signal and the second reflected signal.

DETAILED DESCRIPTION

Described herein are illustrative embodiments for methods and systems for utilizing digital beamforming in generating interferograms. In one illustrative embodiment, such methods and systems may be used on an aircraft or spacecraft radar system to take measurements of the surface of the earth or objects on the surface of the earth.

A method according to an illustrative embodiment includes generating images in three dimension space using a single SAR system with a multiple-channel radar architecture. The method includes obtaining through a computing device, multiple transmit and receive radar channels from a plurality of sub-arrays of an antenna. The method further includes obtaining two or more two-dimensional SAR images of the same region of a ground surface with slightly different look angles. The difference in phase between the images, known as the interferometric phase, is used to obtain a new image of the third spatial dimension.

The method can be achieved by either one of two reciprocal approaches. In the first approach all the radar transmit signals are generated to form a single transmit beam of energy on either side of the flight track. On receive, the reflected energy from the ground is collected by each individual channel and processed as two or more individual receive beams. In the second approach, individual signals are transmitted (by means of time multiplexing or encoding each of the signals) to generate two or more transmit beams. On receive, the reflected energy from the ground is collected by each individual channel and processed as a single receive beam.

In the first approach, the processor generates all the signals with the appropriate amplitude and phases such that when the signals are simultaneously transmitted, the radar generates and steers a single beam of energy to either side of the radar track. The approach also includes receiving the reflected energy by at least two sub-arrays of the plurality of sub-arrays of the antenna. Each of the sub-array signals is processed as an individual beam of energy using SAR focusing techniques to generate an image of the surface. Because of the spatial displacement between the sub-arrays, each of the receive beams views the same region of the ground at a different look angle. The resulting phase difference between the SAR images, called interferometric phase, is proportional to the height of the imaged features in the scene (i.e., the ground surface or objects on the ground surface). The approach further includes generating, by the processor or an offline computer, an interferogram utilizing the phase information between two images.

Another illustrative embodiment includes a memory, a processor coupled, to the memory, and a set of instructions stored on the memory and configured to be executed by a processor. The instructions include instructions that command the processor to generate transmit signals, where each signal is generated with a prescribed frequency, amplitude, and phase. The instructions also command the processor to transmit a particular signal from a particular radar channel corresponding to a particular sub-array of an antenna. The signals frequency, amplitude, and phase can be configured such that when transmitted simultaneously, the signals constructively interact to form a single beam of energy pointed at a specific location. When transmitted individually (time multiplexed or phase encoded), each signal forms a wide beam of energy. A similar wide beam can be achieved when transmitting all the signals simultaneously but using proper phasing among the signals. This is known as phase spoiling. In this way, the SAR system can be configured to form a single transmit beam as in the first approach, or two or more transmit beams with different phase centers, as in the second approach.

The system and methods disclosed herein can also receive all the reflected signals by using a plurality of sub-arrays of an antenna. The received signals are processed depending on either one of the transmit approaches employed. If a single beam is generated on transmit, the received signals are processed as two or more receive beams with different phase centers. If two or more beams are generated on transmit, the received signals are processed as a single receive beam. The system and methods then can generate one or more interferograms utilizing the phase information among images.

A radar system transmits radio waves and senses a part of the transmitted radio waves that are reflected back to an antenna. This allows the radar to determine the location of objects that are reflecting back waves. In interferometry, a radar system generates two separate images of what is being reflected back from transmitted waves. Each of the images is viewed from a slightly different look angle. The two images can be combined to yield an interferogram that shows the object's location in three dimensional space. For example, if such a radar is installed on an aircraft, the aircraft may fly over a particular part of land. The radar may transmit radio waves as it flies over the part of land and record the radio waves that are reflected back. The data generated from recording the reflected back radio waves can be used to generate a first image of the part of land. The aircraft could then fly over the part of land a second time to generate a second image. The two images are then combined to yield the interferogram. In another example, an aircraft may carry on board two radar systems with two separate antenna. In this example, both radar systems can be run during one pass across the part of land. In this way, both images for an interferogram can be generated during one pass.

Advantageously, using the system and methods described herein, an interferogram can be generated doing a single pass and only utilizing one radar system and antenna array. Furthermore, the system and methods disclosed herein yield an interferogram with good resolution. Interferograms as generated by the methods and systems disclosed herein are capable of showing not only topography, but also, for example, biomass, canopies, buildings, etc.

The disclosed systems and methods may be referred to as an Interferometric Syntheic Aperture Radar (InSAR) that utilizes digital beamforming. InSAR is a radar technique that provides three-dimensional information from Synthetic Aperture Radar (SAR) images. In other words, SAR is used to acquire the two images needed for an interferogram, yielding InSAR. As discussed above, InSAR can be implemented with conventional SAR systems in repeat pass flight configuration where interferograms between two SAR images of the same area are generated by flying the radar in two near-identical tracks; or in a single pass configuration where interferograms between two SAR images of the same area are generated using two antennas. Additional information on SAR techniques and physical components of a SAR can be found in Rafael F. Rincon et al., Digital Beamforming Synthentic Aperture Radar (DBSAR) Polarimetric Upgrade (2011) and Rafael Rincon et al.,NASA's L-Band Digital Beamforming Synthetic Aperture Radar, IEEE Transactions on Geosciences and Remote Sensing vol. 49, no. 10 at 3622 (October 2011), the disclosures of which are both incorporated herein by reference in their entirety.

An illustrative embodiment of the systems and methods disclosed herein describes an InSAR system that utilizes a single pass flight configuration with a beamforming radar and a single antenna array. In this embodiment, the beamforming radar is a multi-channel radar system that employs an antenna made up of many elements arranged as sub-arrays. This radar architecture is characterized by a multi-channel operation with software defined wave form generation for each radar transmit channel and a dedicated digital receiver channel for each transmit channel. The antenna sub-arrays in this embodiment are aligned in the flight direction permitting relative amplitude and phase measurements between pairs of radar channels or among groups of radar channels. An example beamforming radar architecture will be discussed below with respect toFIG. 3. Such a beamforming radar architecture allows for the implementation of a multi-channel beamforming radar that allows the synthesis of two or more beams, either in a transmit mode or a receive mode, which in turn can yield pairs of SAR images to generate an interferogram.

Advantageously, the systems and methods disclosed herein make possible advanced radar techniques not possible with conventional radars. Beamforming uses interference among the signals from each of the antenna sub-arrays to generate far-field beam patterns with predefined scan angle, beam-width, and and/or sidelobe level. In transmit beamforming, a radar can use software-defined waveforms to control the amplitude and phase of the signals at each transmitter channel in order to create a pattern of constructive and destructive interference in the wavefront. In receive beamforming, the radar digitizes the return reflected radar signal and uses digital signal processing to attenuate and phase shift the digitized radar returns and generate the far-field beam patterns at the desired scan angles and characteristics.

Using beamforming as disclosed herein, many advantages can be realized. For example, multiple antenna beams can be synthesized simultaneously or time-interleaved, depending on the implementation of different InSAR techniques. The synthesis of two or more transmit or receive antenna beams provides the basis for interferometry. The images collected with each of the antenna beams provide the interferograms that carry three dimensional information of what was scanned by the radar. Since beam generation is performed digitally (whether in transmit mode with software-defined waveforms, or in receive mode with digitized return signal data), the system may synthesize beams in varying directions (or look angles) on both sides of the radar flight-track. Additional advantages of the systems and methods disclosed herein include an increase in the measurement swath without reducing received antenna gain and the suppression of ambiguities or localized interference in the receiver signal by appropriate null-steering of the antenna pattern.

Digital beamforming interferometry may be useful in many applications. The systems and methods disclosed herein enable InSAR measurements using single antenna radars reducing complexity. The methods and systems disclosed herein add a third dimension to the two dimensional mapping capability of SAR systems.

FIG. 1is a diagram illustrating a radar system100used for digital beamforming interferometry in a transmit beamforming mode in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. This embodiment corresponds to the first approach discussed above where the radar transmit signals are generated to form a single transmit beam of energy on either side of the flight track and, on receive, the reflected energy from the ground is collected by each individual channel and processed as two or more individual receive beams. In the embodiment ofFIG. 1, the radar system100is configured to be on an aircraft. The radar system100includes antenna subgroups105and110. Each antenna subgroup105and110is made up of 4 sub-arrays each in this embodiment, yielding 8 sub-arrays total (as will be discussed at length below with respect toFIG. 3). Other configurations are possible for the antenna of the radar system100. For example, the antenna may have 4 sub-arrays total, 5 sub-arrays total, 6 sub-arrays total, 7 sub-arrays total, 9 sub-arrays total, 10 sub-arrays total, 12 sub-arrays total, or another total number of sub-arrays. Additionally, even though in this embodiment the 8 sub-arrays are divided into two antenna subgroups105and110, having 4 sub-arrays each, this grouping is not a physical difference between sub-arrays. In other words, the subgroups are defined by what types of signals are being output from the sub-arrays. In this embodiment, the 4 sub-arrays in antenna subgroup105are outputting similar signals that form a beam signal145, so the 4 sub-arrays in antenna subgroup105are identified together. Similarly, the 4 sub-arrays in antenna subgroup110are outputting similar signals in this embodiment that form a beam signal140, so the 4 sub-arrays in antenna subgroup110are identified together. In this embodiment, beam signals140and145are time multiplexed or are phase encoded to ensure that the two beam signals can be uniquely identified upon receive.

Since the subgroups105and110are defined by the signals being output from the sub-arrays, the subgroups105and110can vary in alternative embodiments depending on signals that are being output from the various sub-arrays. The present embodiment shown inFIGS. 1-3has 8 sub-arrays. In an alternative embodiment still having 8 sub-arrays, there may be 4 subgroups containing 2 sub-arrays each. Other various possibilities for subgroups and the purposes for having different subgroups for the creation of different beam signals is included throughout the present disclosure.

The radar system100having subgroups105and110is on an aircraft that is moving along the y-axis. The y-axis is also referred to as the along-track dimension. The along-track dimension is parallel to the ground flight track line115. The ground flight track line115shows a line on the ground that follows the flight track of the aircraft, and in general corresponds to the part of the surface of the earth that the aircraft is closest to during a flight. The x-axis shown inFIG. 1referred to as the across-track dimension. The across-track dimension is orthogonal to the along-track dimension. The z-axis shown inFIG. 1is orthogonal to both the along-track dimension (y-axis) and the across-track dimension (z-axis). The height of the aircraft can be measured along the z-axis, and the z-axis as shown inFIG. 1connects the flight track of the aircraft and the ground flight track line115.

Across-track ground line120is parallel to the x-axis and is orthogonal to the ground flight track line115. The across-track ground line120shows the area on the ground that can be scanned by across-track radar beams. In this embodiment, the radar system100is aligned to scan areas of the ground along (and incidentally nearby as shown by surface beam region135) the across-track ground line120. In this embodiment, the sub-arrays of the antenna in the subgroups105and110are each aligned to be parallel with the along-track dimension (y-axis). In this way signals can be transmitted from the radar system100that can constructively combine to create beam signals that can scan the ground anywhere along the across-track ground line120. Where the beam signals are not formed, the transmitted signals destructively interact. In other words, any angle θ2can be used to scan the ground, where angle θ2represents the angle between the z-axis and the edge of the beam signals nearest the z-axis. In other embodiments, the radar system could be aligned to scan in other directions with respect to the along-track dimension (or y-axis).

The radar system100inFIG. 1operates by transmitting signals from the sub-arrays in the subgroups105and110. The signals transmitted in each of the subgroups105and110are configured by processors in the radar system (one embodiment of these processors are discussed at length below with respect toFIG. 3. The subgroup105transmits signals that constructively interfere and combine to form the beam signal145. Outside of the beam signal145, the transmitted signals destructively interfere, yielding the narrow field of the beam signal145. This occurs due to the technique of beamforming. The signals transmitted by the subgroup105(which is arranged as a phased array) are configured such that the signals combine at certain angles (constructive interference) and negate each other (destructive interference) at other angles. Beamforming can be practiced at both the transmitting or the receiving end to achieve such spatial selectivity. In this embodiment, the beamforming is occurring at the transmit end. In this way, the transmitted signals constructively interfere to generate the beam signal145. Similarly, the subgroup110transmits signals that constructively interfere to generate the beam signal140.

Beam signal145can be defined by angle θ1and angle θ2. As noted above, θ2represents the angle between the z-axis and the edge of the beam signal145nearest the z-axis. Angle θ1represents the angle between edge of the beam signal145nearest the z-axis and the edge of the beam signal145nearest the x-axis. The beam signal140will also have similar angle measurements. However, the angle θ1and angle θ2of the beam signal140will differ slightly than the angle θ1and angle θ2of the beam signal145. This difference is due to the slightly different positions of the subgroups105and110along the x-axis and the signals being configured to scan the same portion of ground (inFIG. 1the surface beam region135). Meanwhile the relative positions of the subgroups105and110along the y-axis and z-axis are the same, even when the aircraft is in motion. The angle θ1is related to the surface beam region135. This is the area at a given moment that is being scanned by the beam signals140and145. Although inFIG. 1the beam signals140and145are portrayed as extending toward the ground as a planar beam, the beam signals140and145are actually conical or hyperboloidic in shape. In this way, the beam signals140and145scan the surface beam region135. As a result, as the aircraft moves along the y-axis, all of the ground within a swath125is scanned. The width of the swath125is a function of the height of the aircraft and the angles at which the beam signals140and145are directed.

Another way to quantify or identify the beam signals140and145are through a look angle. The look angle is the nominal angle at which the scan is performed using the beam signals140and145. The look angle is defined as the angle between a line through the center of a conical beam signal and the z-axis. Accordingly, if a beam signal was pointed straight down below the aircraft, it would have a look angle of zero degrees. The present embodiment shown inFIGS. 1-3can synthesize beams that have look angles greater than 50 degrees to either side of the z-axis. That is, the radar system100can synthesizes beams with look angles across a range of more than 100 degrees.

In an alternative embodiment, the radar system100may also scan the swath130. In such an embodiment, the radar system may utilize 4 subgroups of sub-arrays of the antenna instead of the 2 subgroups shown inFIG. 1. In another alternative embodiment, the radar system may scan only swath130instead of swath125. In yet another embodiment, the radar system100may scan another swath entirely on the other side of the flight track line115. In another embodiment, the radar system100may scan a swath that intersects with or tangentially touches the flight track line115.

Once the beam signals140and145hit the surface of the earth (or any objects thereon) the beam signals140and145are reflected off of the surface of the earth (or any objects thereon). At least a portion of the reflected beam signals can travel back to the radar system100and be sensed by the antenna of the radar system100. In this embodiment, both subgroups105and110can be used to receive the reflected beam signals. Since the beam signals140and145in this embodiment had different frequencies, a processor of the radar system100is able to differentiate the reflection signals that correspond to each of the beam signals140and145. Objects on the surface of the earth may include such things as plants, other biomass, water, ice, soil, man-made structures or objects, a human being, an animal, a vehicle, a road, etc.

The received reflected beam signals are then processed into images. The images represent how the beam signals140and145have been reflected by the surface of the earth (or any objects thereon) as the aircraft flies along the y-axis. In this embodiment, the images are derived by measuring the phase of the received reflected beam signals as compared to a known phase of the transmitted beam signals140and145. Measuring the phase of the reflected beam signals as the aircraft travels will reveal relative changes in the terrain.

However, just one image generated from the reflected signal of the beam signal140does not reveal a three dimensional topography of the surface of the earth (or any objects thereon) within the swath125. Instead, two images (one from the reflected signal of the beam signal140and one from the reflected signal of the beam signal145) are used to generate a terrain map of the scanned swath125. This terrain map is also referred to as an interferogram, and is generated using phase interferometry and the aforementioned two images. Noise filtering, phase unwrapping, nominal aircraft height or expected terrain elevation, null-steering of the antenna pattern, or another beam signal (and a resulting third image) may also be used to generate the interferogram. Null-steering may be utilized to minimize noise or interference of a particular received or transmitted signal or in a particular channel of the radar system100. In null-steering a received signal is weighted to minimize the effects of noise. For example, consider a radar system forming a single beam signal using four separate signals (or channels). if a particular signal (or channel) is experiencing high levels of interference or noise, that signal can be weighted lower in the processing (either generation of the signal or utilization of the signal to synthesize a beam on receive) to minimize or eliminate the effect of the noise or interference on the combined beam signal.

In the present embodiment, the beam signals140and145are generated simultaneously and continuously. Accordingly, the reflected beam signals are also received simultaneously and continuously. In alternative embodiments, the beam signals may be time-interleaved in a variety of ways.

In a first alternative embodiment, the beam signals140and145may be time-interleaved. In this embodiment, the beam signals140and145would be alternately transmitted such that two images of the swath125may still be generated from the reflected beam signals. Advantageously, this method may utilize only 2 sub-arrays in an antenna, as only one of beam signal140and beam signal145would need to be generated at any one time. However, in various embodiments of this time-interleaved method any number of sub-arrays may still be used. Similarly, power usage of the system may decrease if only one of beam signal140or beam signal145is being generated at any one time. In another embodiment utilizing time-interleaving generation of the beam signals140and145, overall resolution of the images may increase. For example, if the architecture shown inFIGS. 1-3is utilized, the radar system100could utilize all 8 sub-arrays of the antenna to generate beam signal140, and alternate utilizing all 8 sub-arrays of the antenna to generate the beam signal145. Utilizing additional sub-arrays to generate a beam signal may make a beam signal more focused (i.e. a narrower angle θ1) and yield higher resolution images. Thus, it may be advantageous to time-interleave the generation of beam signals140and145.

In another embodiment, the radar system100may be utilized to scan multiple swaths, say swaths125and130for example. In this embodiment, if the swaths125and130were scanned simultaneously, 4 or more separate beam signals may be generated to scan the swaths125and130. However, the swaths may be measured by time-interleaving the generation of the beams for each of the swaths125and130. For example, two (or more) beam signals may be generated to scan swath125alternately with two (or more) beam signals being generated to scan swath130. In this way, the radar system may be able to scan wider areas (i.e., more swaths) without increasing the capabilities of the radar system or the antenna size (i.e. number of sub-arrays in the antenna).

FIG. 8is a diagram illustrating a radar system800used for digital beamforming interferometry in a transmit beamforming mode demonstrating a transmit configuration in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. This embodiment corresponds to the first approach discussed above where the radar transmit signals are generated to form a single transmit beam of energy on either side of the flight track and, on receive, the reflected energy from the ground is collected by each individual channel and processed as two or more individual receive beams.

InFIG. 8, the radar system800transmits a focused beam signal805toward a ground surface. The focused beam signal805hits the ground surface at a swath810. The focused beam signal805also has a look angle θ3. As discussed above with respect toFIG. 1, the look angle, as better represented here inFIG. 8, represents the center of a signal, here the focused beam signal805.FIG. 8illustrates the transmit configuration of the first approach discussed above (also referred to as the transmit beamforming mode).FIG. 9, discussed below, illustrates the receive configuration of the first approach discussed above (also referred to as the transmit beamforming mode).FIG. 8shows only one beam signal805. However, in alternative embodiments, the radar system800may synthesize multiple beam signals that look at swath810or other swaths (i.e., have other look angles) on either side of the radar system (i.e., the other side of the z-axis).

FIG. 9is a diagram illustrating a radar system900used for digital beamforming interferometry in a transmit beamforming mode demonstrating a receive configuration in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. This embodiment corresponds to the first approach discussed above where the radar transmit signals are generated to form a single transmit beam of energy on either side of the flight track and, on receive, the reflected energy from the ground is collected by each individual channel and processed as two or more individual receive beams.

InFIG. 9, the radar system900receives signals at multiple sub-arrays of the antenna in the radar system900. Here, the radar system900is shown as receiving two signals, signal905and signal910. In alternative embodiments, the radar system may receive any number of signals, though the number of received signals may be limited by the number of sub-arrays in the antenna. However, with time-interleaving methods, the radar system900may receive more signals than there are number of sub-arrays. Signal905corresponds to a look angle θ5. Signal910corresponds to a look angle θ4. The received signals905and910bounce from a swath915. In alternative embodiments, the radar system may also receive signals that bounce from other swaths (i.e., have different look angles), including swaths on the other side of the radar system (i.e., the other side of the z-axis).

Although the radar system900may receive signals that bounce from the entire swath915, the radar system900may receive signals corresponding to a smaller portion of the swath915, depending on any beam signals that were transmitted. For example, if the beam signal805ofFIG. 8was transmitted, the radar system could see any signals bouncing back from the entire swath915, but would see strong signals bouncing back from the part of swath915that corresponds to the high energy beam signal805transmitted and aimed at the swath810ofFIG. 8. Although it is beam signal805that is bounced back toward the radar system900, signals905and910would appear as different signals because they correspond to the bounce-back of beam signal805because of the spatial displacement between the different sub-arrays that are receiving signals905and910. Signals905and910are utilized to generate the images that can be used to generate an interferogram. Although,FIG. 9only shows two signals905and910, alternative embodiments may receive any number of signals from a bounced back beam signal, where the multiple signals bounced back are received by different sub-arrays in the antenna of the radar system900.

FIG. 2is a diagram illustrating a radar system200used for digital beamforming interferometry in a receive beamforming mode in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. This embodiment corresponds to the second approach discussed above, where individual signals may be transmitted (by means of time multiplexing or encoding each of the signals) to generate two or more transmit beams and where, on receive, the reflected energy from the ground is collected by each individual channel and processed as a single receive beam.FIG. 2shows a radar system200that includes an antenna with 8 sub-arrays. UnlikeFIG. 1, the sub-arrays are not shown in subgroups, although the physical number and shape of the antenna inFIGS. 1 and 2are not structurally different. Advantageously, this means the same radar system may be used to perform both the receive beamforming mode discussed with respect toFIG. 2and the transmit beamforming mode discussed with respect toFIG. 1.

In the present embodiment, the radar system200generates a wide-field signal205(as opposed to the narrow-field beam signals generated inFIG. 1) that is spread out along a large look angle. Here, the wide-field signal205hits the surface of the earth (or any object thereon) in the surface signal region210. In this embodiment, one central sub-array may be utilized to transmit the wide-field signal205. In other embodiments, multiple sub-arrays may be used to transmit the wide-field signal205.

The wide-field signal205then reflects or backscatters back to the radar system200. The backscattered or reflected wide-field signal205is received by the entire array of the antenna of the radar system200. The radar system200can then process the signals received by the various sub-arrays of the radar system200in order to synthesize receive beams at various scan angles on both sides of the flight track line215. For example, receive beams220,225,230, and235may be synthesized, which correspond to swaths250,255,240, and245, respectively. In this embodiment, to generate two images for each of the swaths250,255,240, and245, at least two beams for each swath can be synthesized. In this embodiment, with 8 sub-arrays in the antenna, 4 separate receive beams may be synthesized at any one moment. Accordingly, in order to generate interferograms for each of the swaths250,255,240, and245, a time-interleaving strategy may be employed to generate the images corresponding to each swath. In alternative embodiments, the number of sythensized beams, swaths measured, images generated, sub-arrays in the antenna, and interferograms generated may be varied.

FIG. 10is a diagram illustrating a radar system1000used for digital beamforming interferometry in a receive beamforming mode demonstrating a transmit configuration in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. This embodiment corresponds to the second approach discussed above, where individual signals may be transmitted (by means of time multiplexing or encoding each of the signals) to generate two or more transmit beams and where, on receive, the reflected energy from the ground is collected by each individual channel and processed as a single receive beam.

InFIG. 10, the radar system1000transmits signals from multiple sub-arrays of the antenna in the radar system1000. Here, the radar system1000is shown as transmitting two signals, signal1005and signal1010. In alternative embodiments, the radar system1000may transmit any number of signals, though the number of transmitted signals may be limited by the number of sub-arrays in the antenna. However, with time-interleaving methods, radar system1000may transmit more signals than there are number of sub-arrays. Signal1005corresponds to a look angle θ6. Signal1010corresponds to a look angle θ7. The transmitted signals1005and1010are signals that hit a swath1015. In alternative embodiments, the radar system may also transmit signals that hit other swaths (i.e., have different look angles), including swaths on the other side of the radar system (i.e., the other side of the z-axis).FIG. 10illustrates the transmit configuration of the second approach discussed above (also referred to as the receive beamforming mode).FIG. 11, discussed below, illustrates the receive configuration of the second approach discussed above (also referred to as the receive beamforming mode).

FIG. 11is a diagram illustrating a radar system1100used for digital beamforming interferometry in a receive beamforming mode demonstrating a receive configuration in accordance with an illustrative embodiment. This embodiment corresponds to the second approach discussed above, where individual signals may be transmitted (by means of time multiplexing or encoding each of the signals) to generate two or more transmit beams and where, on receive, the reflected energy from the ground is collected by each individual channel and processed as a single receive beam.

InFIG. 11, the radar system1100receives a focused beam signal1105that has bounced from a swath1110of a ground surface. The focused beam signal1105has a look angle θ8.FIG. 11shows only one beam signal1105. However, in alternative embodiments, the radar system1100may receive multiple beam signals that look at swath1110or other swaths (i.e., have other look angles) on either side of the radar system (i.e., the other side of the z-axis).

Although the radar system1100may receive the focused beam signal1105from a swath1110, the radar system1100may receive different focused beam signals corresponding to a different swath than the swath1110. For example, if the signals1005and1010ofFIG. 10were transmitted, the radar system could see any focused beam signals bouncing back from the entire swath1015, but the radar system can determine to see one or more of multiple focused beams signals from all of the swath1015or just one focused beams signal, as illustrated inFIG. 11. Different focused beam signals from a single swath, such as swath1110can also be received by different sub-arrays or combinations of sub-arrays of the antenna. Because of the spatial displacement between the different sub-arrays, receiving the focused beam signal1105at different antenna sub-arrays can be used to generate the images that can be utilized to generate an interferogram.

FIG. 3is a diagram illustrating circuit components of a beamforming radar system300in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system. The beamforming radar system300includes a waveform generator & data acquisition and processing system305, radio frequency (RF) transceivers310, and an antenna array315.

The waveform generator & data acquisition and processing system305includes field programmable gate arrays (FPGA)320and325. The FPGA320receives waveform and operation configuration from a host computer through connection392. In one embodiment, this may be from a device such as a computing device400as discussed below with respect toFIG. 4. The FPGA320is used to control the channels (i.e., the signals to each of the sub-arrays of the antenna array315). The FPGA320can be programmed to operate in a variety of embodiments disclosed herein. The signals for each channel are output from the FPGA320to digital to analog converters associated with each channel. An example of one of the digital to analog converters is digital to analog converter330. As will be noted throughoutFIG. 3, there are many similar elements, and many of them will be referred to be example elements, such as the digital to analog converter330. Although the physical components ofFIG. 3that look similar may be similar in their physical makeup, they may not all be functioning exactly the same way or electrically transmitting the exact same signal at any moment. However, the similar elements referred to by the example element inFIG. 3can be expected to behave similarly to its other similar elements if the same signals and conditions are subjected to it.

The signals from the digital to analog converters330are transmitted to the RF transceivers310through connections340, where the signals are up-converted to a higher frequency band at elements350. In this embodiment, an L-band frequency is utilized from frequency generator375. The signals are amplified at amplifiers355, and then are sent to feed networks385of the antenna array315through connections378.

The signals are then transmitted through sub-arrays380that include antenna elements390. In this embodiment, the antenna array315includes 8 sub-arrays380, and each sub-array380includes 8 antenna elements390. The numbers of sub-arrays380and antenna elements390can vary in alternative embodiments, as discussed above with regard to alternative embodiments ofFIGS. 1 and 2.

After the signals have been reflected and returned to the antenna array315, the signals pass back through the antenna elements390, antenna sub-arrays380, the feed networks385, and the connections378to the RF transceivers310. Because the reflected signals received are likely weaker (i.e. have significantly lower amplitudes) than the originally transmitted signals, the signals are amplified at amplifiers365.

The signals are also down-converted from the L-Band at elements370, utilizing again the frequency generator375. In alternative embodiments, other frequencies may be used and generated by the frequency generator375than frequencies within the L-Band. The signals then pass through connections335to analog to digital converters332in the waveform generator & data acquisition and processing system305. The signals then pass to the FPGA325. In this scenario, the signals may be processed at the FPGA325to generate data for images, which are in turn used to create interferograms. In the alternative, the FPGA325may only process the data from the signals for storage so that another processing device can generate the images associated with the signals and the interferograms.

FIG. 4is a block diagram illustrating a computing device400and a data archive425that may be used in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different components may be included in the system.FIG. 4also includes an on board radar system450. The on board radar system450may be any of the radar systems depicted in or discussed in reference toFIGS. 1-3above.

The computing device400includes a processor415that is coupled to a memory405. The processor415can store and recall data and applications in the memory405. The processor415can execute sets of instructions stored on the memory. In an example, a set of instructions may be a browser or a mobile application (app) or other software program. The set of instructions may also be programmed into certain hardware components that make them behave in a certain way, such as an FPGA. The memory405may also store a software program specially designed for use with the system disclosed herein and perform the methods disclosed herein. The processor415may also display objects, applications, data, etc. on an interface/display410. The processor415is also coupled to a transceiver420. With this configuration, the processor415, and subsequently the computing device400, can communicate with other devices, such as the data archive425or the on board radar system450through connections445and455.

The data archive425includes a processor435that is coupled to a memory430. The processor435can store and recall data and applications in the memory430. For example, the data archive425may provide to the computing device400data on a recent flight and signals collected utilizing the on board radar system450. The processor435is also coupled to a transceiver440. With this configuration, the processor435, and subsequently the data archive425, can communicate with other devices, such as the computing device400through the connection445or the on board radar system450through a connection460.

The devices shown in the illustrative embodiment may be utilized in various ways. For example, the connections445,455, and460may be varied. The connections445,455, and460may be a hard wired connection. In such an embodiment, the computing device400, the data archive425, and the on board radar system450may all be on board an aircraft or spacecraft. In other embodiments, the computing device400and/or the data archive425may be physically remote from the on board radar system450(and not on the aircraft or spacecraft). A hard wired connection may involve connecting the devices through a USB (universal serial bus) port, serial port, parallel port, or other type of wired connection that can facilitate the transfer of data and information between a processor of a device and a second processor of a second device, such as between the computing device400and the data archive425. In another embodiment, the connections445,455, and460may be a dock where one device may plug into another device. While plugged into a dock, the computing device400may also have its batteries charged or otherwise be serviced. In other embodiments, the connections445,455, and460may be a wireless connection. Such a connection may take the form of any sort of wireless connection, including but not limited to Bluetooth connectivity, Wi-Fi connectivity, or another wireless protocol. Other possible modes of wireless communication may include near-field communications, such as passive radio-frequency identification (RFID) and active (RFID) technologies. RFID and similar near-field communications may allow the various devices to communicate in short range when they are placed proximate to one another. In an embodiment using near field communication, two devices may have to physically (or very nearly) come into contact, and one or both of the devices may sense various data such as acceleration, position, orientation, velocity, change in velocity, IP address, and other sensor data. The system can then use the various sensor data to confirm a transmission of data over the internet between the two devices. In yet another embodiment, the devices may connect through an internet (or other network) connection. That is, the connections445,455, and460may represent several different computing devices and network components that allow the various devices to communicate through the internet, either through a hard-wired or wireless connection. The connections445,455, and460may also be a combination of several modes of connection.

To operate different embodiments of the system or methods disclosed herein, the various devices may communicate in different ways. For example, the computing device400may download or install software to interact with and/or control the data archive and the on board radar system450. A website and browser interface may also be used. Advantageously, this prevents excessive download of software and programs onto the computing device400. Such websites may perform or allow to be performed some or all of the processes, functions, and/or methods described herein. Additionally, the embodiments disclosed herein are not limited to being performed only on the disclosed devices inFIG. 1. It will be appreciated that many various combinations of computing devices may execute the methods and systems disclosed herein. Examples of such computing devices may include desktop computers, cloud servers, smart phones, personal computers, servers, laptop computers, tablets, blackberries, RFID enabled devices, or any combinations of such devices or similar devices.

The configuration of the data archive425, the computing device400, and the on board radar system450can be one physical system on which the disclosed embodiments may be executed. Other configurations of the devices shown may exist to practice the disclosed embodiments. Further, configurations of additional or fewer devices than the ones shown inFIG. 4may exist to practice the disclosed embodiments. Additionally, the devices shown inFIG. 4may be combined to allow for fewer devices or separated where more than the two devices shown exist in a system. In other embodiments, specialized hardware or software may exist on the devices shown inFIG. 4that is specifically designed to perform or execute the various embodiments disclosed herein.

FIG. 5is a flow diagram illustrating a method500of a transmit beamforming mode in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different operations may be performed. Also, the use of a flow diagram is not meant to be limiting with respect to the order of operations performed. The operations disclosed with respect toFIG. 5may be implemented on the physical systems disclosed herein with respect toFIGS. 1-4discussed above.

In an operation505, a first, second, third, and fourth signals are generated. In an operation510, the first, second, third, and fourth signals are converted from digital to analog signals. In an operation515, the frequencies of the first, second, third, and fourth signals are boosted to the L-Band and amplified to increase the amplitude of the signals.

In an operation520, the first and second signals are transmitted through first and second sub-arrays of an antenna, respectively. The first and second signals are configured so that when transmitted in the operation520, the first and second signals constructively interfere to generate a first beam signal.

In an operation525the third and fourth signals are transmitted through third and fourth sub-arrays of an antenna, respectively. The third and fourth signals are configured so that when transmitted in the operation525, the third and fourth signals constructively interfere to generate a second beam signal.

In an operation530, first and second reflected signals that correspond to the first and second beam signals are received. In an operation535, the first and second reflected signals are amplified to increase the amplitude of the signals. In an operation540, the received first and second reflected signals are down converted out of the L-Band of frequencies to lower frequencies. In an operation545, the received first and second reflected signals are converted from analog to digital signals.

In an operation550, the received reflected signal data is processed, stored, and/or transmitted. If there is no on board computing or processing device, the data from the signals may be stored for future analysis by another machine. If computing capabilities are present on board, the signal data may be used to generate images and interferograms. Additionally, the signal data may be transmitted to other devices either on board or not on board. The signal data may be transmitted to be processed, or the signal data may be transmitted to be stored, or both.

FIG. 6is a flow diagram illustrating a method600of generating an interferogram in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different operations may be performed. Also, the use of a flow diagram is not meant to be limiting with respect to the order of operations performed. The operations disclosed with respect toFIG. 6may be implemented on the physical systems disclosed herein with respect toFIGS. 1-4discussed above.

In an operation605, a first image and a second image are generated based on a first and a second reflected signal, respectively. In this embodiment, transmit beamforming mode is being utilized. In a receive beamforming mode, four reflected signals may be received and two beamformed signals may be synthesized from the four reflected signals. In the receive beamforming mode, these two synthesized beamformed signals may be used to generate the first and second images.

In an operation610, the first image and the second image are utilized to form an interferogram image. In an operation615, noise is filtered out of the interferogram. In an operation620, a phase unwrapping is performed on the interferogram.

FIG. 7is a flow diagram illustrating a method700of a receive beamforming mode in accordance with an illustrative embodiment. In alternative embodiments, fewer, additional, and/or different operations may be performed. Also, the use of a flow diagram is not meant to be limiting with respect to the order of operations performed. The operations disclosed with respect toFIG. 7may be implemented on the physical systems disclosed herein with respect toFIGS. 1-4discussed above.

In an operation705, a wide beam signal is generated by a radar system. In an operation710, the wide beam signal is transmitted through an antenna. In an operation715, receive a reflected signal corresponding to the wide beam signal at first, second, third, and fourth sub-arrays of the antenna.

In an operation720, the reflected and received signal received at the first and second sub-arrays is processed to generate a first image related to a desired scan angle. In an operation725, the reflected and received signal received at the third and fourth sub-arrays is processed to generate a second image related to the desired scan angle. In an operation730, the first and second images are utilized to generate an interferogram. In an example embodiment, a process such as that discussed with respect toFIG. 6may be used to generate the interferogram.

In an illustrative embodiment, any of the operations described herein can be implemented at least in part as computer-readable instructions stored on a computer-readable medium or memory. Upon execution of the computer-readable instructions by a processor, the computer-readable instructions can cause a computing device to perform the operations.