Underwater vehicle inspection method, device and computer program

Abstract

In an embodiment, a system receives a SAR image of at least a portion of an exterior surface of an underwater vehicle, performs CCD processing to compare a baseline SAS image for the underwater vehicle to the received SAR image of the underwater vehicle, and generates a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image of the underwater vehicle. The system determines whether the underwater vehicle has been tampered with based on the measure of similarity.

Description

[Background technology]

[0001] As known in the art, imaging systems can image the exterior of a vessel's hull. Some known systems require close inspection, while others attempt to image the hull using a side scan from the seabed. The images obtained in these systems are difficult to interpret due to geometric distortions caused by oblique angles to the hull. In addition, the data may have limited resolution, so subtle changes to the hull may be missed. Some conventional systems may require large sensor arrays to acquire image data. Summary of the Invention

[0002] Embodiments of the present disclosure provide methods and apparatus for inspecting underwater vehicles, such as unmanned underwater vehicles (UUVs), upon their return. In some applications, UUVs are launched from submarines or ships to perform reconnaissance activities, after which the UUV returns home at the end of its mission. In embodiments, an inspection system images and analyzes the exterior of the returning UUV to detect any changes. For example, an explosive device attached to the UUV can be detected by the inspection system.

[0003] In an embodiment, the inspection system includes one or more sensors that create a series of baseline high frequency synthetic aperture sonar (SAS) images of the UUV before beginning a mission, and uses coherent change detection (CCD) processing to compare the baseline images to images formed upon return of the vehicle. In an example embodiment, the inspection system uses three passes of the UUV to the sensor(s) at a given standoff distance, such as on the order of 100 meters, with detection sensitivity on the order of 0.5 mm. With this example arrangement, the inspection system can detect changes in the shape of the UUV caused by some type of tampering. Inspecting returning UUVs to detect tampering can protect host platforms, such as ships or submarines.

[0004] In one aspect, a method includes receiving a SAS image of at least a portion of an exterior surface of an underwater vehicle, performing a coherent change detection process to compare a baseline SAS image for the underwater vehicle to the received SAS image of the underwater vehicle to generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image, and determining whether there has been tampering with the underwater vehicle based on the measure of similarity.

[0005] In another aspect, an apparatus includes a processor and memory configured to receive a SAS image of at least a portion of an exterior surface of an underwater vehicle, perform a coherent change detection process to compare a baseline SAS image for the underwater vehicle to the received SAS image of the underwater vehicle and generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image, and determine whether the underwater vehicle has been tampered with based on the measure of similarity.

[0006] In a further aspect, the article includes a non-transitory computer readable medium having instructions stored thereon that enable a machine to receive a SAS image of at least a portion of an exterior surface of an underwater vehicle, perform a coherent change detection process to compare a baseline SAS image for the underwater vehicle to the received SAS image of the underwater vehicle and generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image, and determine whether the underwater vehicle has been tampered with based on the measure of similarity.

[0007] The foregoing features of this invention, as well as the invention itself, may be more fully understood from the following description of the drawings. [Brief description of the drawings]

[0008] [Figure 1] 1 is a pictorial representation of a submarine capable of hosting and inspecting underwater vehicles, according to an example embodiment of the present disclosure. [Diagram 2] 1 is a schematic diagram of an example underwater vehicle being inspected by an inspection system, according to an example embodiment of the present disclosure. [Diagram 3] 1 is a high-level block diagram of an example embodiment of an underwater vehicle inspection system, in accordance with an exemplary embodiment of the present disclosure. [Figure 4] 1 is a schematic diagram of an underwater vehicle at a standoff distance from a host underwater vehicle having an inspection system. [Diagram 5] 1 is a flow diagram illustrating an example sequence of steps for inspecting an underwater vehicle, according to an example embodiment of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of an example computer capable of performing at least a portion of the processes described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 illustrates an example host vehicle 100 (which may include a ship or submarine) that can launch an unmanned underwater vehicle (UUV) 102 and inspect the UUV upon return, according to an example embodiment of the present disclosure. The exterior of the UUV 102 may be inspected to detect any tampering that may affect the host vehicle 100. As described more fully below, the inspection system may be configured to inspect the exterior of the UUV 102 using synthetic aperture sonar (SAS) imagery processed using coherent change detection (CCD) to detect any changes to the exterior of the UUV since launch. Changes to the UUV exterior may include various contraband materials or systems, such as chemical agents, biological materials, incendiary devices, explosives, tracking devices, and the like.

[0010] As used herein, tampering refers to any unauthorized addition of material or intentional damage to the exterior surface of a vehicle. For example, a malicious individual may attach explosives to an underwater vehicle with the intent of damaging the host vehicle after the underwater vehicle returns from a mission.

[0011] FIG. 2 illustrates a high level diagram of an inspection system 200 for inspecting the exterior of a UUV 202. In an example embodiment, the inspection system 200 includes a synthetic aperture sonar (SAS) system that acquires images of the UUV 202 as either the UUV or the SAS sensor or both move relative to one another. In the illustrated embodiment, a first pass 204 acquires images with relative motion into the page, indicated by an X in a circle. A second pass 206 may acquire images with relative motion out of the page, indicated by a dot in the center of the circle. A third pass 208 acquires images with relative motion into the page, indicated by an X in a circle. The UUV 202 (or sensor) may rotate 120 degrees after each pass to allow inspection of the entire UUV exterior. In one embodiment, each of the three passes 204, 206, 208 may cover approximately 120 degrees of the UUV 202 exterior for a total of 360 degrees. As will be described more fully below, coherent change detection (CCD) processing may be used to detect any changes on the exterior surface of UUV 202.

[0012] While example embodiments are shown in connection with a particular vehicle that operates underwater or beneath the surface of water, it is understood that embodiments of the present disclosure are applicable to inspection systems generally where it is desirable to detect changes at a surface. It is understood that relative motion between the image capture sensor and the vehicle can be accomplished in a wide variety of ways. For example, the vehicle may be fixed in a fixed position while at least the sensor of the inspection system moves relative to the surface of the vehicle. In other embodiments, at least the sensor of the inspection system is fixed in a predetermined position while the vehicle moves relative to the sensor. In some embodiments, both at least the sensor of the inspection system and the vehicle move relative to one another in a pattern configured to capture a desired image.

[0013] As used herein, SAS refers to a type of sonar that uses the relative motion of a radar sensor over a target area (or vice versa or both) to image objects in two or three dimensions, providing finer spatial resolution than traditional beam scanning radar. The distance the SAS device travels over the target in the time it takes for the sonar pulse to return to the antenna creates a synthetic aperture for the sonar. The aperture size corresponds to the resolution of the image. Thus, SAS systems can create high resolution images using relatively small physical antennas. To create a SAS image, a series of pulses are transmitted to illuminate an area that may contain the target. The transmitted pulses can be reflected from the target and received as signal returns. The transmitted and received signals can be beamformed to meet the needs of a particular application. The signal returns can be processed to combine signals from multiple antenna positions to obtain a synthetic antenna aperture. In general, the range direction is parallel to the motion of the target and perpendicular to the azimuth direction (also known as along track).

[0014] In an embodiment, the 3D processing involves initial processing in the azimuth and range directions to generate a 2D (azimuth-range) high-resolution image, followed by measuring the phase difference between the complex images using a Digital Elevation Model (DEM), which is determined from various viewing angles to recover height information, which together with the azimuth-range coordinates provided by the 2D SAS focusing, provide the third dimension, which is the elevation.

[0015] FIG. 3 illustrates an example inspection system 300 having a SAS system 302 for acquiring images of an unmanned underwater vehicle (UUV) 304 and a CCD system 350 for detecting changes in the surface of the UUV from a baseline SAS image, in accordance with an exemplary embodiment of the present disclosure.

[0016] Coherent Change Detection (CCD) refers to a processing technique for comparing the amplitude and phase of images to detect changes from a baseline image(s) to a more recent image(s). CCD processing can be used on images acquired from a SAS system. CCD can be thought of as overlaying images on top of each other to detect amplitude differences while also considering phase for coherent processing. It is understood that amplitude differences alone can be considered non-coherent change detection (NCCD).

[0017] The SAS system 302 includes a sensor 304, such as an antenna, for generating SAS images. The SAS system antenna 304 collects SAS data by scanning a field of view that includes the UUV. A transmit module 306 and a receive module 308 are selectively enabled to transmit and receive signals to and from the antenna 304. In an embodiment, the transmit and receive systems are separate from one another and may have independent antennas. A beam forming module 310 may form transmit and / or receive beams in a desired pattern. A signal processing module 312 may generate signals for transmission and process signal returns to generate SAS images. A SAS image database 314 may store baseline SAS images for various UUVs and may store SAS images created for UUVs that have recently returned from mission completion.

[0018] Many passes may be made by the sensor 304 or the UUV to achieve relative motion to acquire SAR images that may be stored in database 314. In an embodiment, a baseline SAS image is acquired prior to deploying the UUV. It is understood that the SAS system may take any practical number of passes of the vehicle to achieve the desired resolution that meets the needs of a particular application.

[0019] The CCD system 350 may access the SAS image database 314 to process the SAS images. The CCD system 350 may include a CCD processing module 352 that may compare a baseline SAS image for a given UUV to a more recent SAS image for that UUV. The output module 354 may include a display that may show the CCD results of the UUV inspection upon return. The CCD processing module 352 may generate a measure of similarity between the baseline and the more recent SAS image. In an embodiment, the measure of similarity is indicative of a change in the surface of the UUV of at least 0.5 mm and / or one-fifth of the wavelength of the transmitted signal.

[0020] The CCD processing of the SAS images can be modified to meet the needs of a particular application. In the example embodiment, the CCD processing includes four processing stages. The first is a coarse registration step that relates the approximate location of the target for the two passes, and the second is a fine-scale co-registration that matches features between the two images. third, a local co-registration phase to improve the phase coherence of the images, and finally, an algorithm to detect the phase difference between the two images.

[0021] 4 illustrates an example SAS image acquisition configuration in which a manned or unmanned underwater host vehicle 400 acquires images of an underwater vehicle 402 for which inspection is desired. The underwater vehicle 400 may include a minesweeper-type submarine having a high frequency, wideband, SAS-type sonar capable of providing optical level discrimination of small objects.

[0022] In an embodiment, a linear sensor array for the SAS system can be used. Using a physical aperture side scan from a narrow azimuth beam by focusing a large set of elements, synthetic aperture sonar builds an array of any length by coherently combining data from multiple receivers as the array passes the target (or vice versa). This allows for a range-dependent resolution, allowing the formation of high azimuth resolution images at ranges that would not be possible without an impossibly long physical array. The length of the physical array depends on the range between the array and the target, the relative speed of the sensor passing the target (or vice versa). If the relative speed of the two objects is well controlled, a relatively short array can give accurate results. In an embodiment, the length of the array can vary from less than about 0.1 m to several meters long, depending on the relative speed of the two platforms and the required standoff distance at the closest point.

[0023] FIG. 5 illustrates an example sequence of steps for inspecting an underwater vehicle, according to an example embodiment of the present disclosure. In step 500, the SAS system of the inspection system generates a baseline image of the underwater vehicle. Relative motion between the SAS system sensor and the underwater vehicle is achieved by moving the sensor and / or the underwater vehicle in a selected pattern to obtain the desired image. In step 502, the SAS system generates a new image of the underwater vehicle, such as after the vehicle returns from a mission. In step 504, CCD processing is performed to inspect the surface of the underwater vehicle by comparing the baseline SAS image with the new SAS image to detect any tampering. In step 506, an output of the CCD processing indicates whether tampering has been detected.

[0024] 6 illustrates an exemplary computer 600 capable of performing at least a portion of the processes described herein, such as those of FIGS. 1, 2, 3, and 4. For example, computer 600 may perform processing to generate SAR images and CCD image processing to detect tampering of an underwater vehicle, as described herein. Computer 600 includes a processor 602, a volatile memory 604, a non-volatile memory 606 (e.g., a hard disk), an output device 607, and a graphical user interface (GUI) 608 (e.g., a mouse, keyboard, display, etc.). Non-volatile memory 606 stores computer instructions 612, an operating system 616, and data 618. In one example, computer instructions 612 are executed from volatile memory 604 by processor 602. In one embodiment, article 620 includes non-transitory computer readable instructions.

[0025] The processing may be implemented in hardware, software, or a combination of the two. The processing may be implemented in a computer program executed on a programmable computer / machine, each of which includes a processor, a storage medium, or other article readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and one or more output devices. The program code may be applied to data entered using the input device to perform processing and generate output information.

[0026] The system may process, at least in part, through a computer program product (e.g., in a machine-readable storage device) for execution by or controlling the operation of a data processing device (e.g., a programmable processor, computer, or multiple computers). Each such program may be implemented in a high-level procedural or object-oriented programming language to communicate with a computer system. However, the program may also be implemented in an assembly or machine language. The language may be a compiled or interpreted language and may be arranged in any form (e.g., as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment). The computer program may be arranged to run on one computer, or on multiple computers at one location or on multiple computers distributed across multiple locations and interconnected by a communications network. The computer program may be stored on a general-purpose or special-purpose programmable computer-readable storage medium or device (e.g., CD-ROM, hard disk, or magnetic diskette) such that the computer is configured to operate when the storage medium or device is read by the computer. The process may also be implemented as a machine-readable storage medium configured with a computer program that, when executed, causes a computer to operate according to instructions in the computer program.

[0027] Processing may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as special purpose logic circuitry (e.g., an FPGA (field programmable gate array) and / or an ASIC (application specific integrated circuit)).

[0028] Although exemplary embodiments of the present invention have been described, it will be apparent to those skilled in the art that other embodiments incorporating its concepts may also be used. The embodiments contained herein should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0029] Elements of different embodiments described herein may be combined to form other embodiments not specifically described above. Various elements that are described in the context of a single embodiment may be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. 1. A method comprising: Producing a baseline SAS image for the underwater vehicle using one or more sensors; a host platform launching the underwater vehicle; receiving a SAS image of at least a portion of an exterior surface of the underwater vehicle after the underwater vehicle returns to the host platform; performing a coherent change detection process to compare a baseline SAS image for the underwater vehicle to a received SAS image for at least a portion of an exterior surface of the underwater vehicle and generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image; and determining whether the underwater vehicle has been tampered with based on the measure of similarity.

2. The method of claim 1 , wherein the underwater vehicle comprises an unmanned underwater vehicle.

3. The method of claim 1 , wherein receiving the SAS imagery occurs after the underwater vehicle returns to the host platform from a predetermined mission.

4. The method of claim 1 , wherein the tampering includes attaching an explosive device.

5. The method of claim 1 , wherein the received SAS imagery includes at least three passes of the underwater vehicle or system to generate the SAS imagery.

6. The method of claim 1 , wherein determining whether the underwater vehicle has been tampered with comprises detecting a change to an exterior surface of the underwater vehicle of about 0.5 mm.

7. The method of claim 1 , further comprising making a determination whether there has been tampering with the underwater vehicle by the host platform to which the underwater vehicle is returning.

8. An apparatus comprising: A processor and a memory, the processor and the memory comprising: Producing a baseline SAS image for the underwater vehicle using one or more sensors; a host platform launching the underwater vehicle; receiving a SAS image of at least a portion of an exterior surface of the underwater vehicle after the underwater vehicle returns to the host platform; performing a coherent change detection process to compare a baseline SAS image for the underwater vehicle to a received SAS image for at least a portion of an exterior surface of the underwater vehicle and generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image; determining whether the underwater vehicle has been tampered with based on the measure of similarity; and An apparatus configured to perform a method including the steps of:

9. The apparatus of claim 8 , wherein the underwater vehicle comprises an unmanned underwater vehicle.

10. The apparatus of claim 8 , wherein receiving the SAS imagery occurs after the underwater vehicle returns to the host platform from a predetermined mission.

11. The device of claim 8 , wherein the tampering includes attaching an explosive device.

12. The apparatus of claim 8 , wherein the received SAS imagery includes at least three passes of the underwater vehicle or system to generate the SAS imagery.

13. The apparatus of claim 8 , wherein determining whether the underwater vehicle has been tampered with includes detecting a change to an exterior surface of the underwater vehicle of about 0.5 mm.

14. The apparatus of claim 8 , further comprising: determining whether there has been tampering with the underwater vehicle by the host platform to which the underwater vehicle is returning.

15. Producing a baseline SAS image of an underwater vehicle using one or more sensors; a host platform launching the underwater vehicle; receiving a SAS image of at least a portion of an exterior surface of the underwater vehicle after the underwater vehicle returns to the host platform; performing a coherent change detection process to compare a baseline SAS image for the underwater vehicle to a received SAS image for at least a portion of an exterior surface of the underwater vehicle and generate a CCD output corresponding to a measure of similarity between the baseline SAS image and the received SAS image; determining whether the underwater vehicle has been tampered with based on the measure of similarity; and A computer program for causing a computer to execute a method comprising the steps of:

16. The computer program product of claim 15 , wherein the underwater vehicle comprises an unmanned underwater vehicle.

17. 20. The computer program product of claim 16, wherein receiving the SAS imagery occurs after the underwater vehicle returns to the host platform from a predetermined mission.

18. 17. The computer program product of claim 16, wherein the tampering includes attaching an explosive device.

19. 17. The computer program product of claim 16, wherein the received SAS imagery includes at least three passes of the underwater vehicle or system to generate the SAS imagery.

20. 17. The computer program product of claim 16, wherein determining whether the underwater vehicle has been tampered with includes detecting a change to an exterior surface of the underwater vehicle of about 0.5 mm.

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