N211-061 TITLE: Fast and Efficient Read-Out for Staring Focal Plane Arrays
RT&L FOCUS AREA(S): Microelectronics
TECHNOLOGY AREA(S): Sensors
The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.
OBJECTIVE: Develop an advanced read-out technology that improves the detection of small targets with large, staring, infrared focal plane arrays.
DESCRIPTION: Focal plane arrays (FPAs) are used in narrow field of view (NFOV) sensors (i.e., cameras) to obtain high resolution images and in wide field of view (WFOV) sensors to surveil large areas of interest. In military applications, NFOV sensors typically benefit from powerful optics with high magnification and stabilized gimbal mounts that hold the camera on target and maintain a moving track. In this application, relatively small format FPAs can be used to image individual targets. In contrast, sensors used for persistent surveillance typically stare in a fixed direction to ensure that all possible targets within the field of view are detected. For staring sensors, the only way to increase resolution is to increase the size of the FPA since the magnification of the optics alone canít be increased without changing the angle of view. For WFOV staring sensors therefore, extremely large FPAs must be used to provide the maximum resolution possible. Not only does this drive up cost (FPA cost typically scales with size), it also introduces other design problems in the imaging system. In particular, large FPAs (with pixel counts in the millions) generate a huge amount of data. Not only is processing this data a challenge, but simply moving the image data off of the FPA to the image processor becomes problematic. This is especially so if the system operates at a high frame rate.
In staring sensors, a great deal of the image space does not appreciably change from frame to frame. Empty sky remains empty sky and even clouds, calm water, shoreline, and land features are static when compared to the fast changing features of the image. In typical image file formats, these constant pixels can be compressed, greatly reducing the file size. However, this isnít done until after the image data is read out from the FPA. Capture and read-out of the FPA image data is done by a dedicated circuit, the read-out integrated circuit (ROIC). The ROIC is tightly coupled to the FPA and it is the ROIC that detects and integrates the signal generated by each pixel in the FPA. Therefore, the ROIC largely determines the signal to noise (S/N) ratio, the optical dynamic range, and the frame rate of the sensor. Image data captured and output by the ROIC can be improved by post processing but the ROIC characteristics place a fundamental upper limit on the detection performance of the sensor system. A fixed dynamic range, uniform across the image plane, inhibits simultaneous detection of both extremely dim and intensely bright objects.
Commercially available sensors are subject to this constraint, which is why digital photographs often have areas that are "blown out" and other areas are so dark as to record no detail. This is accommodated for by adjusting exposure to exclude dim subject matter by biasing the sensor to preferentially capture the brightest part of the image. High dynamic range image capture compensates for this by taking multiple images. However, compensation is accomplished in post-processing and no acceptable real-time solution is commercially available. Furthermore, a fixed frame rate, also uniform across the image and limited by the ability of the system to ingest the huge volume of data generated, inhibits the ability to detect and track small, fast moving, or rapidly fluctuating objects. In all such cases, it is "small" targets that are the most difficult to detect. Practical considerations limit the read-out of very large format FPAs to low frame rates. Coupled with the limitations of well capacity, this mean that only a small percentage of the light in a given frame can be captured and imaged by a large format FPA. This results in a reduction in signal-to-noise that effectively "hides" low signature targets.
Optically small targets are not necessarily small in physical dimensions. A large target at great range appears small to the sensor. Such targets may also be unresolvable due to the FPA size and limitations in the imaging optics. In the limit, a detectable target may occupy as little as one pixel. Typically, these targets are also dim as compared to the surrounding image. However, extremely bright small targets cannot be ignored. Motion or fluctuation in intensity of the target further complicates detection. Therefore, multiple, simultaneous, unresolved targets of a few pixels or less, exhibiting large brightness ranges and moving or fluctuating in intensity, present a particular challenge to staring WFOV sensor systems Ė largely due to limitations in the ROIC. Yet itís these targets that are most critical for the system to detect, track, and identify.
A better solution would be to dynamically adjust the read-out of the image to optimize detection performance of the FPA over small, select, "windows" of interest Ė for example, over a 16 by 16-pixel area. Since targets may be fast moving and/or rapidly fluctuating in intensity, the selected window should track with the target and automatically adjust its size and integration time as the localized intensity, contrast, and target motion and fluctuation demand. Since the application envisions very large format staring FPAs that may contain multiple simultaneous targets of interest in the field of view, multiple independent windows (up to 40) are needed.
The Navy needs an innovative FPA read-out technology that automatically identifies and selects regions of interest in the overall image and then interrogates the pixels within that region to define and then dynamically adjust the capture of pixel data within that region for optimum detection. Furthermore, the identified regions of interest should be capable of moving with the target and adjusting in size to maintain the necessary target detection and tracking, thereby minimizing the amount of additional data output from the ROIC. The goal is to increase WFOV sensing in the mid-wave infrared (MWIR) band without significantly increasing sensor cost. Therefore, the solution should not demand the concurrent invention of a new FPA but should be compatible with at least one of the existing families of MWIR FPA technologies (minimum 1 Megapixel format and maximum 12 micron pitch). Validation of the prototype will be accomplished by testing the combined FPA and readout circuit against moving targets (either targets of opportunity or synthesized targets on an outdoor range). Successful demonstration will include detection and tracking of targets as small as one pixel where the target is so dim as to be at least 3 dB below the FPAís normal dynamic range.
PHASE I: Develop a concept for an innovative FPA read-out technology that improves the detection of multiple small and hard=to-resolve targets as described in the Description section. Define the architecture of the read-out technology and identify and select a compatible FPA technology in the MWIR band (minimum 1 Megapixel format and maximum 12 micron pitch). Demonstrate the feasibility of the proposed approach including the ability to scale to large format (tens of Megapixel) FPAs and predict the ability of the concept to achieve the simultaneous detection of targets that exceed the read-out circuitís inherent dynamic range and are undetectable at the read-out circuitís native frame rate. Demonstrate feasibility by some combination of analysis, modelling, and simulation. Analyze and predict the impact of the technology on the volume of image data produced by the read-out circuit. The Phase I Option, if exercised, will include a device specification, initial process description, and test plan in preparation for device prototype development and demonstration in Phase II.
PHASE II: Develop, demonstrate, and deliver a prototype FPA read-out technology as detailed in the Description section. Demonstrate that the technology meets the requirements in the Description section. Demonstrate the technology by selection of and integration with a suitable MWIR FPA (minimum 1 Megapixel format and maximum 12 micron pitch). Additionally, demonstrate the combined FPA and read-out circuit by imaging scenes of suitable complexity that contain combinations of small, dim, bright, moving, and fluctuating (in intensity) targets. After performance testing, deliver two prototype sensors (read-out circuit, FPA, and supporting circuitry) as well as any custom software, specialized test equipment, calibration equipment, fixtures, and targets developed under this effort to the Naval Research Laboratory.
PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Government use. Assist in scaling and applying the design for specific sensor systems. Mature, ruggedize, and validate the prototype designs for application to Navy imaging systems and assist in the transition of the technology to those systems. The technology resulting from this effort will have application in the field of scientific imaging as well as in commercial products for security systems, law enforcement, and search and rescue operations.
KEYWORDS: Read-Out Integrated Circuit; Focal Plane Array; FPA; Staring Sensors; Wide Field of View Sensors; WFOV; Mid-Wave Infrared; Optical Dynamic Range
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