Greg Franks

LWIR NUC using an uncooled microbolometer camera

Performing a good non-uniformity correction is a key part of achieving optimal performance from an infrared scene projector. Ideally, NUC will be performed in the same band in which the scene projector will be used. Cooled, large format MWIR cameras are readily available and have been successfully used to perform NUC, however, cooled large format LWIR cameras are not as common and are prohibitively expensive. Large format uncooled cameras are far more available and affordable, but present a range of challenges in practical use for performing NUC on an IRSP. Santa Barbara Infrared, Inc. reports progress on a continuing development program to use a microbolometer camera to perform LWIR NUC on an IRSP. Camera instability and temporal response and thermal resolution are the main difficulties. A discussion of processes developed to mitigate these issues follows.

Performance improvements in large format resistive array (LFRA) infrared scene projectors (IRSP)

Santa Barbara InfraRed (SBIR) is producing high performance 1,024 x 1,024 Large Format Resistive emitter Arrays (LFRA) for use in the next generation of IR Scene Projectors (IRSPs). The demands of testing modern infrared imaging systems require higher temperatures and faster frame rates. New emitter pixel designs, rise time enhancement techniques and a new process for annealing arrays are being applied to continually improve performance. This paper will discuss the advances in pixel design, rise time enhancement techniques and also the process by which arrays are annealed. Test results will be discussed highlighting improvements in rise time, uniformity and reduced numbers of defective pixels.

Enhanced LWIR NUC using an uncooled microbolometer camera

Performing a good non-uniformity correction is a key part of achieving optimal performance from an infrared scene projector, and the best NUC is performed in the band of interest for the sensor being tested. While cooled, large format MWIR cameras are readily available and have been successfully used to perform NUC, similar cooled, large format LWIR cameras are not as common and are prohibitively expensive. Large format uncooled cameras are far more available and affordable, but present a range of challenges in practical use for performing NUC on an IRSP. Some of these challenges were discussed in a previous paper. In this discussion, we report results from a continuing development program to use a microbolometer camera to perform LWIR NUC on an IRSP. Camera instability and temporal response and thermal resolution were the main problems, and have been solved by the implementation of several compensation strategies as well as hardware used to stabilize the camera. In addition, other processes have been developed to allow iterative improvement as well as supporting changes of the post-NUC lookup table without requiring re-collection of the pre-NUC data with the new LUT in use.

Thermal Resolution Specification in Infrared Scene Projectors

Infrared scene projectors (IRSPs) are a key part of performing dynamic testing of infrared (IR) imaging systems. Two important properties of an IRSP system are apparent temperature and thermal resolution. Infrared scene projector technology continues to progress, with several systems capable of producing high apparent temperatures currently available or under development. These systems use different emitter pixel technologies, including resistive arrays, digital micro-mirror devices (DMDs), liquid crystals and LEDs to produce dynamic infrared scenes. A common theme amongst these systems is the specification of the bit depth of the read-in integrated circuit (RIIC) or projector engine , as opposed to specifying the desired thermal resolution as a function of radiance (or apparent temperature). For IRSPs, producing an accurate simulation of a realistic scene or scenario may require simulating radiance values that range over multiple orders of magnitude. Under these conditions, the necessary resolution or “step size” at low temperature values may be much smaller than what is acceptable at very high temperature values. A single bit depth value specified at the RIIC, especially when combined with variable transfer functions between commanded input and radiance output, may not offer the best representation of a customer’s desired radiance resolution. In this paper, we discuss some of the various factors that affect thermal resolution of a scene projector system, and propose some specification guidelines regarding thermal resolution to help better define the real needs of an IR scene projector system.

A two-color 1024x1024 dynamic infrared scene projection system

We report on the design and testing of a 2-color dynamic scene projector system based on the MIRAGE-XL infrared scene projector. The system is based on the optical combination of two 1024x1024 MIRAGE-XL resistive arrays. Algorithms derived for 2-color operation are discussed and system performance data is presented, including radiometric performance, sub-pixel spatial co-registration and compensation for spectral cross-talk.

An extended area blackbody for radiometric calibration

SBIR is developing an enhanced blackbody for improved radiometric testing. The main feature of the blackbody is an improved coating with higher emissivity than the standard coating used. Comparative measurements of the standard and improved coatings are reported, including reflectance. The coatings were also tested with infrared imagers and a broadband emissivity estimate derived from the imagery data. In addition, a control algorithm for constant slew rate has been implemented, primarily for use in minimum resolvable temperature measurements. The system was tested over a range of slew rates from 0.05 K/min to 10 K/min and its performance reported.

A hybrid approach to non-uniformity correction of large format emitter arrays

Non-uniformity correction (NUC) of emitter arrays is an important part of the calibration of an infrared scene projector (IRSP), necessary to provide precise and artifact-free simulations. Producing an accurate and cost effective NUC of an IRSP is a challenge due to the complexity of the NUC process and the expense of high performance, large format infrared cameras. Previous NUC methods have typically fallen into either the sparse grid method or the flood method. The sparse grid method gives independent measurements of each emitter pixel, however, it is time consuming and becomes impractical for accurate measurements at low radiance levels, especially with lower performance but less expensive cameras such as microbolometers. Flood measurements are fast and can be applied at lower radiance, but do not allow precise measurement of the output of an individual pixel. Santa Barbara Infrared (SBIR) has developed a hybrid approach that makes use of both methods. Sparse grid methods are used at higher radiance levels to perform an initial NUC of the array. Then, a combination of flood and sparse grid data is used to extend the NUC to lower radiance levels and improve the high radiance NUC through iteration. Details of the approach and results from its application to an emitter array are presented.

Rise-time enhancement techniques for resistive array infrared scene projectors

Santa Barbara Infrared (SBIR) produces high performance resistive emitter arrays for its line of IR Scene Projectors (IRSPs). These arrays operate at frame rates up to 200 hertz. The inherent properties of the pixels can result in transitions between two temperatures that are more than the 5 millisecond frame time. Modifying the pixel drive level on a frame by frame basis can lead to improvements in the measured rise times. This paper describes a new capability developed by SBIR that improves the rise time of the pixels. It discusses the process by which array drive levels are modified to achieve quicker transitions together with test results showing improved rise time. In an example transition cited here, the risetime is reduced by more than a factor of two from 8.3 ms to 3.7 ms.

MIRAGE WF infrared scene projector system, with 1536 x 768 wide format resistive array, performance data

MIRAGE WF is the latest high definition version of the MIRAGE infrared scene projector product line from Santa Barbara Infrared Inc. (SBIR). MIRAGE WF is being developed under the Wide Format Resistive Array (WFRA) program. The WFRA development is one of several efforts within the Infrared Sensor Simulator - Preplanned Product Improvement (IRSS P3I) umbrella funded by the Central Test and Evaluation Investment Program (CTEIP) and led by the US Navy at Patuxent River, MD. Three MIRAGE WF infrared scene projection systems are being delivered as part of the WFRA program. The main differences between the MIRAGE XL (1024x1024) and MIRAGE WF are a 1536x768 emitter array and 100Hz true raster capability. The key emitter requirements that have been measured and will be discussed include: Operability, Maximum Apparent Temperature, Rise Time and Array Uniformity. Key System specifications are: 1536x768 pixels, maximum apparent temperature of 600K, maximum frame rate of 100Hz, raster and snap shot updating, radiance rise and fall time less than 5 ms and windowed mode (1024x768) operation at up to 200 Hz.

Development of a high-definition IR LED scene projector

Next-generation Infrared Focal Plane Arrays (IRFPAs) are demonstrating ever increasing frame rates, dynamic range, and format size, while moving to smaller pitch arrays.1 These improvements in IRFPA performance and array format have challenged the IRFPA test community to accurately and reliably test them in a Hardware-In-the-Loop environment utilizing Infrared Scene Projector (IRSP) systems. The rapidly-evolving IR seeker and sensor technology has, in some cases, surpassed the capabilities of existing IRSP technology. To meet the demands of future IRFPA testing, Santa Barbara Infrared Inc. is developing an Infrared Light Emitting Diode IRSP system. Design goals of the system include a peak radiance >2.0W/cm2/sr within the 3.0-5.0μm waveband, maximum frame rates >240Hz, and >4million pixels within a form factor supported by pixel pitches ≤32μm. This paper provides an overview of our current phase of development, system design considerations, and future development work.