Current mid-wave infrared detector technologies, such as Indium Antimonide, Mercury Cadmium Telluride, and Platinum Silicide, require the use of expensive, heavy, and power hungry cryogenic coolers or expensive multistage thermoelectric coolers. There is a need for a low cost uncooled mid-wave infrared (MWIR) technology for use in applications where cost, power, size, and reliability are of most importance. Northrop Grumman Electro-Optical Systems (EOS) is currently developing such a sensor based upon its low cost Lead Selenide (PbSe) detector technology. Utilizing its extensive production experience in producing high performance linear PbSe arrays, EOS has developed a 320X256 staring PbSe Focal Plane Array. This paper provides a summary and status of the development efforts and associated performance of EOS' new PbSe FPA's.
This paper presents the current status and summary of image intensified night vision system technologies using Northrop Grumman Electro-Optical Systems (NGEOS) advanced image intensifier (I2) tubes and associated NGEOS advanced I2 technologies. NGEOS advanced I2 technologies is divided into three fully proven and critical I2 subtechnologies: Unfilmed microchannel plate (MCP) based I2, Autogated power supply technologies, and 16mm halo free I2 technology. The initial discussion in this paper will center around the three major NGEOS advanced I2 subtechnologies and their respective night vision system performance benefits. Secondly, this paper will present and discuss the laboratory and field (ground and aerial) performance results from these various advanced night vision systems and technologies. Finally, this paper concludes with the extension and application of the previously noted advanced image intensifier technologies in digital imaging system applications such as image fusion systems combining image intensification and uncooled infrared sensors (SWIR/MWIR/LWIR).
Fusion of reflected/emitted radiation light sensors can provide significant advantages for target identification and detection. The two bands -- 0.6 - 0.9 or 1 - 2 micrometer reflected light and 8 - 12 micrometer emitted radiation -- offer the greatest contrast since those bands have the lowest correlation, hence the greatest amount of combined information for infrared imaging. Data from fused imaging systems is presented for optical overlay as well as digital pixel fusion. Advantages of the digital fusion process are discussed as well as the advantages of having both bands present for military operations. Finally perception tests results are presented that show how color can significantly enhance target detection. A factor of two reduction in minimum resolvable temperature difference is postulated from perception tests in the chromaticity plane. Although initial results do not yet validate this finding, it is expected with the right fusion algorithms and displays that this important result will be proven shortly.
This paper describes test software developed for both the 480 X 12 X 4 and 256 X 256 InSb focal planes manufactured at Litton EOS, Tempe, AZ. The software controls flux sources, frame grabbers and control electronics to provide a fully automated test environment. As well as providing focal plane screening and characterization, the software is an essential diagnostic tool, whereby critical performance attributes such as R0A, quantum efficiency and noise may be displayed both in histogram form and as spatial color-coded bitmap images. These bitmap images may be scanned using the mouse, so that the performance attributes of each pixel may be directly accessed. The software incorporates an emulation mode, in which the array performance is modeled in complete detail (including parameter spreads), with the data presented in identical format to that from the measured data. This allows theoretical performance to be compared directly with measured performance. The software also has the capability to perform bad pixel identification and substitution--a variety of algorithms are available--as well as detector gain/offset correction coefficients calculation.
A multi-channel, high precision, high detector count, TDI real time multi-spectral infrared focal plane residing in a flight platform generates volumes of image data. Data rates in excess of 50 Mbytes/sec are typical. The design requirements of high dynamic range, low noise, server weight and package constraints place burdens on the system designers. The fielding of a complex instrument of this type with near theoretical noise performance demonstrates that when the important principles of system design such as grounding, shielding, and signal processing are understood, excellent performance may be achieved in the face of the inevitable compromises which must be made to satisfy all the system constraints. This paper discusses the architecture of a multi-channel, multi-spectral high frame rate camera. Several key signal processing philosophies will be illustrated and used to demonstrate the effect upon overall system design. Several electronics modules have been manufactured and integrated with infrared focal plane assemblies, ultimately becoming part of an infrared camera system for a reconnaissance program.
In pursuit of a low cost, high performance IR, Imager Litton Electro-Optical Systems has developed an Uncooled Lead Salt 320 X 240 camera. The 30 um pitch detectors consist of either Lead Sulfide or Lead Selenide photoconductors fabricated onto a CMOS Multiplexer Read-Out Integrated circuit. The multiplexer uses novel techniques to subtract the large bias current adaptively, and to integrate the residual signal current. The image is acquired in `snapshot' mode. A chopper provides a uniform reference. Although not necessary for functionality, a thermo-electric cooler is incorporated to improve performance. The signal is digitized off focal plane, and pixel substitution/correction functions are subsequently performed. The resulting video signal is either observed on a LCD display at the back of the camera or remoted to an external viewing device.
This paper describes a linear CMOS IR multiplexer comprising four spectral bands, each with 480 channels of 12 TDI elements. The multiplexer is designed to interface with high R0A InSb detectors manufactured by Litton EOS, Tempe, AZ. The requirement to handle a wide range of photocurrents down to 100 fA, yet maintaining a signal bandwidth in excess of 2.5 kHz imposed significant demands on the input buffer amplifier design. In addition, each detector cell incorporates a sample/hold stage to allow snapshot operation mode. These features lead to a challenging layout for the 32 micrometers pitch to be met. To optimize dynamic range, each band may be independently operated with one of three gain settings set by switchable capacitors within the unit cell. Other architectural features of the array include bi- directional scanning, externally controllable integration time and electrical test. The array dissipates less than 50 mW of power and exhibits less than 65 noise electrons at high gain setting. A 0.7 micrometers silicon technology was used. Special design techniques were employed to allow operation at 7.5 V, thereby enhancing dynamic range. IR cameras incorporating the multiplexer are currently being delivered to the customer.
A low cost MWIR thermal imaging line scanner based on a multiplexed PbSe FPA has been developed. It was designed to be mounted on the underside of UAVs to remotely map battlefields. It also has many dual-use commercial applications. The first unit has been tested in the laboratory and in roof-top imaging demonstrations. It has produced excellent imagery. The noise equivalent temperature difference has been measured to be 0.55 C in preliminary tests. An improved FPA will be installed soon in the unit which will significantly reduce the NET.
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