The Navy faces an ever evolving threat scenario, ranging from sub-sonic sea skimming cruise missiles to newer, unconventional threats such as that experienced by the USS Cole. Next generation naval technology development programs are developing “stealthy” ships by reducing a ships radar cross section and controlling electromagnetic emissions. To meet these threat challenges in an evolving platform environment, ONR has initiated the “Wide Aspect MWIR Array” program. In support of this program, Raytheon Vision Systems (RVS) is developing a 2560 X 512 element focal plane array, utilizing Molecular Beam Epitaxially grown HgCdTe on silicon detector technology. RVS will package this array in a sealed Dewar with a long-life cryogenic cooler, electronics, on-gimbal power conditioning and a thermal reference source. The resulting sub system will be a component in a multi camera distributed aperture situation awareness sensor, which will provide continuous surveillance of the horizon. We will report on the utilization of MWIR Molecular Beam Epitaxial HgCdTe on Silicon material for fabrication of the detector arrays. Detector arrays fabricated on HgCdTe/Si have no thermal expansion mismatch relative to the readout integrated circuits. Therefore large-area focal plane arrays (FPAs) can be developed without concern for thermal cycle reliability. In addition these devices do not require thinning or reticulation like InSb FPAs to yield the high levels of Modulation Transfer Function (MTF) required by a missile warning sensor. HgCdTe/Si wafers can be scaled up to much larger sizes than the HgCdTe/CdZnTe wafers. Four-inch-diameter HgCdTe/Si wafers are currently being produced and are significantly larger than the standard 1.7 inch x 2.6 inch HgCdTe/CdTe wafers. The use of Si substrates also enables the use of automated semiconductor fabrication equipment.
Programs in both the U.S. and Britain are attempting to apply staring array technology to the ship-board infrared search and track (SBIRST) problem. A prime objective is to speed processing time, the previous generation of 360 deg scanners having a refresh rate of only 0.5-1.0 Hz. Another objective is to enhance sensitivity using much longer integration times. An impediment, though, is that if all pixels of resolution angle ∅ were to be viewed simultaneously with dedicated detectors each of width w, the total net length of detector material would then have to be very large: 2πw/∅ = 1.57 m = 60" for 100 μRad resolution and 25 μm detectors. So the application of staring array technology to horizon surveillance needs some form of wide viewing technique involving a combination of asymmetric resolution, reduced resolution, split optics or LOS stepping. The present paper suggests that conventional NEI is not the preferred unit of measure for guiding design choices but that instead a form of BLIP S/N can be both simple and intuitive. This S/N unit of measure is used to compare the two main choices for how to adapt staring technology to the horizon surveillance problem.
The latest version of the Strategic High-Altitude Radiance Code, is now ready for distribution. It calculates atmospheric radiation and transmission for arbitrary paths between 50 and 300 km altitude. The new version contains significant upgrades which include a fully integrated auroral model with time-dependent chemistry, extension down to 50 km altitude and the important isotopes of CO2.