There is a growing interest in developing helmet-mounted digital imaging systems (HMDIS) for integration into military aircraft cockpits. This interest stems from the multiple advantages of digital vs. analog imaging such as image fusion from multiple sensors, data processing to enhance the image contrast, superposition of non-imaging data over the image, and sending images to remote location for analysis. There are several properties an HMDIS must have in order to aid the pilot during night operations. In addition to the resolution, image refresh rate, dynamic range, and sensor uniformity over the entire Focal Plane Array (FPA); the imaging system must have the sensitivity to detect the limited night light available filtered through cockpit transparencies. Digital sensor sensitivity is generally measured monochromatically using a laser with a wavelength near the peak detector quantum efficiency, and is generally reported as either the Noise Equivalent Power (NEP) or Noise Equivalent Irradiance (NEI). This paper proposes a test system that measures NEI of Short-Wave Infrared (SWIR) digital imaging systems using a broadband source that simulates the night spectrum. This method has a few advantages over a monochromatic method. Namely, the test conditions provide spectrum closer to what is experienced by the end-user, and the resulting NEI may be compared directly to modeled night glow irradiance calculation. This comparison may be used to assess the Technology Readiness Level of the imaging system for the application. The test system is being developed under a Cooperative Research and Development Agreement (CRADA) with the Air Force Research Laboratory.
This paper describes test equipment and methods used to characterize short-wave infrared (SWIR) digital imaging systems. The test equipment was developed under the Air Force Research Laboratory (AFRL) contract Advanced Night Vision Imaging System – Cockpit Integration. The test equipment measures relative spectral responsivity, noise equivalent irradiance, dynamic range, linearity, dark noise, image uniformity, and captures image artifacts.
Night Vision Imaging Systems technology is advancing at a rapid pace. These advances can be broadly divided in two
distinct categories; performance and data management. There is an encouraging trend towards higher sensitivity, better
resolution, and lower power consuming devices. These improvements, coupled with the shift from analog to digital data
output, promise to provide a powerful night vision device. Given a digital system, the data can be managed to enhance
the pilot’s view (image processing), overlay data from multiple sensors (image fusion), and send data to remote locations
for analysis (image sharing).
The US Air Force Research Laboratory (AFRL) has an active program to introduce a helmet mounted digital imaging
system that extends the detection range from the near infrared (NIR) band to the short-wave infrared (SWIR) band.
Aside from the digital output, part of the motivation to develop a SWIR imaging system includes the desire to exploit the
SWIR ambient night glow spectrum, see through some levels of fog and haze, and use a robust sensor technology
suitable for 24 hours per day imaging.
Integrating this advanced SWIR imaging system into a cockpit presents some human factor issues. Light emitted from
illuminated instruments may hinder the performance of the imaging system, reducing the pilot’s ability to detect lowvisible
objects at night. The transmission of light through cockpit transparencies and through the atmosphere may also
impact performance. In this paper we propose a model that establishes cockpit lighting SWIR radiance limits, much like
MIL-STD-3009 specifies NVIS radiance limits for NVGs. This model is the culmination of a two year program
sponsored by AFRL.
Night vision technology has experienced significant advances in the last two decades. Night vision goggles
(NVGs) based on gallium arsenide (GaAs) continues to raise the bar for alternative technologies.
Resolution, gain, sensitivity have all improved; the image quality through these devices is nothing less than
incredible. Panoramic NVGs and enhanced NVGs are examples of recent advances that increase the
warfighter capabilities. Even with these advances, alternative night vision devices such as solid-state
indium gallium arsenide (InGaAs) focal plane arrays are under development for helmet-mounted imaging
systems. The InGaAs imaging system offers advantages over the existing NVGs. Two key advantages are;
(1) the new system produces digital image data, and (2) the new system is sensitive to energy in the shortwave
infrared (SWIR) spectrum. While it is tempting to contrast the performance of these digital systems
to the existing NVGs, the advantage of different spectral detection bands leads to the conclusion that the
technologies are less competitive and more synergistic. It is likely, by the end of the decade, pilots within a
cockpit will use multi-band devices. As such, flight decks will need to be compatible with both NVGs and
SWIR imaging systems.
Insertion of NVGs in aircraft during the late 70's and early 80's resulted in many "lessons learned"
concerning instrument compatibility with NVGs. These "lessons learned" ultimately resulted in
specifications such as MIL-L-85762A and MIL-STD-3009. These specifications are now used throughout
industry to produce NVG-compatible illuminated instruments and displays for both military and civilian
applications. Inserting a SWIR imaging device in a cockpit will require similar consideration. A project
evaluating flight deck instrument compatibility with SWIR devices is currently ongoing; aspects of this
evaluation are described in this paper. This project is sponsored by the Air Force Research Laboratory
The Aerospace and Defense display industry is in the midst of converting light the sources used in AMLCD backlighting
technology from fluorescent lamps to LEDs. Although challenging, the fluorescent backlighting technology delivered
good product in high end applications. LEDs, however, have the promise of even greater efficiency and lower cost. The
history of LED backlighting is short and very dynamic; expectations are high and promises are many. It appears that for
engineers developing backlights for high performance displays life has not become easier with the change of the
technology. This paper will discuss just one of many challenges engineer's face: operation of LED backlights in high
temperature environments. It will present experimental data showing several advantages of the RGB LED technology
over other lamp technologies for high performance commercial and military application.
A `slow scan' CCD camera has been adapted for luminance and radiance measurement of displays used in night vision goggle (NVG) compatible aircraft. A video lightmeter offers several advantages compared to conventional test methods including high speed image capture and color coding of the digital image data. The color coding feature facilitates evaluation of the test display uniformity. Numerical values for luminance and infrared radiance are also extracted from the image data.