M. Münzberg

Shortwave infrared camera with extended spectral sensitivity

The shortwave infrared spectral range (SWIR) has certain advantages for the observation during day under fog and haze weather conditions. Due to the longer wavelength compared to the visible spectrum the range performances in the SWIR is here considerably extended. In addition cooled SWIR focal plane arrays reach in the meantime sensitivities to be useable for night viewing under twilight or moon light conditions. The presented SWIR camera system combines the color imaging in the visible spectrum with the imaging in the SWIR spectrum. The 20x zoom optics is fully corrected between 440 nm and 1700 nm. A dichroic beam splitter projects the visible spectrum on a color chip with HDTV resolution and the SWIR spectrum on a 640x512 InGaAs focal plane array. The open architecture of the camera system allows the use of different SWIR sensors and CMOS sensors. A universal designed interface electronic operates the used cameras and provides standard video outputs and compressed video streams on an ethernet interface. The camera system is designed to be integrated in various stabilized platforms. The camera concept is described and the comparison with pure SWIR or combined SWIR / MWIR dual band cameras are discussed from an application and system point of view.

The infrared-based early warning system for bird strike prevention at Frankfurt airport

Flocks of migratory birds are very often using geographic structures like rivers, valleys or coast lines for orientation. Wherever the preferred migration routes are crossing the approach corridor of an airport there is an increased risk of bird strike. Flocks of birds crossing the runway corridor of the new runway Northwest of the Frankfurt airport are kept under surveillance now with in total three watch towers located at the river Main which in this case is the preferred used line of orientation. Each of the watch towers carries an early warning system which consists of two pairs of stereoscopic thermal imaging cameras sensitive in the mid wavelength infrared range (3 - 5 μm). A stereoscopic pair measures the swarm size, direction of flight and velocity in real time and with high accuracy. From these results an early warning is derived under all relevant weather conditions. The fixed focus thermal imaging cameras are thermally compensated and designed for ultra low image distortion. Each stereoscopic pair is aligned in the sub-pixel range and is controlled by a reference beam to ensure that the alignment is preserved under all environmental conditions and over a very long time. The technical concept is discussed and the design of the realized warning system at the Frankfurt airport is presented.

Compact multispectral continuous zoom camera for color and SWIR vision with integrated laser range finder

In an electro-optical sensor suite for long range surveillance tasks the optics for the visible (450nm – 700nm) and the SWIR spectral wavelength range (900nm – 1700 nm) are combined with the receiver optics of an integrated laser range finder (LRF) .The incoming signal from the observed scene and the returned laser pulse are collected within the common entrance aperture of the optics. The common front part of the optics is a broadband corrected lens design from 450 – 1700nm wavelength range. The visible spectrum is split up by a dichroic beam splitter and focused on a HDTV CMOS camera. The returned laser pulse is spatially separated from the scene signal by a special prism and focused on the laser receiver diode of the integrated LRF. The achromatic lens design has a zoom factor 14 and F#2.6 in the visible path. In the SWIR path the F-number is adapted to the corresponding chip dimensions . The alignment of the LRF with respect to the SWIR camera line of sight can be controlled by adjustable integrated wedges. The two images in the visible and the SWIR spectral range match in focus and field of view (FOV) over the full zoom range between 2° and 22° HFOV. The SWIR camera has a resolution of 640×512 pixels. The HDTV camera provides a resolution of 1920×1080. The design and the performance parameters of the multispectral sensor suite is discussed.

Characterization of SWIR cameras by MRC measurements

Cameras for the SWIR wavelength range are becoming more and more important because of the better observation range for day-light operation under adverse weather conditions (haze, fog, rain). In order to choose the best suitable SWIR camera or to qualify a camera for a given application, characterization of the camera by means of the Minimum Resolvable Contrast MRC concept is favorable as the MRC comprises all relevant properties of the instrument. With the MRC known for a given camera device the achievable observation range can be calculated for every combination of target size, illumination level or weather conditions. MRC measurements in the SWIR wavelength band can be performed widely along the guidelines of the MRC measurements of a visual camera. Typically measurements are performed with a set of resolution targets (e.g. USAF 1951 target) manufactured with different contrast values from 50% down to less than 1%. For a given illumination level the achievable spatial resolution is then measured for each target. The resulting curve is showing the minimum contrast that is necessary to resolve the structure of a target as a function of spatial frequency. To perform MRC measurements for SWIR cameras at first the irradiation parameters have to be given in radiometric instead of photometric units which are limited in their use to the visible range. In order to do so, SWIR illumination levels for typical daylight and twilight conditions have to be defined. At second, a radiation source is necessary with appropriate emission in the SWIR range (e.g. incandescent lamp) and the irradiance has to be measured in W/m2 instead of Lux = Lumen/m2. At third, the contrast values of the targets have to be calibrated newly for the SWIR range because they typically differ from the values determined for the visual range. Measured MRC values of three cameras are compared to the specified performance data of the devices and the results of a multi-band in-house designed Vis-SWIR camera system are discussed.

The new megapixel thermal imager family

For long ranging imaging in high performing electro-optical systems visible cameras with HDTV resolution (1920x1080) are becoming the standard sensor for observation purposes during day. During night and for thermal imaging, significant reduced resolution has to be accepted over a long period of time due to non-availability of adequate infrared detectors. In the meantime standard detectors with 1280x1024 are available on the market which provide at least SXGA resolution. ATTICA M is the newest member of Carl Zeiss Optronics ATTICA family of cooled thermal imagers, which uses an infrared detector with 1280x1024 pixels. ATTICA M can operate with a variety of infrared detectors either based on InSb or MCT as a detector material. ATTICA M is form and fit to the well known ATTICA Z and ATTICA P which is integrated in several military platforms in series production and can consequently be used to upgrade the related platforms. In detail three variants with different zoom optics covering the field of view range between 1,4° - 30° are available for a large scope of applications, on land, on the sea or in the air. A newly developed video electronic is capable to operate the Megapixel detector as well as future dual band thermal imager detectors as soon as they are available on the market. The features and options are discussed as well as the performances compared to the current thermal imager generation.

Unified characterization of imaging sensors from visible through longwave IR

Modern reconnaissance strategies are based on gathering information from sensors that operate in several spectral bands. Besides the well-known atmospheric windows at the visible (VIS), medium-wave IR, and longwave-IR (LWIR) wavelengths, today’s detectors can also operate in the 1–1.7 m window known as shortwave IR (SWIR). SWIR cameras are especially useful in the hazy or misty atmospheric conditions typical of a maritime environment. For optimum application of SWIR cameras, as well as detectors in other bands, it would be useful to have a single, uniform method of characterizing the various sensors. One way to provide such characterization is to use minimum resolvable contrast (MRC) measurements. MRC is a measure of a system’s sensitivity and its ability to resolve data. It was pioneered by John Johnson in the late 1950s when he first described the probability of detecting an object as dependent on the object’s effective resolution.1 This intuitive idea showed that the probability of locating a target increases with the number of resolvable cycles across that target. Johnson’s analysis was initially used to assist the design of image intensifier tubes, which increase the intensity of light in optical systems where there is limited light available. Later—with the growing importance of day sight (surveillance) cameras—Johnson’s work was revived by developers who used MRC measurements to assess electrooptical systems. SWIR imaging makes use of the radiation reflected by observed objects in the same way that visible imaging does. It is therefore possible to use MRC methods to characterize SWIR imaging.2 We have employed MRC measurements to determine the ability of a camera system to resolve detail contrast in the visible Figure 1. Setup used for measuring minimum resolvable contrast (MRC).3 The targets are mounted in front of a light source with specified luminance. The outcoming light is collimated by a parabolic mirror and directed into the aperture of the camera under test. The camera is fixed on a rotatable arm to allow measurements under different angles of incidence.

Thermal imagers: from ancient analog video output to state-of-the-art video streaming

The video output of thermal imagers stayed constant over almost two decades. When the famous Common Modules were employed a thermal image at first was presented to the observer in the eye piece only. In the early 1990s TV cameras were attached and the standard output was CCIR. In the civil camera market output standards changed to digital formats a decade ago with digital video streaming being nowadays state-of-the-art. The reasons why the output technique in the thermal world stayed unchanged over such a long time are: the very conservative view of the military community, long planning and turn-around times of programs and a slower growth of pixel number of TIs in comparison to consumer cameras. With megapixel detectors the CCIR output format is not sufficient any longer. The paper discusses the state-of-the-art compression and streaming solutions for TIs.

A modular packaging approach for upgrading tanks with staring thermal imagers

The thermal imager ATTICA was designed to fit into the thermal sights of the new German Infantry tank PUMA. The flexible approach for the optical concept, using different folding mirrors allows meeting the different available space requirements for thermal sights also of other tanks like the main battle tank Leopard 2 and the infantry fighting vehicle Marder. These tanks are going to be upgraded. The flexible concepts of the thermal imager optics as well as the mechanical packing solutions for the different space volumes of the commander and gunner sights of the vehicles are discussed.

Stereoscopic uncooled thermal imaging with autostereoscopic 3D flat-screen display in military driving enhancement systems

Thermal cameras are widely used in driver vision enhancement systems. However, in pathless terrain, driving becomes challenging without having a stereoscopic perception. Stereoscopic imaging is a well-known technique already for a long time with understood physical and physiological parameters. Recently, a commercial hype has been observed, especially in display techniques. The commercial market is already flooded with systems based on goggle-aided 3D-viewing techniques. However, their use is limited for military applications since goggles are not accepted by military users for several reasons. The proposed uncooled thermal imaging stereoscopic camera with a geometrical resolution of 640x480 pixel perfectly fits to the autostereoscopic display with a 1280x768 pixels. An eye tracker detects the position of the observers eyes and computes the pixel positions for the left and the right eye. The pixels of the flat panel are located directly behind a slanted lenticular screen and the computed thermal images are projected into the left and the right eye of the observer. This allows a stereoscopic perception of the thermal image without any viewing aids. The complete system including camera and display is ruggedized. The paper discusses the interface and performance requirements for the thermal imager as well as for the display.

A night sight clip on module based on uncooled infrared detector technology as one part of a modular equipment for the well-armed soldier

The night sight clip on module based on uncooled infrared detector technology was designed around an infrared camera module. This camera module uses an uncooled 640 x 480 detector and has a highly integrated electronic. The night sight clip on module has a magnification of exactly one and a precisely pre-aligned line of sight with respect input to output. The module is designed to be used in front of a standard day sight telescopic aiming optic on an assault rifle. The sophisticated optical design of the clip on module eliminates the need of a realignment of the day sight optic when the module is placed in front of it. Also there is no need for a precise placement or angular alignment of the module in front of the day sight aiming telescope. The signal of the IR camera is displayed on a small monitor. This picture is then collimated to infinity and used as the input for the daysight telescope. The rifleman sees in the eyepiece of his telescopic daysight an infrared image of the scene. The magnification is done by the setting of his telescope. The aiming reticle is still the one from the day scope. The optical design of the night sight clip on module and the electronic block diagram will be presented.