The scattering properties of materials such as coated and painted surfaces are important in the design of low observable materials. These properties are also important to enable accurate modeling of targets in a scene of different background materials. The distribution of light scatter from surfaces can be determined by measurements of the Bidirectional Reflectance Distribution Function (BRDF) using devices such as scatterometers. The BRDF should ideally be possible to measure both in and outside the plane-of-incidence in order to characterize both isotropic and anisotropic scatter and with suitably high angular resolving power and signal to noise ratio at the wavelengths of interest. Both narrow-band light sources (e.g. lasers) and broad-band light sources in combination with spectral band pass filters may be used in combination with appropriate detectors. This type of instrumentation may consist of complex mechanically moving parts and optics requiring careful alignment to the sample surface to be measured. To understand the synergies and discrepancies between the outputs of different BRDF instruments measuring the same sample set, we have compared BRDF measurement results between our research laboratories in a round robin comparison of an agreed set of sample surfaces and measurement geometries and wavelengths. In this paper, the results from this study will be presented and discussed.
As the sensor technology for polarimetric imaging is advancing into more robust commercial systems such sensors could soon be expected for, e.g., military surveillance and reconnaissance applications in addition to more conventional sensor systems. Thus, there might be an upcoming need to understand limitations on present camouflage systems to meet this new sensor threat. Some of the reasons why polarimetric imaging has drawn attention is the ability to achieve a higher contrast for artificial surfaces against natural backgrounds, by analyzing the degree of linear polarization, which in this work has been analyzed for different types of surfaces as a function of wavelength. We also compare with the polarimetric vision of horse-flies and other aquatic insects via the polarization properties of different colors of horse coat hair in order to give some further insight into polarimetric vision techniques developed by nature. In this work we have used different measurement techniques, such as angle dependent polarimetric spectral directional hemispherical reflectance and polarimetric imaging.
Polarimetric imaging sensors in the electro-optical region, already military and commercially available in both the visual and infrared, show enhanced capabilities for advanced target detection and recognition. The capabilities arise due to the ability to discriminate between man-made and natural background surfaces using the polarization information of light. In the development of materials for signature management in the visible and infrared wavelength regions, different criteria need to be met to fulfil the requirements for a good camouflage against modern sensors. In conventional camouflage design, the aimed design of the surface properties of an object is to spectrally match or adapt it to a background and thereby minimizing the contrast given by a specific threat sensor. Examples will be shown from measurements of some relevant materials and how they in different ways affect the polarimetric signature. Dimensioning properties relevant in an optical camouflage from a polarimetric perspective, such as degree of polarization, the viewing or incident angle, and amount of diffuse reflection, mainly in the infrared region, will be discussed.
In this work a spectral designed coating from SPECTROGON is evaluated. Spectral design in this case means that the coating has a reflectivity equal to one at 3-5 and 8-12 microns were sensors operate and a much lower reflectivity in the other wave length regions. Three boxes are evaluated: one metallic, one black-body and one with a spectral designed surface, all with a 15 W radiator inside the box. It is shown that the box with the spectral designed surface can combine the two good characteristics of the other boxes: low signature from the metallic box and reasonable inside temperature from the black-body box. The measurements were verified with calculations using RadThermIR.
This new security development is expected to increase interest from Northern European states in supporting the development of conceptually new stealthy ground platforms, incorporating a decade of advances in technology and experiences from stealth platforms at sea and in the air. The scope of this case study is to draw experience from where we left off. At the end of the 1990s there was growing interest in stealth for combat vehicles in Sweden. An ambitious technology demonstrator project was launched. One of the outcomes was a proposed Systems Engineering process tailored for signature management presented to SPIE in 2002.(Olsson et.al, A systems approach…, Proc. SPIE 4718 ) The process was used for the Swedish/BAE Systems Hägglunds AB development of a multirole armored platform (The Swedish acronym is SEP). Before development was completed there was a change of procurement policy in Sweden from domestic development towards Governmental Off-The-Shelf, preceded by a Swedish Armed Forces change of focus from national defense only, towards expeditionary missions. Lessons learned, of value for future development, are presented. They are deduced from interviews of key-personnel, on the procurer and industry sides respectively, and from document reviews.
In development of visual (VIS) and infrared (IR) camouflage for signature management, the aim is the design of surface properties of an object to spectrally match or adapt to a background and thereby minimizing the contrast perceived by a threatening sensor. The so called 'ladder model" relates the requirements for task measure of effectiveness with surface structure properties through the steps signature effectiveness and object signature. It is intended to link materials properties via platform signature to military utility and vice versa. Spectral design of a surface intends to give it a desired wavelength dependent optical response to fit a specific application of interest. Six evaluation criteria were stated, with the aim to aid the process to put requirement on camouflage and for evaluation. The six criteria correspond to properties such as reflectance, gloss, emissivity, and degree of polarization as well as dynamic properties, and broadband or multispectral properties. These criteria have previously been exemplified on different kinds of materials and investigated separately. Anderson and Åkerlind further point out that the six criteria rarely were considered or described all together in one and same publication previously. The specific level of requirement of the different properties must be specified individually for each specific situation and environment to minimize the contrast between target and a background. The criteria or properties are not totally independent of one another. How they are correlated is part of the theme of this paper. However, prioritization has been made due to the limit of space. Therefore all of the interconnections between the six criteria will not be considered in the work of this report. The ladder step previous to digging into the different material composition possibilities and choice of suitable materials and structures (not covered here), includes the object signature and decision of what the spectral response should be, when intended for a specific environment. The chosen spectral response should give a low detection probability (DP). How detection probability connects to image analysis tools and implementation of the six criteria is part of this work.
Thermochromic metal oxides with a Mott transition, such as vanadium dioxide (VO<sub>2</sub>) exhibit an extensive alteration in
their infrared reflectivity when heated above the transition temperature. For VO<sub>2</sub> the infrared reflectivity increases as the
material becomes more metal-like above the transition temperature at 68°C.
Given these dynamic electromagnetic properties in the IR-range, it is interesting to study the reflection of the material
also in other wavelength ranges. The microwave properties of VO<sub>2</sub> as a function of temperature have been investigated
Measurements were made with an automated network analyzer combined with an electrical heating unit.
Reflection properties of VO<sub>2</sub> in the microwave region were determined.
Above the transition temperature, an increase in the reflection of the surface was observed. The VO<sub>2</sub> became more
metal-like in the whole measured microwave frequency range, as in the infrared region.
It is concluded that VO<sub>2</sub> not only can be used to adapt the thermal emissivity of a surface but also to control the
microwave reflectivity. Possible applications are switchable radomes, switchable radarabsorbers and heat protection for
The market demand for bright laser pointers has led to the development of readily available devices that can pose a threat
to road safety. Laser pointers can be involved in accidents caused by laser users who do not realise the dangers involved,
but laser pointers can also enable deliberate criminal activity. There are technologies available that can counter the threat
in different ways. A number of protective principles are outlined below. Some technologies built upon Liquid Crystal
Devices are described in greater detail.
Without any knowledge of what laser pointers a potential aggressor has access to, a frequency agile filter seems to be the
most promising way to avoid the most severe consequences of dazzle from laser pointers. Protective systems
incorporating suitable glasses or visors holding frequency agile filters of this kind however, are not commercially
In the present work the infrared-transmission of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrensulfonat)) is
being investigated using three different kind of electrochromic devises. PEDOT:PSS is an electrochromic conducting
polymer able to change its optical properties when it is doped and undoped. The doping is achieved by a voltage applied
across the cell. The optical properties are reversible if the polarity of the voltage is changed. We report here, to our
knowledge, the first cell with adaptive transmission in the infrared wavelength range. The issue for this type of cell is
that all the layers in the device must be transmissive in the whole relevant wavelength range. The results were further
verified by construction of similar cells with different configuration giving adaptable reflectivity.