Dual-channel opto-electronic surveillance systems which operate in visible and infrared spectrum ranges are widespread. Their analysis and design needs suitable tools. A simplified physics-mathematical model of a dual-channel optoelectronic surveillance system was developed to determine energy resolution of the system. Noise equivalent brightness difference and noise equivalent temperature difference were used to define the ability of television and thermal imaging systems to detect objects. As an example of applying the model an algorithm of spectral channel selection depending on the conditions of surveillance was developed.
The paper deals with a design method of multi-order diffractive intraocular lenses (IOL) that we have developed in order to correct chromatic aberration. It is shown that in order to prevent a color halo around the focused image the phasematching number is selected to attend at each point of the image three color components to get quality image. A computer simulation of multi-order diffractive lens (MODL) in a schematic model of the human eye was carried out. The calculated MODL focuses white light into a segment on an optical axis with high diffractive efficiency. More research needed to study an aberration analysis of lenses of this type.
Among the various characteristics of infrared radiation, the degree of polarization is not often used in radiation analysis. The main reason is that polarization is less informative characteristic compared to others for most practical tasks. Also obtaining polarized radiation in infrared spectrum is relative complex and expensive act. In some cases, such as remote sensing, the improvement of spatial, radiometric and spectral resolution approaches it’s physical limit. It becomes relevant to obtain additional information of a different nature, such as polarization information. Modern infrared radiation polarizers based on diffraction gratings are quite expensive. The article explores the possibility of creating infrared polarizers based on a planeparallel plate, to which radiation falls at an Brewster angle. It is shown that the polarizer operating on transmittance will be more efficient than reflecting radiation polarizer, since it does not deviate the optical axis by a significant angle. Such a polarizer provides a polarization degree of 90% and a transmittance of about 50%.
In this article, the coherent optical spectrum analyzer (COSA), which consists of a spatial light modulator, a Fourier lens and a digital camera is explored. Spatial resolution (spatial spectral resolution), which is determined by the parameters of the components of the spectrum analyzer is one of the main characteristics of the COSA. The analysis of the COSA model allowed to develop a method for calculating the spatial spectral resolution taking into account the phase position of the diffraction maximums relative to the pixels of the matrix detector. When the modulator is illuminated with an inclined plane wave, the resolution of the spectrum analyzer can be doubled. The influence of modulator parameters and lens aberrations on the spectrum analyzer resolution is investigated.
Method of infrared lenses field of view step variation is discussed in this paper. Simple afocal lens caps based on the classic Kepler or Galilee telescopic schemes are considered. The afocal cap have to provide acceptable vignetting of the extreme rays and moderate transverse dimensions. Mersenne two-mirror system of Galilean-type was selected as the most suitable lens cap. Equations were obtained to calculate dimensional parameters of the cap in respect that vignetting coefficient should be minimal.
This article researches the proposed physical and mathematical model of a digital coherent optical spectrum analyzer, the spatial spectral bandwidth of which is limited by the diffraction of light on the matrix structure of the modulator. To expand the bandwidth of the spectrum analyzer, proposed to illuminate the modulator with a plane wave that incident on the modulator at a certain angle, similarly to the Leit-Upatnieks hologram. The research of the model has shown that when the modulator is illuminated with an inclined plane wave, the form of the diffraction pattern does not change, but the whole picture is shifted. To expand the operating spectral range (bandwidth), it is necessary that two diffraction maximum of the 0-th and + 1st orders incident into the entrance pupil of a Fourier lens, and when they are recorded, the entire sensitive surface of the matrix radiation detector is fully used. In this case, the operating range of the spectrum analyzer is equal to twice the Nyquist frequency of the modulator.
In recent years, a tendency is established to reduce the size of orbital spacecrafts while preserving their functional capabilities. The modern element base allows to create inexpensive Earth-sensing satellites having 1U-2U form factor, which are capable to form images of the Earth's surface with the medium spatial resolution. To perform synthesis of such optoelectronic remote sensing equipment, a relatively simple calculation technique is required. In this article, a technique has been developed to estimate an information system "Earth’s surface – atmosphere – television camera". It allows to determine the basic parameters of a lens and a matrix detector of the television camera, based on harmonization of their resolution and providing a given spatial resolution on the surface of the Earth. By using the proposed technique, a lens and a matrix detector have been selected. They provide geometric resolution of 25 m at the orbit with a height of 600 km. The resulting technical solution enables to fulfil applied tasks, for example, in agriculture, and can be implemented in a nanosatellite with the 1U-2U form factor.
In this article, we research the physic and mathematical model of a digital coherent optical spectrum analyzer, which made it possible to obtain an analytical expression for calculating the spatial spectral resolution of the spectrum analyzer depending on the parameters of the spatial light modulator, the Fourier lens, and the matrix detector. To determine the spatial resolution of the aberrational Fourier lens, it is proposed to use a criterion similar to the Rayleigh criterion. Obtained the formula for determining the dependence of the spectral resolution of the processor on the aberration parameter of the Fourier lens, the research of which showed that for small pixel sizes of the detectors the resolution is determined by the size of the modulator matrix, and for large pixels by the pixel size.
In this article, we investigate the mathematical model of a digital optoelectronic processor for the purpose of determining the signal at the processor’s output. The study of the model allows us to determine the distortions of the input signal of the processor, which are caused by the matrix spatio-temporal modulator. The developed physical and mathematical model of the processor made it possible to obtain an analytical expression for the signal at the processor’s output. Its analysis shows that the formula for determining the spatial frequency differs significantly from the traditional formula. The spatial frequency depends on positions of the central and side maxima in the first-order diffraction maximum. In this case, the signal spectrum can be determined by measuring the lateral maximum, which is located closer to the optical axis of the processor. This allows to use of smaller matrix detectors, as well as to investigate the signal spectrum beyond the Nyquist frequency of the modulator.
In this article, the limiting characteristics of a digital optoelectronic processor are explored. The limits are defined by diffraction effects and a matrix structure of the devices for input and output of optical signals. The purpose of a present research is to optimize the parameters of the processor’s components. The developed physical and mathematical model of DOEP allowed to establish the limit characteristics of the processor, restricted by diffraction effects and an array structure of the equipment for input and output of optical signals, as well as to optimize the parameters of the processor’s components. The diameter of the entrance pupil of the Fourier lens is determined by the size of SLM and the pixel size of the modulator. To determine the spectral resolution, it is offered to use a concept of an optimum phase when the resolved diffraction maxima coincide with the pixel centers of the radiation detector.
Simplified model of image forming in spaceborne linear array sensors at arbitrary sight angles is proposed in this paper. On basis of evaluation of system "lens - linear array detector" modulation transfer function (MTF), the equations were obtained that allow you to determine spatial resolution on Earth’s surface. An example of pushbroom imager’s MTF determination at sight of Nadir and with different slopes of lens optical axis is given. Image quality changes, which accompany lens optical axis angular inclination were studied. More research needed to determine the impact of lens aberrations on imager’s MTF with arbitrary viewing angles.
This article examines a systematic error that occurs in optical spectrum analyzers and is caused by Fresnel approximation. The aim of the article is to determine acceptable errors of spatial frequency measurement in signal spectrum. The systematic error of spatial frequency measurement has been investigated on the basis of a physical and mathematical model of a coherent spectrum analyzer. It occurs as a result of the transition from light propagation in free space to Fresnel diffraction. Equations used to calculate absolute and relative measurement errors depending on a diffraction angle have been obtained. It allows us to determine the limits of the spectral range according to the given relative error of the spatial frequency measurement.
Proc. SPIE. 9809, Twelfth International Conference on Correlation Optics
KEYWORDS: Thermography, Signal to noise ratio, Visual process modeling, Visualization, Spatial frequencies, Sensors, Visual system, Modulation transfer functions, Minimum resolvable temperature difference, Thermal modeling
Calculating methods, which accurately predict minimum resolvable temperature difference (MRTD), are of significant interest for many years. The article deals with improvement the accuracy of determining the thermal imaging system MRTD by elaboration the visual perception model. We suggest MRTD calculating algorithm, which is based on a reliable approximation of the human visual system modulation transfer function (MTF) proposed by N. Nill. There was obtained a new expression for the bandwidth evaluation, which is independent of angular size of the Foucault bar target.
The purpose of this article is to improve methods of calculating generalized characteristics of the coherent spectrum analyzers, which define the device’s properties and operation. These are the working range of spatial frequencies, the spatial spectral resolution and the energy resolution. Due to these methods, it is possible to choose optimal dimensions and parameters of components of the device to improve the properties of the last.
The quality of thermal image is determined by the imager’s spatial resolution, a modulation transfer function of which depends on the lens’ aberrations and the detector’s matrix structure. It is proposed to determine the spatial resolution by using the geometric noise bandwidth GNBW, which is an analogue to video signal processing electronic system’s effective noise bandwidth. A relationship is established between the spatial resolution and the bandwidth GNBW. An example is presented for calculating the angular resolution of the imager having a diffraction-limited lens and a matrix detector.