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.
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.
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.
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.
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.