V. V. Belov

Atmospheric bistatic communication channels with scattering. Part 1. Methods of study

The paper considers the methods for theoretical and experimental study of bistatic optical communication schemes. A laboratory model of an optoelectronic communication system has been developed for experimental studies. Copper-vapor laser radiation at a wavelength of 510 nm was used as a source of signals. Test demonstration experiments were performed in the real atmosphere through atmospheric channels with a reflecting surface and a dense nonstationary aerosol-molecular structure. For theoretical studies, software means were developed for numerical statistical estimation of the energy and transfer characteristics of the bistatic atmospheric communication channels by the Monte Carlo method.

On the accuracy and operation speed of RTM algorithms for atmospheric correction of satellite images in the visible and UV ranges

Algorithms for retrieving the reflection coefficient of the Earth’s surface from satellite measurement data are proposed. They permit one to take into account the main components of the radiation forming the Earth’s surface image with different degrees of accuracy. The algorithms include solving the radiative transfer equation by use of the theory of linear systems, the Monte Carlo method, approximation formulas, and the image isoplanarity criterion. The algorithms were validated based on numerical experiments and comparisons with calculation results obtained by other authors.

Software Package for Reconstructing Reflective Properties of the Earth's Surface in the Visible and UV ranges

A description of a software package for reconstructing the distribution of the reflection coefficient of the Earth’s surface, as well as procedures developed for a considerable reduction of the computation time, is presented. By an example of a test region in the western coast of Africa, a comparison has been performed for results obtained by the proposed algorithm, the algorithm of homogeneous correction, and the standard MOD09 NASA algorithm. The correlation coefficients of results for this test region are as follows: between the new algorithm and homogeneity correction algorithm, 0.999; between the new algorithm and the MOD09 algorithm, 0.984.

Parallel computations for solving problems of the reconstruction of the reflection coefficient of the Earth’s surface by satellite data

The question of the application of parallel computations for solving the problem of atmospheric correction of satellite images is considered. It is shown that parallelization of algorithms of the Monte Carlo method with respect to packets of trajectories makes it possible to significantly reduce the computation time.

Atmospheric bistatic communication channels with scattering. Part 2. Field experiments in 2013

Results of field experiments on the influence of atmospheric conditions and some instrumental characteristics on the quality of information transfer in a bistatic optoelectronic communication system (OECS) operating in the visible wavelengths range are considered. The length of the atmospheric channel reached 17 km. Radiation of a copper bromide vapor laser with a wavelength of 510.6 nm was used as a signal source. It is shown that bistatic or over-the-horizon OECSs can operate both under the conditions of a cloudy and cloud-free atmosphere. Average values and standard deviations of communication errors were estimated under different atmospheric-optical conditions when some characteristics of individual instrumentation units varied.

Bistatic atmospheric optoelectronic communication systems (field experiments)

Some results of field experiments on atmospheric optoelectronic communication carried out in spring-summer-fall period in 2013 are considered. Experiments were performed to estimate the possibility of test signal transfer through bistatic communication channels extending up to 17 km under conditions of cloudless and cloudy atmospheres at radiation wavelength of 510.6 nm.

The study of the dependence of object contrast on the background of the sky on observation conditions in the UV wavelength range

We discuss the results of mathematical simulation of a field experiment on determining the contrast of an object’s image on the background of the sky in the UV wavelength range. The influence of the aerosol component of the atmosphere on this characteristic of image quality is analyzed. For experimental data, we used the field measurements carried out in the Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences. Mathematical simulation was performed by the Monte Carlo method. The model of the atmosphere was specified by a generator of optical models based on LOWTRAN-7. Comparison of the results of mathematical simulation and measurement data shows almost full coincidence in the character of the variation of the normalized contrast of the object’s image on the background of the sky depending on the optical length of the path between the object and the optical system.

Three algorithms of statistical modeling in problems of optical communication on scattered radiation and bistatic sensing

Three algorithms of the Monte Carlo method for the calculation of the pulse reaction in channels of laser sensing and communication are considered: the local estimation algorithm, double local estimation algorithm, and proposed modified double local estimation algorithm. Results of testing the algorithms and their comparison are shown. For the case of a homogeneous medium, the performances of the algorithms are compared. The comparison shows conditions for which the proposed algorithm has the advantage over the double local estimation algorithm. The contribution of double, triple, and higher multiplicity scattering is estimated. The high contribution of multiple scattering justifies the applicability of the Monte Carlo method for solving such problems.

t-, Shower-Curtain, or Tracing-Paper Effect?

The dependence of the quality of object imaging through a localized scattering layer is interpreted. It is shown that this dependence is determined not only by the optical characteristics of the medium but also by the brightness structure of the objects and by the presence (or absence) of an external illumination source.

Observation of the Earth’s surface from the space through a gap in a cloud field

For purposes of atmospheric correction of satellite images, the problem of estimating the distance from the cloud gap center at which the effect from cloudiness on the satellite image can be neglected is posed. The Monte Carlo method with the backward simulation scheme is used. The value for the radius of the gap in continuous cloudiness at which the influence of clouds changes the received radiation intensity by 10% has been obtained. Dependences of the received intensity on the gap radius have been obtained and explained.