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An algorithm is considered for retrieving the reflection coefficients of the Earth’s surface taking into account radiation polarization. The algorithm was tested for five MODIS channels in three areas: south of Tomsk region, Moscow region, and Irkutsk region. Test points at the center of coniferous forest massifs in the summer season were used to estimate the error of the algorithm. Results from our algorithm with and without accounting for polarization, from the MOD09 algorithm, and results without atmospheric correction were compared with measurements taken as reference. The comparison shows that the average values obtained by our algorithm taking into account polarization are closer to the reference data than those obtained using the MOD09 NASA algorithm in MODIS channels 1 (0.620–0.670 μm), 3 (0.459–0.479 μm), and 4 (0.545–0.565 μm), and the difference on the same order of magnitude is observed in MODIS channel 2 (0.841–0.876 μm). In MODIS channel 8 (0.405–0.420 μm), one algorithm is preferable in some situations and the other otherwise.

The results obtained at the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, from 2010 to 2019 regarding problems on atmospheric correction of satellite images of the Earth’s surface and of optical communication based on the scattered laser radiation in the optical wavelength range in the atmosphere and under water are briefly reviewed.

The article describes the results of experiments with underwater bistatic optoelectronic communication systems with scattered laser radiation as the source of information and the valid signal. The information reception distance of up to 40 m was gained in field conditions of lake water.

The impulse response of a diffuse non-line-of-site underwater communication link at a wavelength of 0.5 μm is simulated using a modified double local estimate Monte Carlo algorithm for base distances between the source and receiver from 10 to 100 m. The power of radiation received and the maximal data rate are estimated based on the impulse response.

The simulation program by the Monte Carlo method of pulse reactions of bistatic atmospheric aerosol-gas channels of optical-electronic communication systems (OECS) is created on the basis of the modified double local estimation algorithm. It is used in a series of numerical experiments in order to evaluate statistically the transfer characteristics of these channels depending on the optical characteristics of an atmosphere plane-parallel model for wavelengths λ = 0.3, 0.5, and 0.9 μm at a meteorological visibility range SM = 10 and 50 km. The results are obtained for a set of basic distances between the light source and the light receiver up to 50 km and for the angular orientations of the optical axes of a laser radiation beam and of the receiving system in a wide range of their values. The dependences of the pulse reactions maximum values over-the-horizon channels of the OECS on the variations of these parameters are established.

Results of theoretical and experimental investigations of NLOS communication systems in the atmosphere, under water, and in mixed media based on publications of authors from China, Canada, Greece, the USA, Great Britain, Russia and other countries are discussed in the present work. The theory of radiative transfer and the linear systems theory provide the basis for theoretical research.

Results of theoretical and experimental research of NLOS (NonLine of Sight) communication systems in the atmosphere, under water, and in mixed media based on publications of authors from China, Canada, Greece, the USA, Great Britain, Russia, and other countries are discussed in the present work. The theory of radiation transfer and the linear systems theory provide the basis for theoretical research. The radiation transfer equation is solved by the Monte–Carlo method in the singlescattering approximation. It is demonstrated that approximate methods are applicable when the average scattering multiplicity in open communication channels does not exceed 1. The Monte Carlo method is used to study the influence of opticalgeometric parameters of schemes of communication channels on the probabilities of communication errors, signal/noise ratios, limiting base lengths, attenuation of informationcarrying signals, and their superposition leading to communication errors. Examples of communications in the atmosphere in the UV range at distances up to 1300 m, in the visible range up to70 km, and under water up to 20 m are given. Search for optimal methods of signal modulation, development of software and hardware complexes for numerical simulation of the transfer properties of communication channels, refinement of analytical models of impulse transfer characteristics of noncoplanar schemes of bistatic optoelectronic communication systems (OECS), and research of the effect of winddriven sea waves and processes of radiation scattering in water are planned to study the efficiency of operation of the communication systems and to expand ranges of variations of the input NLOS and OECS parameters in the experiments carried out in natural water reservoirs.

Results of laboratory experiments on studying the influence of scattering and absorbing media on the quality of object imaging with active pulsed television optoelectronic systems (OESs) are discussed. It is shown that the quality of object images in active pulsed vision systems or their frequency-contrast characteristics can be studied both by direct measurements or indirectly using Fourier transforms of test object images or derivatives of functions determined in experiments. A previously formulated theoretical statement that the image quality for objects screened by turbid media when using active pulsed OESs with backscattered noise signal selection can be higher almost by an order of magnitude than when using an OES operating with laser side illumination and constantly opened receiver has been confirmed experimentally.

Data from aircraft and satellite sensing at the ocean–land boundary in the region of the Kara Sea in October 2014 are compared, using 11 and 7 profiles, which were synchronously measured over a continental part and ocean, respectively. It was found that the satellite usually overestimates the CH4 and CO2 concentrations in the 0–8-km layer over the continental part of the Arctic region and underestimates them over the ocean. Over continent, the satellite overestimates the methane concentrations by 28 ppb in the boundary layer and by much more in the middle (182 ppb) and upper (113 ppb) troposphere. Over ocean, the satellite measurements are, on average, lower by 37 ppb in the boundary layer, by 73 ppb in the middle troposphere, and by 71 ppb in the upper troposphere. Over continent, the discrepancy in CO2 concentrations, measured with different instruments, is, on average, 18.2 ppm in the boundary layer and can vary from 3.2 to 26.5 ppm. In the middle troposphere (4 km), the average differences decrease to 10.8 ppm, with the range of differences even increasing somewhat, to 0.6–25.5 ppm. In the upper troposphere (8 km), the average difference in measurements between the instruments decreases to 2.8 ppm. The underestimation turns out to be greater in amplitude over the ocean. It is noteworthy that the comparison yielded acceptable results for CO and O3.

Previous and new results on the problems of optical communication in scattered laser radiation in the UV wavelength range, obtained at the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, are discussed. Field experiments on optoelectronic communication in night- and daytime conditions in 2017 and 2018 are presented.

The problem of taking into account the polarization effect in atmospheric correction of satellite images of the Earth’s surface in the visible wavelength range is considered. Some software for the calculation of radiation components forming satellite images has been developed with and without allowance for polarization in the approximation of a homogeneous surface. Conditions under which neglecting polarization properties of the radiation can lead to significant errors in the retrieval of reflection coefficients of lowreflecting surfaces have been obtained.

For implementation of non-line-of-sight optical communication, the wavelength from the range 200–400 nm at which the signal-to-noise ratio reaches a maximum depending on the baseline distance is estimated. The estimates are performed in the daytime, at moonlit night, and without background radiation. The results obtained allow us to recommend λ = 290 n m for the implementation of the long-range communication in the daytime and λ = 350 n m at night. For impulse response that provides the basis for estimating the communication channel quality, four algorithms of the Monte Carlo method are considered. The algorithm with modified double local estimate provides the least error for the same number of photon trajectories. UV radiation is potentially dangerous to humans, and therefore, the illuminance of the Earth’s surface is estimated under the optical axis of the source for baseline distances of 2, 10, and 100 m together with the time period of a continuous communication session safe for operators.

Results of the experimental study of the influence of turbid media (fog and smoke) on the quality of images of objects observed through the media using active pulsed optoelectronic systems (OES) operating with a permanently open receiver and with its control (in the mode of backscattered noise signal selection) are considered. It is experimentally confirmed that the quality of images of objects screened by a turbid medium in active pulsed OES with backscattered noise signal selection can be almost 10 times higher than in the case of operation with a permanently open receiver. The image quality of vision systems with controllable reception is affected not only by the optical length of the observation path but also by such parameters as the mean particle size and their scattering and absorption properties.

Results of simulations of the pulse response of an atmospheric optical communication channel on scattered radiation at wavelengths of 0.3, 0.5, and 0.9 μm are considered. The performed analysis shows that the maximum power of the received information signal at base distances of 2–3 km and less between the source and receiving system is reached at λ = 0.3 μm; for longer base distances and low turbidity of the atmosphere, λ = 0.5 μm. The highest maximum power is observed at λ = 0.5 μm under high turbidity of the atmosphere and base distances of 3–10 km. However, if the base distances are longer than 10 km, the maximum of the information signal power is reached at λ = 0.9 μm. For an example of a laser source and receiving system, using calculation results for the pulse reaction of the atmospheric communication channel at λ = 0.5 μm, we estimate the limiting base distance between the source and receiver, as well as the limiting pulse frequency which is not filtered by the communication channel.

Results of field experiments performed with bistatic optoelectronic communication systems in artificial and natural water reservoirs in 2015 are discussed. The experiments were aimed at estimation of the communication quality from the communication error probabilities and their standard deviations. Results of the experiments assume possibilities of creating optoelectronic communication systems capable of effectively operating in water and complex media (water–atmosphere and atmosphere–water, including ice interface) with communication line lengths from several tens to several hundreds of meters.

The software has been developed for thematic processing of data of Russian satellite systems. It is based on the algorithm of atmospheric correction developed by IAO SB RAS. The software allows retrieval of the reflection coefficients of the Earth’s surface with the RTM atmospheric correction algorithm in the visible and near-IR range on the assumption of a uniform surface. The software includes converters for reading and unpacking input formats of satellite data and related metadata, an atmospheric correction module, and an auxiliary module for formation of the atmospheric model. The atmospheric correction includes procedures for statistical simulation of the Earth’s surface illumination and for calculation of the spherical albedo of the atmosphere, intensity of radiation noninteracting with the surface, and intensity of radiation reflected by the surface.

Using the developed algorithm of the Monte-Carlo method with modified double local estimation, the impulse response of the link of non-line-of-site underwater communication on scattered radiation is simulated for base distances between the source and the receiver from 10 to 100 m. The quality characteristics of the communication link, including the received radiation power and the maximal repetition frequency of pulses transmitted through the communication link, are estimated based on the impulse response characteristics calculated for the transceiving system at a wavelength of 0.5 μm.

The atmospheric channel of optical non-line-of-site communication is considered. Minimal ratio of the source power to the maximal sensitivity of the receiving system is estimated at which communication is still possible.

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.

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.

The problem of allowance for polarization in statistical simulation of satellite imaging of the surface of the Earth in the optical wavelength range is considered. It is shown that the neglect of polarizing properties of radiation can lead to significant errors when retrieving the reflection coefficients of low-reflectivity surfaces.

In this paper, we present investigations of non-line-of-sight (NLOS) communication carried out in Russia and in collaboration with researchers in Israel. The theories of radiative transfer and linear systems provide the theoretical basis for this joint research, and experimental results demonstrate that maximal ranges for NLOS communication through atmospheric channels can reach hundreds of kilometers in the visible range and tens of kilometers in the ultraviolet (UV) range of the spectrum. Finally, we predict the range of bistatic underwater communication systems can reach hundreds of meters.

Previous and new results obtained at the IAO SB RAS on problems of optical communication on scattered laser radiation in the UV wavelength range are discussed in the report. Examples of implementation of optical communication in field experiments at night and in the daytime are presented.

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.

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.

Prototypes of a typical automated station for monitoring the atmospheric composition and state, as well as lidars and sodars, have been designed and manufactured within the project, which are to be the components of monitoring stations. Experimental tests of the instruments confirmed their designed-in specifications and functions. For contact measurements of air parameters, a complex air monitoring station and an aerosol multiwave diffusion spectrometer have been also designed and manufactured in accordance with technical assignment requirements. The measurement results have shown a continuous increase in the concentrations of carbon dioxide and nitrous oxide, as well as a renewed increase in the methane concentration in the layer from 0 to 7 km.

Impulse response of non-line-of-sight atmospheric communication channels at wavelengths of 0.3, 0.5, and 0.9 μm are compared for the case in which the optical axes of the receiver and laser radiation lie in the plane perpendicular to the Earth’s surface. The most efficient communication channel depending on the base distance is determined. For a wavelength of 0.5 μm and a concrete variant of the transceiving part of the communication system, the limiting communication range and the limiting repetition frequency of pulses that can be transmitted through the communication channel are estimated.

In the report a review is given and new results obtained at the IAO SB RAS on problems of optical communication on scattered laser radiation in the atmosphere and water media are presented. Examples of its implementation are presented under various optical-geometrical conditions and with high quality of field experiments at distances up to 70 km in the atmosphere and up to 25 m in the water medium.

The problem of taking into account the effect of polarization is considered for correction of satellite images of the Erath’s surface in the visible wavelength range for the distorting effect of the atmosphere. A program complex for calculation of the radiation components forming the satellite images has been developed with and without allowance for radiation polarization in the approximation of the homogeneous surface. Conditions are considered under which the neglect of polarization properties of radiation can lead to significant errors in reconstruction of the reflection coefficients of weakly reflecting surfaces.

The vertical profiles of the O3, CO, CO2 and CH4 concentrations measured onboard the Optik Tu-134 aircraft laboratory and retrieved from data obtained with an IASI Fourier transform spectrometer operating aboard a MetOp satellite (European Space Agency) have been compared. This comparison shows that absolute differences between aircraft satellite ozone concentrations may vary from 55 to 15 ppb at the land surface and within the lower boundary layer and from 30 to −15 ppb at a height of 7000 m. Their relative differences range within 60 to 30% at a height of 500 m and 30 to −35% at a height of 7000 m. Absolute differences between aircraft and satellite carbon-monoxide concentrations may vary from 80 to 2300 ppb, while their relative differences range within −140 to 98%. For methane, the mean difference is maximal within the atmospheric boundary layer (90 ppb). According to the data on all profiles, the maximum and minimum differences reach 220 and 8 ppb, respectively, within the atmospheric boundary layer. Minimum differences range from zero at the land surface to −100 ppb in the upper troposphere. For carbon dioxide, the mean difference between the results of aircraft and satellite measurements ranges from −2 to −9 ppm. In the free troposphere, at a height of more than 3000 m, this difference is almost constant and amounts to −6 ppm. Over all flights, the maximum and minimum differences between aircraft and satellite CO2 concentrations range from 14 to −4 ppm and from −7 to −16 ppm, respectively, within the atmospheric boundary layer. In this case, the maximum and minimum relative deviations over all flights amount to 3.4 and −4.2%, respectively, within the atmospheric boundary layer. These differences are significantly larger than those found earlier for the background conditions. It is necessary to improve the vertical gas distribution models used in the algorithms of satellite-data processing.

Some theoretical and experimental results related to atmospheric optoelectronic communication are considered. The experiments were carried out to evaluate the feasibility of text information transmission through bistatic communication channels based on the effects of scattering and reflection under conditions of a cloudless or cloudy atmosphere and through plumes of artificial aerosol-gaseous media.

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.

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.

Time distribution of the monostatic sodar signal intensity has been obtained in the report with allowance for the contribution of multiply scattered radiation. Dependences of the sodar signal intensity on its parameters and atmospheric meteorological conditions are analyzed.

An algorithm for reconstructing the Earth’s surface reflection coefficients from the data of MODIS satellite measurements is considered. For six channels of the MODIS device in the visible and near-IR ranges, the influence of a 10% error in the assignment of the aerosol and molecular extinction on the accuracy of reconstructing of the Earth’s surface reflection coefficients is estimated. A comparison of this error with the error of reconstructing the reflection coefficient for a surface area in the Tomsk Region by the suggested algorithm and the algorithm MOD09 is performed. Results of comparison show that the error in assignment of the input optical parameters can be the main source of the error of the correction algorithms for wavelengths 0.4–0.85 μm. For the channel centered at 1.25 μm the error of the algorithms is much greater than the error caused by a 10 % error of assignment of the optical parameters.