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It is shown that the a priori data on the atmospheric conditions, in addition to the climate’s characteristics, can enhance the efficiency of the algorithms for reconstructing the atmospheric profiles using satellite microwave radiometric observations. Such additional data are sought and their efficiency in remote sensing is estimated. The possibility of expanding the statistical approach by including new types of a priori data on the temperature and humidity of atmospheric conditions is discussed. It is demonstrated that the developed technique can be used to estimate the efficiency of using the following types of additional a priori data in the statistical regularization method: (i) the covariance matrix of the full vector of temperature and humidity variations within a vertical atmospheric column, (ii) the covariance matrix of the temperature and humidity variations within horizontal atmospheric strata, (iii) physical limits of the humidity variation amplitude, and (iv) statistically average model representations of the microwave radiation transfer parameters in the cloud layer.

Specific features of radio reflection of coniferous forest in decimeter- and meter-wavelength ranges are considered. The study is stimulated by the upcoming (in five-to-seven years) spaceborne experiments using synthetic-aperture radars (SARs) working in the P-band (430 MHz), which is important for sounding of forests. Experimental results on the reflection characteristics of pine forests obtained with the aid of multifrequency polarimetric SAR are presented. Reflection from forests is simulated for the meter-wavelength range for horizontal (HH) and vertical (VV) polarizations. It is shown that different effects may determine reflection of meter-wavelength waves with HH and VV polarizations. New results on specific features of airborne and spaceborne radar images (RIs) of forests in the L, P, and VHF bands are obtained. Typical features of the RIs of coniferous forests are revealed. Such features are difficult to interpret and need to be further studied using RI analysis and results of simultaneous measurements of soil and forest parameters. Several examples show that RI interpretations may cause doubts concerning the correctness.

The features of the influence of the Earth ionosphere on the radio wave propagation at the frequencies 200—1200 MHz are considered by the bicharacteristic method. The phase incursion and refraction errors are investigated. The values of the Faraday rotation angle depending on the mutual orientation of the ray trajectories and the vector of the intensity of the external magnetic field are estimated.

A study of the change in the polarization characteristics of high-frequency radio waves, caused by the influence of the Earth's ionosphere in the region of the equatorial anomaly, is carried out on the basis of the Hamilton-Lukin bicharacteristic method. The dependence of the group time of signal arrival on the coordinate of the ray exit is considered. The rate of phase change along the rays from height, phase deviation as a function of group time and horizontal coordinates, as well as differences of refraction indicators of ordinary and unusual wave as the function of height along the rays are investigated. The angle of Faraday rotation in the meridian direction at the receiving point is calculated taking into account the change in the magnitude and orientation of the magnetic field and the influence of the equatorial anomaly of the ionosphere and its surroundings. The calculations are made for three frequencies: 336 MHz, 436 MHz and 536 MHz

Large data bank of images has been accumulated during atmospheric cloudinessground-based observations from 2017 to 2020 near Fryazino city, Moscow Region. The problemof obtained images classification into several types is considered. The types are clear sky (noclouds); cumulus cloudiness of various extent (humilis, mediocris, congestus); very powerfulclouds such as cumulonimbus or nimbostratus; stratus cloud cover; stratocumulus clouds; lightand high-positioned clouds (altocumulus, cirrus, cirrostratus and cirrocumulus). A qualitativeanalysis of the key features of gray, blue, green and red level co-occurrence matrices for variouspixel distances and directions (angles) is performed to solve the problem. An image classification algorithm based on these and other key features retrieved during image preprocessingis developed. The quality evaluation is performed. The developed software tool is currentlysuccessfully used for atmospheric radiometry problems support.

Planck’s model for random discontinuous cloud fields generation in a three-dimensional computational domain is considered. An algorithm has been developed for computation a 2D picture of downwelling microwave radiation brightness temperature distribution from altitude profiles of the main meteorological parameters, including liquid water profile obtained during the generation of cloud field. The inverse problem of integral moisture content parameters distribution retrieval by means of dual-frequency method is solved. Systematic errors in the cloud liquid water content estimation associated with the use of a homogeneous flat-layered model of the cloud field, which ignores its real, inhomogeneous structure, are investigated.

An analysis of polarimetric synthetic aperture radar (SAR) space observations usage for measuring Faraday rotation angle of plane-polarized electromagnetic radiation on the satellite-Earth-satellite route and calibrating the radar is performed. It is shown that technical characteristics of SAR, the radar movement during the survey and features of electromagnetic waves reflection from the rough Earth’s surface, as well as small-scale ionospheric inhomogeneities affect the results of comparison the radar images at HV and VH cross-polarizations. As a result, there is a problem of SAR signal polarization plane Faraday rotation angle measuring accuracy, which is needed for proper calibration of linearly polarized polarimetric long-wave band SAR using methods proposed by soviet and foreign specialists. Currently, there are no studies of Earth’s surfaces reflection properties carried out by means of space-based long-wave band polarimetric synthesized aperture radars at HV and VH polarizations. At the same time, the authors are not aware of any works, in which the reciprocity principle of cross-polarized HV and VH radar images is analyzed. An attempt to use aircraft P-band radar images at HV and VH polarizations for studying the reciprocity principle is performed in this work.

A web portal that provides a wide range of tools for convenient interaction with microwave radiometric measurements data of atmospheric descending radiation in the band of resonant water vapor absorption (22.235 ± 4 GHz) has been developed. The measurements were carried out via special 47-channel spectral radiometer from a ground-based observation point located in Fryazino, Moscow Region. The portal represents a server application that allows to obtain RAW data of the measurements, perform primary digital data processing (including external calibration using specified parameters), obtain processed data in CSV files and compute necessary data metrics, for instance spatial-temporal structural function values. Algorithms for determination of total water vapor mass and integral liquid water content in clouds are implemented.

Additional a priori and/or supplementary information on the state of the atmosphere potentially improves the efficiency of retrieval algorithms in comparison to the usage of mean climatic statistics of the atmosphere. Exploration and evaluation of the efficiency of the application of such additional information is the main point of this work. To achieve this goal, this work investigates the statistical approach expansion by including new types of a priori information about the temperaturehumidity state of the atmosphere. The developed methodology introduces an efficiency measure that allows the estimation of the efficiency of the following a priori information types for atmospheric profile retrieval from satellite MW data processing: 1) covariance matrices of the full vector temperature-humidity state of the atmosphere along a vertical profile, 2) covariance matrices of atmosphere variations along the atmospheres horizontal layer, and 3) physical limits of humidity profile variations. The results of atmospheric profile retrieval, based on the Levenberg-Marquardt algorithm, confirm the possibility of using this approach to restore atmospheric parameters in real time, i.e. for times shorter than the correlation intervals in the atmosphere.

Using the bicharacteristics method, mathematical modeling of the polarization parameters of P-band radio waves in the Earth’s ionosphere in the vicinity of the equatorial anomaly along the meridian path was carried out. The influence of the ionosphere on the phase deviation and the angle of the Faraday rotation during the passage of the spacecraft is studied taking into account changes in the magnitude and orientation of the Earth’s magnetic field.

Nowadays the importance of using synthetic aperture radar (SAR) in the P and VHF bands for object recognition, as well as for surface and subsurface sensing of the Earth’s surface has been proven. However, the space experiment using P-band SAR has not yet been implemented. One of the most important reasons for this is destructive influence of the ionosphere on the quality of synthesized images. It is expected that the polarimetric radar survey of the Earth’s surface in the years to come will be provided by two spacecraft – ”BIOMASS” and ”ISS-SAR(P) (International space station-SAR(P)”, operating at frequencies ∼435 MHz. Variety of phenomena related to radio wave propagation through the ionosphere, as well as the temporal and spatial inhomogeneities of its properties, has been the subject of research for many decades. In the case of the use of SAR of P and VHF bands for remote sensing of the Earth (ERS), the situation is aggravated by the fact that various processes in the ionosphere begin to concentrate, that reduces the unique properties of the performance of these devices to a minimum. As a result, a number of provisions concerning the application of the SAR of P and VHF bands for remote sensing require clarification and additional studies of the ionospheric influence on electromagnetic radiation passing the ”Satellite – Earth – reflection from the Earth’s surface – Satellite” route. Such studies can be carried out directly in the course of the space experiment (SE) by creating specialized ground test sites, equipment of which works according to the program coordinated with the operation of SAR. The ISS-SAR(P) experiment in the area of a ground-based test site should primarily be considered as the development of methods for additional ionosphere research, and also as an improvement in methods for compensating the influence of the ionosphere on radar images.

Possibilities of utilization of two frequencies synthetic aperture radar (SAR) operating simultaneously in P-band and S or L-band are considered. Advantages of such system are shown. They are caused by improvement of data interpretation and by decrease of ionosphere influence. Tasks of surface and subsurface sensing by the complex SAR were under investigation for vegetation, soil covers are given. As an example, the investigation results of coniferous forest areas backscattering by the spaceborne P-band SAR together with L-band SAR in the September-February period are presented. Studies have shown that the joint use of the results in L and P bands offer unique opportunities to explore the effects of changes in the backscattering properties of forest surfaces.

A method for calculating the angle of Faraday rotation of the polarization plane in the ionosphere is developed for P-band synthetic-aperture radars. In combination with the methods for processing of radar signals, this approach allows elimination of the ambiguity of this angle. The method uses the model of the geomagnetic field based on expansion into spherical harmonics. It is shown that the use of the conventional dipole model in the vicinity of geomagnetic anomalies may result in substantial errors.

Synthetic aperture radar (SAR) is a widely used technique suited for real-time and all-weather imaging of natural surfaces and artificial objects. To improve image resolution and increase accuracy of estimation parameters the problem of statistical synthesis of signal processing algorithm in SAR is solved. Proposed method allows to form images with super-resolution in azimuth and range. Synthesis is performed using modern theory of radio engineering systems statistical optimization.

The problem of statictical synthesis of correlated spatio-temporal signal processing algorithm (at the output of M-element antenna array) in an analytical form is solved by the developed mathematical apparatus of integral V-transformation that allows to remove the limitation on the synthesis of UWB spatio-temporal signal. More specifically the algorithm of optimal signal processing at the output of M-element antenna array is derived in the analytical form. It allows to analyze the quality of estimations obtained according to this algorithm and to give physical interpretation of radiometric images formed at the output of UWB complexes. The structural scheme of UWB complex with variable antennas quantity is developed in the simulation environment. The ambiguity functions of such complexes calculated for certain fixed antenna array geometries are studied.

Measurements were made with use of microwave radiometer-spectrometer P22M working in the range of 18–27.2 GHz with a spectral resolution of 200 MHz. Experimental results were compared with model calculations. Along with general correspondents of experimental and model results, there are some mismatches in the details. Variability of spectral characteristics of radiation is analyzed on a series of measurements obtained under different weather conditions: clear sky, clouds and the initial stage of precipitation. Such measurement may be useful for development of new techniques in vertical atmospheric profiles retrieval.

Using the concept of the search for the optimal signal parameter estimates and related to them parameters of electromagnetic and regression models of scattering and radio-thermal radiation of electromagnetic waves by various objects and natural medias on the basis of modern theory of statistical decisions and estimates of probability distribution parameters, a number of fundamental results developing the theory and methods of optimal spatio-temporal signal processing are obtained for the first time. Corresponding directions of their practical application in active, passive, and combined (complex) active-passive radar and remote-sensing radio systems are considered. Special attention is given to application of Kravchenko weight functions (windows) in problems of radio engineering systems synthesis.

Deviations of the astronomic radio refraction from average values are calculated as functions of the real elevation angle of a radiation source. The deviations are related with various irregularities of the air refractive index.

Existing methods for calculating the microwave-radiation characteristics of the ocean surface using the Kirchhoff method are considered. The practice of application of the empirical dependences typical for developed sea waves is analyzed. A joint analysis of wave-graphic and radiometric data of an early experiment on bistatic sensing of the sea surface in which the Sun was used as a powerful natural source of sensing microwave radiation is made. The existing method for theoretical calculations is improved. It is demonstrated that, while the improvement is evident, the method of calculation based on the assumption that the sea waves are developed can provide a high accuracy at most in 20% of all possible cases.

A review of modern optimal and quasi-optimal algorithms for radiometric signal processing, which provide images with a high spatial resolution is given. It is shown that the high resolution is achieved with ultra-wideband or multi-band time or space-time signal processing. Analytical expressions for the limiting error of image estimation, ambiguity functions and potential fluctuation sensitivity of systems designed according to the algorithms are derived.

A two-fraction model that makes it possible to calculate analytically the complex dielectric permittivity of ice in the far infrared and submillimeter wavelength ranges is proposed. The librational and vibrational fractions are considered. The first fraction, consisting of rigid dipoles executing anharmonic reorientations in defects of the structure, gives rise to the librational band of ice at 800 cm−1. The second fraction consists of elastically vibrating oppositely charged H-bonded molecules. This fraction describes two bands of ice in the range 100–300 cm−1, and the nonresonant background of dielectric losses in the submillimeter wavelength range. The dielectric permittivity spectra of ice calculated for the temperature of −7°C are consistent with the experimental spectra. The spectra of ice at the temperature −30°C are predicted.

Stages in the development of radar astronomy and the main methods and scientific results obtained at the Institute of Radio Technology and Electronics (IRE) beginning in the 1960s are discussed. The fundamental importance for manned space flight of the radical improvement in the accuracy of the astronomical unit achieved using radar measurements of planets is underscored, together with other important results of studies of planetary surfaces. Studies of the atmosphere and surface of the Earth using radio-astronomy methods are described in detail, including satellite techniques. The results of radio-physical studies of the ionospheres of the Moon and planets carried out by analysing signals transmitted by spacecraft and received on the Earth are also presented.

The use of hydrological (surface wind and sea wave slope) dependencies for calculation of microwave characteristics of the ldquoocean-atmosphererdquo system by Kirchhoff method is discussed here. As an important example, we review results of our experiment on bistatic sensing of the sea surface. In this experiment Sun is a powerful natural source of noise microwave radiation for the sea surface sensing. For the receiving of solar radiation in the region of quasi-specular scattering three two-polarization radiometers (0.8, 2.25 and 6.0 cm) were used. The results of joint hydrological and radiometric experiments are reported.

The utilization of hydrological (surface wind and sea wave slope) dependencies in radio physical calculations is discussed. An account is given of the results of joint hydrological and radiometric experiments. A quantitative model for microwave (3-50 GHz band) calculations in remote sensing of the "ocean-atmosphere" system is presented.

The basic principles of space-borne two dimensional synthetic aperture microwave polarimetric interferometer function are considered. The main advantages of these systems over the well-known systems ESMR, SMMR and SSM/I are: a high rate of the observation scene image construction; the finite angular resolution; besides, they have no movable onboard construction elements on the spacecraft board, like the scanning antenna, and etc. The advantages of the synthetic aperture systems with hexagonally sampled interferometric radiometers are discussed.

We describe the experimental procedure for measuring fluctuations in atmospheric radio emission. We present the results of measurements, beth with and without clouds, at a wavelength of 1.35 cm. The structure function for the radio-brightness temperature is observed to increase monotonically with increasing time interval (from 6 to 240 sec) and increasing angular interval (from 1 to 18~ the increase is close to a power law. Onthe basis of experimental data at a wavelength of 1.35 cm, we estimate the intensity of fluctuations in atmospheric radio emission at wavelengths between 0.6 and 10 cm on account of fluctuations in water vapor. We discuss the results which we have obtained. w 1o With incr easing r ec eiver s ens itivity, the pos s ibility of observing faint s our c es of radio emis s ion will be determined to a considerable extent by fluctuations in the antenna temperature of the radio telescope. Radio thermal emission from the atmosphere enters both the main lobe and the side lobes of the directional diagram of the antenna. The effect of this emission on the antenna temperature depends on meteorological conditions, and it becomes more serious at wavelengths shorter than 3 cm. Fluctuations in atmospheric radio emission are due to nonuniformities in meteorological parameters, such as humidity, amount of water, temperature, phase composition, etc. These nonuniformities arise from turbulent motions in the troposphere. Between 0~ and 2.0 cm, under a cloudless sky, theoretical and experimental data indicate that the major contribution to the intensity of fluctuations in atmospheric radio emission comes from pulses of humidity [1,2]. Experimental data on fluctuations in atmospheric radio emission have been given in [3-6]. These data were obtained with a receiver having a sensitivity considerably lower than that which can be achieved at the present time, and they refer mainly to measurements in cloudy weather. There are no experimental data in the literature concerning variations of fluctuations in radio-brightness temperature of a cloudless atmosphere as functions of time and angle. In the present work, we describe a procedure for measuring the variations of the fluctuations in radiobrightness temperature of the atmosphere as functions of time and angle. We present results for various weather conditions in wintertime and in summertime at a wavelength of 1.35 cm. From the experimental values of the fluctuations in radio emission from a cloudless atmosphere we estimate the effect of the fluctuations on the sensitivity of a radio telescope at wavelengths between 0.6 and 10 cm. w We used a superheterodyne modulation radiometer for the observations, with a fluctuation sensitivity of 0.16~ for a time constant of 1 sec in the output device. The temporal instability of the gain coefficient of the radiometer was 1o5-2.0% in a time of 30 min. In the summertime, the measurements were made on the RT-22 telescope of the P. N. Lebedev Physics Institute of the Academy of Sciences of the USSR. For the winter observations, we used a horn antenna to pick up the emission: the antenna had a beamwidth of 6.5 ~ at the half-power level. The antenna and the VHF unit of the radiometer were mounted on a movable platform: this permitted us to vary the zenith angle of the antenna in steps.