Space Radar Research Articles

Multi‐Layer Cloud Detection and Distributions Over the Asia–Pacific Region Based on Geostationary Satellite Imagers

AbstractA large portion of cloud scenes over the globe shows multiple layers composed of different phases, in general with ice clouds on the top and liquid water clouds beneath. Such multi‐layer (ML) clouds constitute major challenges in cloud observations and weather and climate modeling. This study improved a threshold algorithm for detecting ice‐over‐water ML clouds using geostationary satellites. Optimal thresholds were established for the spectral characteristics of the Advanced Himawari Imager (AHI) and the Advanced Geostationary Radiation Imager (AGRI), accounting for differences between land and ocean surfaces. Validation with collocated space radar and lidar measurements indicated the identification accuracies of approximately 82% over the land and 76% over the ocean. Annual distributions of ML clouds inferred by AHI and AGRI exhibited strong similarity. Furthermore, 6 years of hourly observations revealed distinct monthly and daily variations in ice‐over‐water clouds over the Asia–Pacific region. The ML cloud monthly variations were similar to those of the seasonal convection cycle, with occurrence frequencies over the typical regions higher in summer (maximum ∼27%) and lower (minimum 6%–10%) in winter. Regarding daily variations, ice‐over‐water clouds occurred more frequently around local noon over most of the six time zones (from UTC + 06 to UTC + 11) throughout all seasons. The refined spatiotemporal distribution of ML clouds, particularly the daily variations, is possible to improve our understanding of cloud vertical distributions and radiative effects, and has the potential to promote subsequent validation and parameterization of cloud overlapping in global climate modeling.

Assessment of ISRO’s S-band polarimetric Doppler Weather Radar (DWR) at SHAR with IMD-DWR and GPM-Ku radar

ABSTRACT This paper describes the first assessment of ISRO’s indigenously developed S-band Polarimetric Doppler Weather Radar (DWR) at Sriharikota High Altitude Range (SHAR), Sriharikota (13.66°N, 80.23°E). The assessment is done during the passage of a tropical cyclone ‘Phethai’ and four different cases of Mesoscale convective systems. A comparison of reflectivity measured from SHAR-DWR with India Meteorological Department (IMD) DWR located at Chennai (13.07°N, 80.28°E) and Ku-band space-borne radar of the Global Precipitation Mission (GPM) is done using the common volume matching method. A good comparison is observed between SHAR-DWR with IMD-DWR and GPM-Ku radar in both space and height. The vertical structure of the cyclone is provided using Contour Frequency by Altitude Diagrams (CFAD) which show the vertical extent up to an altitude of 16 km with a reflectivity between 25 and 30 dBZ. Maximum occurrence of 30 dBZ occurs below 6 km. Bright band signatures show ~ 25 dBZ between 4 and 5 km depicting the stratiform precipitation of the cyclone. Further rain rate is estimated using both reflectivity and the polarimetric product which compared well with rain estimated from IMD-DWR and rainfall observed from rain gauges. Rain rate is observed from 5 to 35 mm hr−1. Hydrometer classification during the passage of tropical cyclone ‘Phethai’ shows the presence of rain below 4 km and graupels, ice crystals, and large droplets above.

A priori parameter estimation of space SAR operating in the sliding spotlight scan mode and in the terrain observation mode by progressive scans

In the detailed mode of operation of the synthetic aperture radar (SAR), an improved level of geometric resolution of the terrain in a small frame is achieved. If, however, the frame length exceeds the size of the bottom trace in the azimuthal direction, then it is necessary to use a sliding spotlight operation mode (SSL), in which antenna pattern is scanned in the swath along the azimuth angle. To increase the width of the swath, ScanSAR mode is used. In the traditional implementation of this mode, image serration occurs. This effect can be eliminated by using terrain observation by progressive scans mode (TOPS)). In this mode, when shooting a frame, the antenna pattern runs quickly and alternately through all the specified partial swath bands. Despite the presence of a large number of publications in domestic and foreign literature devoted to the analysis of the main parameters of SAR operating in SSL and TOPS modes, there is a need to clarify calculation methods and increase the number of system parameters issued by them, which generally determine the basic appearance of the equipment. The purpose of the work is to clarify and detail the presentation of the methodology for a priori estimation of an increased number of parameters describing the main system characteristics of space SAR operating in SSL and TOPS. The paper develops and describes in detail a methodology with an exhaustive list of calculation ratios for a priori estimation of parameters describing the main system characteristics of space SAR operating in SSL and TOPS. Based on it, algorithms and software modules have been developed that allow you to perform calculations and display the results in a visual graphical form. Examples of computer calculations of 12 system parameters dependencies on the angle of sight of space radars operating in these two modes are given. The application of the developed methodology makes it possible to quickly perform an a priori assessment of a variety of basic system parameters of space radars operating in SSL and TOPS modes, which facilitates the selection of the most acceptable basic appearance of the equipment for practical implementation.

Digital Beamforming Features in Subaperture Antenna Arrays of Highly Informative Space Radars with Aperture Synthesis

It is shown that during digital beamforming in a subaperture antenna array of highly informative space radars with synthetic aperture, it is necessary to provide a procedure for equalizing the time delays of the subaperture output signals for transmission and reception. It has been established that losses in the signal-to-noise ratio on a radar image of a point target for a typical aperture size at an elevation angle of 0.7 m and a signal spectrum width of 600 MHz reach 2.1 and 7.5 dB for off-nadir angles of 21° and 50°, respectively. Recommendations are formulated for equalizing time delays for transmission and reception based on spectral processing. Simulation results are presented.

A generalized indicator of the efficiency of the use of the spacecraft radar to solve the remote sensing of earth problems by synthesizing the aperture. Part 1. Methodological foundations

The importance of the article is determined by the following factors: the increasing use of spacecraft radars and, at the same time, the extension of the range of tasks to be solved for remote sensing of the Earth; using a wide range of orbits for the output of remote sensing radars of the spacecraft; a large number of parameters of the remote sensing radar of the spacecraft, which determines the purposive characteristics in accordance with the tasks to be solved; conflicting requirements for parameter values when solving various remote sensing tasks. Under these conditions, the substantiation of the parameters of the onboard radar of the spacecraft, as well as any complex technical system, is impossible without a generalized indicator that takes into account heterogeneous and often contradictory requirements for their values. The methodological basis for the formation of a generalized indicator of the effectiveness of the use of space radar is to take into account the main objective characteristics of the remote sensing spacecraft, including: the area of the observed surface of the Earth per unit of time (productivity); spatial resolution along and across the path line; radiometric sensitivity, radiometric resolution. Using the specified objective characteristics and variable indicators of the degree to which each of them is built, a generalized indicator of the efficiency of the spacecraft is formed in the form of multipliers. The number of multipliers is equal to the number of objective characteristics. The first and second factors represent a weighted ratio (taking into account the corresponding exponents) of the first and second objective characteristics and determine the geometric component of the received volume of radar information. The third and fourth factors determine the possibility of radar discrimination of objects on the ground in terms of their reflectivity and represent a weighted ratio of radiometric sensitivity and radiometric resolution. On the basis of the radar equation, taking into account the relationship of the parameters of the spacecraft radar with the objective characteristics, analytical relations are obtained linking the parameters of the space radar and a generalized indicator of the effectiveness of the use of the space-based radar for remote sensing of Earth. This makes it possible to determine the requirements for the main resources of the on-board radar complex, namely, the radiated power and dimensions of the antenna system of the on-board radar.

COST-EFFICIENT METHODS OF DERIVING SLOPE INFORMATION FOR ROAD SEGMENTS IN DRIVER-ASSISTANCE APPLICATIONS

Abstract. An advanced driver-assistance system (ADAS) is any of a group of technologies that assist drivers in driving and parking functions. Through a safe human-machine interface, ADAS increase car and road safety. These Advanced driver-assistance systems rely on special maps with extended geometry and attribute information. This extra information includes slope, curvature, and speed limit. ADAS-enabled maps are usually rather expensive in the industry. This paper is focused on finding cost-efficient alternatives for generating the slope aspect of ADAS maps. Slope and height information is not only used in ADAS but is a critical aspect of calculating electronic vehicle (EV) ranges, and truck fuel-efficiency calculations as well. ADAS slope information usually requires high-accuracy surveys. This paper researches the possible generation of slope information for road segments with the use of digital elevation models (DEM) or crowdsourcing with low-cost sensors and Kalman filtering. The first approach is based on globally available DEMs with interpolation and filtering with road geometry. DEMs have variable accuracy depending on the type of technology used in producing them. Such technologies include photogrammetry, aerial and terrestrial laser scanning (ALS, TLS), or aerial or space radar measurements. The other method is by using low-cost GPS and IMU sensors for generating altitude profiles. These produced altitude profiles are compared with a profile generated from a high-accuracy survey using large-resolution DEMs produced by aerial photogrammetry or aerial laser scanning. This paper proposes metrics with which these datasets can be compared, one is using the height differences, and the other compares the slope values at discrete common points. In the conclusion, the paper tries to find use cases for the low-accuracy data.

Imaging of the internal structure of an asteroid analogue from quasi-monostatic microwave measurement data

Context.The internal structure of small Solar System bodies (SSSBs) is still poorly understood, although it can provide important information about the formation process of asteroids and comets. Space radars can provide direct observations of this structure.Aims.In this study, we investigate the possibility to infer the internal structure with a simple and fast inversion procedure applied to radar measurements. We consider a quasi-monostatic configuration with multiple measurements over a wide frequency band, which is the most common configuration for space radars. This is the first part (Paper I) of a joint study considering methods to analyse and invert quasi-monostatic microwave measurements of an asteroid analogue. This paper focuses on the frequency domain, while a separate paper focuses on time-domain methods.Methods.We carried out an experiment in the laboratory equivalent to the probing of an asteroid using the microwave analogy (multiplying the wavelength and the target dimension by the same factor). Two analogues based on the shape of the asteroid 25143 Itokawa were constructed with different interiors. The electromagnetic interaction with these analogues was measured in an anechoic chamber using a multi-frequency radar and a quasi-monostatic configuration. The electric field was measured on 2372 angular positions (corresponding to a sampling offering complete information). We then inverted these data with two classical imaging procedures, allowing us to reach the structural information of the analogues interior. We also investigated reducing the number of radar measurements used in the imaging procedures, that is both the number of transmitter-receiver pairs and the number of frequencies.Results.The results show that the 3D map of the analogues can be reconstructed without the need for a reference target. Internal structural differences are distinguishable between the analogues. This imaging can be achieved even with a reduced number of measurements. With only 35 well-selected frequencies over 321 and 1257 transmitter-receiver pairs, the reconstructions are similar to those obtained with the entire frequency band.

Practical imaging algorithms in ultra-wideband radar systems using active aperture synthesis and stochastic probing signals

The subject of the manuscript is the algorithms for radar imaging. This research develops imaging methods and algorithms for wideband and ultrawideband active aperture synthesis systems with antenna arrays and stochastic probing signals. The use of antenna arrays makes it possible to obtain radar images without the need to move radar or antenna system in space. The use of wideband and ultra-wideband stochastic probing signals is justified by their narrow autocorrelation functions. This increased the resolution of the obtained images. The main idea of the proposed algorithms is to filter the original wideband signal into several narrowband processes. Furthermore, only the central frequencies of each narrowband signal were processed. This approach allows us to use the classical widespread methods of aperture synthesis for the case of a wideband signal. Usually, they are applicable only for narrowband signals that satisfy the condition of a quasi-monochromatic approximation. This significantly reduces the overall computational complexity of the imaging algorithm, which simplifies its further practical implementation on the existing radioelement base. Because of the simulation, a primary radar image has been obtained and the overall performance of the proposed approach to processing wideband signals has been confirmed. An increase in the quality of the obtained image when using a multiple of frequency ranges is shown. An experimental study of the effect of processing a wideband signal only at its centre frequency instead of the entire frequency band is conducted. During the experiment, the correlation functions of the signals received by two spaced receivers were obtained. As a result, the Van Cittert-Zernike theorem has been experimentally confirmed. It allows signal processing only at its centre frequency instead of the entire frequency band. Simultaneously, the prospect of expanding the bandwidth of the probing signal is indicated. It, in the presence of a wideband element base and devices for high-speed signal processing, will further increase the imaging resolution of a radar system.

Design and Development of Frequency Agile Reflectarray Antenna

This paper presents the design of a frequency reconfigurable reflectarray with concentric circular rings. The PIN diode connected between a phase delay line and the ring produces reconfigured resonances at 16 GHz and 10.4 GHz. The variation in the size of the concentric rings offer a phase change of 356º during the OFF state of the PIN diode. 360° phase variation in the PIN ON condition is achieved by varying the delay line length. A 225-element centre-fed reflectarray antenna is constructed with square geometry. A simulated gain of 23 dBi is obtained with -17 dB side lobe level and -28 dB cross-polarization level at 16 GHz. In the PIN ON condition, a simulated gain of 22 dBi is obtained with -12 dB side lobe level and -28 dB cross polarization level. This reconfigurable reflectarray finds its applications in space research, satellite communication, and RADAR.

A methodology to upscale IMD ground radar observations at the same resolution with TRMM PR reflectivity using ANN

This work presents a direct comparison of Ground Radar (GR) located in Delhi against Space Radar (SR) onboard the Tropical Rainfall Measuring Mission (TRMM). At first, the GR observations made by the India Meteorological Department (IMD) for the Indian summer monsoon months of 2013 over Delhi are matched with SR observations using a three-dimensional volume matching methodology (VMM). We found that the matched GR and SR reflectivity data points at common volumes have a high correlation coefficient with a high RMS error. Further, due to the beam broadening of the GR, the matched reflectivity has the exact horizontal resolution of 5 km but a different vertical resolution based on the distance from the GR site and the elevation angle. An upscaling methodology is proposed to obtain GR observations at an equal resolution (5km×0.25km) as that of SR. We observe a better agreement between GR and SR data following our approach. Further, the high vertical resolution GR reflectivity is “corrected” for bias and other sources of error using SR observations with artificial neural networks (ANN) based approach. Our results show that the ANN-corrected high-resolution GR reflectivity observations have a root mean squared (RMS) error of 3.98 dBZ, which reduced significantly from 16.35 dBZ.

False Detections Revising Algorithm for Millimeter Wave Radar SLAM in Tunnel

Millimeter wave (MMW) radar simultaneous localization and mapping (SLAM) technology is an emerging technology in a tunnel vehicle accident rescue scene. It is a powerful tool for statistic-trapped vehicle detection with limited vision caused by darkness, heat, and smoke. A variety of SLAM frameworks have been proven to be able to obtain 3-degree-of-freedom (3-dof) pose estimation results using 2-dimention (2D) MMW radar in open space. In the application of millimeter wave radar for pose estimation and mapping in a closed environment, closed space structures and artificial targets together constitute high-intensity multi-path scattering measurement data, leading to radar false detections. Radar false detections caused by multi-path scattering are generally considered to be detrimental to radar applications, such as multi-target tracking. However, few studies analyze the mechanism of multi-path effects on radar SLAM, especially in closed spaces. In order to address the problem, this paper first presents a radar multi-path scattering theory to study the generation mechanism difference of false and radar true detection and their influences on radar SLAM 2D pose estimation and mapping in tunnel. According to the scattering mechanism differences on SLAM, a radar azimuth scattering angle signature is proposed, which allows distinguishing radar false detections from real ones. This is useful in avoiding using unreliable radar false detections to solve a radar SLAM problem. In addition, two different radar false detection revising methods combined with the CSM (correlative scan matching) algorithm are proposed in this paper. The HTMR-CSM (hard-threshold-multi-path-revised correlative scan matching) algorithm only depends on a hard threshold of radar azimuth scattering angle signature to eliminate all radar false detections as much as possible before CSM. Another idea is the STMR-CSM (soft-threshold-multi-path-revised correlative scan matching) algorithm. All the radar false detections are classified according to the distribution model of radar azimuth accuracy, and part of more reliable radar false detections are retained to estimate a more accurate pose. All the ideas in this paper are validated by using an MMW 2D radar mounted on a rail-guided robot in a tunnel. Two cars on fire were set as the targets. The experimental results show that the STMR-CSM algorithm that keeps the reliable radar false detections improves the positioning accuracy by 20% compared with CSM.

Detection characteristics and features of signal processing of aerial objects on images of spacborne synthetic aperture radars

The article considers the possibilities of detecting airborne moving targets by space radars with aperture synthesis using interferometry mode along the path. The method of calculating the signal-to-noise ratio, the characteristics of detecting aerial targets in the mode of selection of moving targets is described. Based on calculations, it is shown that the dynamics of the underlying surface caused by fluctuations in grass, foliage or an agitated sea surface significantly reduces the ability to detect aerial objects by space radars with aperture synthesis in the selection of moving targets mode. It is shown by the examples of existing space radars with aperture synthesis that when using the interferometry method along the path, at least 2 interferometric bases and refocusing on the marks of bright moving targets in the mode of selection of moving targets channel, the effectiveness of the detection procedure can be sufficient for practical applications. However, the region of small radial velocity values remains a blind zone for any multi-base circuit configurations and can only be reduced by increasing the energy potential of the space radars with aperture synthesis.

Near-Field High-Resolution SAR Imaging with Sparse Sampling Interval.

Near-field high-resolution synthetic aperture radar (SAR) imaging is mostly accompanied by a large number of data acquisition processes, which increases the system complexity and device cost. According to extensive reports, reducing the number of sampling points of a radar in space can greatly reduce the amount of data. However, when spatial sparse sampling is carried out, a ghost normally appears in the imaging results due to the high side lobes generated in the azimuth. To address this issue, a technique is introduced in this paper to recover the blank data through amplitude and phase compensation based on the correlation between sparse array sampling through adjacent points. Firstly, the data sampled by the sparse array is compressed in the range direction to obtain the expected data slices in the same range direction. Then, the blank element of the slice is compensated for with amplitude and phase to obtain full aperture data. Finally, the matched filter method is used to aid in the image reconstruction. The simulation results verified that the method proposed in this paper can effectively reconstruct the image under two kinds of sparse sampling conditions. Thus, a simple single-input single-output (SISO) synthetic aperture radar imaging test bench is established. Compared with the results of a 1 mm (1/4 ) sampling interval, the quality of the reconstructed image under the condition of a 4 mm (1 ) sampling interval still stands using our proposed method. Demonstrated by the experiment, the normalized root-mean-square error(NMSE) is 5.75%. Additionally, when the spatial sampling points are sampled randomly with 30% of the full sampling condition, this method can also restore and reconstruct the image with high quality. Due to the decrease of sampling points, the data volume can be reduced, which is beneficial for improving the scanning speed and alleviating the pressure of data transmission for near-field high resolution SAR imaging systems.

Monitoring of displacements and deformations of the earth's surface at the Annensky field

In connection with the ongoing depletion of mineral reserves located in relatively favorable conditions, at shallow depths, it is increasingly necessary to involve deposits located in complex mining and geological conditions; occurring at great depths, in complex, poorly studied and potentially dangerous conditions. The deposits developed by the underground method are no exception. Safe and efficient development of mineral deposits by underground method, occurring at great depths, is complicated by the fact that with an increase in the depth of mining, the nature of the course of deformation processes in the rock mass and the degree of their impact on the environment change. Studies of deformation processes, their control and forecast in many cases determine the efficiency and safety of the development of deposits of solid minerals. A practical forecast can be made as a result of continuous tracking in space and time of deformation processes. Currently, to determine the displacements and deformations of the earth's surface of the field, complex monitoring is used, which includes the following methods: - methods of preliminary diagnostics of the rock massif; - repeated high-precision leveling; - satellite geodetic methods, primarily interferometry methods; - other methods of instrumental observations in regional and local areas. It should be noted that ground-based methods used for geomechanical monitoring of earth surface deformations, such as repeated geodetic leveling, as well as the use of satellite geodesy methods, do not fully reflect the temporal detail and spatial scale of the changes in the earth surface deformations. Today, the methods and technologies of space radar interferometry are of particular practical value, which make it possible to obtain areal estimates of vertical and planned displacements of the earth's surface with an accuracy of a few millimeters, regardless of illumination and cloudiness conditions. Space radar interferometry (CRI) is an effective tool for direct mapping of the earth's surface movements and deformations of structures over large areas of the study areas.

Detecting Supercooled Water Clouds Using Passive Radiometer Measurements

AbstractSupercooled water clouds (SWCs) have significant impacts on the Earth's radiation balance, aircraft ice accretion and precipitation augmentation. This study introduces an efficient algorithm to detect SWCs from passive radiometers, which combines information from the reflectance difference between 1.61 and 2.25 μm channels, the brightness temperature difference between the 8.5 and 11 μm channels, and the cloud top temperature. Validated by space radar and lidar measurements, our algorithm can correctly detect 91% of SWC pixels, better than current Visible Infrared Imager Radiometer Suite operational product. SWCs are found mostly over the mid‐ to high‐latitude oceans and have a global occurrence frequency of ∼8% in cloudy skies. Since the channels used for the detection are available in most current operational polar and geostationary satellite radiometers, this SWC detection algorithm can be easily implemented for operations such as cloud monitoring, aviation safety, and SWC‐related weather modification.

Улучшение характеристик космических РСА в режимах высокого разрешения

The methods of increasing the size of the radar image obtained by space radars with synthesized aperture in high-resolution mode are analyzed. The image size increase is achieved due to the extended scanning of the antenna beam in the azimuthal plane. The basis of the considered methods is the classical searchlight mode. The modes of composite (multi-frame) searchlight shooting and sliding searchlight shooting are compared. The dependences of azimuthal resolution and frame size on the size of the scanning sector are estimated. Numerical examples are based on the parameters of COSMO-SkyMed and TerraSAR-X radars. A list of the main ways to increase scanning is provided. A brief description of the Staring Spotlight mode is given, as an example, which allows to significantly increase the detail and quality of images.

MIMO Radar Waveform Design for Simultaneous Space–Time–Doppler Domain Optimization: Framework and Implementation

Waveform design has become an attractive topic in the field of colocated multiple-input multiple-output (MIMO) radar that allows antennas to transmit different waveforms. Waveform properties of MIMO radar in space, time and Doppler domains determine the performances of resource utilization, interference suppression, and moving target detection. Therefore, simultaneous optimization of multi-domain properties through waveform design is significant to improve the performance of MIMO radar. In this paper, a novel MIMO radar waveform design framework that constrains the beampattern while maximizing the similarity between the designed and desired waveforms is proposed for simultaneous space-time-Doppler domain optimization. To solve the resulting multi-constraint non-convex problem, an efficient beampattern control and similarity maximization (BCSM) algorithm is developed and its convergence is demonstrated. Especially, the coupling problem due to the similarity constraint is handled by transforming the number domain and introducing the proximal algorithm. While reducing the target distortion in mainlobe region and interference in sidelobe region, the proposed method can also maximize the similarity of MIMO transmit waveforms. Numerical simulation results, apart from verifying that the proposed method outperforms existing methods in space-time-Doppler domain, also illustrate the robustness of proposed method in terms of mainlobe width and desired peak sidelobe level (PSL).

Investigation of the hydrodynamics of man-made water by remote methods (on the example of southern Kryvbas)

The purpose of this study was to identify the degree and nature of man-made changes in the condition of the hydrogeological structure of the upper part of the earth's crust in the south of the Kryvyi Rih iron ore basin (Kryvbas). Another goal was the search and localization of sources of highly mineralized waters of the studied territory. To understand the nature of the watering (dewatering) of the section, the results of mapping the deformation of the terrain on the Sentinel-1 IW SLC space radar images were used. The resulting changes in the relief of the area were compared with the results of repeated geoelectrical observations, which showed zones of the day surface to the south of the "Livoberezhny" dumps, which are subject to subsidence and have areas of local flooding and waterlogging. They are mainly associated to the complex structure of zones of tectonic disturbances, zones of intersection of Precambrian faults of sub-meridional extension and west-northwest, which affect the distribution and localization of mineralized waters. Analysis of the data of hydrogeological, hydrological, engineering-geological and geophysical studies of the territory at the end of the 20th and beginning of the 21st centuries showed the degree of change in the hydrogeological environment over several decades. A comprehensive interpretation of space radar and geophysical survey data made it possible to assess the physical processes that take place from the surface to depths of tens of meters below it. The carried out geoelectrical research made it possible to establish the width of the rock water table in the upper part of the section, which ranges from 50 to 150 m, and the presence of a local depression on the roof of the foundation, under pond "Lebiazhyi". The latter is due to the specificity of the connection (knot) of differently oriented faults, where highly mineralized waters preserved in the Kryvyi Rih fault system are still stored and accumulated in the form of lenses. The conclusion is the integration of remote methods that study various properties of the geological environment increase the possibility of operational and scientifically based identification of problems of flooding of the territory and allow to control safe activities in the zone of influence of man-made objects.

Experimental assessment of the information content of long-range portraits of radar objects

At present, the scientific and technical literature discusses in detail the issues of obtaining information about the geometric characteristics of airborne radar targets (RC), which can be used as recognition signs. However, these issues and the methods being developed are considered in relation to single-position radar stations (radars) using simple or complex signals. Purpose of the work is determination of the informative value of the parameters of the long-range portraits of the RLS obtained by the method of statistical and physical modeling based on the processing of experimental data. A method is proposed for assessing the informativeness of long-range portraits of radar objects obtained as a result of processing reflected signals by various methods, including using weight processing based on a priori information about the structure of probing signals. Based on the analysis of the experimental data, it was found that the weight processing of the long-range portraits of the RLS provides an increase in the contrast of the portraits (an increase in the steepness of the portrait peaks and the depth of the dips), which, in turn, leads to an increase in the information content of each element of the long-range portrait and the totality of the features of the long-range portrait as a whole when recognizing RLO. The use of the technique allows us to assess the quality of the long-range portraits of the radar, obtained by various methods of processing radar signals and develop algorithms that increase the information content of radar systems with the recognition mode both for air and space radar and for objects against the background of the underlying surface during remote sensing.

Analysis of full microwave propagation and backpropagation for a complex asteroid analogue via single-point quasi-monostatic data

Context.Information carried by the full wave field is particularly important in applications involving wave propagation, backpropagation, and a sparse distribution of measurement points, such as in tomographic imaging of a small Solar System body.Aims.With this study, our aim is to support the future mission and experiment design, such as for example ESA’sHera, by providing a complete mathematical and computational framework for the analysis of structural full-wave radar data obtained for an asteroid analogue model. We analyse the direct propagation and backpropagation of microwaves within a 3D printed analogue in order to distinguish its internal relative permittivity structure.Methods.We simulate the full-wave interaction between an electromagnetic field and a three-dimensional scattering target with an arbitrary shape and structure. We apply the Born approximation and its backprojection (the adjoint operation) to evaluate and backpropagate the wave interaction at a given point within the target body. As the data modality can have a significant effect on the distinguishability of the internal details, we examine the demodulated wave and the wave amplitude as two alternative data modalities and perform full-wave simulations in frequency and time domain.Results.The results obtained for a single-point quasi-monostatic measurement configuration show the effect of the direct and higher-order scattering phenomena on both the demodulated and amplitude data. The internal mantle and void of the analogue were found to be detectable based on backpropagated radar fields from this single spatial point, both in the time domain and in the frequency domain approaches, with minor differences due to the applied signal modality.Conclusions.Our present findings reveal that it is feasible to observe and reconstruct the internal structure of an asteroid via scarce experimental data, and open up new possibilities for the development of advanced space radar applications such as tomography.