Search

The advantages of sub-terahertz technology (sub-THz, 200–700 GHz) have already been advanced for imaging and recognition of a space object's state from a space-based sensor using inverse synthetic aperture radar (ISAR). The technology benefits from wide absolute signal bandwidths, giving high range resolution and from enhanced sensitivity to surface texture. An experimental validation of such a system in controlled laboratory conditions is presented. Possible image formation methods are proposed and evaluated experimentally. Images of real parts of satellites have been produced at sub-THz frequencies and compared to lower frequency images. Other results include sub-THz bistatic ISAR, and sub-THz cross-polarized images which highlight the scattering from rough surfaces while attenuating the very bright scatterers seen from conventional monostatic images. [ABSTRACT FROM AUTHOR]

In this article, an active multireceiver low-THz imaging radar is used to generate 3-D images of automotive environments by combining time (difference) of arrival (TDoA) information with backprojection techniques to give height profiles of the objects in the scene. The large bandwidth of this system facilitates noncoherent height reconstruction using time of arrival alone. In doing so, the constraints on receiver coherency are relaxed compared to many height-finding techniques. 3-D reconstructions of common roadside targets and scenes are generated through a modified form of backprojection, adapted to use the time of arrival information of the signals from multiple receivers with different sensitivities, which are arranged in a quasi-multistatic configuration. Here, it is experimentally shown that the use of three vertically-aligned receivers is sufficient to provide a fine resolution in range, cross-range, and height. The system is used to generate 3-D reconstructions of a number of different scenarios, including pedestrians moving through a scene, and complex real-world road scenes. [ABSTRACT FROM AUTHOR]

The concept of sub-terahertz (sub-THz) imaging and recognition of space objects by a satellite-based inverse synthetic aperture radar (ISAR) is proposed and analyzed in this article. Operation at sub-THz frequencies in the band 200–400 GHz benefits from wide available bandwidth, high sensitivity to surface texture, and very small target features, and requires an antenna of small physical size. A feasibility study is presented based on use case scenarios of the relative motion of monitoring satellite and observed objects. Expected resolutions, power budget, and oscillator stability requirements in this frequency band are discussed. Image formation methods are proposed and evaluated with simulations. A simple electromagnetic modeling capability is proposed to create a comprehensive dataset of sub-THz ISAR images, with the orientation and aspect angles seen by the sensors, which can be used to train semantic classifiers. [ABSTRACT FROM AUTHOR]

This article examines methods for and results of determining the instantaneous kinematic state of a target, i.e., its velocity and heading, using passive multistatic radar. This is achieved by combining bistatic target range and Doppler information obtained by multiple bistatic transmitter–receiver pairs, to estimate the appropriate target velocity vector. This estimation is provided as a set of closed-form equations, derived for a general case applicable to an arbitrary number of transmitters. The feasibility of the proposed approach and its accuracy predictions, as a function of the number of transmitters, are experimentally confirmed via a dedicated experimental campaign with Global Navigation Satellite Systems as transmitters of opportunity, where two different and relatively slow-moving maritime targets were in the field of view of up to 12 satellite transmitters belonging to different satellite constellations (GPS, GLONASS, and Galileo) simultaneously. [ABSTRACT FROM AUTHOR]

This article explores the possibility to exploit global navigation satellite systems (GNSS) signals to obtain radar imagery of ships. This is a new application area for the GNSS remote sensing, which adds to a rich line of research about the alternative utilization of navigation satellites for remote sensing purposes, which currently includes reflectometry, passive radar, and synthetic aperture radar (SAR) systems. In the field of short-range maritime surveillance, GNSS-based passive radar has already proven to detect and localize ship targets of interest. The possibility to obtain meaningful radar images of observed vessels would represent an additional benefit, opening the doors to noncooperative ship classification capability with this technology. To this purpose, a proper processing chain is here conceived and developed, able to achieve well-focused images of ships while maximizing their signal-to-background ratio. Moreover, the scaling factors needed to map the backscatter energy in the range and cross-range domain are also analytically derived, enabling the estimation of the length of the target. The effectiveness of the proposed approach at obtaining radar images of ship targets and extracting relevant features is confirmed via an experimental campaign, comprising multiple Galileo satellites and a commercial ferry undergoing different kinds of motion. [ABSTRACT FROM AUTHOR]

This paper is concerned with modelling of the transmissivity of Low-Terahertz waves through automotive bumper and headlight cover material. This work is part of wider comprehensive studies on the potential for the use higher frequency bands for future automotive sensors. Theoretical models for transmissivity prediction are described, the methodology of experimentation is discussed and experimental results are presented. The theoretical models of reflection and transmission of different base materials which are covered by different layers of paint are based on Fresnel theory, and the phenomena caused by the half wavelength thickness of the medium is analyzed mathematically. The experimental verification of the models in this paper have been undertaken at 300 GHz and 670 GHz, using 77 GHz as a reference frequency. [ABSTRACT FROM AUTHOR]

This article investigates passive synthetic aperture radar (SAR) image formation using Terrestrial Digital Video Broadcast (DVB-T) transmitters of opportunity and an airborne receiver. The proposed airborne system does not use separate channels for direct and reflected signal reception. The proposed image formation algorithm suppresses artifacts due to the presence of the direct signal in radar echo data using modified CLEAN method and accounts for unknown irregularities in airborne platform motion using a map-drift autofocus (MDA) technique. The algorithms are theoretically derived and experimentally confirmed via an appropriate airborne campaign, and their experimental performance is measured. [ABSTRACT FROM AUTHOR]

Wave attenuation through rain with different rainfall rates at millimeter wave ($f = 77$ GHz) and low-terahertz (Low-THz) ($f = 300$ GHz) frequencies is studied in this article. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties [rainfall rate and drop size distribution (DSD)] are measured simultaneously. The measured DSD is fit with gamma and Weibull distributions and is also compared to the frequently used distribution Marshall and Palmer (MP) model; Weibull is shown to be a better fit to the measured DSDs. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/h) is determined using Mie scattering theory, and the fit gamma and Weibull, and MP distribution models; as well as using the International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time. [ABSTRACT FROM AUTHOR]

This paper explores radar methods to measure the coordinates (distance and height) of objects on or beside a road. Knowledge of these parameters is essential in the development of autonomous or semi-autonomous cars, as well as to improve driving safety. It is shown that the height is best found by trilateration from sensors at multiple locations on a vehicle. The novelty of the work consists in the formulation of the problem and in its solution using a low-THz radar trilateration approach. The expressions obtained allow calculating the coordinates of targets using a number of different methods of radar trilateration. The influence of the system parameters on the accuracy of measurement using different methods of trilateration has been analyzed. The assumptions made were verified by the experimental system based on a 300-GHz ultra-wideband radar. Experimental results are in good agreement with theoretical calculations; they confirmed the practicality of obtaining high-accuracy height measurements on distributed targets such as pedestrians. The physical basis of the techniques developed would also allow the plan position of a target to be found using the same approach. [ABSTRACT FROM AUTHOR]

This paper addresses the exploitation of Global Navigation Satellite Systems (GNSS) as transmitters of opportunity in passive bistatic radar systems for maritime surveillance. The main limitation of this technology is the restricted power budget provided by navigation satellites, which makes it necessary to define innovative moving target detection techniques specifically tailored for the system under consideration. To this aim, this paper puts forward long integration time techniques able to collect the signal energy over long time intervals (tens of seconds), allowing the retrieval of suitable levels of signal-to-disturbance ratios for detection purposes. A local plane based technique is first considered, providing target detection in a plane that represents the section of maritime area covered by the radar antenna. As a suboptimum solution in terms of achievable integration gain, but more efficient from a computational point of view, a second technique is considered working in the conventional bistatic range and Doppler plane (basic plane based). Results against synthetic and experimental datasets show the effectiveness of the proposed techniques. [ABSTRACT FROM AUTHOR]

Over the last decades spaceborne synthetic aperture radar (SAR) has proved its capability as a remote sensing technique of great power and value. A number of precise SAR instruments (e.g., [1]–[4]) have been developed by space and defense agencies around the world and are being used today for a wide range of applications in wide-area land (e.g., [5]–[8]) and sea monitoring (such as [9]–[11]). [ABSTRACT FROM AUTHOR]

This paper examines the potential in extracting the instantaneous location of maritime moving targets using a passive multistatic radar with Global Navigation Satellite Systems (GNSS) as illuminators of opportunity and a single receiver. This paper presents a theoretical framework for the localization of a moving target from a set of bistatic range measurements. The algorithm and its predicted accuracy are presented. The localization is achieved by what is essentially a multilateration technique, which can be applied while the transmitting platform is also in motion. The algorithms and the accuracy predictions, as a function of the number of transmitters, have been experimentally confirmed via a dedicated experimental campaign, where two different maritime targets were detected by up to 12 GNSS satellites belonging to different satellite constellations (GPS, GLONASS, and Galileo) simultaneously. To the best of the author’s knowledge, these are the first results of their kind and on this scale not only for GNSS-based passive radar but also for multistatic radar in general. [ABSTRACT FROM AUTHOR]

This paper is a first introduction to the concept of using global navigation satellite systems (GNSS) as illuminators of opportunity in a passive bistatic real-time radar system for maritime target indication applications. An overview of the system concept and the signal processing algorithms for moving target indication is provided. To verify the feasibility of the system implementation as well as test the developed signal processing algorithms, an experimental test bed was developed and the appropriate experimental campaign with the new Galileo satellites and a ferry as the target was carried out. The results confirm the system concept and its potential for multistatic operation, with the ferry being detected simultaneously by two satellites. [ABSTRACT FROM AUTHOR]