Andrey Zhuravlev

Holographic Subsurface Radar of RASCAN Type: Development and Applications

Holographic subsurface radars (HSR) are not in common usage now; possibly because of the historical view amongst radar practitioners that high attenuation of electromagnetic waves in most media of interest will not allow sufficient depth of penetration. It is true that the fundamental physics of HSR prevent the possibility to change receiver amplification with time (i.e., depth) to adapt to lossy media (as is possible with impulse subsurface radar or ISR). However, use of HSR for surveying of shallow subsurface objects, defects, or inhomogeneities is an increasingly proven area of application. In this case, HSR can record images with higher resolution than is possible for ISR images. The RASCAN family of holographic radars is presented along with technical specifications and typical case histories. Among the applications considered are civil and historic building surveys, nondestructive testing of dielectric materials, security applications, and humanitarian demining. Each application area is illustrated by relevant data acquired in laboratory experiments or field tests. This paper presents experiments with RASCAN imaging in media with different degrees of attenuation, and illustrates the principle of HSR through an optical analogy.

Holographic subsurface radar RASCAN-5

This paper describes the implementation of a holographic subsurface radar for sounding at shallow depths. The radar uses continuous signal with frequency switching and records phases of reflected signal at several operating frequencies. Two versions of the radar with frequency bandwidths 6.4-6.8 and 13.8-14.6 GHz were designed and tested. The data acquisition is accomplished by manual scanning along parallel equidistant lines. Upon acquisition, this two-dimensional interference pattern, or hologram, can be focused by the outlined Fourier-based back propagation algorithm into an image that reflects distribution of sources. Experimentally obtained and demonstrated in the paper images with plan view resolution of the order of 1 cm suggest application of the radar in civil engineering and non-destructive testing.

Comparison of different methods for reconstruction of microwave holograms recorded by the subsurface radar

A family of holographic subsurface radars, named RASCAN, has been produced during more than fifteen years. Until recently RASCAN radar had the direct-gain receiver that was registering amplitude of reflected signal only. Therefore, the obtained images were used without any processing. New generation of RASCAN radars with quadrature receiver allows recording two quadratures of reflected signal and finding its amplitude and phase. The performance of such devices crucially depends on the frequency bandwidth of sounding signal and on the appropriate reconstruction algorithms. The goal of this paper is to discuss the basics of various approaches such as single-frequency, two-frequency and wide-band. The comparison of the methods was carried out on the simulated and experiment holograms.

Bioradar for monitoring of human adaptive capabilities

This paper sums up the results of bioradiolocation experiments dedicated to the monitoring of human adaptive capabilities, which were conducted at Remote Sensing Laboratory (Bauman Moscow State Technical University) during last two years. The main task of bioradiolocation is remote or non-contact measurement of movement, breathing and pulse parameters of biological objects behind an obstruction or in open space at some distance. This method can be used in sleep medicine, functional diagnostics, pharmacology, zoo-psychology, restorative medicine and disaster medicine. Description of the bioradar experimental procedure is given.

Combined holographic subsurface radar and infrared thermography for diagnosis of the conditions of historical structures and artworks

This paper describes a new application of holographic radar for non-destructive testing applied to cultural heritage items. A holographic radar, called RASCAN, operates in continuous wave multi-frequency mode at 4 GHz range and produces images with high in-plane resolution (about 2 cm). Marble items and other stones have been investigated to validate the method to search for subtle cracks, moisture or to unveil details of structures at shallow depth (up to 2 wavelengths). Other important materials are aged wood items that are investigated for tunnels made by insects. Then the holographic radar imaging has been experimentally compared with infrared thermography to understand the advantages and disadvantages of these methods and to derive indications for solving the problem common in all geophysics of inherent non-uniqueness.

ISAR for concealed objects imaging

A new promising architecture of microwave personnel screening system is analyzed in this paper with numerical simulations. This architecture is based on the concept of inverse aperture synthesis applied to a naturally moving person. The extent of the synthetic aperture is formed by a stationary vertical linear antenna array and by a length of subject’s trajectory as he moves in the vicinity of this antenna array. The coherent radar signal processing is achieved by a synchronous 3D video-sensor whose data are used to track the subject. The advantages of the proposed system architecture over currently existing systems are analyzed. Synthesized radar images are obtained by numerical simulations with a human torso model with concealed objects. Various aspects of the system architecture are considered, including: advantages of using sparse antenna arrays to decrease the number of antenna elements, the influence of positioning errors of body surface due to outer clothing. It was shown that detailed radar images of concealed objects can be obtained with a narrow-band signal due to the depth information available from the 3D video sensor. The considered ISAR architecture is considered perspective to be used on infrastructure objects owing to its superior qualities: highest throughput, small footprint, simple design of the radar sub-system, non-required co-operation of the subject.

Microwave imaging of moving subjects by combined use of video-tracker and multi-static radar

This paper presents preliminary experiments with a geometrically simple target and a new architecture of the microwave screening system capable of obtaining radar images of moving subjects. The system is based on the combined use of a video-tracker and a linear antenna array. Inverse synthetic aperture is formed by arbitrary motion of the target in the vicinity of the array. A video-based system tracks the target and allows coherent processing of synchronously registered radar data, and eventually obtaining detailed radar images of concealed objects.

Microwave holography for NDT of dielectric structures

Methods of ultrasonic diagnostics, which are widely applied for non-destructive testing of different constructions, are ineffective for foam insulation, the silicate fiber tiles or honeycomb prepregs due to their high porosity, which leads to high levels of acoustic wave attenuation. Microwave diagnostics using holographic subsurface radars RASCAN-5, which operate in the gigahertz band, could be a good alternative to ultrasonic testing. Experimental results demonstrate the effectiveness of the technology on an example of honeycomb dielectric composite materials.

Inverse synthetic aperture radar imaging for concealed object detection on a naturally walking person

This paper describes the architecture of a microwave radar system intended for imaging concealed objects under clothing as a subject walks through the inspection area. The system uses the principle of inverse aperture which is achieved by a person’s movement past a stationary microwave sensor array. In the system, the vertical resolution is achieved by arranging microwave sensors vertically while the horizontal resolution is due to the subject’s horizontal motion. The positioning of the objects is achieved by employing a synchronous video sensor that allows coherent radar signal processing. A possible radar signal processing technique based on signal accumulation is described. Numerical experiments are conducted with the described object trajectory model. The influence of positioning errors attributed to the video positioning system is also modeled numerically. An experimental setup is designed and proposed to evaluate the suggested signal processing techniques on real data with an electro-mechanical scanner and single transceiver. It is suggested that the signal acquisition with the system can be accomplished using the stop motion technique, in which a series of changing stationary scenes is sampled and processed. Experimental radar images are demonstrated for stationary objects with concealed items and considered as reference images. Further development of the system is suggested.

Processing of holographic subsurface radar data

A backward propagation algorithm of reconstructing images is considered with experimental data obtained by holographic subsurface radars of RASCAN type. This family of radars uses stepped frequency continuous wave signals and can record in-phase and quadrature components of the reflected signal with a frequency bandwidth of 0.5 to 1 GHz with a center frequency ranging from 2 to 14.5 GHz (depending on radar modification). Among examined data acquiring scenarios were both contact and stand off measurements in media with different attenuation. The reconstructed images were shown to have high plan resolution and easy to interpret as the reconstructed microwave images preserve shape and other features of the optical images. Further modifications are suggested to improve the performance of the system.