Vladimir Razevig

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.

Microwave hologram reconstruction for the RASCAN-type subsurface radar

In this paper the mathematical models and results on processing the experimental single-frequency microwave holograms received by scanning subsurface radar with sine wave signal are submitted. The holograms reconstruction method with the use of support functions, which take into account the near field of the aperture antenna with round cylindrical waveguide, is analysed. The models consider both known and unknown phase shift of the signal reflected from the point object. It is theoretically and experimentally shown that single- frequency holograms reconstruction allows to estimate depth of shallowly buried objects and improve the resolution on the probing surface with the growth of objects depths.

Remote control mine detection system with GPR and metal detector

In this paper we describe a method of minefield reconnaissance with the use of the multi-frequency ground-penetrating radar (GPR) combined with a metal detector. This method allows the mine images in the soil to be obtained in the band of the mine detector sensors. An experimental installation with remote control and scanning sensors has been designed and built. A mine detector of this kind can be used in peacekeeping and humanitarian operations.

RASCAN holographic radar for detecting and characterizing dinosaur tracks

The development of high lateral resolution holographic radar imaging has stimulated new research on mapping of exposed dinosaurs and detection of tracks hidden in the uppermost layers of potential track-bearing rocks, as well as for the characterization of rock features around tracks. This project involves experiments on tracksites, museum specimens, and laboratory models from around the world. Preliminary experiments indicate that holographic radar will be able to provide comprehensive tracksite mapping with objectivity and total non-invasiveness.

Concrete floor inspection with the help of subsurface radar

The purpose of our investigation is to develop sounding radar for non-destructive inspection of buildings and structures designed for different uses, which can obtain high resolution radio-images representing the interior structure, objects and heterogeneities in load bearing and protecting construction. Our primary goal is to resolve problems dealing with the determination of strength of structures in service, repair and renovation of buildings.

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.

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.