Bistatic Mode Research Articles

EXPERIMENTAL ASSESSMENT OF MICROWAVE DIAGNOSTIC TOOL FOR ULTRA-WIDEBAND BREAST CANCER DETECTION

An ultra-wideband microwave imaging system that employs a heterogeneous breast phantom and covers the ultra-wideband (UWB) frequency range (3.1 GHz to 10.6 GHz) is presented. The platform scanning system allows monostatic and bistatic mode of operation. In this work, developed heterogeneous phantoms are used to mimic the realistic breast tissues. A utilized tapered slot antenna array allows for a high resolution hemispherical scan, achieved by rotating the imaged object on a turntable. Full design details of the scanning system and the utilized post-processing algorithm are explained. To validate the reliability of the presented system, the results of several imaging cases, including the challenging low dielectric contrast case, are presented.

Microwave Remote Sensing of Ionized Air

We present observations of microwave scattering from ambient room air ionized with a negative ion generator. The frequency dependence of the radar cross section of ionized air was measured from 26.5 to 40 GHz (Ka-band) in a bistatic mode with an Agilent PNA-X series (model N5245A) vector network analyzer. A detailed calibration scheme is provided to minimize the effect of the stray background field and system frequency response on the target reflection. The feasibility of detecting the microwave reflection from ionized air portends many potential applications such as remote sensing of atmospheric ionization and remote detection of radioactive ionization of air.

High Spectral Resolution LIDAR Receivers to measure Aerosol to Molecular Scattering Ratio in Bistatic mode for use in Atmospheric Monitoring for EAS Detectors

We present the design of a bistatic High Spectral Resolution Lidar (HSRL) aiming at measuring the aerosol phase function for applications in Ultra High Energy Cosmic Ray experiments. The expectation is to give accurate data for the aerosol phase function, needed to correct the Extended Air Shower (EAS) signal of air-fluorescence detectors for the air Cherenkov contamination, caused mainly by the aerosols. In this work we mainly focus on the design principles of the HSRL receiver for recording the aerosol to molecular scattering ratio as a function of height. We present results from testing an SLM CW diode laser of 120 mW at 532 nm, to be used as a LIDAR emitter in the transmitting telescope, and verify the design coherence length according to the manufacturer. As receiver we consider a system two different Fabry-Perot etalons having free spectral ranges 0.1 cm − 1 and 1 cm − 1 respectively, corresponding to the molecular and aerosol channels. The fringe patterns are analyzed over 2 π polar angle range using appropriate algorithms.

Theoretical and experimental study of through-wall microwave tomography inverse problems

We consider the problem of building structure estimation using microwave ray tomography. A Bayesian formulation is developed, and a Markov chain Monte Carlo (MCMC) procedure is used to sample the posterior distribution, which is based on a data likelihood defined in terms of a residual misfit between observed and predicted waveforms. To accelerate model optimization, a simulated annealing approach is combined with the MCMC, using specific model moves to explore each component of the model space. Our approach is applicable to data acquired in the frequency or time domain and for monostatic or bistatic acquisition modes. Experimental data for a multi-wall laboratory test structure were acquired using a horn antenna connected to a vector network analyzer and used to validate both the forward model and the inversion approach. Although, in true remote sensing problems for building structure, the model order is usually unknown, in this initial study, the actual inversion experiment is performed in a reduced-dimension model space for which a subset of the variables are taken as known or fixed. Generalization to the variable-dimension problem can be achieved by using reversible jump MCMC sampling procedures.

Buried small objects detected by UWB GPR

A ground penetrating radar (GPR) using short-pulse is developed to detect small and shallow metal objects buried underground. A bistatic mode in which the GPR system uses separate transmitting and receiving antennas is applied. A modified fat dipole antenna is developed for the transmitting and receiving antennas. The prototype of the system is tested in the real environment and 2D visualization of raw data is achieved. We show that the developed system has a good ability to detect underground metal objects, and even small targets of several centimeters.

HF pump‐induced large scale radial drift of small scale magnetic field‐aligned density striations

A powerful high frequency (HF) electromagnetic pump wave transmitted into the ionospheric F region excites filamentary density irregularities stretched along the geomagnetic field. We present experimental results of small scale (5–15 m across the geomagnetic field) magnetic field‐aligned striations (FAS) excited using the Sura HF pump facility, Russia. The FAS were observed by resonant HF scatter in bistatic mode utilizing continuous wave broadcasting transmissions from near Moscow and reception with the UTR‐2 radio telescope as well as in nearly monostatic mode using a pulsed radar transmitter of Kharkov National University and reception at UTR‐2. The radar scatter showed that the previously observed split Doppler spectra in scattered continuous wave sounding is a result of pump‐induced large scale outward radial drift of the FAS during HF pumping. For sufficiently short pump pulses the radial drift reverses from outward during pumping to inward after pump‐off as the FAS decay. This drift reversal does not occur after longer pump pulses. The drift speed amounts to 2–4 m/s.

Technical aspects of the comprehensive acoustic simulation system (CASS) reverberation model and comparisons with measured data

The Comprehensive Acoustic Simulation System (CASS) has recently received interim acceptance into the United States Navy’s Atmospheric and Oceanographic Master Library (OAML). This paper focuses on the application of the CASS to computing reverberation in shallow water. The first topic reviews the numerical approach. This is based on the usual assumption that reverberation received at a specific time can be found by integrating returns from ensonified scattering areas on the ocean boundaries and from ensonified volumes within the ocean proper. The same approach is used for monostatic and bistatic modes of operation. CASS contains various methods for integrating over bearing and frequency. The second topic compares computed results with torpedo data measured off the waters of southern California. This data confirms the requirement for including range-dependent effects in shallow-water reverberation modeling. Fortunately, the measured reverberation was accompanied by an excellent survey of bottom properties. Since this is typically not the case, current modeling developments in CASS include the extraction of environmental properties from measured reverberation. Future developments may reduce some of the known deficiencies.

Evaluation of GPR techniques for civil-engineering applications: study on a test site

Different ground-penetrating radar (GPR) techniques have been tested on the same site in order to establish the performance and reliability of this method when applied to civil-engineering problems. The Laboratoire Central des Ponts et Chaussées (LCPC) test site at Nantes, France, was selected because it includes most of the underground heterogeneities commonly found in urban contexts, such as pipes, small voids, etc. The GPR survey consisted in recording measurements in tomographic (surface to horizontal borehole measurements), monostatic (2D surface profiling) and bistatic (Common Mid Point [CMP]) modes above various buried heterogeneities. Different processing techniques were also performed, such as tomographic inversion, 2D and 3D migration, velocity analysis, as well as numerical simulations, the results of which can be summarized in three points. (1) Although the different filling materials of the site can be distinguished by velocity and attenuation tomography, the buried heterogeneities are more difficult to identify because of limited resolution related to angular aperture and Fresnel zone. (2) 2D surface profiling can detect the different shallow heterogeneities, such as pipes and voids, down to a depth of several meters. Additional processing, such as forward modeling and attenuation curve analysis, provides more quantitative information related to the medium. A comparison between 2D and 3D migrated data highlights the error introduced when the structures are considered to be perfectly cylindrical. (3) CMP analysis gives relatively good estimations of vertical velocity contrasts when the medium is layered. A lithologic log can be derived assuming that the velocity changes are related to material variations.

Estimating time-varying DOA and Doppler shift in radar array processing

The authors consider the problem of retrieving information about space debris in low-Earth orbit by means of a radar system operating in a bi-static mode. More exactly, a pulse radar steers a beam in a prescribed region of space. When crossing the main lobe of the radar, a moving object will reflect energy towards a ground-based array of sensors. The signal is affected by Doppler shift, which is related to radial speed. Additionally, its direction-of-arrival (DOA), related to the orthoradial speed, will be time-varying. Maximum likelihood (ML) solutions to the problem of estimating both the Doppler shift and the time-varying DOA are proposed. Since the exact ML solution is computationally intensive, a simpler alternative is presented that relies on the extended invariance principle. The new method is shown to be simple as it only entails Fourier transforms and linear computations. Its performance is illustrated via numerical simulations.

Acoustic imaging by backward propagation: An overview of algorithm structure and configurations

The backward propagation technique is known as one of the most widely used algorithms in acoustic imaging for its simplicity, stability, and resolving capability. This presentation provides an overview of the development of backward propagation based algorithms for various system configurations in a systematic manner, from the simple case of coherent systems with stationary sources to the more complex wideband pulse-echo systems for time-varying objects, in both monostatic and bistatic modes. With this treatment, it is now possible to establish an accurate assessment of systems’ performance in terms of computation complexity, algorithm structure, sensitivity, and limitations.

Computer simulation of ultrasonic testing

Electromagnetic Investigation of the Sub-Surface (EISS) is a Ground Penetrating Radar (GPR) operating at very low frequencies in the HF range (2–4 MHz) that was designed to investigate the composition and structure of the Martian subsurface to depths of ~1 km. EISS can operate in both a monostatic and bistatic configuration, the latter being made possible by the simultaneous operation of two separate instrument platforms. The first, a fixed lander, utilizes one surface-deployed dipole antenna made of two 35 m-long resistively-loaded monopoles to transmit radar pulses into the subsurface. Echoes from subsurface reflectors are then received by either similar electrical receiving antennas (on the lander) or by a much smaller magnetic sensor that can be mounted either on the lander or on a mobile platform, such as a rover.In this paper, we report on the successful test of EISS bistatic mode of operation during a field campaign in the West Egyptian desert. From the analysis of the measured propagation delays, the dielectric constant and the depth of several reflecting subsurface interfaces were retrieved. Up to 226 coherent additions (or stacking) were performed resulting in the detection of buried interfaces and in particular of the Nubian Aquifer at a depth >200 m. The results obtained with the small magnetic sensor were consistent with those obtained with the electrical antennas, suggesting that such an experiment can meet the constraints of a space mission.

On the structure of background winds near the summer mesopause

Meteor wind radar observations in bistatic mode from two locations in the British Isles have led to the identification of planetary waves in the Summer season near the top of the Middle Atmosphere. By virtue of increased spatial resolution compared with traditional, monostatic radar it has been possible to identify waves with a scale size of around 4000 km and a phase speed of 12ms−1. There is some evidence for cyclonic wind motions similar to those observed in the lower atmosphere.

The PROUST radar: First results

The stratosphere‐troposphere radar PROUST (prototype de radar pour l'observation en UHF de la stratosphère et troposphère) is located at Saint Santin, France (44°39′N; 2°12′E), a place devoted to the French ionospheric incoherent scatter facility whose frequency is 935 MHz. The use of this equipment as stratosphere‐troposphere radar has required important modifications of the transmitting and receiving systems, which have been planned in several steps. In a first one, the radar works in a bistatic mode with a 600‐m height resolution, allowing measurements in the altitude range 3–10 km. The first results presented here have been obtained with this configuration during two campaigns. In the first one, observations can be interpreted in terms of lee waves; in the second, an intense turbulence activity associated with a high‐altitude temperature inversion is observed. In this last case, the oscillations observed in the vertical wind are consistent with trapped gravity waves generated by a decaying turbulence in a stratified medium. In a second step, now operating, a 30‐m height resolution has been implemented and will allow a better understanding of these phenomena. In its final version, the PROUST radar will operate in a monostatic mode that will permit to extend the observations up to 15 km.

Simultaneous operation of a sodar system in monostatic and bistatic modes: Preliminary results

Abstract A three-axis Doppler system has been set-up in a configuration that allows for simultaneous monostatic and bistatic modes of operation. Each of the antennas radiates a different frequency, and each is allowed to receive and process signals at three frequencies. A considerable increase in the information retrieved appears to be possible: preliminary experimental results are presented.

Foreword

Radars have had a long and illustrious history in the investigation of the atmosphere. Beginning with verification of the existence of the ionosphere in the mid‐1920's [Appleton and Barnett, 1925; Breit and Tuve, 1926], radars have been operated in monostatic and bistatic modes to probe the atmosphere and have acquired names such as bottomside or topside ionosonde, meteor radar, auroral radar, meteorological radar, incoherent scatter radar, etc. It is therefore remarkable that such an old technique would warrant a special issue of Radio Science in 1980. The reason seems to be that the scientific community was slow to recognize and exploit the potential of radar for sensing the nonionized clear atmosphere.

Bistatic Radar Detection of the Melting Layer

Recent operation of the Valley Forge-Wallops Island bistatic radar link during two days characterized by light rain and drizzle provided some detailed, bistatically derived information on atmospheric structure in the vicinity of Wallops Island. Data are presented that give unambiguous evidence of the simultaneous bistatic and monostatic radar detection of the melting layer. The height of the melting layer, as measured in the bistatic mode, has been confirmed by both radar backscatter measurements and radiosonde data. Methods used in interpreting forward-scatter data are discussed and approximate values for the layer thickness and reflectivity are derived.