<title>Random-noise polarimetry applications to subsurface probing</title>

Abstract

Random noise polarimetry is a new radar technique for high-resolution probing of subsurface objects and interfaces. Detection of buried targets is accomplished by cross-correlating the reflected signal by a time-delayed replica of the transmitted waveform. A unique signal processing scheme is used to inject coherence in the system to permit extraction of the wideband polarimetric scattering response of the buried object. This facilitates computation of the Stokes matrices of the target response which enhances the detection and identification process. Random noise polarimetry also possesses additional desirable features for subsurface probing such as immunity from detection and jamming. The paper discusses the theoretical foundations of random noise polarimetry and presents data acquired from various targets using a 1-2 GHz radar system fabricated by the University of Nebraska under contract to the U.S. Army Waterways Experiment Station. In addition, various signal processing algorithms used to analyze the polarimetric data are presented.

<title>Random noise radar interferometry</title>

“…3 The University of Nebraska has developed a coherent ultrawideband random noise radar system for the detection of shallow subsurface objects, such as land mines.4 This system utilizes the polarimetric phase information of the buried object as obtained from the dual-polarized receive antenna feeding each of the receive chains, and has been shown to enhance the detection of shallow buried objects. 5 The system was configured as a radar interferometer, and our experimental results confirm its ability to exploit the phase information for target location in azimuth.…”

Enhanced detection of objects obscured by dispersive media using tailored random noise waveforms

“…Further assume that the object is buried at a depth d, and its complex reflectivities are R exp{jçb0} and R exp{jox} for co-polarized and cross-polarized backscatter respectively. Under these circumstances, we can show that the outputs of the logarithmic amplifiers AMP 7 and AMP 6 are, respectively Prc = KR (4) Prx KR (5) The ratio of Prx to Prc gives us the depolarization ratio of the buried object, D, as follows From the raw data collected by the radar system, we generate images based on the Stokes matrix formulation for facilitating the detection and recognition of targets using the polarimetric information on the buried target.…”

“…Our results indicate that this unique system is indeed capable of detecting buried metallic and non-metallic objects, and use of polarimetry significantly enhances the detection of buried targets. 4 Our prior simulation studies and experimental measurements were performed under the assumption that a uniform power spectral density (i.e., constant amplitude) within the 1-2 GHz frequency band was being transmitted. This type of transmit spectrum works well if the obscuring medium is non-dispersive and possesses constant (albeit nonzero) attenuation versus frequency characteristics.…”