This paper considers scattering by a buried, dielectric mine simulant at standoff distances of approximately 10 feet and
depth one inch. It presents measured data, ray analyses, estimates of ray magnitudes for scattering centers, and an image
formed from the data. The purpose was to understand the scattered field. Measurements, in the band 2 GHz to 6 GHz,
used a fixed transmit antenna and a receive antenna that was moved over a linear path on one side of the transmit
antenna. Complex reflectance was measured at one-inch intervals on the linear path. Range profiles were calculated by
transforming reflectance over frequency for specific receive antenna positions. Separations of profile maxima agreed
with ray path lengths fi-om the simulant's scattering centers. An image was calculated from two-dimensional spatial
spectra produced by continuing the spatial spectrum of the measured data. The image had maxima near scattering
centers, and it had another laterally displaced maximum. The displaced image maximum may result because the
measured data maxima were spaced by 3 wavelengths, possibly generating a grating lobe. Further, reflectance was
calculated as a sum of-rays-for the regions near reflectance maxima. Ray magnitudes from the front and back edges
were generally larger than those for internal reflections, and magnitudes were largest near the center of antenna travel.
Images of buried ordnance can accelerate remediation through identification. This paper presents images of a buried, inert projectile. The images are plan views, at fixed but variable depths. The images were formed by processing measured reflectance through Fourier transformation, backward propagation, and inverse transformation. Data were measured in two tests. Both tests utilized a towed array of seven antennas. One test, in 1995, used frequencies between 187.5 and 487.5 MHz; the best images were from the 387.5 MHz data. An earlier test, in 1994, used frequencies 200, 350, and 500 MHz; the best images were formed from the 500 MHz data. The procedures for the two sets of data differed in relative orientation of the sensor antennas and projectile; in addition, soil dielectric constant values differed. Image displays also differed in image data interpolation.
This paper describes imaging of buried objects and fluids. The motivations are to locate pipe leakage and unexploded ordnance. The method is to radiate and receive continuous, discrete frequency radio waves with antennas near the ground, to synthesize sampled area arrays of reflectance data, and to process the data into images with an algorithm based on angular spectrum diffraction theory. Experimental results are presented for three setups. An initial, laboratory setup had a single, spatially scanned antenna; it was used to image buried mud. The second with an array of five antennas on a vehicle, images a buried creosote pit. The third, with a vehicular array of seven antennas, imaged buried metallic objects and depressions in the soil surface.
The nearfield reflectance of a buried, dielectric object of circular shape was measured with an antenna operating in its and the object's nearfield region for two orthogonal linear polarizations. Reflectance depended on polarization. Mutual coupling between individual antennas was also measured and found to depend on polarization.
This paper describes the detection and identification of buried objects, at shallow depths, from the complex-valued reflectance of electromagnetic waves that are radiated and received by an antenna. The antenna is scanned over an area to search for the object. Because object depth is shallow, the antenna is placed in the object's nearfield. The measured distribution of reflectance is processed to form an image which gives shape because diffraction spreading is slight in the nearfield. The reflectance over the object's center is processed by inversion to yield object depth, thickness, and refractive index from multiple frequency measurements; the object is assumed homogeneous as is the contiguous region.
In microwave systems for detecting or imaging buried dielectric anomalies, a common
technique is to search for reflectance variations by mechanically scanning an antenna over
an area. The antenna usually operates in its and the object's nearfields to reduce diffraction
spreading so that the reflectance distribution resembles the object's shape and is thus an
image. Although mechanical scanning is reliable, it is slow because data acquisition is
sequential. Data acquisition can be accelerated by an antenna array. An array provides
spatially parallel data channels. If a single transmitter and receiver unit are used, acquisition
is sequential but very fast with solid state switches. If each antenna has a transmitter and
receiver, acquisition is simultaneous, and costs increase.