David G. Falconer

Through-the-wall differential radar

We have designed and built an ultra-wideband differential radar that images targets moving behind walls, fences, trees, and other obstacles. We have demonstrated the differential-radar concept in anechoic, indoor, and outdoor environments. The outdoor demonstration proved the radars ability to detect people moving behind walls and illustrated its capability for suppressing high-level clutter from the radar imagery.

Image Enhancement and Film-grain Noise

Film-grain noise severely limits the possibilities for enhancing degraded photographic images. Because the grain noise increases monotonically with the photographs mean or bias transmittance, poor signal-to-noise ratios result whenever the emulsion receives a low-contrast, high-level exposure. Image degradation—such as that resulting from inadvertent camera motion—preserves the level of the exposure, but lowers the image contrast inversely at the spatial frequency in question. Consequently, the observed signal-to-noise ratio and the theoretical enhanceability of the degraded image drop with increasing spatial frequency. Unfortunately, the tendency for low spatial frequencies to dominate the highs in the typical object scene, and the relative importance of the highs in obtaining quality image recordings, compound the enhancement problem still further. Nevertheless, Wiener-filter theory—reworked under the assumption of multiplicative film-grain noise—still provides some resolution improvement for imaging d...

Robot-mounted through-wall radar for detecting, locating, and identifying building occupants

We have assembled programmed, and demonstrated a robot-mounted motion-detection radar suitable for through-wall operation. Our radar, which employs of pulse-Doppler techniques, is designed to look through building walls and locate moving targets. The radars signal-processing algorithms use both time-domain and frequency-domain clues to classify detected motion as arising from: (1) the ambient background; (2) mechanical motion; or (3) human activity. In the case of human motion, our routines also attempt to identify the occupants particular activity, e.g., resting, walking, talking.

Optical processing of bubble chamber photographs.

The processing of bubble chamber photographs has emerged as a major task in the experimental study of sub-atomic decays and interactions. Although electronic computer techniques have proved useful in reconstructing the geometry and ascertaining the kinematics of high-energy events, the scanning and measuring of bubble chamber photographs has remained for the most part unautomated. An alternate approach to the computerization of the scan-measure task is through the newly developed optical computer, a device which accepts input data on photographic film and thus obviates the need for digitizing photographs before processing. The optical computer can aid the scan-measure task by suppressing beam tracks, measuring track widths, and determining scattering angles.

Detection, location, and identification of building occupants using a robot-mounted through-wall radar

We have assembled, programmed, and demonstrated a robot- mounted motion-detection radar suitable for through-wall operation. Our radar, which employs pulse-Doppler techniques, is designed to look through building walls and locate moving targets. The radars signal-processing algorithms use both time-domain and frequency-domain clues to classify detected motion as arising from: (1) the ambient background; (2) mechanical motion; or (3) human activity. In the case of human motion, our routines also attempt to identify the occupants particular activity, e.g., resting, walking, talking.

Tomographic imaging of radar data gathered on a circular flight path about a three-dimensional target zone

We have coded a tomographic-style algorithm that is capable of imaging radar data obtained on a circular flight path about a 3D target zone. Our imaging algorithm is designed to image field data collected with Mireages new Subsurface Imaging Synthetic Aperture Radar (SISAR), a ground-penetrating device operating in the spotlight mode. The SISAR algorithm operates on radar data gathered in (or converted to) the range-azimuth domain--the so-called sinogram plane. On the sinogram plane, the impulse response of a point scatterer is sinewave- shaped curve. The amplitude of the sinewave is related to the targets radial coordinate, its phase to the targets azimuthal coordinate, and its bias to the targets burial depth. When flown on a circular path about a 3D target zone, SISAR generates 3D-style sinograms. Our imaging algorithm produces 3D maps of the target zone by converting each sinewave trace on the sinogram plane to a delta function in three-space. The code is fast (in the FFT sense). Moreover, it avoids the laborious, and often inaccurate conversion of the collected radar data from cylindrical coordinates to rectangular ones, as in conventional radar imaging.

Detection of chemical contraband using spectroscopic microwave imaging

We have developed and demonstrated a microwave technique for detecting high explosives, illegal drugs, and other chemical contraband in checked airline baggage. Our technique isolates suspicious materials using microwave tomography and identifies chemical contraband using microwave spectroscopy. Measurements in the frequency range 2 - 18 GHz indicate that microwave energy will penetrate nonmetallic suitcases and that contraband materials feature distinct dielectric spectra at these wavelengths. We have also formed microwave images of a soft-sided suitcase and its contents. After manually segmenting the microwave imagery, we successfully identified chemical simulants for both high explosives and illegal drugs.

Floor plan radar

Urban-warfare specialists, law-enforcement officers, counter-drug agents, and counter-terrorism experts encounter operational situations where they must assault a target building and capture or rescue its occupants. To minimize potential casualties, the assault team needs a picture of the buildings interior and a copy of its floor plan. With this need in mind, we constructed a scale model of a single- story house and imaged its interior using synthetic-aperture techniques. The interior and exterior walls nearest the radar set were imaged with good fidelity, but the distal ones appear poorly defined and surrounded by ghosts and artifacts. The latter defects are traceable to beam attenuation, wavefront distortion, multiple scattering, traveling waves, resonance phenomena, and other effects not accounted for in the traditional (noninteracting, isotropic point scatterer) model for radar imaging.

Spatial modulation display using spatial light modulators

A spatial modulation display is described that permits the observation of a phantom or transparent image by several persons simultaneously and is suitable for medical imaging. The display uses spatial light modulators and large format convex lenses within a Schlieren optical system. The number of sectional images in a three-dimensional image is limited by the number of spatial light modulators. The display is electro-optical and requires no moving parts.

Radar imaging using statistical orthogonality

Statistical orthogonality provides a mathematical basis for imaging scattering data with an inversion algorithm that is both robust and economic. The statistical technique is based on the approximate orthogonality of vectors whose elements are exponential functions with imaginary arguments and random phase angles. This orthogonality allows one to image radar data without first inverting a matrix whose dimensionality equals or exceeds the number of pixels or voxels in the algorithmic image. Additionally, statistical-based methods are applicable to data sets collected under a wide range of operational conditions, e.g., the random flight paths of the curvilinear SAR, the frequency-hopping emissions of ultra- wideband radar, or the narrowband data collected with a bistatic radar. The statistical approach also avoids the often-challenging and computationally intensive task of converting the collected measurements to a data format that is appropriate for imaging with a fast Fourier transform (FFT) or fast tomography algorithm (FTA), e.g., interpolating from polar to rectangular coordinates, or conversely.