Due to the lack of high-power sources along with strong electromagnetic absorption by water vapor at frequencies between ~100 GHz and ~10 THz, there are very few radar systems, or any other systems for that matter, operating in this region of the spectrum. For this reason, it is sometimes referred to as the terahertz gap. Source technology, however, is improving, thus facilitating radar systems operating in this new frontier of the electromagnetic spectrum. At the lower end of this spectral region near the millimeter/submillimeter transition, components are more readily available and atmospheric attenuation is moderate in comparison to higher frequencies. Utilizing components that can generate on the order of 50 mW of power, a real aperture radar for imaging surfaces up to several hundred meters has been developed. The goal of this research is to determine if this frequency can provide adequate 3D surface imaging through Degraded Visual Environments (DVEs) yet consume less volume than existing systems at 94 GHz. Transmitting a vertically oriented fan beam to scan the Field of View (FOV) in azimuth and receiving at two vertically, displaced locations with identical fan beams forming an interferometer, three dimensional images of the surface topography (in range, azimuth and height) can be generated. This paper describes the design of the prototype system and presents initial results.
The design of an open-path 320 GHz - 340 GHz coherent transmissometer for experimental measurements of amplitude
scintillation, phase scintillation, angle-of-arrival (AoA) fluctuations, and transverse coherence near the 325.1529 GHz
water absorption resonance is presented. The system uses a uni-directional transmitter and two phase-coherent receivers
with adjustable transverse. The objective of the experiment is to verify and improve existing propagation models for use
by designers of applied THz systems for remote sensing, radiolocation, or communications. System stability will be
verified using a short range near-ground test path of several ~10's of meters length using a cable for locking the
transmitter local oscillator (LO) to the receivers' LOs. This short range configuration, similar to tests conducted at
Flatville, Illinois during the 1980s, permits characterization of system errors in all of the above parameters, thus
yielding a baseline for the long range experiments. Characterization of the phase-coherent RF link will be studied vis-à-vis
anticipated theoretical performance based on the Rytov approximation. The system will then be configured for long
term open-path measurements on a 1.78 km elevated link between the University of Colorado at Boulder (CU) and the
National Telecommunications and Information Administration (NTIA) Mesa site at the NOAA-NIST campus in
Boulder, Colorado. The system will provide long range coherent THz propagation statistics during continuous longduration
study of turbulent atmospheric propagation effects over an extensive array of atmospheric conditions in a
realistic operational environment.
KEYWORDS: Radar, Synthetic aperture radar, Device simulation, Backscatter, Polarimetry, Data modeling, X band, Signal attenuation, S band, Reflectivity
Recent advances in X-band Synthetic Aperture Radar (XSAR) technology have revived meteorological applications
with this type of radar. At this wavelength, attenuation and backscatter caused precipitation can be
detected, and has been observed in current and past XSAR systems. Based on real fully polarimetric S-band
ground radar observations of storms, a model is constructed to simulate spaceborne XSAR observations. Simulation
results are compared to storm observations from several repeat pass dual polarization TerraSAR-X
acquisitions over Florida. Development of these simulations provides a mechanism to explore the capabilites of
precipitation surveillance from from XSAR as well as progress towards mitigation of storm effects for traditional
SAR applications.
Recent research in haptic systems has begun to focus on the generation of textures to enhance haptic simulations. Synthetic texture generation can be achieved through the use of stochastic modeling techniques to produce random and pseudo-random texture patterns. These models are based on techniques used in computer graphics texture generation and textured image analysis and modeling. The goal for this project is to synthesize haptic textures that are perceptually distinct. Two new rendering methods for haptic texturing are presented for implementation of stochastic based texture models using a 3 DOF point interaction haptic interface. The synthesized textures can be used in a myriad of applications, including haptic data visualization for blind individuals and overall enhancement of haptic simulations.
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