KEYWORDS: Solids, Acoustics, Data modeling, Signal attenuation, Commercial off the shelf technology, Inspection, Databases, Target detection, Fluctuations and noise, Error analysis
Many small Unmanned Underwater Vehicles (UUVs) currently utilize inexpensive, low resolution sonars that are either
mechanically or electronically steered as their main sensors. These sonars do not provide high quality images and are
quite dissimilar from the broad area search sonars that will most likely be the source of the localization data given to the
UUV in a reacquisition scenario. Therefore, the acoustic data returned by the UUV in its attempt to reacquire the target
will look quite different from the original wide area image. The problem then becomes how to determine that the UUV is
looking at the same object. Our approach is to exploit the maneuverability of the UUV and currently unused information
in the echoes returned from these Commercial-Off-The-Shelf (COTS) sonars in order to classify a presumptive target as
an object of interest. The approach hinges on the ability of the UUV to maneuver around the target in order to insonify
the target at different frequencies of insonification, ranges, and aspects. We show how this approach would allow the
UUV to extract a feature set derived from the inversion of simple physics-based models. These models predict echo
time-of-arrival and inversion of these models using the echo data allows effective classification based on estimated
surface and bulk material properties. We have simulated UUV maneuvers by positioning targets at different ranges and
aspects to the sonar and have then interrogated the target at different frequencies. The properties that have been extracted
include longitudinal, and shear speeds of the bulk, as well as longitudinal speed, Rayleigh speed, and density of the
surface. The material properties we have extracted using this approach match the tabulated material values within 8%.
We also show that only a few material properties are required to effectively segregate many classes of materials.
The inferred line-spread function is an easy technique for measuring orthogonal components of the two-dimensional modulation transfer function (MTF), even from the air. However, it has been most commonly used for cameras for which the resolution is nowhere near the Nyquist frequency. The purpose of such limitation is so that the pixel sampling does not have a serious consequence on the measurement of the MTF. The binning capability of the purely digital DIPOL camera is used to demonstrate that using this method even in moderately oversampled systems does not impact results as long as certain averaging techniques are used. A brief tutorial of the normalization and pitfalls of the method will also be given so that this powerful and simple measurement will become more widely used. Example images will also be shown of mine simulators, together with polarization-product images.
We have developed a new and widely-applicable chemical sensing technology based on the coordinated detection of photo-induced charge movements (PICM) of reporter molecules embedded in polymer films. This general technique has been successfully applied to the detection of biomolecules such as sugars as well as other biochemicals. By detecting specific pathogen derived biomolecules, a pathogen-specific sensor can be constructed. We have shown the feasibility of this approach by fabricating a sensor sensitive to the presence of molecules of bacterial origin. These sensors can have a real-time response. They are also inexpensive to manufacture and can be made disposable. We are developing a miniature array of such sensors that may be able to concurrently determine a variety of analytes. Besides biomolecules, this sensing technology can also be applied to the quantification of other organic and inorganic chemicals such as oxygen and ions. The ability of oxygen as well as other molecules to interact with singlet states of molecules and quench fluorescence can also affect the mechanisms that product PICM. For some molecules the quenching of PICM can be shown to follow typical Stern-Volmer quenching. We have investigated the oxygen-sensitivity of several families of compounds known to produce PICM, including the fullerenes.
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