Abstract: We describe an efficient algorithm for evaluating the (weighted bipartite graph of) associations between two sets of data with gaussian error, e.g., between a set of measured state vectors and a set of estimated state vectors. First a general method is developed for determining, from the covariance matrix, minimal d-dimensional error ellipsoids for the state vectors which always overlap when a gating criterion is satisfied. Circumscribing boxes, or d-ranges, for the data ellipsoids are then found and whenever they overlap the association probability is computed. For efficiently determining the intersections of the d-ranges a multidimensional search tree method is used to reduce the overall scaling of the evaluation of associations. Very few associations that lie outside the predetermined error threshold or gate are evaluated. Empirical testing for variously distributed data in both three and eight dimensions indicate that the scaling is significantly reduced from N2, where N is the size of the data set.

Abstract: A method and apparatus for real-time monitoring of particulates in a fluid. The fluid is illuminated, and an image formed of the interior of the fluid. The image is then detected, and processed to determine the size, shape, etc. of particulates within the fluid.

Abstract: A method for enhancing signal-to-noise ratio and resolution of amplitude stable signals wherein underwater acoustic data is first collected with an array of hydrophones, and then the data is digitally sampled. After producing spectra of sequential time snapshots of the digitally-sampled data, the spectra are beamformed for a single frequency. Next the low resolution beamformer response is deconvolved from the data by use of a calculated beam response pattern for the hydrophone array, so that many high-resolution estimates are created for each time snapshot. Finally, the resulting high resolution estimates are reduced to a single estimate for each spatial bin across all of the time snapshots, and the high resolution, high gain results are displayed.

Abstract: An acoustic classification system in which echoes from sediment-sediment or water-sediment interfaces are compared to model waveforms predicted by Biot's equations for a given set of acoustic material parameters. The selection of parameters are varied until a match occurs, indicating the correct parameters of the reflecting sediments. Preferably, the variation of selected test parameters is conducted by formal search algorithms, such as simulated annealing or genetic algorithms, to increase computational efficiency.

Abstract: A thin film reflecting interference filter (RIF) is designed to suppress unwanted harmonics thereby improving the monochromaticity of the radiation. An interference layer of material which has a well-defined plasma oscillation is deposited on a substrate and a mismatch layer is formed thereon. This interference layer exploits the interference between wavefronts reflected from the layer-substrate and the vacuum-layer interfaces to suppress higher order harmonics, while allowing good reflectance at the fundamental wavelength. This is achieved by positioning the RIF in the radiation at an angle of incidence which is greater than the critical angle of the desired fundamental wavelength, but less than critical angles of the harmonics to be suppressed. The mismatch layer increases the reflectance of the unwanted harmonics at the vacuum-layer interface, thus allowing more complete destructive interference of the unwanted harmonics.

Abstract: A signal filter, and method of signal filtering, in which an optical signal s spatially dispersed according to frequency, and undesired frequencies blocked out. In an embodiment, a Bragg cell receives a (typically microwave) signal, and transduces it to an acoustic signal. A light source, e.g. a laser diode, directs light through the acoustic signal in a known manner so as to produce an optical output which is spatially dispersed according to frequency. A programmable spatial light modulator blocks out unwanted frequency components. Upon removal of the optical carrier, e.g. by heterodyning the spatial light modulator's output with a reference signal from the light source, the components can be recombined into a resultant filtered signal. The invention can be used as a repeater, a military electronic countermeasure, in environments which have large amounts of electromagnetic clutter but in which one does not want the clutter repeated.