Bruce D. Hansche

Quad-phase correlation filters for pattern recognition

A quad-phase-only filter (QPOF) is introduced. It is shown that the QPOF can have improved correlation response and signal-to-noise ratio with respect to the Hartley binary phase-only filter for some objects.

Quad-phase-only filter implementation.

Some of the fastest commercially available coherent spatial light modulators are binary. This fact has motivated research on the binary phase-only filter, which is unfortunately unable to represent a complex filter function. A technique is introduced here with which a single binary device can be used to represent a complex filter with independent binary representation of real and imaginary parts. The technique is analyzed theoretically, and simulation and laboratory results are presented.

A Comparison Of Real-Time Optical Correlators For Pattern Recognition

Two types of optical correlators have been built to investigate real-time pattern recognition. The first employs one-dimensional devices to perform the two dimensional correlation in real time. This architecture uses an array of light emitting diodes (LEDs) to input an electronically stored reference image into the processor in parallel. The input scene data is introduced into the processor one line at a time using an acousto-optic device (AOD). Multichannel time integrating correlations are performed in the row direction using the AOD and in the column direction using a charge coupled device (CCD) operating in the time delay and integrate mode. A processor has been built using this technology which correlates a 64 x 44 pixel binary reference image with a 256 x 232 input scene at video rates. The second correlator is a space integrating Fourier transform based correlator. A magneto optic-device (MOD) is used at the Fourier transform plane to rapidly change filter functions. The binary nature of the MOD device necessitates using either a binary phase or binary amplitude representation of the desired complex filter function. For this reason, several types of Binary Phase-Only Filter (BPOF) representations have been analyzed and experimentally investigated. Experimental correlation results have been obtained using both the Hartley BPOF and a newly developed class of complex binary filters, called Quad-Phase-Only Filters (QPOF). The performance of the two systems will be compared on the basis of processing speed, space bandwidth product, processor size and light efficiency. The inherent differences between incoherent and coherent processing and their implications for filter design will also be discussed. Finally, estimates of future performance will be presented.

Holographic Interferogram Analysis from a Single View

Quantitative analysis of a holographic interferogram requires either multiple interferograms and hence a great deal of data or strict a priori assumptions. This work presents a class of assumptions that reduces to one the number of views necessary for three-dimensional motion. The method involves relating points on the body via rigid-body theory and calculating deviations from this ideal deformation. It requires knowledge of the expected deformation. An example is given using internally pressurized spherical shells.

Health monitoring studies on composite structures for aerospace applications

This paper discusses ongoing work to develop structural health monitoring techniques for composite aerospace structures such as aircraft control surfaces, fuselage sections or repairs, and reusable launch vehicle fuel tanks. The overall project is divided into four tasks: Operational evaluation, diagnostic measurements, information condensation, and damage detection. Five composite plates were constructed to study delaminations, disbonds, and fluid retention issues as the initial step in creating an operational system. These four square feet plates were graphite-epoxy with nomex honeycomb cores. The diagnostic measurements are composed of modal tests with a scanning laser vibrometer at over 500 scan points per plate covering the frequency range up to 2000 Hz. This data has been reduced into experimental dynamics matrices using a generic, software package developed at the University of Colorado at Boulder. The continuing effort will entail performing a series of damage identification studies to detect, localize, and determine the extent of the damage. This work is providing understanding and algorithm development for a global NDE technique for composite aerospace structures.

Optical temporal frequency low-pass filtering and heterodyning with a microchannel plate

A microchannel plate is demonstrated as both an optical low-pass filter and a heterodyning modulator. The frequency response function of the microchannel plate indicates it behaves as a low-pass filter. Antialiasing with the microchannel plate is demonstrated using a two-tone amplitude modulated laser beam, with the higher tone above the cutoff frequency being successfully suppressed while the frequency within the bandwidth of the filter is passed through. Selection of different commercially available phosphors controls the filtering and frequency response characteristics of the optical filter, effectively moving the cutoff frequency. By gating the microchannel plate at different frequencies, the microchannel plate can also be used analogously to a heterodyning spectrum analyzer, supplying all of the required functions of a local oscillator, mixer, and filter.

Initial Studies on the use of Laser Velocimetry in the Inspection and Health Monitoring of Aircraft

A major portion of the structure of a modern transport aircraft consists of a relatively thin skin fastened to underlying elements such as stringers, frames, and ribs. All of these structural elements are critical, and flaws such as corrosion, cracks, and fastener or bond failure must be detected at an early stage. Flaws like cracks or failed fasteners in substructure (stringers, frames, etc.) are currently detected by a painstaking internal visual inspection, which requires complete teardown of the aircraft. Some flaws, such as corrosion, may manifest on the surface of the aircraft and can be detected by an external visual inspection. Even in this case, the internal extent of the flaw cannot be easily determined, and inspectors must determine whether to remove the skin for further inspection. These expensive disassembly and inspection processes create a great interest in nondestructive inspection techniques which can detect subsurface defects by observations made on the surface of the aircraft.

Binary Computer Generated Holograms As Spatial Filters

We are interested in making computer generated holographic spatial filters on a graphics device which can plot only a limited number of points (such as a storage-tube terminal). The Generalized Binary Computer Generated Hologram is an algorithm which makes efficient use of available plotting points, thus making it attractive for use with these limited plotters. In this paper we study the nature of the set of complex amplitudes one can code with this algorithm. Our main topic is amplitude quantization noise. We show that, since the quantization steps vary in size, the optimum signal normalization is not necessarily that which uses all the quantization steps. We analyze the amplitude quantization noise in several types of real-valued holograms to demonstrate this behavior. We give the results of a measurement of errors in dot size and dot position on a storage tube terminal, and relate this noise to our analysis of amplitude quantization noise.

Space-bandwidth product of some deblurring filters

We present an estimate of the space-bandwidth product of a filter of the form W(f) = [H(f)]/[H(2)(f) + C(f)], which is often encountered in image processing. The estimate applies to blur functions H(f) which are similar to the linear motion blur in that they oscillate smoothly under a decreasing envelope.