Results of a hydrogen sensor based on light scattering from a porous silicon surface coated with a thin
palladium film are discussed. Reflected light scattered from the rough surface of porous silicon surface
with a thin palladium film is compared before and after exposure to hydrogen gas. After exposure to
hydrogen gas the sensor's optical reflectance is decreased indicating the presence of hydrogen.
In this paper we excite the surface of porous silicon with incoherent, broad band white light and observe the
spectrum of colors reflected from the surface. Using an atomic force microscope images from red and green
porous silicon samples are collected. In this paper we relate the optical color of the surface to the size of
scattering features on the textured surface. From image segmentation using the watershed transform the
height distributions of the optical scattering features are determined. The heights of these surface features
are then used as input variables to a computer simulation of a reflective grating. The computer predicted
color is compared to the measured color. In this manner, by inspection of the reflected color from the
textured porous silicon surface the physical size of the surface features can be estimated.
A method of infrasonic signal classification using hermite polynomials for signal preprocessing is presented. Infrasound is a low frequency acoustic phenomenon typically in the frequency range 0.01 Hz to 10 Hz. Data collected from infrasound sensors are preprocessed using a hermite orthogonal basis inner product approach. The hermite preprocessed signals result in feature vectors that are used as input to a parallel bank of radial basis function neural networks (RBFNN) for classification. The spread and threshold values for each of the RBFNN are then optimized. Robustness of this classification method is tested by introducing unknown events outside the training set and counting errors. The hermite preprocessing method is shown to have superior performance compared to a standard cepstral preprocessing method.