Photoacoustic spectroscopy is a useful noninvasive technique for monitoring chemical composition in liquid. The resolution capability of photoacoustic methods is limited due to the low absorbance factor of some liquid. To increase effective absorbance distance of laser beams, two novel photoacoustic cell structures are introduced, in which multi-beam photoacoustic sources are produced respectively by zigzag reflection and inner-circle reflection of a single incident laser beam. Approximate surface acoustic waves can be produced in the two cell structures. The mathematical models are also labored, which can provide preliminary simulation results. Using which, A conclusion can be drawn that the acoustic pressure produced by the zigzag reflecting multi-beam acoustic source can reach at about 500 times than that produced by single-beam source with same incident laser power. A rough estimate can also be made that with a large number of reflecting, the acoustic pressure produced by the inner-circle reflecting multi-beam source can easily reach 50 times than that produced by single-beam source with same incident laser power.
A novel tilt measurement method is proposed based on self-demodulated fiber Bragg grating (FBG) sensor system, which consists of a couple of matched FBGs and a cantilever-based pendulum clinometer. With a cantilever structure, the tilt angle is measured by means of a differential form of Bragg wavelength shifting, with which the cross-sensitivity of temperature is eliminated simultaneously. It has been proved by both simulations and preliminary experimental results that a high resolution better than 0.0022 degree can be achieved in the range of +/-10 degrees.
High-pressure measurement is made by demodulating Bragg grating peak splitting caused by transverse stress differences in the core of a high-birefringence (HB) single-mode fiber, which is bonded on the exterior surface of a free active element bulk modulus. The two orthogonally polarized signals reflected from the HB fiber Bragg grating (FBG) can be independently detected with a simple FBG interrogation system, which is based on the light intensity measurement method. In addition, the cross-sensitivity of the FBG sensor can be self-compensated by this method. The measurement principle is introduced, and preliminary experimental results indicate that the measurement sensitivity is estimated to be ~12 pm/N in a linear measurement range from 0 to 120 N.
Based on near-infrared spectral absorption and fiber-optic sensor technology, an experimental setup for low-water-content measurement of crude oil is developed. The advantages of this method include fast measurement, high accuracy, keeping the measured oil free of pollution, and being suitable for long-term on-line continuous monitoring. This technology can be used for those applications that require high-quality water-in-oil measurement and process control. The measurement resolution for water content is better than 0.005% in the range from zero to 2% by volume. Measurement errors are estimated to be ±0.01% in the range from zero to 1%.
In this paper, a new method is proposed for supervised classification of ground cover types by using polarimetric synthetic aperture radar (SAR) data. The concept of similarity parameter between two scattering matrices is introduced and it is shown to be able to maintain some intrinsic properties of scattering mechanism. Four similarity parameters of each pixel in image are used for classification. The scattering matrix span of each pixel is also used to establish the feature space. The principal component analysis is adopted for extracting the feature transform vector and for making classification decision. The classification result of the new method is given with comparison to that of the maximum likelihood method, demonstrating the effectiveness of the proposed scheme.