Determination of the Refraction Coefficient and Its Uncertainty by Using Modern Hydrostatic Levelling Systems

In spite of the technological development of the last decades in the field of the geodetic instruments,some parameters,which affect their performance,are difficult to be eliminated.One of these parameters is the geodetic refraction.The refraction describes the alteration in the direction of the light curve as it propagates through the different layers of the lower part of the Earth’s atmosphere.The purpose of this research work is to investigate the uncertainty of the refraction coefficient of a new proposed methodology.This methodology is based on:(a)the exploitation of the full trigonometric height equation,(b)the ability of the Hydrostatic Levelling System(HLS)to provide height differences with±10μm accuracy.The experimental application has been set up in a section of the underground tunnel complex at the European Organization for Nuclear Research.In this indoor application,the determination of the refraction coefficient at a Laser Tracker station using the precise height differences provided by an HLS has been performed.In addition,this methodology has been tested by comparing its results with those that have been obtained from the Temperature Gradient(TG)method for the determination of the refraction coefficient.The results are very encouraging for the efficiency of the methodology.At the same time,some limitations on the implementation of the proposed methodology have been highlighted.

Reflection and refraction of attenuated waves at boundary of elastic solid and porous solid saturated with two immiscible viscous fluids

The propagation of elastic waves is studied in a porous solid saturated with two immiscible viscous fluids. The propagation of three longitudinal waves is represented through three scalar potential functions. The lone transverse wave is presented by a vector potential function. The displacements of particles in different phases of the aggregate are defined in terms of these potential functions. It is shown that there exist three longitudinal waves and one transverse wave. The phenomena of reflection and refraction due to longitudinal and transverse waves at a plane interface between an elastic solid half-space and a porous solid half-space saturated with two immiscible viscous fluids are investigated. For the presence of viscosity in pore-fluids, the waves refracted to the porous medium attenuate in the direction normal to the interface. The ratios of the amplitudes of the reflected and refracted waves to that of the incident wave are calculated as a non- singular system of linear algebraic equations. These amplitude ratios are used to further calculate the shares of different scattered waves in the energy of the incident wave. The modulus of the amplitude and the energy ratios with the angle of incidence are computed for a particular numerical model. The conservation of the energy across the interface is verified. The effects of variations in non-wet saturation of pores and frequencies on the energy partition are depicted graphically and discussed,

The Approach of Compensation of Air Refractive Index in Thermal Expansion Coefficients Measurement Based on Laser Feedback Interferometry

We present the thermal expansion coefficient （TEC） measurement technology of compensating for the effect of variations in the refractive index based on a Nd： YA G laser feedback system, the beam frequency is shifted by a pair of aeousto-optic modulators and then the heterodyne phase measurement technique is used. The sample measured is placed in a muffle furnace with two coaxial holes opened on the opposite furnace walls. The measurement beams hit perpendicularly and coaxially on each surface of the sample. The reference beams hit on the reference mirror and the high-refiectivity mirror, respectively. By the heterodyne configuration and computing, the influences of the vibration, distortion of the sample supporter and the effect of variations in the refractive index are measured and largely minimized. For validation, the TECs of aluminum samples are determined in the temperature range of 29-748K, confirming not only the precision within 5 × 10-7 K-1 and the accuracy within 0.4% from 298K to 448K but also the high sensitivity non-contact measurement of the lower reflectivity surface induced by the sample oxidization from 448 K to 748 K.