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Near-surface geophysics is the use of geophysical methods to investigate small-scale features in the shallow (tens of meters) subsurface. [1] It is closely related to applied geophysics or exploration geophysics. Methods used include seismic refraction and reflection, gravity, magnetic, electric, and
Refraction at interface Many materials have a well-characterized refractive index , but these indices often depend strongly upon the frequency of light, causing optical dispersion . Standard refractive index measurements are taken at the "yellow doublet" sodium D line , with a wavelength (λ) of 589 nanometers .
Diagram showing displacement of the Sun's image at sunrise and sunset Comparison of inferior and superior mirages due to differing air refractive indices, n. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. [1]
In the Abbe refractometer the liquid sample is sandwiched into a thin layer between an illuminating prism and a refracting prism. The refracting prism is made of a glass with a high refractive index (e.g., 1.75) and the refractometer is designed to be used with samples having a refractive index smaller than that of the refracting prism.
Geodesy or geodetics [1] is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D.It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems. [2]
A geodetic control network is a network, often of triangles, that are measured precisely by techniques of control surveying, such as terrestrial surveying or satellite geodesy. It is also known as a geodetic network , reference network , control point network , or simply control network .
Geodetic measuring devices measure georeferenced (relative to established locations outside the monitoring area) displacements or movements in one, two or three dimensions. It includes the use of instruments such as total stations , levels , InSAR , [ 2 ] and global navigation satellite system receivers .
Levelling refraction can be eliminated by either of two techniques: Measuring the vertical temperature gradient within the atmospheric boundary layer. Typically two temperature-dependent resistors are used, one at 50 cm (20 in), the other at 250 cm (98 in) height above the ground, mounted on a staff and connected in a Wheatstone bridge .