Research On The Atmospheric Refraction In The Near Ground Survey Based On Plateau Climate

Atmospheric refraction is one of the main errors in survey, and it depends on the interior structure of atmosphere to a large extent. The particular climate condition and geography characteristic in the plateau areas will affect the high-precision survey more prominently. With the rapid growth of constructional engineering in the plateau areas, it is urgent that how to improve the level of survey data processing in the particular areas such as Tibetan plateau in home. It requires that we have a sufficient research on the internal mechanism of the errors of atmospheric refraction and the correlativity between the errors and the natural condition of this area, and find out the method of atmospheric refraction correction which is suitable for the plateau areas.This paper points out the trait of the atmospheric refraction for near ground survey in the areas of plateau climate. It summarizes the basic characters and leading state of earth atmosphere, and the variational rule of the meteorological elements. Then it, using turbulent transfer model and combining with the practical utilization, deduces the refraction coefficient formula, refraction angle and refraction curvature formula strictly. These formulas are different from old refraction formulas. They are dealed with separately by dividing it into three regions, according to the height which is close to the ground, so that they can describe the refraction influence accurately. The temperature gradient generally is calculated out through determining temperatures on different height in the past, which is very difficult to realize in some surveying areas, and maybe it has the error of the height-temperature model. The temperature gradient based on turbulent transfer model in this paper has considered many kinds of meteorological parameters synthetically, for example, heat flux, cloud cover, surface wetness condition, sight height, etc., so that these formulas can reflect the refraction influence in the areas of plateau climate more properly. And then, it introduces fundamental principle of the electromagnetic distance measurement, and deduces the refraction correction formulas of each kind of rangefinder in detail, namely, meteorological correction formula and curvature correction formula. In addition, it analyses the atmospheric influences in horizontal angle, vertical angle and precise leveling, and puts forward the measures of eliminating and weakening the influence of atmospheric refraction. It analyses the data of Erlang mountain tunnel detailedly, and corrects the atmospheric influence, with these corrective formulas and these meteorological parameters which are estimated through the local climate. But, these atmospheric corrections are not ideal at all. Finally, it analyses the reason of these unideal atmospheric corrections, and points out the next researchful questions of these refraction formulas for the plateau areas.