Mansoor Sabzali^1,, Lloyd Pilgrim¹

Refraction is always a major problem for the near-ground geodetic measurements. Thus far, there have been numerous studies showing the influences of atmosphere on the refracted ray leading to the variation in the distance and direction measurements. The refraction is projected into two non-correlated components on horizontal and vertical planes called horizontal and vertical refraction, respectively. Both impact the measurements in their corresponding directions. It is noted that, in terms of magnitude, the refracted zenith angle, in vertical plane, has always been assumed to be far larger than refracted horizontal angles (i.e., refracted horizontal angle is imagined to be minor or negligible). There are considerable productive understandings of vertical refraction influencing the vertical/zenith direction in the literatures. However, the limitation in determination of the horizontal (side or lateral) refraction is still a debatable issue. The research aimed to reveal the broader comprehension of the horizontally refracted ray affecting horizontal angle measurements. The presented model embraces the relationship between the zenith angle and refracted horizontal angle, which could be the desirable technique to computation of refracted horizontal angle at each zenith angle (i.e., ideally, it can be employed in the case of terrestrial laser scanning due to the change of zenith angle for every individual measured point). Thus, the dependency between vertical and horizontal refraction will be obvious.

dependency, horizontal refraction, influence of atmosphere, vertical refraction