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I. Kabashi, G. Retscher:
"High frequent simultaneous zenith angle observations using video theodolites for deformation monitoring";
accepted as talk for: International Conference "Dynamic Planet 2005" (IAG), Cairns, Australia; 2005-08-22 - 2005-08-26.

The design of measuring robots with video sensors enables to achieve geodetic precision measurements highly accurate, reliable and under the aspect of economy. Since in these geodetic instruments a CCD camera is integrated, it is for the first time possible to determine refraction effects `high frequent´ from continuous zenith angle observations. The paper will present the application of two automated theodolites (so-called video theodolites) for simultaneous zenith angle observation during long periods with high frequency in open environment. By simultaneous reciprocal zenith angle observation (by means of trigonometric leveling) the difference in height is derived from these series of measurements. Using the system, accuracy levels for the height difference estimation in the same range as usually only achieved by the means of precise leveling could be obtained. Test measurements have been carried out for different distances up to 400 m between the two sations where accuracies of  1 mm for the height differences could be achieved. Using the developed fully automatic and continuous measuring system the high frequent observation of height changes in deformation monitoring can be a typical application. Thereby the simultaneous observations can be carried out with frequencies up to 25 Hz.