Geodetic Refraction

With very few exceptions, geodetic measurements use electro­ magnetic radiation in order to measure directions, distances, time delays, and Doppler frequency shifts, to name the main ter­ restrial and space observables. Depending on the wavelength of the radiation and the purpose of the measurements, the follow­ ing parameters of the electromagnetic wave are measured: ampli­ tude, phase, angle-of-arrival, polarisation and frequency. Ac­ curate corrections have to be applied to the measurements in order to take into account the effects of the intervening medium between transmitter and receiver. The known solutions use at­ mospheric models, special observation programs, remote sensing techniques and instrumental methods. It has been shown that the effects of the earth's atmospheric envelope present a fundamental limitation to the accuracy and precision of geodetic measurements. This applies equally to ter­ restrial and space applications. Instrumental accuracies are al­ ready below the atmospherically induced limitations, and thus the accuracy demands on the geodetic refraction solutions are entering a new magnitude zone. This monograph is primarily devoted to the properties of the at­ mospheric effects on various geodetic measurements and to their evaluation. Ten review papers cover the most pressing aspects of the atmospheric effects on geodetic measurement~. Ttiese state­ of-the art papers were written by eminent specialists in their respective research fields.