Geodetic Refraction

Book excerpt: 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.