Atmospheric Attenuation and Scintillation Effects on the Range of EDM Instruments

Abstract

This investigation aimed to study the range of various electronic distance measurement (EDM) instruments used in survey engineering, assuming different weather conditions and different terrain altitudes, by controlling every parameter influencing the measurements and contrasting the results with the information provided by the manufacturers. The first step consisted of determining the EDM real optical wavelength to be used for control against the manufacturers provided values. Consequently, a spectroscopy test of the lasers installed in every EDM instrument was carried out at the ESA-VSC [European Space Agency (ESA) and Val Space Consortium (VSC)] laboratory. The second step was to study the total measurement range of each instrument in different weather conditions and at different altitudes. Three experimental tests were carried out at three different locations in eastern Spain, separated by distances of less than 90 km, and altitudes ranging from sea level to about 2,000 m. Owing to the influence of atmospheric effects on the EDM ranges, some atmospheric parameters were carefully measured during the process (i.e., pressure, temperature, and humidity). From the experiments, a large dependence of altitude on the EDM ranges was detected. A decrease in range at midday hours was observed in all cases studied. Aerosol scattering was found to cause a reduction of EDM range in all cases. A marked influence of atmospheric scintillation on the EDM ranges became evident in all results. Furthermore, as expected, a correlation between laser beam divergence and range, which increased with altitude, was also found. In certain projects where range in EDM is essential, it is advisable to conduct a preliminary study to evaluate the actual range of the particular instrument before it is used.