This book provides an introduction, at academic level, into the field of surveying and mapping. The book has been compiled based on hand-outs and readers written for the third-year course Surveying and Mapping, in the bachelor program Civil Engineering at Delft University of Technology. This book covers a wide range of measurement techniques, from land surveying, GPS/GNSS and remote sensing to the associated data processing, the underlying coordinate reference systems, as well as the analysis and visualization of the acquired geospatial information.@en

The backbone of the Amsterdam Ordnance Datum (NAP) is a network of about 400 primary subsurface markers. Relative movements between the primary subsurface markers are measured with spirit levelling once in 10-20 years. However, little is known about absolute vertical movements of the primary network. This information is indispensable for the interpretation of water level measurements at the tide gauges along the Dutch coast. It may be provided by gravity measurements. Here we present a time-series analysis of more than twenty years of gravity measurements at the stations Westerbork, Epen, Zundert, and Radio Kootwijk. It reveals that only station Epen shows a statistically significant movement of -0:252±0:066 μGal yr-1, which corresponds to an uplift of 1:3±0:5mmyr-1. For the other stations, the trends are statistically not different from zero at a significance level of 0.05. Corrections for water table variations are found to be indispensable; peak-to-peak amplitudes range from 4 μGal (Westerbork) to 28 μGal (Radio Kootwijk). Depsite some fundamental objections, corrections for instrumental offsets reduce the data scatter. First experiments with 7 years of soil moisture data acquired at station Radio Kootwijk reveal that the gravity signal of soil moisture variations has a standard deviation of 2:2 μGal, which is comparable to the noise standard deviation of measured gravity.

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The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in the spring of 2018.

Here we present the list of the participants who actually performed measurements during the comparison, the data submitted by the operators as well as the results of the determination of the gravity as a function of height at the comparison sites. The measurement strategy is briefly discussed and the results of the data harmonization is documented. Finally, the results of the constrained least squares adjustment are presented including the degrees of equivalence of each gravimeter and the key comparison reference values.@en

In 2014 a team of researchers from five European universities reported on a high tilt susceptibility of the Scintrex CG-5 Autograv land gravity meter. In a series of experiments they demonstrated that the instrument provides incorrect readings after being tilted by angles of at least about 6∘ for a period of at least a few minutes. The readings may be offset by tens of μGal, and it may take hours before the first reliable readings can be taken. They recommend to keep the instrument in upright position within less than the critical angle of about 6∘ during transits, which may be unrealistic during field operations in hilly terrain, during car transportation or when walking with the instrument in a backpack. The instruments tested in 2014 were purchased between 2003 and 2011. Here, we report about the results of a series of experiments with the latest release of the Scintrex CG-5 purchased in 2015 using the same experimental set-up as in 2014. We show that the instrument is still susceptible to tilting though the initial offset has been reduced by about 50%. However, readings may still be offset by tens of μGal if the tilt exceeds about 6∘ and lasts for more than 1 min. Moreover, the time it takes the instrument to provide reliable readings in line with the specifications may still take several hours depending on the temporal duration of instrument tilting. From this we conclude that the problem of tilt susceptibility has not been solved yet.@en