Java·Applied·Geodesy·3D

Statistically based deformation analysis

Plot of the resulting point shifts derived by JAG3D's observations based deformation analysis of the Delft network
Plot of the resulting point shifts derived by JAG3D's observations based deformation analysis

Monitoring measurements are a main task in geodetic engineering to detect changes at technical facilities, like e. g. bridge works or storage dams, or natural objects, like e. g. hillside or coasts. By applying statistical analysis methods, it is proven whether an object has shifted or has deformed. For this purpose, the object is periodically controlled by measurements. Such a measurement campaign is denoted as epoch. To ensure a ratio of about 1:5 between the measurement uncertainties and the expected deformation patterns, generally high precision instruments, like e. g. total stations and levelling instruments, are used within the measurement epochs.

The congruence of a network under consideration can be proven, if at least two measurement epochs are available. Usually, the resulting point sets of the individual adjusted epochs are compared to each other. However, the deformation analysis implemented in JAG3D bases on the observation level. For that reason, the full set of information provided by the measurement epochs are taken into account within the analysis procedure. Rigorous statistical test methods are used to identify individual point shifts but also common shifts or strains of a point group of the network.

Monitoring measurements at Onsala Space Observatory

Precise levelling to verify the stability of a bubble mareograph at the Onsala Space Observatory
Precise levelling to verify the stability of a bubble mareograph at the Onsala Space Observatory

The Onsala Space Observatory (Sweden) is a geodetic fundamental station. The station hosts several permanent GNSS antennas and four VLBI radio telescopes. The observatory is located close to the Kattegat and operates one GNSS marigraph, one radar marigraphs, and several so-called bubble marigraphs. This tide gauges observe changes at the mean sea level.

Since 2015, the observatory is an official gauging station of the Swedish Meteorological and Hydrological Institute (SMHI). The invariance of the gauges must be verified routinely. For that reason, several levelling measurement epochs are analysed using the software package JAG3D, and the stability of the station network as well as the gauges are proven.