Most of our knowledge of the Earth’s interior results from seismological observations. The measurements are based on the fact that different rock types show different physical properties, and that seismic waves (e.g., from earthquakes or explosions) travelling through the Earth can be observed at the surface and be used to infer the internal architecture. Early seismological observations revealed the layered structure of the Earth, and today scientists are working on imaging the regional and local structural variations to better understand the geological processes and dynamics forming the Earth. However, seismic methods are also utilized to reveal the shallow parts bearing important resources such as hydrocarbons, water, or mineral deposits. In every case, the challenge for these seismic methods is to provide ever detailed images of the subsurface. One important step toward this aim is to increase the number of observations which can often be achieved by increasing the number of recording instruments. Recent technological advances in the field of A/D-converters, GPS receivers, and data storage led to the development of very compact autonomous recorders with a significantly reduced power consumption. Now, more instruments can be transported and installed with less personnel and costs, which results in significantly denser spatial sampling of the seismic wave field, thus eventually yielding better resolved subsurface images.