Digital seismic recordings always contain noise. The level of noise in any seismic recording depends on the natural sources of noise near the site, the design and quality of the seismic vault, the installation method of the seismic equipment and the instrumental noise. To improve the quality of a seismic network to observe natural (and induced) seismicity it is necessary to have knowledge of these different types of noise in the recordings. In cooperation with the University of Utrecht the KNMI has developed a new technique to isolate and quantify instrumental self-noise of seismic instrumentation in a broad frequency band. On the other hand, the monitoring of ambient noise is a well-established technique to detect instrumental features that may bias the analysis of natural seismicity.

• R. Sleeman, A. van Wettum and J. Trampert, Three-channel correlation analysis: a new technique to measure instrumental noise of digitizers and seismic sensors
  Bulletin of the Seismological Society of America, 2006, 96, 1, 258-271.
• Vila, J., R. Macia, R. Sleeman and A.M. Correig, On the stability of the Earth's fluctuations spectral peaks at their lowest amplitude level
  Fluctuation and Noise Letters (FNL), 2008, 8, 3, L237-L248.