Sten Bergstrand

BIFROST: Noise properties of GPS time series

The BIFROST project uses GPS to observe the intra-continental deformation of Fennoscandia caused predominantly by Glacial Isostatic Adjustment (GIA). The noise in GPS position time series has been proven correlated, so we investigate a fractal model in order to obtain a parameter that can gauge our network stations true velocity uncertainties and utilize an empirical orthogonal function (EOF) to remove the inherent common mode. We employ a Kaiser window to reduce the power spectrum variance and retain independent power estimates based on the window’s main lobe width ratio compared to that of a boxcar. As power spectra lack Gaussian distribution properties, we devise a transform that normalizes the power spectrum and subsequently iterate a fractional power law noise model.

Intercomparison of lateral scales of scanning electron microscopes and atomic force microscopes in research institutes in Northern Europe

An intercomparison of lateral scales of scanning electron microscopes (SEM) and atomic force microscopes (AFM) in various research laboratories in Northern Europe was organized by the local national metrology institutes. In this paper are presented the results of the comparison, with also an example uncertainty budget for AFM grating pitch measurement. Grating samples (1D) were circulated among the participating laboratories. The participating laboratories were also asked about the calibration of their instruments. The accuracy of the uncertainty estimates seemed to vary largely between the laboratories, and for some laboratories the appropriateness of the calibration procedures could be considered. Several institutes (60% of all results in terms of En value) also had good comprehension of their measurement capability. The average difference from reference value was 6.7 and 10.0 nm for calibrated instruments and 20.6 and 39.9 nm for uncalibrated instruments for 300 nm and 700 nm gratings, respectively. The correlation of the results for both nominally 300 and 700 nm gratings shows that a simple scale factor calibration would have corrected a large part of the deviations from the reference values.

Evaluation of GNSS Monument Stability

We report on an evaluation of the stability of four different GNSS monuments that was conducted in the summer of 2010. The monuments were monitored by forward intersections using a survey system consisting of two robotic total stations and a set of retro reflecting prisms. The system was operated for almost 3 months, performing observations in two faces with a repetition cycle of 5min. Movements in excess of 6 mm were detected. The results show clear evidence that the detected deformations are related to variations in temperature and solar radiation and can be suppressed by simple shielding of the monument. Furthermore, our project is a step towards the realization of continuous cartesian connections at geodetic fundamental stations.