An Accuracy Assessment of Absolute Gravimetric Observations in Fennoscandia

We compare a suite of absolute gravimeters used to monitor the temporal changes of gravity at a number of sites in Fennoscandia. Direct comparisons are made from simultaneous observations at selected sites within and outside of the postglacial uplift region. We also compare results at sites visited by two instruments with some separation in time. We conclude from four years of data that gravity differences are obtained within an rms error of ± 3 Gal. The data reveal no systematic biases between the instruments, but occasional shifts from one year to another are noted. We consider that annual instrument comparisons are required to ensure data integrity in a regional observing program that extends over more than a decade

Astrometry, Morphology, and Polarimetry of Comet Donati in 1858

We present unpublished observations of Comet Donati 1858 V recently recovered in an old storage facility at the University Observatory in Oslo. Carefully-made drawings reveal temporal changes in the appearance of this comet. Fine structures in the tail were noted, some of which were short lived. Envelopes in the comet's head, apparently due to outgassing from the nucleus, were monitored over several days. Astrometric positions of the comet's head derived by various combinations of telescopes and micrometers reveal a standard deviation of ± 6". Visual polarimetry of the coma and tail revealed polarized light and determined that the polarization plane contained the comet and the Sun. Thus the polarized light from the comet was reflected sunlight. The observations are discussed in relation to contemporary publications. Made available with permission from the journal

Merz Telescopes at the University Observatory in Christiania, Norway

: Four telescopes with optics by Merz in Munich were acquired for the University Observatory in Christiania between 1840 and 1882. Two had equatorial mountings by Merz, one by Repsold, and one by Olsen. We describe the acquisition process from correspondence located in archives and libraries. The observing programs are outlined from publications in Norwegian and German, highlighting some results obtained with these instruments.publishedVersio

The Postglacial Rebound Signal of Fennoscandia Observed by Absolute Gravimetry, GPS, and Tide Gauges

We have compiled time derivatives of gravity and vertical motion for a dozen sites in Fennoscandia. Time series of absolute gravimetry and permanent GPS cover a time span of about a decade. Tide gauges have operated for many decades near seven of the sites. Linear relations are found to range from −0.17 to −0.22 for the slope between gravity and vertical uplift rates. An eustatic sea level rate of 1.2 mm/year is derived from these data. This compares well with results for North America and with theoretical predictions for viscoelastic Earth models

Merz Telescopes at the University Observatory in Christiania, Norway

: Four telescopes with optics by Merz in Munich were acquired for the University Observatory in Christiania between 1840 and 1882. Two had equatorial mountings by Merz, one by Repsold, and one by Olsen. We describe the acquisition process from correspondence located in archives and libraries. The observing programs are outlined from publications in Norwegian and German, highlighting some results obtained with these instruments

Norwegian Validation and Exploitation of GOCE Gravity Data, 2012

The Nordic countries constitute a key study region for research in Earth system sciences, especially oceanography and solid earth physics. The climate in the Nordic area is strongly affected by ocean currents in the North Atlantic. A detailed description of the currents is a key to a better understanding of regional and interrelated global climate mechanisms. A crucial quantity for respective investigations is detailed knowledge of the marine geoid, the horizontal surface at mean sea level, from which the time averaged ocean surface deviates due to steady-state ocean circulation. On March 17th 2009, the European Space Agency (ESA) launched its first Earth Explorer Core Mission, the highly sophisticated dedicated gravity satellite GOCE. The mission will deliver homogeneous information on the static geoid with unprecedented accuracy and spatial resolution

Absolute gravity observations in Norway (1993–2014) for glacial isostatic adjustment studies: The influence of gravitational loading effects on secular gravity trends

AbstractWe have compiled and analyzed FG5 absolute gravity observations between 1993 and 2014 at 21 gravity sites in Norway, and explore to what extent these observations are applicable for glacial isostatic adjustment (GIA) studies. Where available, raw gravity observations are consistently reprocessed. Furthermore, refined gravitational corrections due to ocean tide loading and non-tidal ocean loading, as well as atmospheric and global hydrological mass variations are computed. Secular gravity trends are computed using both standard and refined corrections and subsequently compared with modeled gravity rates based on a GIA model. We find that the refined gravitational corrections mainly improve rates where GIA, according to model results, is not the dominating signal. Consequently, these rates may still be considered unreliable for constraining GIA models, which we trace to continued lack of a correction for the effect of local hydrology, shortcomings in our refined modeling of gravitational effects, and scarcity of observations. Finally, a subset of standard and refined gravity rates mainly reflecting GIA is used to estimate ratios between gravity and height rates of change by ordinary and weighted linear regression. Relations based on both standard and refined gravity rates are within the uncertainty of a recent modeled result