We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.

The objective of the International Earth Rotation and Reference Systems Service (IERS) Working Group on Site Survey and Co-location is to improve local measurements at space geodesy sites. We appointed dedicated Points of Contact (POC) with the four different services of IERS as well as the NASA Space Geodesy Project in order to improve the efficiency of internal communication within the working group. Following the REFAG2014 conference, the POCs agreed on a common and general terminology on local ties that clarifies the communication regarding site surveying and co-location issues between and within the IERS services. We give brief introductions to the different observation techniques and mention some contemporary issues related to site surveying and co-location.

The key comparison EURAMET.L-K1.2011 on gauge blocks was carried out in the framework of a EURAMET project starting in 2012 and ending in 2015. It involved the participation of 24 National Metrology Institutes from Europe and Egypt, respectively. 38 gauge blocks of steel and ceramic with nominal central lengths between 0.5 mm and 500 mm were circulated. The comparison was conducted in two loops with two sets of artifacts. A statistical technique for linking the reference values was applied. As a consequence the reference value of one loop is influenced by the measurements of the other loop although they did not even see the artifacts of the others. This influence comes solely from three "linking laboratories" which measure both sets of artifacts. In total there were 44 results were not fully consistent with the reference values. This represents 10% of the full set of 420 results which is a considerable high number. At least 12 of them are clearly outliers where the participants have been informed by the pilot as soon as possible. The comparison results help to support the calibration and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA.

The key comparison EURAMET.L-K8.2013 on roughness was carried out in the framework of a EURAMET project starting in 2013 and ending in 2015. It involved the participation of 17 National Metrology Institutes from Europe, Asia, South America and Africa representing four regional metrology organisations. Five surface texture standards of different type were circulated and on each of the standards several roughness parameters according to the standard ISO 4287 had to be determined. 32 out of 395 individual results were not consistent with the reference value. After some corrective actions the number of inconsistent results could be reduced to 20, which correspond to about 5% of the total and can statistically be expected. In addition to the material standards, two softgauges were circulated, which allow to test the software of the instruments used in the comparison. The comparison results help to support the calibraton and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA.

The Global Geodetic Observing System, an entity under the International Association of Geodesy (IAG) has undertaken the task of advocating for the geodetic infrastructure necessary to meet the global change and other societal challenges, and defining the requirements for the geodetic observatories that constitute it. In this role, GGOS will work with the IAG Measurement Services, the scientific Community, and national and international agencies to bring a combined effort to bear on these areas of international concern. A major task within this effort is the upgrading, expansion, and maintenance of the global ground network of co-located Core Sites for geodesy to enable the realization and maintenance of the International Terrestrial Reference Frame (ITRF), Earth orientation parameters and precision orbits to meet the needs of Earth orbiting missions, Earth Surface and interior programs, and deep space navigation. GGOS and the geodetic Core Sites should be compliant with the UN resolution from Feb 26, 2015. See http://www.unggrf.org/. This Site Requirements Document outlines what is needed for that compliance.

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.

Real Time Kinematic (RTK) is a system that utilises Global Navigation Satellite Systems (GNSS) to provide accurate positioning in real time. The contribution of the troposphere, the ionosphere and local effects, such as receiver noise and multipath are the most significant error sources affecting network RTK measurements We show how measurements with network RTK are affected by these different error sources under varying circumstances such as time of year or time of the day, network infrastructure, satellite systems and processing techniques We find that, for Scandinavian conditions, the effect of the ionospheric spatial variability on network RTK measurements is greater during nighttime than during daytime. The effect is also largest in the months October and November and smallest in the months of June and July. A densification of the reference network from 70 km to 35 km between the reference stations results in improved measurements. The error in the measured vertical position coordinate is reduced from 26 mm to 17 mm. The access to new GNSS reduces error in the measured vertical position coordinate from 26 to 21 mm. By using the L3-combination, the contribution from the ionosphere is reduced to virtually zero. However, this has been at the expense of the local errors

A part of the atmosphere is ionized by the UV radiation from the Sun. This part is often referred to as the ionosphere. The resulting free electrons influence the GNSS signals as they propagate through the ionosphere. We have studied how the spatial variations of electron density in the ionosphere affect measurements with network-RTK. The aim is to predict what we can expect from measurements during the next solar maximum that is expected to occur around 2012. In order to perform a spatial characterization of the ionosphere, we have used archived GPS data from SWEPOS from a five year period, 1999-2004, around the previous solar maximum. We find that the effect of the ionospheric spatial variability on network-RTK measurements is greater during night time than during day time. It is also clear that the effect is larger for northern Sweden than for the southern part. This is especially true during night time. The effect is also largest in the months October and November and smallest in June and July. Also the number of cycle slips is larger in northern Sweden than in southern Sweden. We find that when monitoring the ionosphere and its influence on network-RTK performance it is desirable to have several different geographical regions under observation. The effects in northern Sweden may, for example not be that relevant for a user in southern Sweden. In this report we define the ionospheric delay errors as the standard deviation of the difference between the ionospheric delay at L1 at one location and the estimated value of this based on the three surrounding reference stations with 70 km separation. Using GNSS equipment that is state-of-the art around 2010, we find that when conditions are such that the ionospheric delay error is below 10 mm, which occurs some 70% of the time, a rover is able to fix the ambiguities more than 90% of the time. This ability decreases with increasing ionospheric variability and when the ionospheric delay error is larger than 25 mm, which occurs some 10% of the time, the rover ability to fix is less than 50%. When measuring with network-RTK during the next solar maximum, approximately, 80% of the time, we have conditions such that a rover has at least 75% chance of fixing the solutions. Overall the probability to find a correct fix solution when performing RTK measurements during the next solar maximum is approximately 85% and the mean time to fix is 55 seconds.