Impact of atmospheric turbulence on geodetic very long baseline interferometry

We assess the impact of atmospheric turbulence on geodetic very long baseline interferometry (VLBI) through simulations of atmospheric delays. VLBI observations are simulated for the two best existing VLBI data sets: The continuous VLBI campaigns CONT05 and CONT08. We test different methods to determine the magnitude of the turbulence above each VLBI station, i.e., the refractive index structure constant C-n(2). The results from the analysis of the simulated data and the actually observed VLBI data are compared. We find that atmospheric turbulence today is the largest error source for geodetic VLBI. Accurate modeling of atmospheric turbulence is necessary to reach the highest accuracy with geodetic VLBI

”Try to relax” - A survey study in Sweden among native Swedes and Arabic immigrants concerning views on stuttering

Studies performed in various countries have shown that negative attitudes and beliefs towards stuttering and People Who Stutter (PWS), which can lead to stigmatization, discrimination and social anxiety, are widespread across different societies. It is important that clinicians are aware that patients can meet different attitudes in their daily life, affecting health care seeking behavior and self-image. These can also be affected by the cultural background. Combined with different views on disorders and individualist versus collectivist societal constructions, this has clinical impacts for the treatment. For measuring these attitudes and beliefs, a questionnaire (POSHA-S) has been developed in the USA with the aim of being a worldwide instrument. We translated POSHA-S to Swedish and conducted a survey among native Swedes and immigrants with an Arabic background, as the latter group is one of the largest, and growing, minorities in Sweden. We contacted schools around Sweden for the distribution of the survey. They received either a paper version or an online version of the questionnaire. We obtained answers from 42 native Swedes, seven Arabic immigrants and 13 respondents with a background in another country. The results show that in an international comparison, native Swedes have a positive/accurate view on stuttering and PWS; notwithstanding, the attitudes towards the PWS abilities at the labor market were negative. The Arabic group holds a more negative/inaccurate view on certain items, specifically regarding the cause of stuttering and the traits attributed to PWS. The low number of Arabic respondents, however, prevents us from drawing general conclusions as the statistical power is too low

Oceanic tidal angular momentum and Earth’s rotation for diurnal/semidiurnal bands

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月29日（木） 統計数理研究所 ３階セミナー

Using ground-based GPS to characterize atmospheric turbulence

A new method for measuring and studying atmospheric turbulence is presented. The method uses data from a local network of GPS receivers. The GPS data are processed in a way that assures that the estimated zenith total delays (ZTD) contain the effects of atmospheric turbulence present in the GPS observations. The turbulence is characterized using the spatial structure function for the atmospheric zenith total delay. The structure function is modeled by an expression with unknown parameters which contains information about the turbulence. The unknown parameters are solved by a fit to the observed ZTD variations. We apply the method to GPS data from the Yucca Mountain network, Nevada, USA. The results show that the magnitude of the turbulent variations in that region have a strong seasonal dependence, with much larger variations in summer compared to winter

Estimating integrated water vapor trends from VLBI, GPS,and numerical weather models: sensitivity totropospheric parameterization

©2018. American Geophysical UnionIn this study, we estimate integrated water vapor (IWV) trends from very long baseline interferometry (VLBI) and global navigation satellite systems (GNSS) data analysis, as well as from numerical weather models (NWMs). We study the impact of modeling and parameterization of the tropospheric delay from VLBI on IWV trends. We address the impact of the meteorological data source utilized to model the hydrostatic delay and the thermal deformation of antennas, as well as the mapping functions employed to project zenith delays to arbitrary directions. To do so, we derive a new mapping function, called Potsdam mapping functions based on NWM data and a new empirical model, GFZ‐PT. GFZ‐PT differs from previous realizations as it describes diurnal and subdiurnal in addition to long‐wavelength variations, it provides harmonic functions of ray tracing‐derived gradients, and it features robustly estimated rates. We find that alternating the mapping functions in VLBI data analysis yields no statistically significant differences in the IWV rates, whereas alternating the meteorological data source distorts the trends significantly. Moreover, we explore methods to extract IWV given a NWM. The rigorously estimated IWV rates from the different VLBI setups, GNSS, and ERA‐Interim are intercompared, and a good agreement is found. We find a quite good agreement comparing ERA‐Interim to VLBI and GNSS, separately, at the level of 75%.DFG, 255986470, GGOS-SIM-2: Simulation des "Global Geodetic Observing System

Ny teknik för kombisådd

The use of combi-drilling during spring tillage has become very common in southern Sweden in recent years. Combi-drilling leads to fewer passes on the field and better plant nutrient utilisation. An example of a combi-drill is the Väderstad Rapid, which is very widely used in spring tillage in southern Sweden. The Rapid has separate fertiliser and seed coulters, which means that the draught requirement is relatively high. It thus requires large, heavy tractors, which compact the soil and are comparatively expensive to buy and run. A few years ago the Finnish combi-drill Tume Nova Combi came onto the Swedish market. This machine places the seed and fertiliser using the same coulter, with the fertiliser placed just below the seed. The risk with placing the fertiliser so near the seed is that it can lead to a relatively high salt content in the vicinity of the seed, which can result in lower yields. In this work, we evaluated the Tume Nova Combi combi-drilling method and compared it with the conventional combi-drilling method in the form of Väderstad Rapid. The work comprised three sub-sections: 1. An overview of the literature on combi-drilling in Sweden 2. A practical field experiment in which we used Tume Nova Combi and Väderstad Rapid to combi-drill malting barley. The results were evaluated by counting plant emergence in experimental plots drilled by the two different combi-drilling methods. 3. An interview survey of farmers with experience of Tume Nova Combi. We found that there were significant differences in emergence of malting barley between the two combi-drilling methods at the Lönnstorp Experimental Station in the very dry spring of 2005. Tume Nova Combi, which places the fertiliser near the seed, gave a somewhat lower emergence (around 15% less) than the Väderstad Rapid. The poor plant emergence was probably due to the fertiliser burning off some of the seed. Furthermore, the effects of high salt concentration in the immediate vicinity of the seed may have been particularly large in this experiment, since only 5 mm of rain fell between drilling and emergence.Användning av kombisådd vid vårbruk i södra Sverige har blivit mycket vanlig under de senaste åren. Kombisådd leder till färre överfarter på fältet och bättre växtnäringsutnyttjande. Ett exempel på kombisåmaskin är Väderstads Rapid som är mycket vanligt förekommande i det sydsvenska vårbruket. Rapiden har både gödnings- och utsädesbillar, vilket gör att dragkraftsbehovet blir relativt stort. Därmed behövs stora och tunga traktorer som packar marken och som är förhållandevis dyra att äga och köpa. Sedan några år tillbaka finns den finska kombisåmaskinen Tume Nova Combi på den svenska marknaden. Denna maskin sår ut utsäde och gödning med samma bill, men gödningen läggs strax under utsädet. Risken med att lägga gödningen nära utsädet är att det kan leda till en relativt hög salthalt i utsädets närhet, vilket kan resultera i en lägre avkastning. Vi har i detta arbete utvärderat Tume Nova Combis kombisåmetod och jämfört den med konventionell kombisåmetod i form av Väderstad Rapid. I arbetet finns tre delmoment: 1. En översiktlig litteraturgenomgång om kombisådd i Sverige. 2. Ett praktiskt fältförsök där vi använde Tume Nova Combi och Väderstad Rapid för kombisådd av maltkorn. Resultatet har utvärderats genom att räkna plantuppkomsten i försöksleden från de båda kombisåmetoderna. 3. En intervjuundersökning av lantbrukare med erfarenhet av Tume Nova Combi. Vi har kommit fram till att det finns signifikanta skillnader i uppkomst mellan de olika kombisåmetoderna vid sådd av maltkorn under den mycket torra våren 2005 på Lönnstorps försöksstation. Tume Nova Combi, som lägger gödningen nära utsädet, har en något sämre uppkomst, i vårt försök ca 15 %, jämfört med Väderstad Rapid. Rekommendationen att öka på utsädesmängden med cirka 20 % verkar därför ganska rimlig. Den sämre plantuppkomsten beror sannolikt på att gödningen har ”bränt” bort en del av utsädet. Vidare kan effekten av höga salthalter i utsädets omedelbara närhet ha varit speciellt stort i detta försök, eftersom det mellan sådd och uppkomst kom endast fem millimeter regn

Prospects for UT1 Measurements from VLBI Intensive Sessions

Very Long Baseline Interferometry (VLBI) Intensives are one-hour single baseline sessions to provide Universal Time (UT1) in near real-time up to a delay of three days if a site is not e-transferring the observational data. Due to the importance of UT1 estimates for the prediction of Earth orientation parameters, as well as any kind of navigation on Earth or in space, there is not only the need to improve the timeliness of the results but also their accuracy. We identify the asymmetry of the tropospheric delays as the major error source, and we provide two strategies to improve the results, in particular of those Intensives which include the station Tsukuba in Japan with its large tropospheric variation. We find an improvement when (1) using ray-traced delays from a numerical weather model, and (2) when estimating tropospheric gradients within the analysis of Intensive sessions. The improvement is shown in terms of reduction of rms of length-of-day estimates w.r.t. those derived from Global Positioning System observation

Short-baseline interferometry local-tie experiments at the Onsala Space Observatory

We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: nu Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10-15 ps using group-delays and 2-5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset similar to+3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset