1,061 research outputs found
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
âTry to relaxâ - 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 Earthâs rotation for diurnal/semidiurnal bands
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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, GFZâPT. GFZâPT differs from previous realizations as it describes diurnal and subdiurnal in addition to longâwavelength variations, it provides harmonic functions of ray tracingâderived 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 ERAâInterim are intercompared, and a good agreement is found. We find a quite good agreement comparing ERAâInterim to VLBI and GNSS, separately, at the level of 75%.DFG, 255986470, GGOS-SIM-2: Simulation des "Global Geodetic Observing System
Ny teknik för kombisÄdd
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 VĂ€derstad 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 VĂ€derstad 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
VĂ€derstad 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 VĂ€derstad 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.AnvÀndning av kombisÄdd vid vÄrbruk i södra Sverige har blivit mycket vanlig under de
senaste Ären. KombisÄdd leder till fÀrre överfarter pÄ fÀltet och bÀttre vÀxtnÀringsutnyttjande.
Ett exempel pÄ kombisÄmaskin Àr VÀderstads Rapid som Àr mycket vanligt
förekommande i det sydsvenska vÄrbruket. Rapiden har bÄde gödnings- och utsÀdesbillar,
vilket gör att dragkraftsbehovet blir relativt stort. DÀrmed behövs stora och tunga
traktorer som packar marken och som Àr förhÄllandevis dyra att Àga och köpa.
Sedan nÄgra Är tillbaka finns den finska kombisÄmaskinen Tume Nova Combi pÄ den
svenska marknaden. Denna maskin sÄr ut utsÀde och gödning med samma bill, men
gödningen lÀggs strax under utsÀdet. Risken med att lÀgga gödningen nÀra utsÀdet Àr att
det kan leda till en relativt hög salthalt i utsÀdets nÀrhet, vilket kan resultera i en lÀgre
avkastning.
Vi har i detta arbete utvÀrderat Tume Nova Combis kombisÄmetod och jÀmfört den med
konventionell kombisÄmetod i form av VÀderstad Rapid.
I arbetet finns tre delmoment:
1. En översiktlig litteraturgenomgÄng om kombisÄdd i Sverige.
2. Ett praktiskt fÀltförsök dÀr vi anvÀnde Tume Nova Combi och VÀderstad Rapid
för kombisÄdd av maltkorn. Resultatet har utvÀrderats genom att rÀkna
plantuppkomsten i försöksleden frÄn de bÄda kombisÄmetoderna.
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
kombisÄmetoderna vid sÄdd av maltkorn under den mycket torra vÄren 2005 pÄ
Lönnstorps försöksstation. Tume Nova Combi, som lÀgger gödningen nÀra utsÀdet, har en
nÄgot sÀmre uppkomst, i vÄrt försök ca 15 %, jÀmfört med VÀderstad Rapid.
Rekommendationen att öka pÄ utsÀdesmÀngden med cirka 20 % verkar dÀrför ganska
rimlig.
Den sĂ€mre plantuppkomsten beror sannolikt pĂ„ att gödningen har âbrĂ€ntâ bort en del av
utsÀdet. Vidare kan effekten av höga salthalter i utsÀdets omedelbara nÀrhet ha varit
speciellt stort i detta försök, eftersom det mellan sÄdd och uppkomst kom endast fem
millimeter regn
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
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
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