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| 2. |
- Emardson, R., et al.
(författare)
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Uncertainty evaluation in multivariate analysis : A test case study
- 2005
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Ingår i: Journal of Mathematical Modelling and Algorithms. - : Springer Science and Business Media LLC. - 1570-1166 .- 1572-9214. ; 4:3, s. 289-305
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Tidskriftsartikel (refereegranskat)abstract
- We have used different multivariate analysis methods to estimate quantities in the fields of food control and atmospheric remote sensing. In order to estimate the uncertainties in these estimates we studied analytical as well as non-parametric numerical methods. The methods have been evaluated by comparison between obtained results and independent sets of measurements. We present one test case from each field, including results, where these methods have been applied. For the food control test case reduced chi-squared (? ?2) of approximately unity indicate that both the analytical and numerical methods used for uncertainty estimation produce uncertainties of reasonable size. In the atmospheric remote sensing test case, a ??2 = 46 indicated that the uncertainties from the numerical method were far too small, whereas a ??2 = 1.5 indicate that the size of the analytically determined uncertainties can represent the size of the "true" errors. © Springer 2005.
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| 3. |
- Graziani, A., et al.
(författare)
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A simulation tool for assessing the influence of atmospheric turbulence in a Media Calibration System
- 2012
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Ingår i: 12th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment, MicroRad 2012 - Proceedings. Rome, 5-9 March 2012. - 9781467314701
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Konferensbidrag (refereegranskat)abstract
- Turbulence is an important effect for different applications including different aspects of electromagnetic propagation in the atmosphere, especially for frequencies in the microwave part of the spectrum. Our parameter of interest is an integrated effect, namely the propagation delay of a signal propagating through the Earth's atmosphere to a receiver on the ground. A simulation method has been implemented in order to predict the statistics of atmospheric turbulence. For systems where calibration for the wet delay is done by means of radiometric measurements there is an uncalibrated remainder of the variability due to imperfections of the method: (1) the radiometer location, which may not be identical to the location of the receiving antenna that is subject to calibration, (2) a pointing offset on the sky, and (3) the radiometer beam that may sense another volume of the air than does the original signal. The size of the remainder depends on the assumptions made about the atmospheric variability when the instrument is calibrated. The analysis shows that the overall performance of the system to a significant level depends on the uncertainty in the true range of variation for the turbulence strength parameter C n 2.
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| 4. |
- Tortora, P., et al.
(författare)
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Instruments, data and techniques for the assessment of tropospheric noise in deep space tracking
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012. - 9781457709180 ; , s. 106-110
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Konferensbidrag (refereegranskat)abstract
- This paper describes the techniques currently in use and those proposed for a precise estimation of the Earth troposphere path delay for Deep Space probe tracking purposes. The different proposed techniques could be selected according to the to the mission goals and tracking accuracy requirements. In this paper, they are sorted by an increasing accuracy but also level of complexity.
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| 5. |
- Bergstrand, Sten, 1971, et al.
(författare)
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Ionospheric Corrections for Accurate Positioning in Real Time
- 2005
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Ingår i: in Proc. Radio Science and Communication (RVK), eds. O. Gustafsson, P. Löwenborg, Linköping, Sweden, June 14-16, 2005. - 9170561222 ; , s. 391-394
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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Time Transfer over a 560 km Fiber Link
- 2008
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Ingår i: EFTF 2008 - 22nd European Frequency and Time Forum. ; , s. Paper E5A04 -
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Konferensbidrag (refereegranskat)
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| 7. |
- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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Time transfer using an asynchronous computer network: An analysis of error sources
- 2007
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Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
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Konferensbidrag (refereegranskat)abstract
- We have performed a time transfer over a distance ofapproximately 75 km using an asynchronous computer networkbased on optical fibers. In order to validate the results from thisfiber-link, we have compared the results with a GPS-link, whichconsists of carrier phase observations. All electronic cabinetswere equipped with temperature and humidity sensors. Here wepresent experiments where the temperature and humidity of thedelay in the electrical components were investigated. Allcomponents showed some temperature dependence, but nosignificant humidity dependence was found. By using thederived temperature coefficient for the components the standarddeviation of the difference between the fiber link and GPS linkdecreased from 243ps to184ps.
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| 8. |
- Elgered, Gunnar, 1955, et al.
(författare)
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Validation of climate models using European ground-based GNSS observations
- 2009
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Ingår i: Proc. of 2nd Colloquium Scientific and Fundamental Aspects of the Galileo Programme, European Space Agency, 15-19 October, 2009, Padua, Italy. ; CD ROM
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We summarize an ongoing research project where we assess the quality of time series of the Integrated Water Vapour in the atmosphere estimated from ground-based GNSS data for the application of validating and possibly improving climate models. The focus is on the factors limiting the accuracy and especially the long-term stability of the GNSS technique.Higher order ionospheric corrections have been studied, using realistic values for the Total Electron Content (TEC) close to the solar maximum in 2002. Averaged over ten days we find that the impact in the mean IWV is less than 0.1 kg/m^2. Another factor is the model used for antenna phase centre variations. We have studied this effect on the IWV estimates by simulations and by studying estimates of the IWV based on observed GPS signals. We find that ignoring satellite antenna phase variations, when processing GPS data from 2003-2008, can significantly influence the values of the estimated linear trends. The value depends on the latitude of the site as well as on the elevation cut-off angle used in the data analysis. Finally, we show a significant correlation between estimated linear trends in the IWV and the corresponding linear trends in the independently observed ground temperature.
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