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- Carozzi, Tobia, 1966, et al.
(author)
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A Fundamental Figure of Merit for Radio Polarimeters
- 2011
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 59:6, s. 2058-2065
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Journal article (peer-reviewed)abstract
- Many modern radio applications, such as astronomy and remote sensing, require high-precision polarimetry. These applications put exacting demands on radio polarimeters (antenna systems that can measure the state of polarization of radio sources), and in order to assess their polarimetric performance, a figure of merit (FoM) would be desirable. Unfortunately, we find that the parameter commonly used for this purpose, the cross-polarization ratio, is not suitable as a polarimetry FoM unless it is given in an appropriate coordinate system. This is because although the cross-polarization ratio is relevant for raw, uncalibrated polarimetry, in general it is not relevant to the quality of the polarimetry after polarimetric calibration. However, a cross-polarization ratio can be constructed from invariants of the Jones matrix (the matrix that describes the polarimetric response of a polarimeter) that quantifies polarimetric performance even after calibration. We call this cross-polarization ratio the intrinsic cross-polarization ratio (IXR) and conclude that it is a fundamental FoM for polarimeters. We then extend the IXR concept from the Jones calculus to the Mueller calculus and also to interferometers, and we give numerical examples of these parameters applied to the Parkes radio telescope, the Westerbork synthesis radio telescope, and the Effelsberg telescope.
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| 2. |
- Carozzi, Tobia, 1966, et al.
(author)
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Towards a uniform evaluation of the science quality of SKA technology options: Polarimetrie aspects
- 2012
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In: 2012 14th International Conference on Electromagnetics in Advanced Applications, ICEAA 2012. Cape Town, 2 - 7 September 2012. - 9781467303354 ; , s. 543-546
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Conference paper (peer-reviewed)abstract
- We discuss how to evaluate SKA technology options with regard to science output quality. In this work we will focus on polarimetry. We review the SKA specification for polarimetry and assess these requirements. In particular we will use as a illustrative case study a comparison of two dish types combined with two different feeds. The dish types we consider are optimized axi-symmetric prime-focus and offset Gregorian reflector systems; and the two feeds are the Eleven-feed (wideband) and a choked horn (octave band). To evaluate the imaging performance we employ end-to-end simulations in which given sky models are, in software, passed through a model of the telescope design according to its corresponding radio interferometrical measurement equation to produce simulated visibilities. The simulated visibilities are then used to generate simulated sky images. These simulated sky images are then compared to the input sky models and various figures-of-merit for the imaging performance are computed. A difficulty is the vast parameter space for observing modes and configurations that exists even when the technology is fixed. However one can fixed certain standard benchmark observation modes that can be applied across the board to the various technology options. The importance of standardized, end-to-end simulations, such as the one presented here, is that they address the high-level science output from SKA as a whole rather than low-level specifications of its individual parts.
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| 3. |
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| 4. |
- Moldón, J., et al.
(author)
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The LOFAR long baseline snapshot calibrator survey
- 2014
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In: Proceedings of Science. - 1824-8039. ; 2014
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Conference paper (peer-reviewed)abstract
- With a current maximum baseline of 1300 km, the International LOFAR array is capable of attaining an angular resolution of 0.4 arcsec at a frequency of 140 MHz, opening for the first time the possibility of true subarcsecond imaging at wavelengths longer than 1 m. We used the multibeaming capability of LOFAR to conduct a fast and computationally inexpensive survey to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Here we summarize the characteristics of the survey, and its main results. In particular we have obtained the density of calibrators on the sky that are sufficiently bright to calibrate dispersive and non-dispersive delays for the International LOFAR. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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| 5. |
- Young, A., et al.
(author)
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Toward a practical demonstration of physics-based beam calibration models - CBFPs and the LOFAR-LBA antenna array radio telescope
- 2014
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In: Proceedings - 2014 International Conference on Electromagnetics in Advanced Applications, ICEAA 2014. - 9781467357104 ; , s. 462-465
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Conference paper (peer-reviewed)abstract
- We consider the application of the Characteristic Basis Function Pattern (CBFP) method to calibrate for direction-dependent gain effects of the LOFAR Low Band Antenna (LBA) array. The use of array-based calibration models, as opposed to element-based calibration models, is proposed in order to reduce the number of solvable beam model parameters.
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