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Directional Calibration of LOFAR data

Arendse, N. (2015) Directional Calibration of LOFAR data. Bachelor's Thesis, Astronomy.

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Interferometers such as LOFAR provide a way to increase the diameter of radio telescopes, hence increasing the angular resolution. Since the radio waves enter the ionosphere at different positions, they experience a different phase shift. To produce one consistent image all the data from the stations needs to be calibrated for this phase shift. In the measurement equation the corruption of the data is represented by a gain matrix, and solving for this matrix gives a quadratic matrix equation. The approach used in my thesis to approximate the true value of the gain matrix is inspired by the work of Cyril Tasse and is a direction dependent extension of ’StEFCal’: Statistically Efficient and Fast Calibration. The method used is Alternating Direction Implicit, combined with a relaxation step after every second iteration. The aim of this thesis is to explain the underlying principles of interferometry and directional calibration, provide an algorithm that can successfully calibrate the data of LOFAR and evaluate the effects of different frequencies, numbers of stations and numbers of directions on the convergence of the gain matrices.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Astronomy
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 08:06
Last Modified: 15 Feb 2018 08:06

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