The MIM-Principle Where GNSS and Radio Astronomy Collide

E. Noordam

Abstract:	Free electrons in the ionosphere affect the propagation of radio waves. This manifests itself as a phase error between the individual elements of radio telescopes. Correcting for this error is referred to as calibration. Apart from possible other applications, this is of particular importance for the new generation of large phased array radio telescopes such as LOFAR. In order to properly calibrate these telescopes, the Total Electron Content (TEC) from an arbitrary receiver position (x,y,z) in an arbitrary direction (l,m) is required. Enter the MIM. MIM stands for Minimum Ionospheric Model. This is a model of the ionospheric TEC that contains a minimum number of parameters and a minimum number of assumptions about the ionosphere. The MIM postulates the existence of a smooth 6D function (x,y,z,l,m,t) that describes the ionospheric TEC. The MIM coefficients are solved from the available TEC measurements. Consequently the MIM will become more accurate if the sampling function is denser. Unfortunately the lack of many bright radio sources within the LOFAR field of view leads to large gaps in the MIM sampling function. These gaps may be bridged by encompassing GNSS TEC measurements and constraint equations. The MIM function is constrained by observations of radio sources, GNSS TEC measurements and a number of constraint equations. It its turn the MIM can harmonize all these measurements by making any free parameters consistent with each other. A framework for creating the MIM is described. The MIM approach also has other applications
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	321 - 326
Cite this article:	Noordam, E., "The MIM-Principle Where GNSS and Radio Astronomy Collide," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 321-326.
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