Research Note

Beam profile determination by tomography of solar scans

¹ INPE – Instituto Nacional de Pesquisas Espaciais, S. J. Campos, SP – Brazil
² CRAAM – Universidade Presbiteriana Mackenzie, S. Paulo, SP – Brazil
³ IAP, University of Bern – Switzerland

Corresponding author: J. E. R. Costa, jercosta@craam.mackenzie.br

Received: 31 January 2002
Accepted: 4 March 2002

Abstract

Beam patterns of radio telescopes with moderate (arcmin) angular resolution in the millimeter and sub-millimeter range are difficult to measure as only weak sources are available in that spectral range. This limitation can be overcome with the deconvolution of radial scans over the knife edge of the solar limb which provides beam profiles down to secondary lobe levels. Numerous applications, such as quick adjustments and checkups of telescope optics, efficiency estimates and the reconstruction of partially unresolved structures such as active regions, become possible. We investigate here the inverse problem of the beam profile reconstruction from the beam convolution with the solar limb. With simple derivatives of solar radial scans we obtained line integrals of the beam profile under different scanning angles. Reconstruction methods used in tomography of filtered reverse projection allowed us then to obtain beam profiles down to the level of secondary lobes. Tests of the algorithm were carried out with simulated data and solar scans that are verified by planet observations and terrestrial beam pattern measurements.