Dirty beam

Dirty beam

Le dirty beam est la fonction d'étalement du point d'un interféromètre. Il intervient en imagerie par synthèse d'ouverture, dans la mesure où l'obtention de l'image finale (clean map) nécessite la déconvolution du dirty map par le dirty beam. Le dirty beam B est la transformée de Fourier de la fonction d'échantillonnage S de l'interféromètre :

B(l, m) = \iint \mathrm{e}^{-2\pi i(ul + vm)} S(u,v)\,\mathrm{d}u\,\mathrm{d}v,

où l et m sont les coordonnées spatiales (en radians) ; u et v les fréquences spatiales réduites (en multiples de la longueur d’onde).

Plus l'échantillonnage des fréquences spatiales est lâche, plus le dirty beam présente des lobes secondaires qui rendent l’interprétation du dirty map hasardeuse.


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