  A number of important processes taking place around strong shocks in
supernova remnants (SNRs) depend on the shock obliquity. The measured
synchrotron flux is a function of the aspect angle between interstellar
magnetic field (ISMF) and the line of sight. Thus a model of non-thermal
emission from SNRs should account for the orientation of the ambient magnetic
field. We develop a new method for the estimation of the aspect angle, based on
the comparison between observed and synthesized radio maps of SNRs, making
different assumptions about the dependence of electron injection efficiency on
the shock obliquity. The method uses the azimuthal profile of radio surface
brightness as a probe for orientation of ambient magnetic field because it is
almost insensitive to the downstream distribution of magnetic field and
emitting electrons. We apply our method to a new radio image of SN 1006
produced on the basis of archival VLA and Parkes data. The image recovers
emission from all spatial structures with angular scales from few arcseconds to
15 arcmin. We explore different models of injection efficiency and find the
following best-fitting values for the aspect angle of SN 1006: phi=70 +/- 4.2
deg if the injection is isotropic, phi=64 +/- 2.8 deg for quasi-perpendicular
injection (SNR has an equatorial belt in both cases) and phi=11 +/- 0.8 deg for
quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is
expected to have a centrally-peaked morphology contrary to what is observed.
Therefore, our analysis provides some indication against the quasi-parallel
injection model.
