  We report on the simultaneous Giant Metrewave Radio Telescope (GMRT) and
Algonquin Radio Observatory (ARO) observations at 550-750 MHz of the
scintillation of PSR B1508+55, resulting in a $\sim$10,000-km baseline. This
regime of measurement lies between the shorter few 100-1000~km baselines of
earlier multi-station observations and the much longer earth-space baselines.
We measure a scintillation cross-correlation coefficient of $0.22$, offset from
zero time lag due to a $\sim 45$~s traversal time of the scintillation pattern.
The scintillation time of 135~s is $3\times$ longer, ruling out isotropic as
well as strictly 1D scattering. Hence, the low cross-correlation coefficient is
indicative of highly anisotropic but 2D scattering. The common scintillation
detected on the baseline is confined to low delays of $\lesssim 1 \mu$s,
suggesting that this correlation may not be associated with the parabolic
scintillation arc detected at the GMRT. Detection of pulsed echoes and their
direct imaging with the Low Frequency Array (LOFAR) by a different group enable
them to measure a distance of 125~pc to the screen causing these echoes. These
previous measurements, alongside our observations, lead us to propose that
there are at least two scattering screens: the closer 125 pc screen causing the
scintillation arc detected at GMRT, and a screen further beyond causing the
scintillation detected on the GMRT-ARO baseline. We advance the hypothesis that
the 125-pc screen partially resolves the speckle images on the screen beyond
leading to loss of coherence in the scintillation dynamic spectrum, to explain
the low cross-correlation coefficient.
