  We study the azimuthal variation in the backscattered intensity that is seen
when polarised light is scattered by a turbid medium. We present experimental
observations of these intensity variations in colloidal suspensions over a wide
range of optical densities. For a medium composed of spherical scatterers, we
have developed using Mie scattering theory and Monte Carlo simulations of
photon transport, a model which calculates the constant intensity contours of
the backscattered intensity. Comparisons of calculated and experimentally
obtained contours show very good agreement. To our knowledge, this is the first
model to provide a quantitative comparison with experimental data. Close to the
exact backscattering direction, where we have made our intensity measuements,
we show that the patterns are formed by what we have called `reflected snake
photons'. These are photons that have been backscattered once and have
maintained their direction of propagation thereafter until they exit the
medium. We also find that the reflected snake photons originate within a depth
of about $4l^{*}$ from the point of entry of the incident beam, where $l^{*}$
is the photon transport mean free path. Further, in a novel approach, we have
used these patterns as a probe of the assumptions underlying the diffusion
approximation and present new results on the position of the apparent source of
diffusing radiation within the medium. Possible applications are also
discussed.
