  In Polarization Discrimination Imaging, the amplitude of a sinusoid from a
rotating analyzer, representing residual polarized light and carrying
information on the object, is detected with the help of a lock-in amplifier.
When turbidity increases beyond a level, the lock-in amplifier fails to detect
the weak sinusoidal component in the transmitted light. In this work we have
employed the principle of Stochastic Resonance and used a 3-level quantizer to
detect the amplitude of the sinusoids, which was not detectable with a lock-in
amplifier. In using the three level quantizer we have employed three different
approaches to extract the amplitude of the weak sinusoids: (a) using the
probability of the quantized output to crossover a certain threshold in the
quantizer (b) maximizing the likelihood function for the quantized detected
intensity data and (c) arriving at an expression for the expected power in the
detected output and comparing it with the experimentally measured power. We
have proven these non-linear estimation methods by detecting the hidden object
from experimental data from a polarization discrimination imaging system. When
the turbidity increased to L/l = 5.05 (l is the transport mean-free-path and L
is the thickness of the turbid medium) the data through analysis by the
proposed methods revealed the presence of the object from the estimated
amplitudes. This was not possible by using only the lock-in amplifier system.
