The theory of transmission fluctuation spectrometry (TFS) was recently developed for particle size analysis in dilute flow particle systems, whereby the statistical transmission fluctuations are used to extract the particle size distribution and particle concentration. In this paper, a new method of transmission fluctuation spectrometry with signal correlation is presented, whereby the beam diameter is assumed to be much less than the particle diameter. The transmission fluctuations are expressed in terms of the expectancy of the transmission product (ETP) and are obtained as a spectrum with respect to the variable correlation time. An analytical expression of the ETP through a monolayer is derived and the ETP of a 3-dimensional system is formulated based on the layer model.