An Optical method for instantaneous measurement of suspended particle size distribution shows promise for the study of boundary layer dynamics in the ocean, where suspended particles affect boundary layer flow through stratification. The method is based on observing the an-gular distribution of scattered light from a sample, and inversion to produce the suspended particle size distribution, n(x). In a previous paper, an analytic inversion based on the Fraunhoffer approximation was examined. The function 03I(0) was found approximately to be related by a Fourier transform to xn(x), with the result that elementary signal processing concepts apply. In this work, the issues of uniqueness and stabilty of the inversion are considered. Instability of inversion for small particles is observed, and has the result that while matrix inversion algorithms show promise, those which manipulate small eigenvalues distort inversions for small sizes. Uniqueness in terms of sampling is revisited, yielding a refined Nyquist sampling criterion. The validity of these results, derived from approximate diffraction theory, is demonstrated for "exact" Mie theory.