  We develop a maximum likelihood method to infer relevant physical properties
of elongated active particles. Using individual trajectories of advected
swimmers as input, we are able to accurately determine their rotational
diffusion coefficients and an effective measure of their aspect ratio, also
providing reliable estimators for the uncertainties of such quantities. We
validate our theoretical construction using numerically generated active
trajectories upon no-flow, simple shear, and Poiseuille flow, with excellent
results. Being designed to rely on single-particle data, our method eases
applications in experimental conditions where swimmers exhibit a strong
morphological diversity. We briefly discuss some of such ongoing experimental
applications, specifically, in the characterization of swimming E.coli in a
flow.
