In aquaculture farms, long-lines are used to grow kelp for food, pharmaceuticals, and biofuel. As these farms become larger and move offshore, acoustic sensing with high-frequency broadband echosounders is likely a scalable option for large-scale monitoring, making understanding of the scattering properties of the long-lines critical. However, the boundary conditions for the long-lines are complicated, and field data show that the long-lines occupy only a small number of Fresnel zones. To determine the influence of Fresnel zone interference, cylindrical targets with known boundary conditions but a small number of Fresnel zones insonified were studied. Using a formulation involving a monopole line source and an infinitely long cylinder excited at normal incidence relative to the cylinder axis, an apparent volume flow is derived for the case of a spherically spreading source with Bessel function transceiver directivity. Element pressure derived using this volume flow is integrated along the length of the cylinder to yield the scattered field. Theoretical results using this method are validated experimentally at angles near normal incidence. The theoretical formulation is then extended for larger angles by deriving the volume flow based on the analytic solution to an obliquely excited infinite elastic cylinder. [Work funded by ARPA-E.]