The normal mode model for scattering in shallow water is employed to investigate the forward scattering with a target crossing the source-receiver axial line. An experiment was conducted in a littoral environment to analyze forward scattering by a slowly moving object. The theoretical and experimental results show that the sound field aberration takes minimum values if the object is located mid-point along the source-receiver line, whereas it attains its maximum if the object is close to the source or receiver. The total field is either enhanced or suppressed if the object crosses different Fresnel zones. In addition, the duration of shad- ow-induced aberration is dependent on the width of the first Fresnel zone, which is longest at the mid-point of the source-receiver line.
