Acoustic arrays transmitting and/or receiving multiple, angularly dispersed acoustic beams are used to generate 2D and 3D images. The acoustic arrays may comprise frequency-steered acoustic arrays provided in one-dimensional linear and two dimensional planar and curvilinear configurations, which may be operated as single order or multiple order arrays, may employ periodic or non-periodic transducer element spacing, and may be mechanically scanned to generate 2D and 3D volumetric data. Methods and systems for operating acoustic arrays in a frequency-steered mode in combination a mechanical beam steering mode, electronic time-delay and phase shift beam forming modes, and phase comparison angle estimation modes are also provided. Methods for generating two and three dimensional images of underwater target scenes using multi-beam acoustic imaging systems are disclosed.