Techniques, systems, and devices are disclosed for synthetic aperture ultrasound imaging using a beamformer that incorporates a model of the object. In some aspects, a system includes an array of transducers to transmit and/or receive acoustic signals at an object that forms a synthetic aperture of the system with the object, an object beamformer unit to (i) beamform the object coherently as a function of position, orientation, and/or geometry of the transducers with respect to a model of the object, and (ii) produce a beamformed output signal including spatial information about the object derived from beamforming the acoustic echoes; a data processing unit to process data and produce an image of the object based on a rendition of the position, the orientation, the geometry, and/or the surface properties of the object, relative to the coordinate system of the array, as determined by the data processing unit.