1. A method for spatial compound imaging, comprising steps of: a) receiving a component image C(i,j) of a current steering scan cycle i and a steering angle j, wherein a steering scan cycle comprises capturing a respective component image at each of a plurality of steering angles; b) using a processor to obtain a differential image D(i,j) by subtracting a component image C(i−1,j) of a previous scan cycle i−1 from the component image C(i,j) of the current scan cycle i, wherein the component images C(i,j) and C(i−1,j) are of the same steering angle j; c) pre-processing said differential image D(i,j); d) compounding the pre-processed differential image D(i,j) of the current scan cycle i and a compounded image Co(i−1,j) of a previous scan cycle i−1 to form a compounded image Co(i,j) of the current scan cycle i; and e) storing the component image C(i,j) for use in a subsequent scan cycle.