2. Direct imaging for point targets From Born approximation the reflected signal at the j-th transducer is M N f()=邋G(x,x,)G(x,x() k=1i=1 where G(x,x): the Greens function the reflectivity of the k-th scatters k located at x he location of the i-th transducers (過两科学大季 A Direct Numerical Imaging Method 6 National University of Defense TechnologyA Direct Numerical Imaging Method 2. Direct imaging for point targets ❖ From Born approximation, the reflected signal at the j-th transducer is 6 0 G x ( , ) : x 0 0 1 1 ˆ ( ) ( , ) ( , ) ( ) M N j j k k i k i k i r G G e w t w = = = 邋 x x where the Greens function : k t the reflectivity of the k-th scatters located at xk . : i x the location of the i-th transducers