2. Direct imaging for point targets An improved imaging function X n?1 x ax Where I(x)=22 g(x u k=1 (過两科学大季 A Direct Numerical Imaging Method 10 National University of Defense TechnologyA Direct Numerical Imaging Method 2. Direct imaging for point targets 10 An improved imaging function max ( ) ( ) , 1. ( ) n n I x I x n I x 轾 = ? 犏犏犏臌 where 2 1 ( ) ( ) . M T k k I x g x u = = å