Direct imaging for extended targets (1 Sound-soft target ( Dirichlet boundary condition D(x)+k2(x)=0,x蜊C?i l(x)=-l(x),x味W ku÷?0.asr (過两科学大季 A Direct Numerical Imaging Method 11 National University of Defense TechnologyA Direct Numerical Imaging Method Direct imaging for extended targets 11 (1) Sound-soft target (Dirichlet boundary condition) 2 ( ) ( ) 0, ( ) ( ), s s C d s i u k u u u ìï D + = 蜽 ? ïï í ï ï = - 味 W ïî x x x ¡ x x x 1 2 0, . m u r iku as r r - 骣ç ¶ ÷ ç ÷ ç ÷ ç桫¶ ÷ x