3. Multiples ground roll 3 levels the first primary reflection I first order multiple in tnet 300 the second primary reflection the third primary reflection 500 600 multiples 700 800 900 1000 70 科学技街大学 A Direct Numerical Imaging Method 23 National University of Defense TechnologyA Direct Numerical Imaging Method 3. Multiples 23 3 levels 10 20 30 40 50 60 70 80 90 100 100 200 300 400 500 600 700 800 900 1000 the first primary reflection ground roll first order multiple in the top layer miltiples the second primary reflection the third primary reflection