kx_e sin(theta0) Plane wave direction, x ky_e -cos(theta0) Plane wave direction, y k0 intop2(acpr.k) Free-field wave number kx k0*kx_e Background plane wave k_x ky k0*ky_e Background plane wave k_y p_inc 1[Pa]*exp(-i*(kx*x+ky*y)) Incident plane wave p_scat p-p_inc Scattered wave (air domain) Z intop1(acpr.p_t)/intop1(-ppr(nx*acpr.vx+ny*acpr.vy))/intop2(acpr.rho*acpr.c) Specific surface impedance alpha 1-abs(p_scat/p_inc)^2 Absorption coefficient