How to calculate flux through a plane parallel to the XZ plane? Given a 3d vector field.

Say we have a 3D vector field, let's say the field and grid are already defined

n = 100;
rmax = 10000;
x = linspace(-rmax,rmax,n)
y = linspace(-rmax,rmax,n)
z = linspace(-rmax,rmax,n)

% Say FX,FY, and FZ are the components of the vector field and we want to calculate the flux through the plane y = 9800

Fy9800 = (FY(Y==y(n-2)))'; %Picks out the Y- component of the vector field in the y = 9800 plane

Fy9800R = reshape(Fy9800,[n,n]); 

[X2,Z2] = meshgrid(x,z)

surf(X2,Z2,Fy9800R) %Graphs the flux through the y=9800 plane

xlabel('X-Axis')
ylabel('Z-Axis')
zlabel('Flux')

Would this work? Thanks in advanced for the help.