Rotation around y-axis to make a 3D image

I'm struggling with the following problem:

I have a matrix containing values (no formula!) and if I plot these values I get a plot that looks like this:

Want I want to do is center this around the 0 and rotate the image 180 degrees (it is the same as rotating half of the image 360 degrees) to make a 3D volume. Then I want to view this from above (which will look like a perfect round circle with intensity fluctuations). At the end I want to have a matrix containing these intensities (2D matrix from the top layer of this plot)

Can anyone help me with this?