You can view your surface in Surfer's 3D View, then rotate it with the Trackball to view the surface from any angle, including from underneath: 

1. Have your grid-based map open in a 2D plot window.
2. Click Map Tools | View | 3D View. The map opens in 3D view.
3. Click 3D View | View | Trackball.
4. Using the mouse in the 3D view window, click and drag the surface to your preferred viewing angle.

Updated November, 2021