This diagram depicts a satellite observing backscattered sunlight in the nadir viewing geometry.
<a href="//commons.wikimedia.org/wiki/User:PlanetUser" title="User:PlanetUser">PlanetUser</a>
<a href="//commons.wikimedia.org/wiki/File:Nadir_Viewing_Geometry.jpg" title="File:Nadir Viewing Geometry.jpg">File:Nadir Viewing Geometry.jpg</a>