See angle of incidence.

For radar imaging, the angle (measured from vertical) between an object and a satellite that is observing the object. An incidence angle of 0° is called a "nadir" (NAY-deer) view.

Derived for the center of the image, this is the angle between the Sun and a "normal" drawn perpendicular to the surface of the planet at the time the image was acquired. A higher incidence angle means that a person standing on the ground would see the sun lower toward the horizon.