what is the relationship between the angle of insulation and the intensity of the radiation striking the ground ?other

Insulation is a measure of how much of the radiation that is
coming from the sun actually reaches the earth's surface.  This energy depends on a number of
variables including:  the sun's angle, the length of the day, the slope of the ground, the path
length that the radiation has to travel to reach the surface, and the conditions of the
atmosphere (clear, cloudy, dusty, etc.)

The intensity is greatest
when the sun's radiation is striking the ground at a 90 degree angle - the sun is directly
overhead.  This condition happens most frequently at or near the
equator.

As the angle increases, the amount of energy decreases so
that when you are at either the north pole or south pole the angle at which the radiation strikes
the ground is almost parallel to the surface and most is reflected back into the air instead  of
warming the ground.