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On Fri, 31 Jan 1997, =^.^= wrote:
> >
> >If the sun is behind me, the spot is in front of me on the ground.
> >If the sun is to the right, the spot is on the left. That is what I
mean
> >by "opposite" the sun's position. Shoot a line from me to the
> >sun, then extend it to the ground, and the spot is where the
> >line hits the ground.
> >
.
.
.
> >It is as if the ground was preferentially reflecting back directly
> >along the line from the spot to the illumination source.
.
.
.
> >But I do not understand why totally random objects (cornfield,
> >snow, forest, water) should seem to reflect directly back in
> >the direction of illumination.
> >
if the ground were reflecting directly back to the sun and _only_
back to the sun, you wouldn't see the reflection... right? and
you mentioned that the bright spot only subtends the shadow of your
airplane when you're flaring to land, so you can't be directly
between the sun and the bright spot when you're at altitude. therefore,
the ground _must_ be reflecting in other directions than back
to the source. draw yourself a ray diagram to convince yourself of
what's going on.
you're essentially correct about relfection phenomena: specular reflection
back to the source is the domain of wierd nonlinear optics
(phase conjugation) except of course in the case of a smooth, flat
surface with surface normal pointed directly at the source. cheers,
dave
- David W. Tyler ``It is reasonable," he admitted, ``and
- WJ Schafer Associates therefore I suspect it. Whenever you
- USAF Phillips Laboratory find a perfectly reasonable explanation
- University of New Mexico of anything in nature or human conduct,
Center for Advanced Studies look for something else."
- dave_at_freestyle.plk.af.mil John Taine, _The Time Stream_
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