As for sensing microseisms by laser, several years ago we attempted to =
use a laser beam and photocells as a shortcut to seismic copy.  In =
setting up the system, we bounced the beam off of front surface mirrors =
for a total length of 500 ft or so.  By using a one-half milliwatt =
standard  laboratory laser, the beam enlarged to about the size of a =
tennis ball.  The system was very sensitive, and we thought at that time =
we were seeing only the mechanical vibrations of the building--we were =
at ground lever on a gravel floor in an unused part of the science =
building.  Other interests took us elsewhere, and we never pursued this =
further.
                                             J. Lehman
                                                Virginia, USA=20







As for sensing microseisms by =
laser,=20
several years ago we attempted to use a laser beam and photocells as a =
shortcut=20
to seismic copy.  In setting up the system, we bounced the beam off =
of=20
front surface mirrors for a total length of 500 ft or so.  =
By using a=20
one-half milliwatt standard  laboratory laser, the beam enlarged to =
about=20
the size of a tennis ball.  The system was very sensitive, and we =
thought=20
at that time we were seeing only the mechanical vibrations of the=20
building--we were at ground lever on a gravel floor in an unused part of =
the=20
science building.  Other interests took us elsewhere, and we never =
pursued=20
this further.
          &nbs=
p;            =
;            =
         =20
J. Lehman
          &nbs=
p;            =
;            =
             =

Virginia, USA