Fiber Bragg gratings (FBG) seismic activity sensors coupled in sensor
arrays provide increased sensitivity to seismic activities, lower strain
values and an absence of EMI allowing detection of troop and vehicle
movements based on ground vibrations generating seismic signals. The FBG
sensor head features a spring-mass configuration with a head surface,
fiber optic cable and the FBG sensor attached to a spring that stretches
during the acceleration of the mass. Waves propagating inside the earth
and along the ground arriving at the sensor locations cause movement of
the seismic activity sensors embedded in the ground and this movement
induces an acceleration-dependent change in the FBG gratings placed on
the sensors. In multiple sensor configurations, the cable will be
connected to the other sensors in the network. FBG sensors, sensor arrays
and sensor methods are provided in several embodiments.