A system for monitoring temperature of a subsurface low temperature zone
is described. The system includes a plurality of freeze wells configured
to form the low temperature zone, one or more lasers, and a fiber optic
cable coupled to at least one laser. A portion of the fiber optic cable
is positioned in at least one freeze well. At least one laser is
configured to transmit light pulses into a first end of the fiber optic
cable. An analyzer is coupled to the fiber optic cable. The analyzer is
configured to receive return signals from the light pulses.