E. Hurtig et al., FIBER OPTIC TEMPERATURE SENSING - APPLICATION FOR SUBSURFACE AND GROUND TEMPERATURE-MEASUREMENTS, Tectonophysics, 257(1), 1996, pp. 101-109
The Distributed Fibre Optic Temperature Sensing Technique represents a
new physical approach for temperature measurements. It is based on op
tical time domain reflectometry (OTDR). A laser pulse is coupled into
an optical fibre and a small part of the light is backscattered as the
pulse propagates through the fibre. Intensity and spectral compositio
n of the backscattered light are determined by the molecules in the op
tical fibre. The Raman backscattering component is caused by thermally
influenced molecular vibrations. Thus, its intensity depends on tempe
rature. The velocity of light propagation in an optical fibre is well
known, therefore, the backscattering intensity can be allocated to dis
tance using the travel time of the backscattered light. Thus, an optic
al fibre works as a distributed temperature sensor which gives tempera
ture and distance simultaneously for the entire length of the optical
fibre. To test the method studies have been made on the temperature re
solution, the consistency with high-resolution borehole measurements u
sing standard temperature probes, the capability of the method for mea
suring short-term temperature variations during fluid logging experime
nts, for long-term technically induced temperature variations in boreh
oles as well as for studying the two-dimensional distribution of the g
round surface temperature for a given area. From the measurements it f
ollows that the optical fibre temperature sensing technique can be use
d under field conditions. The optical sensing cable can be installed i
n any horizontal, vertical, inclined or areal configuration. The metho
d should be used especially for surveying the temperature field and it
s variations with time rather than for standard borehole logging.