  We present a novel distributed Brillouin optical time domain reflectometer
(BOTDR) using standard telecommunication fibers based on single-photon
avalanche diodes (SPADs) in gated mode, hd-BOTDR, with a range of 120 km and 10
m spatial resolution. We experimentally demonstrate the ability to perform a
distributed temperature measurement, by detecting a hot spot at 100 km. Instead
of using a frequency scan like conventional BOTDR, we use a frequency
discriminator based on the slope of a fiber Bragg grating (FBG) to convert the
count rate of the SPAD into a frequency shift. A procedure to take into account
the FBG drift during the acquisition and perform sensitive and reliable
distributed measurements is described. We also present the possibility to
differentiate strain and temperature.
