The detection of the surrounding environment is one of the most fundamental challenges in optical fiber sensors research. In this Letter, we report two new, to the best of our knowledge, phenomena in large effective area fiber (LEAF), which are the linear dependence of the radial acoustic mode induced forward Brillouin scattering (FBS) spectral linewidth on temperature and the linear dependence of the radial acoustic mode induced FBS spectral frequency shift on acoustic impedance. By utilizing these linear relationships, we present a novel temperature and acoustic impedance simultaneous measurement method based on FBS in LEAF. With a fiber Sagnac loop structure, the obtained measurement uncertainties of temperature and acoustic impedance surrounding LEAF are 0.1°C and 0.006 k g / ( s ⋅ m m 2 ) , respectively. The corresponding measurement uncertainties in the form of relative percentage values are 0.5% and 0.4%, respectively.

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