We report an experimental study of the scattering of ultrasonic plane waves on a turbulent jet in air (Pr = 0.7). The jet is weakly heated so that the temperature fluctuations act as a passive scalar. In the backscattering geometry one measures the Fourier components of the temperature field $\tilde{T}(q, t)$. The time averaged characteristics are analyzed in detail; in particular we observe a Kolmogorov “-5/3" power law behavior for the passive scalar spectrum in the inertial range of scales. The study of the time fluctuations shows that the histograms of $\tilde{T}(q, t)$ remain close to a Gaussian at all scales.