  We measured the power spectrum and two-point correlation function for the
randomly fluctuating free surface on the downstream side of a stationary flow
with a maximum Froude number $F_{\rm max} \approx 0.85$ reached above a
localised obstacle. On such a flow the scattering of incident long wavelength
modes is analogous to that responsible for black hole radiation (the Hawking
effect). Our measurements of the noise show a clear correlation between pairs
of modes of opposite energies. We also measure the scattering coefficients by
applying the same analysis of correlations to waves produced by a wave maker.
