  Internal waves propagate obliquely through a stratified fluid with an angle
that is fixed with respect to gravity. Upon reflection on a sloping bed,
striking phenomena are expected to occur close to the slope. We present here
laboratory observations at moderately large Reynolds number. A particle image
velocimetry (PIV) technique is used to provide time resolved velocity fields in
large volumes. The generation of the second and third harmonic frequencies are
clearly demonstrated in the impact zone. The mechanism for nonlinear wavelength
selection is also discussed. Evanescent waves with frequency larger than the
Brunt-V\"ais\"al\"a frequency are detected and experimental results agree very
well with theoretical predictions. The amplitude of the different harmonics
after reflection are also obtained.
