Modulations of laser signals by water waves observed by a boxcar integrator

This paper describes a new measurement technique for active remote sensing of water waves using a lidar. To demonstrate this technique, a series of experiments studying interactions of laser pulses with water waves was performed in an NRL wave tank. This technique used a commercially available boxcar integrator to sample IR laser pulses reflected from water waves. These water waves were generated either by artificial winds or a mechanical paddle in the wave tank. The boxcar integrator samples these laser waveforms as a function of windspeeds and paddle frequencies. This paper describes the experimental technique, the measurements, and the data analyses. For wind-generated water waves, results of the data analyses show that lidar-detected laser energies and the lidar-detected water-wave frequencies are functions of windspeeds. For paddle waves, the measurement data show that the laser backscattering cross-section from a water wave is a function of height positions within the water wave. The measurement data successfully demonstrate a boxcar-integrator waveform-sampling technique as an alternative technique to, and possible improvement over, a conventional waveform digitizer. The potential application of this technique in active remote sensing is discussed.