The results of seawater sensing by use of an airborne lidar with a changeable field of view (FOV) are presented, together with the results of numerical simulation of lidar operation by the Monte Carlo method. It is demonstrated that multiple scattering and wind-driven sea waves have opposite effects on the measured attenuation coefficient. At small FOVs the wind-driven sea waves cause the lidar signal decay rate to increase compared with the size of the plane surface and hence result in an overestimation of the retrieved attenuation coefficient. Inefficient operation of lidars with small FOVs is caused by strong fluctuations of lidar signal power that cannot be described by a normal distribution. Specific features of the fluctuations can be interpreted as manifestations of the well-known effect of backscattered signal amplification caused by the double passage of radiation through the same inhomogeneities. As for the plane air-water interface, multiple scattering is significant for large FOVs and compensates for the effect of wind-driven sea waves. The applicability of simple sea-surface models to a description of lidar signal power fluctuations is discussed.