The Effect of Shear Flow on the Structure of Lidar Images of Nonlinear Internal Waves

Abstract

Modification of the analytical model of lidar images of the nonlinear internal wave which was developed earlier in our works is performed. The influence of background horizontal current on the lidar signal is studied. The two-layer ocean with background flow in the upper layer is considered. For a theoretical description of moderate amplitude solitary waves in shallow water, the Korteweg— de Vries equation is used. Characteristic features of lidar images of nonlinear internal waves are calculated and analyzed using actual profiles of hydrooptical and hydrologic data obtained in the Barents Sea. It is shown that background horizontal flow can significantly affect the structure of lidar image of internal wave. The character of these variations depends on the profile of the attenuation coefficient. In particular, if a turbid layer is situated near the pycnocline, then with a current in an upper layer the reflective image of soliton is formed with higher level of returned signal than in the absence of current. It occurs due to the shift of the turbid layer upwards. The shadow image results not in attenuation but in amplification of the signals coming from the bottom water layer with homogeneous optical properties. It occurs due to thickening of the lower less turbid water layer affected by an internal wave. These results can be used for solution the problems of lidar remote sensing of internal waves and shear flows.