Physical Oceanography (Feb 2023)
Estimation of Internal Wave Parameters in the Arctic Based on Synthetic Aperture Satellite Radar Data
Abstract
Purpose. The work is aimed at developing a technique for calculating the solitary internal wave parameters (solitons generated by a semi-diurnal tide) based on their manifestations on the ocean surface in the presence of ice. Methods and Results. Sequential soundings of the Sentinel-1A and Sentinel-1B radar satellites west of the deep-sea part of the Fram Strait in August, 2018 were analyzed. Identification of the internal waves’ surface manifestations on the radar satellite images is reduced to finding thin bright bands elongated along the wave crests. Bright pixels, the distance between which is less than the visual width of the ridges, are united into the clusters. The clusters whose sizes exceed the threshold value and for which the anisotropy (the ratio of the semi-axes of the approximating ellipse) is also high, are considered to correspond to the internal waves (in contrast to ice). For each such cluster, the interpolated spatial coordinates are calculated along the corresponding wave extremum. Based on the proposed method, the horizontal size (“wavelength” ~ 1.5 km) and the phase speed (~ 1 m/s) of solitary internal waves are assessed. The repetition period of solitons was ~ 24 min. The leading wave propagation speed appeared to be 10 % higher than that of the next one. During the time between soundings (~ 48 min), this leads to a "wavelength" increase (red shift) between them – from 1.3 to 1.6 km. The curvature radii’ values of each wave front are also calculated. The information on spatial position of the fronts’ curvature centers permits to assume the place of generation of the analyzed internal waves, namely the underwater bank (80° 45' N, 8° 30' W), the depth above which is less than 20 m. Conclusions. The proposed method for identifying internal waves can be used to assess their kinematic and dynamic characteristics.
