Investigations of the Large-scale Sea Surface Structure and Wave Interactions with Airborne Radiophysical and Optical Instrumentation

Abstract

A remote sensing package features a 2-cm side-looking radar, a two-channel microwave radiometer making along-track measurements at 8 and 18 cm and a multispectral photo camera MKF-6 with a high spacial resolution. One of the tasks of the package is to get experimental data about a large-scale structure of the sea surface, about the dynamics of energy-carrying waves, roughness spectrum generation, wave breaking and foam formation. Observations are made in the open sea. under appropriate hydrometeorological conditions when it is possible to identify over large-scale areas - subsequent stages of wind-induced wave generation, from still to stable storm. Though such situations occur seldom, several experiments yield the required data arrays as radar CRI3 and optical CO13 images of the sea surface, over which the roughness dynamics could be easily followed. Concurrent microwave radiometry in two long-wave channels practically not affected by the atmosphere and cloudiness, give radiobrightness temperature variations caused by a general change in the surface condition, in particular, by changing roughness and foam coverage percentage. The main mathematical tool with which to get information about the condition and texture of the ocean surface from the romotely sensed data, are computer-aided procedures for video image processing, relying upon the high-capacity computer systems CKTS and SVI73. The software i ncludes both the global procedures for statistical analysis of images C two-dimensional Fourier transform 256x3563 and local proceduresfor metric analysis of bright areas on images. These procedures, if applied to RI or 01. would permit; a detailization of the spatial s tructure and energy-carrying-wave spectrum as well as calculations of geometric characteristics of foam generation over the ocean surface. The procedure of radiometric signals processing includes a regression and a statistical analysis of brightness temperatures measured in two channel s. The coefficient of regression appears to be sensitive to the sea surf ace condi ti on and i s an addi ti onal measur e of roughness. Radiometry may help recover the parameters of the spectrum of small-scale sea surface roughness and the related dynamic characteristics of the surface layer. The data of comprehensive processing of a number of thematic experiments point to new regularities in the mechanisms of large-scale sea surface structure formation in a nonstationary and i nhomogeneous wi nd f i el d. Among them are - spatial spectrum transformation near the energy-carrying peak region - due to non-linear interaction and breaking of waves; - generation of a group structure of wams and packets modulations which leads to the formation of a complicated 3D-picture of the sea in the conditions of a fully developed stable storm; - changes in geometric and statistical characteristics of foam cover ; - manifestations of the fractal s tructure of wave breaking zones Cfoam. whitecaps:, and detection of fractal dimentionality dependance on sea surface roughness; - qUantitatiVf3 relationship existing between the spectrum shape and the overall foam percentage. The presentation offers available experimental data and the results of their processing, ’ illustrating the above concepts.