Introduction

This chapter summarizes those open ocean and floating ice properties that modify the surface and affect the emitted and reflected radiation at all frequencies. For the open ocean, these properties include wind-generated capillary and gravity waves, breaking waves, the generation and decay of foam, and the modulation of short waves by long waves and currents. Natural and human-generated slicks also suppress short waves. At longer time periods and over larger spatial scales, ocean currents, eddies and Rossby and Kelvin planetary waves generate large-scale changes in ocean surface elevation. Polar ice properties that affect the radiation include the areal extent and type of pack ice, and the presence and size of icebergs.

In the following, Section 2.2 discusses the oceanic winds and the ocean surface wave properties important to remote sensing: in particular the difference between the short-period capillary waves and the longer-period gravity waves, the changes that occur in the gravity-wave profile with increasing wave amplitude, the growth of capillary waves on the surface of the longer-period waves, the effect of wave breaking and the generation of foam. Because foam consists of air bubbles and is highly reflective, it changes the reflectivity and emissivity of the ocean surface, which makes it important at all remote sensing frequencies. The section also discusses the distribution of wave surface slopes as a function of azimuth angle relative to the wind direction. Although this topic seems obscure, it is essential for determination of sun glint, which can overwhelm satellite observations at all frequencies, and for the measurement of vector wind speeds at microwave frequencies. The section concludes with a discussion of surface slicks. Section 2.3 discusses the changes in sea surface height induced by ocean currents and long-period planetary waves, and Section 2.4 discusses sea ice.