Polarization of Light in the Ocean

The effects of polarization on our perception of the environment about us have been recognized for at least 1000 years. The earliest reports were in response to the polarization in blue skylight as observed through various polarizing crystals. Since blue skylight is a source of polarized light, and atmospheric observations are a quite natural part of our daily routine, it is not surprising that an extraordinary amount of research on the polarization of skylight has been undertaken. Study of the polarization properties of the ocean and the hydrosols contained therein has, unfortunately been very limited, perhaps because man has not been a natural resident of the sea. This chapter will introduce a description of the polarized light field beneath the sea by first providing a brief history of polarization. This will familiarize the reader with its rather ubiquitous presence in our environment, even though our visual perception of it is very weak. Finally, a method is presented (Mueller matrices) to fully characterize the polarization properties of the submarine light field and the polarized effects that various hydrosols have on the light field. For a collection of the many diverse applications of polarization, the reader is referred to the excellent book by Gehrels (1974) About 1000 years ago, the Vikings discovered the dichroic properties of crystals such as cordierite. This property of exhibiting various colors when viewed from different directions is due to the selective absorption of waves oscillating along a particular plane of the crystal. When Vikings viewed the blue skylight through such crystals held in a certain orientation, they located portions of the sky relative to the solar position that seemed to disappear. With this discovery of the polarization of the blue sky, they learned to navigate even in the absence of the sun (e.g., when it was below the horizon). It was another six and one-half centuries before other polarization properties were reported (see Table 11-1 taken from Gehrels, 1974, and Können, 1985).