Remote sensing of sea state through a Polaroid

Abstract

The visible light reflected from a wind-roughened sea surface contains information about the sea state in the form of its polarisation status. Each sea state is characterised by a specific wave-slope distribution depending upon the nature of surface winds. This in turn, imparts unique polarisation characteristics to the light reflected from a wind-roughened sea surface in accordance with Fresnel’s reflection laws as established by earlier studies. In this paper, we discuss the significance of surface reflected light in the context of using it for remote sensing of sea state. We propose the design for an instrument that will view the wind-roughened sea surface over a period of time and compute the fraction of plane polarised light received by it. The results then can be related to the sea state and the wind speed prevailing over the sea. The instrument can be made to view the sea surface at any look angle though the angles in the range of 30-40 and 65-70 degrees are found to be preferable for better resolution of sea states. The proposed instrument can be mounted on an observation tower, aircraft or a satellite. The range of wind speeds that can be sensed by the proposed instrument is 0-60 knots.