The impact of polarization on infrared sea-surface temperature sensing

Abstract

One of the most strongly polarized natural infrared sources is the sea surface, yet polarization is rarely considered in infrared radiometric sea-surface temperature sensing. For an off-nadir incidence angle, sea-surface emission is vertically polarized, and reflected atmospheric radiance is horizontally polarized. The net degree of polarization is determined by the relative magnitudes of reflected and surface-emitted radiances, which actually tend to offset one another because of their orthogonal orientations. The significance of partially polarized radiances on radiometric sea-surface temperature measurements is determined primarily by the viewing angle and the inherent polarization sensitivity of the radiometer. This paper discusses several ways that polarization can affect infrared radiometric measurements of sea-surface temperature. A specific example is shown, wherein the polarization sensitivity of a Fourier transform infrared (FTIR) spectrometer results in small errors that are significant for high-accuracy radiometry.

Retrieval of refractive index over specular surfaces for remote sensing applications

“…For example, the use of infrared (IR) polarization is becoming increasingly common in remote sensing, especially for water, which is perhaps the most strongly polarized thermal IR source in nature [6]. Even non-polarimetric remote sensing applications for water require consideration of polarization when the sensor response varies with polarization [7,8]. Most passive remote sensors observe the brightness temperature or radiance, which contains the information about polarized reflectivities of a surface at a given view angle without having knowledge of the dielectric property of the material.…”

Degree of linear polarization in spectral radiances from water-viewing infrared radiometers

“…Polarization adds a dimension to passive infrared sensing that can yield information about a source or its environment beyond that conveyed by brightness and spectral content. As sophisticated infrared sensors have become more widely available, infrared polarization 1 has evolved from its largely astronomical roots into fields as diverse as environmental remote sensing, [2][3][4][5][6][7] military surveillance, 8 -15 and machine vision. 16,17 For example, in both ocean remote sensing and military surveillance, Fourier-transform infrared spectrometers are being used increasingly as passive emission spectroradiometers, sometimes without sufficient consideration of the instrument polarization sensitivity or the scene polarization state.…”

“…Therefore radiometric sea-surface measurements at large incidence angles require a polarization-dependent surface emissivity, and polarization may still cause errors if the instrument polarization sensitivity is not considered fully. 7 Furthermore, the polarization signature of water may lead to identification of false targets when polarimetric infrared sensors are used to search for manmade objects in an otherwise unpolarized thermal background. In these and similar applications, there is a need for quantitative estimates of the polarization state of infrared radiances from water.…”