Polarization of light in UV‐visible limb radiance measurements

Abstract

Solar light propagating in the atmosphere becomes polarized when it is scattered by air molecules and aerosol particles. Remote‐sensing instruments that use grating spectrometers are sensitive to the polarization state of light. Therefore polarization has to be taken into account in the analysis of measurement data. In this paper we characterize the effects of polarization in UV‐visible radiance measurements by a limb‐viewing satellite‐based spectrometer. Special emphasis is on the Optical Spectrograph and Infra‐Red Imager System instrument designed for measuring ozone profiles in the stratosphere. The variation of polarization as a function of the aerosol conditions of the stratosphere, solar illumination geometry, tangent altitude of the measurement, wavelength, and surface albedo is investigated using a backward Monte Carlo radiative transfer model. Two possible correction schemes for instrument polarization sensitivity are discussed in view of these simulations: scaling of data by a reference spectrum measured at a high altitude and modeling of polarization by a single‐scattering model. Multiple scattering intensities calculated by a radiative transfer model that treats light as a scalar quantity are compared to values obtained by a model that takes polarization into account. In limb‐viewing geometry the scalar approximation is shown to cause an error of maximum ∼6% in the intensity.