S. Mukai

Investigation of Atmospheric Aerosols Based on Polarization Measurements and Scattering Simulations

For an ongoing project involving ocean color and temperature scanner and polarization and directionary of the earth’s reflectance onboard the advanced earth observing satellite, the radiance and degree of polarization of atmospheric aerosols were measured with a portable photopolarimeter (FPR2000) at wavelengths of 0.559, 0.760 and 0.811 μm. The observations were undertaken over the ocean around Shikoku Island of Japan on clear days with few clouds in July, 1995. The measurements were compared with simulations of polarization fields. This work also describes retrieval algorithms for aerosols. It is shown that: (1) the radiance decreases with wavelength, (2) oceanic type aerosols are available to evaluate the degree of polarization over the Pacific Ocean, and (3) polarization data in the Seto Inland Sea are explained by a water-soluble aerosol model.

Polarimetric properties of atmospheric aerosols

This work presents an aerosol model interpreting photopolarimetric measurements of skylight over the ocean. Polarization degree and optical thickness of the atmospheric constituents have been simultaneously measured by a photopolarimeter, whose spectral bands are set up to correspond to the ADEOS/POLDER. Our algorithms are based on light scattering simulations of the polarization field. It is shown that such a Maxwell-Garnett mixing rule as small water-soluble inclusions is an oceanic matrix is available to interpret the polarization measurements over the Seto Inland sea and its volume fraction of inclusions to matrix varies with time polarimetric properties of atmospheric aerosols, and that magnitude of polarization degree is reduced due to multiple scattered light, especially in the visible wavelengths.

Polarimetric properties of aerosol particles

Retrieval algorithms for scattering particles are shown based on photopolarimeric measurements of sky light over the ocean and multiple scattering simulations of the polarization field. Polarized components of the atmospheric constituents have been measured by a photopolarimeter (named PSR1000) with spectral bands set up to correspond to the ADEOS/POLDER. The POLDER is the first sensor on board the satellite to be designed to observe polarization.It is shown that heterogeneous grains are better than homogeneous models to explain polarimetric properties of atmospheric aerosols, and a Maxwell-Garnett mixing rule for small water-soluble (WS) inclusions in an oceanic (OC) matrix is available to interpret the polarization measurements of atmospheric aerosols over the Seto Inland Sea. We also found during our observations that the value of refractive index of the aerosol, i.e., its chemical composition, varies with time and place rather than particle size.

Retrieval algorithms for photopolarimetric properties of aerosols

Abstract Retrieval algorithms for atmospheric aerosols are proposed in this paper using photopolarimetric measurements based on simulations of polarization fields. The radiance and degree of polarization of atmospheric aerosols were measured with a portable photopolarimeter (FPR2000) at wavelengths of 0.559, 0.662 and 0.811 μm which correspond to the wavelengths of the Optical Sensor (OPS) aboard the Japanese Earth Resources Satellite (JERS), in order to confirm the accuracy of the JERS observations. Our algorithms are based on an idea that aerosol characteristics can be estimated in terms of the scattering behavior. It is shown here that polarization is a powerful tool in determining aerosol characteristics and their variation on spatial and temporal scales.

Algorithms for aerosol retrieval based on scattering calculations

Abstract This paper focuses on how to determine an accurate aerosol model based on simulations of light scattering. Our algorithms come from an idea that aerosol characteristics can be estimated in terms of the scattering behavior. The correlation coefficients between measurements of atmospheric aerosols and the simulated values for model particles are used to retrieve aerosol characteristics. The space-borne data by Nimbus7-CZCS at a wavelength 0.67 μm and the photopolarimetric measurements of aerosols with a portable photopolarimeter (FPR2000) at wavelengths of 0.559, 0.662, and 0.811 μm are examined in this work. It is shown here that aerosol models are precisely determined by combining use of polarization measurements and radiance data.

Similarity and diversity of OCTS and POLDER from an ocean color analysis point of view

Abstract Comparison and combination of two ocean color sensors, ADEOS/OCTS and POLDER, are treated in this work. These new sensors possess high radiometric sensitivity and multi-spectral bands in the visible and near-infrared wavelengths. It is of interest to mention that the POLDER provides the data at the multiviewing angles. These directional measurements include significant information of atmospheric aerosols. In addition POLDER measures polarization as well as radiance. It is shown here that aerosol retrieval can be efficiently pursued by a combination of radiance and polarization. As a result, it is found that the retrieved distribution of aerosol optical thickness and the phytoplankton pigment concentration near the sea surface obtained from the OCTS data coincide with those from the POLDER data within the tolerances required at the present time.

Removal of scattered light in the Earth atmosphere

Atmospheric correction algorithm, which means a procedure to remove scattered light in an atmosphere from the spaced-based data, are shown for ocean color data given by the satellite ADEOS. In order to achieve better atmospheric correction, this paper proposes two subjects; one is how to determine aerosol characteristics by referring to both of radiance and polarization, and the other is introduction of atmospheric correction coefficients.At first it is shown that a heterogeneous grain model according to Maxwell-Garnett mixing rule as small water-soluble (WS) inclusions in an oceanic (OC) matrix is available to interpret ADEOS/OCTS and POLDER data observed over the Arabian Sea. Our algorithm is based on an idea that aerosol characteristics can be estimated in terms of scattering behavior in the polarization field. Then atmospheric correction, which is based on radiative transfer process in an atmosphere-ocean model involving the retrieved aerosol model, is applied to ocean color data given by ADEOS/OCTS. Finally our atmospheric correction provides an expected chlorophyll map near the sea surface.It is of interest to mention that retrieval of atmospheric aerosols is improved by combination use of radiance and polarization, moreover atmospheric correction process is progressed by using the correction coefficients.

Multispectral polarization measurements of atmospheric aerosols

This work presents the polarization measurements of atmospheric aerosols and how to estimate optical properties of aerosols based on simulations of polarization field. Polarization degrees of aerosols were measured with our new portable polarimeter, whose spectral coverage is [0.443, 0.865] μm. The observations were undertaken at Meteorological Research Institute (Tsukuba) and Kinki University (Osaka) in 1996. We found the sequential change of aerosol characteristics according to the variation of polarization data on temporal scale.

Evaluation of retrieval algorithms for atmospheric aerosols with multi-directional observations by ADEOS/POLDER

Abstract The first space-based polarization measurements were undertaken by ADEOS/POLDER. The POLDER has supplied the observed data not only in the multi-wavelength bands but also at the multi-viewing angles. These directional measurements include significant information of atmospheric aerosols. This work is a feasibility study of multi-directional data for the retrieval of aerosols characteristics. The basic algorithms for aerosol retrieval is based on light scattering simulations of polarization field, where the heterogeneous aerosol model according to Maxwell-Garnett mixing rule is considered. It is shown that polarization data observed at multi-angles is a powerful tool to retrieve aerosol characteristics, and that the obtained aerosol distribution indicates the regional trend of atmospheric condition over the North Pacific Ocean near Japan.

Aerosol distribution based on polarization and radiance measurements by ADEOS/POLDER

This work shows how to estimate the characteristics of atmospheric aerosols using space-based observations of polarization and radiance taken by POLDER equipped on the satellite ADEOS. The retrieval algorithms for aerosols are based on light scattering simulations of polarization field. The model aerosol has taken into account the heterogeneous grain model with Maxwell-Garnett mixing rule for typical oceanic and water-soluble aerosol models. It is found that polarization information is useful to retrieve aerosol properties. As a result, aerosol distribution over the Pacific ocean near Japan is obtained, and we found that aerosol characteristics change in temporal and regional scales.