New shipborne aureolemeter was developed to improve the sun-tracking performance for accurate measurements of not only direct but also circumsolar radiation, even on a vessel weltering. Sun position is determined by a real-time image processing system with a CCD camera. The accuracy of the sun position determination is finer than 0.01°. The radiometer is tracked the sun under a feedback control with the derived sun position. For a sky radiance distribution measurement, the control target position on the CCD camera image is shifted a pixel corresponding to a measuring scattering angle. In the case of a scattering angle larger than 7°, the radiometer’s tracking is conducted under feed forward control on the basis of the angle of roll and pitch monitored with a gyroscope. The instrument constants were determined from a Langley plot method. Test observation was conducted onboard the Antarctic research vessel (R/V) <i>Shirase</i> during the 56th Japanese Antarctic Research Expedition (JARE-56; 2014-2015). Aerosol optical thickness (AOT) was measured. The measurement of the sky radiance distribution is being analyzed to derive the aerosol optical properties.
Polarization optical particle counter (POPC) capable of measuring particle shape or sphericity was developed, which uses detection of polarization of light scattered by particles. Sensors that detected P and S polarization components are incorporated at scattering angle of 120˚ in addition to ordinary sensor located at the angle of 60˚. The particle size is derived from the pulse height detected with the ordinary sensor. The size thresholds were determined by measurements of PSL standard particles. Polarization of particle is calculated as the ratio of S polarization component to the sum of all components. The POPC field observations were started in Fukuoka, Japan on 15 March 2012 and in Matsue, Japan on 28 February 2012. Air pollution with high particle number concentration was observed in Fukuoka on 11 April. In that time, the particles with polarization lower than 0.3 constituted 90% of particles in the size range from 0.5 µm to 3 µm and 70-90% of those from 3 µm to 5 µm. Most of the atmospheric aerosol particles were consisted of spherical particles. Significant Asian dust transport was observed in Fukuoka on from 31 March to 1 April. The particles with polarization lower than 0.3 constituted 80% of those from 0.5 µm to 1 µm, 55-65% of those from 1 µm to 5µm. The increase of the ratio of non-spherical particles to all particles in Asian dust event was confirmed. The POPC thus is capable of measuring particle shape as well as size for each individual particle.
Optical observation around near UV spectral region potentially enables us to retrieve light absorbing features of aerosol,
such as type as well as optical thickness. We analyzed near UV observation data to identify haze properties around
Japan in the autumn of 2003, using Global Imager onboard Advanced Earth Observing Satellite-II (ADEOS-II/GLI),
which has 380nm and 400nm window channels. At the same time, we had optical observation, such as a ground-based
LIDAR measurement and a shipborne skyradiometer measurement, so as to retrieve vertical profile, particle sphericity,
particle size distribution, and optical thickness of the haze.
Based upon the three kinds of analyses with remotely sensed data, such as satellite, LIDAR, and skyradiometer, we have
the following characteristics of the haze: little UV absorbing, of optical thickness 0.5 (around 500nm), within lower
boundary layer (less than around 1km a.s.l.), and of spherical and fine particles (0.2 μm in radius).
We also have some direct sampling measurements onboard Research Vessel Shirase, such as integrated nephelometer,
particle soot / absorption photometer, and optical particle counter, so as to identify optical and microphysical properties
of the haze as well as chemical composition analyses. The results of the surface direct sampling showed the dense haze
dominantly consisted of smaller (0.2 μm in radius) and sulfate particulates, which is consistent to the remotely sensed
Backward trajectory simulations also indicate that the hazy air mass had arrived from / through some mega cities over
East Asia. Further, we are going to investigate the consistency between optical, microphysical, chemical, and
dynamical aspects using a chemical transport model.
This study shows match-up analysis of chlorophyll-a concentration in coastal area in Upper Gulf of Thailand. An applicability of atmospheric correction are investigated in turbid area. When a suspended matter concentration is over 7 g/m3 in a mouth of Bangpakong river, atmospheric correction was failed, then chlorophyll-a concentration could not be estimated. Three algorithms which are MODIS (Moderate Resolution Imaging Spectroradiometer) standard, neural network for GLI (Global Imager) and regional empirical algorithm are compared using match-up data set. The regional algorithm has better correlation than other algorithms and its RMSE was minimum in three algorithms. MODIS standard algorithm has good performance in higher than 1mg/m3, however, CHL was overestimated in lower concentration.
This paper proposes scheme of absorptive aerosol correction for ocean color data of Global Imager (GLI). 380 nm band (GLI band 1) is used to detect absorptive aerosol, and to correct absorption. Spectral dependency of absorption is given empirically from GLI scenes with absorptive aerosol. It is built in GLI atmospheric correction. Satellite-derived water-leaving radiance is compared with in-situ data over East China Sea under presence of absorptive aerosol. Estimation error of water-leaving radiance is decreased from 79 to 49% at 380nm, though error still remained. The scheme applied to GLI data with absorptive aerosol, and it was confirmed that this atmospheric correction was effective.
Asian dust aerosol layer of 4-6 km altitude accompanied by low clouds was observed with a LIDAR in Tokyo urban area on April 10 2001. In addition, column-integrated size distribution of aerosol was measured with a SkyRadiometer. To synthesize the top of atmosphere (TOA) reflectance, radiative transfer simulation was conducted assuming aerosol/cloud vertical structure and aerosol size distribution that were estimated after the ground observations. The refractive index of Asian dust was derived from a laboratory measurement of sampled Chinese soil particles. The synthesized TOA reflectance was compared to the SeaWiFS-derived one sampled at the low cloud pixels whose airmass is the same as the one passed at the observation site. TOA reflectance of the one of Asian dust models compare generally well with few percent difference in reflectance. We estimated an affect of Asian dust aerosol to ocean color remote sensing. Simulated TOA radiance absorbed by Asian dust was 20.0 W/m<sup>2</sup>/μm/sr in 443 nm. It is suggest that the existence of Asian dust occurs to dervie negative water-leaving radiance.
A radiative transfer model for a coupled atmosphere-ocean system was developed for satellite remote sensing of costal pollution to estimate water-leaving radiance from polluted sea surfaces. The optical properties of suspended substances in the ocean such as phytoplankton (Skeletonema costatum and Heterosigma akashiwo), detritus, submicron particles, and inorganic particles were measured or estimated. The equation of radiative transfer in the coupled atmosphere-ocean system was solved by using the invariance imbedding method. The water-leaving radiance in clear and Case II waters, turbid waters with soil particles, and red tide waters, were calculated. It was possible to estimate the soil particle concentration of water by using the ratio of the upward radiance at different wavelengths with a high resolution sensor for the land like the Landsat TM. However, estimating the red tide phytoplankton concentration using Landsat TM was difficult, because the water-leaving radiance varies little with phytoplankton concentration, and is affected by assumed amounts of detritus.
The presentation focuses on the peculiarity of Asian waters with respect to the atmospheric correction of the satellite ocean color data such as of Ocean Color and Temperature Scanner (OCTS). We first demonstrate the effect of highly turbid case 2 waters on the atmospheric correction via non- zero water reflectance in the near infrared region. The results of applying the OCTS standard correction scheme to typical Chinese coastal OCTS scenes reveal that a significant portion of the area is masked due to the negative water reflectance retrieved by the scheme, even using 765 nm and 865 nm bands instead of 670 and 865 nm pair to determine aerosol contribution. An optical model that relates suspended solid (SS) and chlorophyll-a (Chl-a) concentrations to the near infrared water reflectances was implemented into the atmospheric correction, together with a neural network that estimates Chl-a and SS concentrations. The new iterative scheme is applied to the Chinese coastal scenes and the results are assessed to be favorable. The paper then discuss the modeling of Asian dust aerosol in hope of establishing aerosol models that can be used for atmospheric correction. A set of models are designed with varying controlling parameters such as size distribution, vertical profile, and imaginary part of the refractive index. A series of radiative transfer simulation is conducted and the spectrum of the top-of- atmosphere radiance is compared to that of a Sea Wide Filed- of-view Scanner (SeaWiFS) data obtained under Asian dust event. The results of the comparison suggest that the Asian dust aerosol has unique spectral absorption feature at the blue region (in 412 nm band, i.e.).