Kazuhiko Masuda

Atmospheric correction of ASTER

An atmospheric correction algorithm for operational use for the high-spatial resolution, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is presented. The correction is a straightforward approach relying on inputs from other satellite sensors to determine the atmospheric characteristics of the scene to be corrected. Methods for the solar reflective and thermal infrared (TIR) are presented separately. The solar-reflective approach uses a lookup table (LUT) based on output from a Gauss-Seidel iteration radiative transfer code. A method to handle adjacency effects is included that relies on model output, assuming a checkerboard surface. An example of a numerical simulation shows that the effect of a land surface on the radiance over the ocean is stronger just off the coastal zone and decreases exponentially with increasing distance from the land. A typical numerical simulation is performed over the Tsukuba lake area in Japan. The TIR approach relies on the radiative transfer code Moderate Resolution Atmospheric Radiance and Transmittance Model (MODTRAN). The code is run for a given set of atmospheric conditions for multiple locations in the scene for several representative elevations. Pixel-by-pixel radiances are then found using spatial interpolation. Sensitivity analysis of the methods indicate that the results of the atmospheric correction will be limited by the accuracies of the input parameters.

Atmospheric correction for ocean color remote sensing: optical properties of aerosols derived from CZCS imagery

A procedure for an accurate atmospheric correction for ocean color remote sensing is described. It is shown that an appropriate aerosol model is the key factor for pursuing the atmospheric correction, including multiple scattering light in the atmosphere-ocean system. An algorithm for estimating the aerosol models suitable for the Nimbus-7 CZCS image of interest is proposed. As a result, phytoplankton pigment concentration near the sea surface is derived through the atmospheric correction and biooptical algorithms. The treatment is found to provide an improved pigment map of the sea surface near Japan. >

Degree of radiance and polarization of the upwelling radiation from an atmosphere–ocean system

The radiance and degree of linear polarization of the upward radiation emerging from the top of the terrestrial atmosphere bounded by a ruffled ocean surface are computed in the wavelength region ranging from 0.40 to 0.80 microm with the aid of the adding method. The ruffled ocean surface is treated as an interacting interface, where the radiation transmitted diffusely from below the ocean surface into the atmosphere is also taken into account. Computational results show that the simultaneous measurement of radiance and polarization degree from space makes it possible to derive atmospheric and oceanic parameters.

Dependence of the radiation just above and below the ocean surface on atmospheric and oceanic parameters

Radiance and degree of linear polarization of the upwelling and the downwelling radiation just above and below a ruffled ocean surface in a model atmosphere-ocean system are computed at the wavelengths of 0.5 and 0.75 microm with the doubling-adding method. Computational results show that: (1) maximum degree of polarization (P(max))a nd radiance in the corresponding direction (R(max)) f the upwelling radiation below the ocean surface are strongly dependent on the oceanic condition and that P(max) is affected by the atmospheric condition. The effect of surface wind is negligible. (2) P(max) and R(max) of the downwelling radiation just above the ocean surface are strongly dependent on the atmospheric condition, but are little affected by oceanic and surface conditions. A combined measurement of P(max) and R(max) is expected to provide useful information to infer atmospheric and oceanic conditions.

Feasibility study of derivation of cirrus information using polarimetric measurements from satellite

Monitoring techniques for deriving cirrus information over the ocean using polarimetric measurements from satellite are studied. Radiance and degree of linear polarization of the upwelling radiation at the top of a model atmosphere-ocean system are computed at the wavelength of 0.88 μm with the aid of the doubling-adding method, and where cirrus cloud is assumed to be composed of water droplets or randomly oriented hexagonal ice crystals (columns and plates). The computational results show, in particular, the following features. Degree of polarization observed at the Brewster angle in the solar plane is suitable to derive cloud optical thickness (τ) for large solar zenith angles, particularly in the case of τ < ∼ 5 while the radiance off the sunglint is suitable to infer τ in the range of τ < ∼ 30. However, for improvement of accuracy, cloud information such as thermodynamic phase, size distribution, and shape of cloud particles should be separately obtained, in particular for utilization of degree of polarization. The difference of degree of polarization appears between water particles and hexagonal ice crystals at the top of the atmosphere when the scattering angle is within 50–100°. Using this property, it should be possible to distinguish the thermodynamic phase of cloud particles. Furthermore, the feasibility of discrimination of the shape of the hexagonal ice crystals using the position of the neutral point is discussed, where phase angle is shown to shift to the backscattering direction at τ < 10. Hence, it is necessary to obtain τ separately.

Deriving cirrus information using the visible and near-IR channels of the future NOAA-AVHRR radiometer

Abstract A method is suggested for deriving cirrus parameters over the oceans using the visible and near IR channels ( λ = 0.63, 0.86, and 1.61 μ m) of the future series of NOAA-AVHRR radiometers. Reflectance and radiance of the upwelling radiation at the top of a model atmosphere-ocean system are computed at the above wavelengths with the aid of the doubling-adding method, and where multiple scattering effect is considered. The computational results show the feasibility of deriving cirrus parameters using the proposed channels. In particular, the following features are noted: 1) Thermodynamic phase of cloud particles and the shape and orientation of ice crystals of cloud, together with the water content, affect reflectance of cloud in an atmosphere-ocean system. 2) Subsun and subparhelic circle, etc. are noted only for two-dimensional orientations of ice crystals. These phenomena may discriminate the state of ice crystals. 3) It is possible to distinguish the thermodynamic phase of cloud particles using multichannels that include 1.61 μm. 4) The wavelength 0.86 μm is more suitable for thin cirrus observation than that of 0.63 μm due to the effect of absorption by stratospheric ozone and scattering by molecules.

Operational procedure for atmospheric correction on ASTER-radiance data allowing for the adjacency effect

To derive the earth surface (ocean) parameters quantitatively, a contamination of the atmospheric constituents is to be eliminated. Especially VNIR on ASTER provides data with respect to surface characteristics with a fine spacial resolution of 15 m. In this case, the adjacency effect due to the inhomogeneous surface on satellite data should be included in the investigation. At present, right after the launch the version 3 of the atmospheric correction algorithm is scheduled to be inclusive of this effect. Based on the simulation of atmospheric effects on the emergent radiation over a checkerboard type of terrain, an operational procedure of the atmospheric correction is outlined. The present new version enables us to quantitatively discuss radiative transfer over the non- uniform surface. The look-up-table method is used for the derivation of parameters.

Sensitivity of shortwave radiation absorbed in the ocean to cirrus parameters

Abstract To develop a monitoring technique for estimating the shortwave radiation absorbed in the ocean (I abs w ) from space, sensitivity of I abs w , and the upward irradiance at the top of the atmosphere (I t ) to cirrus parameters are investigated in a model atmosphere — ocean system in the wavelength region ranging from 0.285 to 5.0 μm. The cirrus is assumed to be composed of hexagonal ice crystals (columns and plates). The effects of orientation of crystals are also estimated, both for where they are randomly oriented in space and where their long axes are randomly oriented in a horizontal plane. The relationships between I abs w (or I t ) and radiance measured by the NOAA-AVHRR radiometer are discussed. Numerical simulation shows that the type and orientation of the ice crystals cannot be neglected to achieve the accuracy of 10 Wm −2 that is required for climate understanding.

Role of scattering process by atmospheric aerosol in the ASTER SWIR cross-talk effect

The ASTER SWIR radiation characteristics are evaluated when it decreases with increasing a distance from the edge. This phenomena is known as cross-talk due to a structure of the ASTER SWIR sensor. Similar characteristics is known as an adjacency effect due to atmosphere surface. In this paper, a possible contribution of adjacency effect is discussed at SWIR channels in conjunction with cross-talk phenomena. ASTER and MISR on Terra satellite adopted the dust-like aerosol model. Therefore, the aerosol model is in accordance to this model. The radiation characteristics at bands, 4(1.65 micrometers ), 5(2.165 micrometers ) and 9(2.395 micrometers ) on the sample data over Cape Atsumi peninsula near Nagoya indicates cross talk phenomena due to a structure of the ASTER SWIR sensor. It would not be due to the adjacent effect. A further sample data analysis is required.

Evaluation of the effect of spherical atmosphere on satellite data

Algorithm deriving the upwelling radiation from the top of the spherical atmosphere-ocean system is proposed. The method was developed using a technique similar to that of the plane parallel atmosphere bounded by a heterogenous surface. Numerical result indicated an effect of spherical atmosphere if the incident solar zenith angle is over 80 degrees.