Yasunori Sasaki

Microwave emission and reflection from the wind-roughened sea surface at 6.7 and 18.6 GHz

Microwave radiometric observations were made with specially designed microwave radiometers at 6.7 and 18.6 GHz, and the results were compared with those of other investigators, over the frequency range of 1-40 GHz. Dependences of sea surface emission and reflection on wind speed, frequency, incidence angle, and polarization type are discussed in detail, following discussions of the reflective processes of sky radiation and error estimation in the retrieval of mainlobe-averaged brightness temperature. The wind speed sensitivity of brightness temperature, emissivity, and reflectivity is formulated with respect to frequency and incidence angle in each polarization. The brightness temperature, emissivity and reflectivity at arbitrary wind speed are derived employing this formulation. Based on the results obtained it is suggested that the 10-19-GHz band may be optimal for satellite microwave radiometer observations of sea-surface wind. >

Satellite thermal observation of oil slicks on the Persian Gulf

Abstract A possibility of oil slicks detection is discussed for oil slicks spread in the vicinity of the Nowruz oil fields on the Persian Gulf since March 1983 to July 1983 with considering an apparent thermal inertia. The apparent thermal was computed from continuous observations of sea surface temperature and albedo by the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-7 through day and night with 12 h interval. The apparent thermal inertia is defined as a function of a temperature difference between the daytime and the nighttime and an apparent albedo. Sea surface temperature used for computing the apparent thermal inertia was obtained through an atmospheric correction with an empirical equation which uses an energy difference between two thermal channels of the AVHRR. Although there was an ambiguity on a selection of same object on water body, the computed apparent thermal inertia showed the possibility of oil slicks detection from sea water.

An Application of NOAA AVHRR for Oceanography in the East China Sea

Abstract Two sets of NOAA AVHRR imagery in spring and fall of 1980 are used to study hydrography of the sea southwest of Kuyshu, Japan. Comparison with hydrographic observations delineates two anticyclonic warm water eddies, which had diameters of 60 to 100 km determined from the satellite imagery. The high temperature and salinity of the eddies suggests that they originate from the Kuroshio. The bottom topography seems to influence strongly shape, spatial scales and locations of these eddies. The generation of the eddies may be caused by shear instabilities of the shore side edge of the Kuroshio. The eddies may supply the Kuroshio water to the Tsushima Current. This suggests that formation of the Tsushima Current southwest of Kyushu is of the episodic nature.

A Simplified Microwave Model and Its Application to the Determination of Some Oceanic Environmental Parametric Values, Using Multichannel Microwave Radiometric Observations

This paper proposes a simplified microwave model, linerized by Taylor expansion and incorporating observed fundamental microwave emissive properties, and discusses its application along with the least square method for determining some oceanic environmental parametric values from multichannel observation data. As a case study, microwave radiometric observations were made in vertical and horizontal polarizations at 6.7 and 18.6 GHz at incidence angles from 200 to 700 at steps of 100, and sea-surface temperature, wind speed, and sky brightness temperatures at the above dual frequencies at zenith angles from 200 to 700 were determined from a set of observed data at each incidence angle. The algorithm-derived results were compared with observed ones and showed good agreements within 10 percent of errors at incidence angles from 200 to 600; however, no good agreement was attained at large incidence angles such as 70°, except sky brightness temperature at 6.7 GHz. This disagreement may be attributed mainly to the difficulty and incompleteness in corrections such as estimation of reflected sky radiation and antenna characteristics, both for retrieval of the antenna temperature averaged over the main lobe and observation errors. This fact, however, may also suggest that observations at such larger incidence angles are of less utility.

Data processing techniques of remote sensing for oceanography

Abstract Satellite remote sensing can provide oceanographers with powerful tools for collecting data, since it covers a wide area instantaneously and as frequently as several times a day. In order to extract meaningful information from data collected by satellites, special data processing is an absolute necessity. Techniques for data processing are different, depending on characteristics of the data, measurement principles and the oceanographic requirements. Three systems of satellite sensing, AVHRR, CZCS and SAR, are particularly useful for oceanography but need special techniques for data processing. Several techniques developed by JAMSTEC and IBM-Japan for these systems are described with examples applied to oceanography.