Tadakuni Miyazaki

High-speed spectroradiometer for remote sensing

A high-speed spectroradiometer designed for spectral reflectance measurement in remote sensing is described. This instrument uses a monochromatic grating and a photomultiplier system for light detection and sweeps over the 400-850-nm wavelength spectral range with the spectral resolution of 2 nm within 1 s. The instrument has the inherent advantage of portability and speed of operation which make it particularly suitable for field work in the area of fast moving surfaces, e.g., water with wave motion. Some applications of its use in laboratory and field experiments also have been presented. The instrument would seem to be an appropriate instrument for ground data collection in remote sensing.

Field survey and hydraulic study of Aoshio in Tokyo bay

Abstract We have studied the so-called “Aoshio” phenomenon for years. In Japanese, “ao” means blue and “shio” means tide. The color of the sea surface changes to milky-blue and lots of shells and fish are killed when the “Aoshio” water covers them. This phenomenon has appeared only in a particular eutrophic coastal area of Tokyo Bay in Japan in summer time. The “Aoshio” phenomenon has been explained as follows: The origin is believed to be an anoxic bottom water mass in the offshore area, which develops in summer time and contains much H2S. This water mass arises in the coastal area when an offshore-ward wind blows several days in a row. When the anoxic water mass meets oxygen under the sea, the dissolved H2S turns into colloidal sulfur particles. The milky-blue color is attributed to the random reflection of sunshine in the water with these particles. To explain such water mass ascent, we considered two simple hydraulic mechanisms and conducted numerical simulations using two dimensional equations for stratified flow. We also conducted field surveys on the sea and from the sky, to assess the “Aoshio” physicochemically and biologically and to develop a “Aoshio” monitoring procedure by remote sensing.

Measuring the coral reef distribution of Kuroshima Island by satellite remote sensing

Measuring the spectral signatures of under water coral reefs and mapping of coral reefs by satellite remote sensing are described. The spectral signatures of different species of the coral reefs were measured using a spectroradiometer off Kuroshima Island, Okinawa, Japan and investigated spectral difference between different species of the coral reefs. As well as the field experiments, laboratory experiments for measuring the spectral signatures of 9 different species of coral reefs were carried out with the same spectroradiometer. The spectral reflectance of each coral reef showed a significant result that a narrow absorption band exists in the spectral region between 66a0 and 680 nm, and very strong spectral reflectance from about 700 nm towards the longer wavelength range. On the other hand, absorption and the high reflectance region were not observed from the bottom sands or bare rocks underwater. These experiments suggest that there is a significant spectral difference between coral reefs and bottom sands or bare rocks and so the best spectral range for separating the coral reefs from other underwater objects in the ocean would be between 700 and 800 nm. As well as the basic spectral measurement either in the field or at the laboratory, SPOT satellite imageries were used to classify the underwater coral reefs. Classification methods used here were the principal component analysis, and the maximum likelihood. Finally, the evaluation of classification method for extracting the coral reefs was introduced.