LANDSAT/TM-Based Analyses of the Problems Related to the Red-Silt Outflow from the Okinawa Island

Abstract

Recent aggravation of the problems related to the outflow of the eroded silty red- soil from the Okinawa Island and its subsequent deposition on the coral reef needs more comprehensive and quantitative methods to analyse their actual situation. For this purpose, in the present paper, a new methodology mainly based on LANDSAT/TM data has been developed for the analyses not only of the islands as the source area of the red-silt but also of the surrounding coral reef as the deposition area of the silt.
Although there have been no attempts to detect the information of the deposition on the seabed from LANDSAT/TM data, the present study has succeeded in that by using the visible light band data and by developing a new data processing technique derived from the light transmission and reflection theory. For the analysis of the land area, LANDSAT/TM-based NVI (Normalized Vegetation Index) has been found to provide the information of the land covering rate by vegetation.
Finally, the interrelationship between the source-related factors in the island area, such as precipitation and land slope as well as the land covering by vegetation, and the deposition of the effluent silt on the coral reef area has been examined by using the quantification theory of type II. The result of the analysis shows that among these factors the covering by vegetation is the most influential factor on the red-silt outflow and its deposition on the reef.