| |
|---|---|
 (320Kb)
|
9,634,000 Yen (FY1996 3,046,000 Yen)
In order to monitor natural and antholopogenic variations of coral reefs widely by satellites, algorism to detect the variations from satellite data taken at different dates was investigated. It was found that the LANDSAT-TM data were available for the purpose because of its high resolution, frequent picture taking and variety of picture bands. The pictures without cloud coverage over Okinawa Island were analyzed. Difference between the data taken at different dates does not represent the real difference of underwater targets because the data vary not only with reflection by underwater targets but also with solar latitude, transparency of sea water and depth of the targets. Therefore, the influence of solar latitude was eliminated and the influence of light dissipation in the water was made decrease by introducing the ratio of data on the two appropriate bands at the same date and by drawing pictures with the difference between the ratios at different dates. Underwater coverages by the red soil sediment taking place between June 5, 1989 and November 4, 1992 were confirmed on the picture drawn with the difference of the ratio. Further, the influence of geographic depth change was eliminated by drawing the picture with the ratio of the ratios at different dates. Only the influence of sea level remains without being eliminated but the tide calendar makes it possible to estimate the influence. Transparency or light dissipation coefficient of seawater can vary with seasonal change of primary production progress of eutrophication and resuspension by storms. These influences should be estimated from in situ observations.
Coral Reef Variation, Satellite Monitoring Algorism, LANDSAT Data Analysis, Ryukyu Islands