1-h and 10-min rain precipitation data observed in central Japan from noon on the 13th to midnight on the 14th, August 1999 (36 h) have been analyzed in order to find a method indicating any temporal change in spatial rainfall patterns of a series of heavy rain. The analysis is mainly based on correlation coefficient and covariance not only of precipitation data between each pair of sequential recording times, but also variogram values obtained from the data. The temporal change of the correlation coefficients and the covariance values suggest the following possibilities for detecting change in rainfall pattern: 1) 10-min precipitation is more useful than 1-h precipitation; 2) covariance values are more useful than correlation coefficients; 3) covariance of variogram values in the polar and rectangular coordinates is the best indicator for the detection on not only intensity but also directional anisotropy; and 4) covariance values of omnidirectional variogram values are also a good indicator, but probably fail to indicate some important change in rainfall pattern.

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Mount Sakurajima, situated in the southern Kyusyu district of southwest Japan, is known as one of the most active volcanoes in Japan. It has erupted intermittently, ejecting large volumes of volcanic materials including lava, scoria, and ash. We have adopted a SAR interferometry method using JERS-1 images to monitor volcanic activity and estimate accompanying topographic changes in order to mitigate hazard from the inevitable eruptions and debris flows. A map expressing the phase-difference distribution for pairs of images recorded on two acquisition dates is produced for this purpose. This map, obtained by subtracting orbital and topographic fringes from the initial interferogram, is capable of quantifying vertical displacements at each point on the SAR image. Considering the acquisition-date intervals for the images used, three phase-difference maps are generated for the period from January 1996 to March 1997. These show that relatively large displacements occurring along the valleys on the northern slopes of the volcano are common to the three pairs. Because the volcanic activity was low during the period, the displacements may be caused chiefly by the erosion of the surface materials. Differential SAR interferometry is thus thought to be capable of estimating temporal fluctuations of topography during arbitrary periods, detecting regions that are readily aggraded or eroded, and helping to determine the position and dimensions of debris barriers.

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