摘要： The temporal variations (diurnal and annual) in arboreal (εTree) and bare soil (εSoil) dielectric constants and their correlation with precipitation were examined for several trees in Japan. A significant (1 σ (standard deviation) and 2 σ) εTree increase is observed after rainfall at 89.8% and 90.5% probability. However, rainfall does not always induce significant εTree increases. Rainfall of more than 5 mm/day can induce 1 σ εTree increase at a 59.6% probability. In order to examine whether the increase in εTree affects the L-band σ0 variation in a forest, the four-year temporal variation of the L-band backscattering coefficient (σ0) was estimated from observations by the Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar. Observed maximum absolute deviations from the mean over the forest area were 1.0 and 1.2 dB for σ0 HV, respectively, and 4.0 and 3.0 dB over open land. σ0 and rainfall correlations show that εTree and σ0 Forest are proportional to precipitation integrated over seven or eight days; εSoil and σ0 Open land are proportional to precipitation integrated over three days. This finding indicates that εTree variations influence σ0 Forest areas. A stronger correlation between σ0 HV and precipitation is observed in several sites with low σ0 HV, where less biomass is expected, and several sites with high σ0 HV, where more biomass is expected. A weaker correlation between σ0 HV and precipitation is observed for several sites with high σ0 HV. These differences may be explained by the different contributions of double bounce scattering and potential transpiration, which is a measure of the ability of the atmosphere to remove water from the surface through the processes of transpiration. The two other results were as follows: 1) The functional relation between aboveground biomass and σ0 showed dependence on precipitation data, this being an effect connected with seasonal changes of the εTree. This experiment reinforces the fact that the dry season is preferable for retrieval of woody biomass from inversion of the functional dependence of SAR backscatter and for avoiding the influence of rainfall. 2) The complex dielectric constant for a tree trunk, which is measured between 0.2 and 6 GHz, indicates that free water is dominant in the measured tree.