The freshwater in aquifers of coral atolls whose averages of elevation are a few meters is often distributed as lenses floating on salt water underneath the islands. The coastal aquifers are possibly salinized by the sea-level rise, the decrease of rainfall recharge rate associated with the climate change, the increase of storm overwash, extractions due to the overpopulation. There is high possibility that the salinization of the aquifers damages the important natural ambience for the people living habitat such as crops field and vegetation. In this study, the aquifer salinization was evaluated by electrical resistivity, hydrological and long-term meteorological data in three low-lying coral atolls ; Laura islet and Kolalin island of Majuro Atoll in Marshall islands and Fongafale islet of Funafuti atoll in Tuvalu. The hydrological surveys conducted in Kolalin island, where is relatively small and hardly anthropogenically-influenced, revealed the dynamics of the pore freshwater layer in Holocene aquifer. The horizontal migration, separation, and coalition of the pore freshwater were clearly forced by the tide, indicating that the freshwater lens cannot be steady in the small atoll islands. On the other hand, the freshwater lens in the relatively large atoll islands such as Laura islet, which is mainly influenced by global and anthropogenical factor, varied interannually. The interface between seawater and freshwater in Laura islet was shallowed in August 2009 as a result of the decadal decrease of the rainfall and/or the sea-level rise. The detailed structure of the freshwater lens indicated the saline water intrusion from the lagoon and the upcoming of saline water caused by over-pumping associated with the urbanization and modernization of the atoll. In Fongafale islet which is relatively large, however, the soil and groundwater salinization was mainly caused by the tidal forcing during spring tides, indicating that the vadose zone cannot retain the pore freshwater. Coastal aquifers beneath low-lying areas during flood tides were intruded by the brackish pore water mixed with the rain water and sea water in phase with the semi-diurnal tide. The aquifer allowing the intrusion can be formed by gravel retaining high porosity due to the past reclamation resulting from the airfield construction.
In September 2004, Typhoon 200418 created very strong winds in Hokkaido, Japan, causing large-scale windfall forest damage in the region, especially in Tomakomai City near Shikotsu Lake. We applied remote-sensing techniques using SPOT2 satellite images to estimate the distribution and area of the windfall damage. The total area of windfall damage resulting from the typhoon was estimated to be 1,122ha in Tomakomai. We examined the accuracy of the analyzed area based on a damage report. Using SPOT2 satellite images, we could evaluate large-scale (≥1ha) windfall damage, and we found that the analysis results can be used to reduce the effort of a field survey.
The National Institute of Advanced Industrial Science and Technology (AIST) conducted the field experiment for the vicarious calibration of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) onboard Terra satellite from September 20 to 27, 2010. The vicarious calibration is a radiometric calibration method for satellite sensors by the radiative transfer model simulation based on the ground-based measurements of the surface and atmosphere on the target. The dry lakes in the desert regions of Nevada and California (U.S.), such as Ivanpah Playa, Railroad Valley and Alkali Lake, are used as the vicarious calibration sites. In the field experiment, the surface reflectance is measured by the spectroradiometer, and the atmospheric properties, such as ozone, water vapor, and aerosol, are measured by the ozonometer and skyradiometer. In addition, the field experiment for the vicarious calibration of RSI (Remote Sensing Instrument) onboard Formosat-2 satellite launched by Taiwan was also carried out. Synchronous measurements with the overpass time of ASTER/Terra and RSI/Formosat-2 on scheduled days were performed successfully.
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