資源探査に関する研究の動向と大規模データプロセッシング

[3601-07-03] レゴリス卓越の半乾燥地域における高精度な地下水資源ポテンシャル図作成を目指した光学とマイクロ波センサ衛星画像の組み合わせ

○マガイア ルイス¹、後藤 忠徳¹、マスウド アラー²、小池 克明¹ (1. 京都大学、2. タンタ大学)

司会：桑谷 立（国立研究開発法人海洋研究開発機構）

キーワード：地下水、後方散乱係数、粘土指数、植生指数、資源評価マップ

Unlike in coastal and sedimentary basins, in consolidated rocks such as volcanic rocks and crystalline basement complex in Africa, regional scale exploration of groundwater resource using exclusively geophysical methods is costlier due to large horizontal and vertical heterogeneities of basement aquifers. Therefore, integration of surface geophysical methods with remotely-sensed data is highly crucial as demonstrated by our research group (Magaia et al., 2017: Nat. Resour. Res.). Here, this study proposes a method of integrating satellite data by optical remote sensing and synthetic aperture radar (SAR) for accurate potential mapping of groundwater resource in crystalline rock areas in semiarid region. Analysis of the modified soil adjusted vegetation index (MSAVI) from two representative distinct seasons revealed the zones of high vegetation even in dry season. Ancillary information from SAR data analysis of the backscattering coefficient was decisive to map the zones of relatively high weathering degree, which was aimed to detect thick permeable zones of the regolith. In addition, a clay index calculated from the reflectance of four bands: red, near infrared, and two shortwave infrared bands was applied to discriminate clay-rich zones from the high vegetation activity zones. The clay-rich zones detected were in good agreement with the zones of low SAR backscattering coefficient. Accordingly, the narrow zones of high vegetation activity were marked by the high values of SAR backscattering coefficient as the result of volumetric scattering and the presence of retained high moisture content. These zones are regarded to indicate shallow groundwater occurrence. Further integration of this technique with other ancillary information from drilled wells and geophysical surveys can be expected to yield a more reliable potential map of regional groundwater resource for hard rock terrains in arid and semiarid regions characterized of low precipitation in efficient and cost-effective manner.