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Title: 中国タリム盆地北部における土壌環境変化の特徴抽出 : 衛星データによる塩類集積土壌の時空間変化の解析
Other Titles: Characterization of Soil Environmental Changes in Northern Tarim Basin in China : Spatio-Temporal Variation Analyses of Salinized Soils Derived from Satellite Data
Authors: 瓦依提, 阿依仙姑  KAKEN_name
小池, 克明  kyouindb  KAKEN_id
石山, 隆  KAKEN_name
Author's alias: WAYIT, Ayshamgul
KOIKE, Katsuaki
Keywords: 沙漠化
ASTER image
Normalized difference indices
Issue Date: Mar-2010
Publisher: 日本情報地質学会
Journal title: 情報地質 = Geological data processing
Volume: 21
Issue: 1
Start page: 19
End page: 33
Abstract: ASTERとLandsatによる計40シーンの衛星画像データを用い, 塩類集積土壌域の空間分布とその時間変化を詳細に抽出できる手法について検討し, これをタリム盆地北部のオアシス周辺に適用した. まず, 衛星画像データの反射スペクトル情報から, 植生の活性度, 表土の性質, および土壌の含水の程度に対する正規化指標SAVI, NDSI, NDWIを計算し, これらの大小関係を同時に表せるNDXI画像を提案した. 2004年のASTERデ-タからNDXI画像を作成した結果, 雨期では塩類集積土壌が雨水と混合するので塩類集積土壌の分布域は特定できないが, 乾期(夏季)になれば植生の分布域・活性度の時間的変化は小さくなり, 塩類集積土壌の分布が顕著になることがわかった. このNDXI画像によれば土壌水分量の大小によって塩類集積のメカニズムが異なることが示された. 次に, LandsatとASTERのNDXI画像を最尤法によって分類した結果, 固定砂丘の変化が最も大きく, 面積が半減し, この多くが農地を含む植生域と塩類集積土壌の面積の単調増加に寄与していることがわかった. さらに, 土壌サンプルに対して測定された反射スペクトルと塩分濃度から, 反射率と塩分濃度との相関性に対する1次回帰式を求め, これを塩分指標(SI)と定義した. 衛星画像にSIを適用した結果, 2003年になると塩分濃度が全体的に増加し, 塩類集積土壌の大部分は30 ppt以上の高濃度であり, 流動砂域も塩分濃度が高い状態にあることが明らかになった.
Leakages from the soil waterway, improper irrigation, and incomplete drain system have raised the groundwater levels in arid areas and caused salinization, i.e. accumulation of salts in the top soils. Vulnerability of salinization is also controlled by topographic properties and soil conditions. This study focuses on a desert area in the northern Tarim Basin, northwest China, because the rapid progress of salinization has been reported. One main factor for the salinization in the study area is the excessive water supply in the agriculture lands. For clarifying the salinization process, 40 scenes of satellite imagery in total by Landsat T‚l/ETM+ (acquisition years: 1990 and 2000) and Terra/ASTER (acquisition years: 2003, 2004, and 2006) were selected. Three normalized difference indices on vegetation, soil, and water and a color composition of the indices were adopted to detect surface changes in the period from 1990 to 2006. As a result, the salinized soils were found to have extended in the downstream, and their area increased monotonously with the time while the area of fixed dunes decreased largely. We proposed a Salinity Index to extract correctly the salinized areas from the ASTER images by refereeing to the reflectance spectra of the soil samples. This Salinity Index clarified that the salinized soils have high salt concentrations over 30 ppt and the concentrations of the moving sands are also high. In addition, the high salinity accumulation in the downstream of farmlands was identified, which implied a strong effect of agricultural development on the salinization.
DOI(Published Version): 10.6010/geoinformatics.21.19
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