Digital Mapping of Soil Drainage Classes Using Multitemporal RADARSAT-1 and ASTER Images and Soil Survey Data

Abstract

Discriminant analysis classification (DAC) and decision tree classifiers (DTC) were used for digital mapping of soil drainage in the Bras-d’Henri watershed (QC, Canada) using earth observation data (RADARSAT-1 and ASTER) and soil survey dataset. Firstly, a forward stepwise selection was applied to each land use type identified by ASTER image in order to derive an optimal subset of soil drainage class predictors. The classification models were then applied to these subsets for each land use and merged to obtain a digital soil drainage map for the whole watershed. The DTC method provided better classification accuracies (29 to 92%) than the DAC method (33 to 79%) according to the land use type. A similarity measure (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>S</mml:mi></mml:math>) was used to compare the best digital soil drainage map (DTC) to the conventional soil drainage map. Medium to high similarities (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>0.6</mml:mn><mml:mo>≤</mml:mo><mml:mi>S</mml:mi><mml:mo>&lt;</mml:mo><mml:mn>0.9</mml:mn></mml:math>) were observed for 83% (187 km 2 ) of the study area while 3% of the study area showed very good agreement (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>S</mml:mi><mml:mo>≥</mml:mo><mml:mn>0.9</mml:mn></mml:math>). Few soil polygons showed very weak similarities (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>S</mml:mi><mml:mo>&lt;</mml:mo><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:mn>3</mml:mn></mml:math>). This study demonstrates the efficiency of combining radar and optical remote sensing data with a representative soil dataset for producing digital maps of soil drainage.