Spatial Discrimination of Salt–affected Soil Surfaces Using Landsat TM Data : A Preliminary Study in the Middle Reaches of the Heihe River, China

A preliminary study has been conducted to test the effectiveness of the canonical discriminant approach to making spatial discrimination of salt-affected soil surfaces, using the Landsat TM data taken in the middle reaches of the Heihe River, China. A saline area can be considered a mixture of salt-affected patches which differ in degree, and hence we tried to make discrimination of salt-affected soil surfaces by canonical discriminant approach. Three 360X360 m test plots with different land surface conditions, "Bare-soil surface area (strongly saline), "Reed area (moderately saline), "Barley field (weakly saline)", were selected as training areas or groups. Five indices, B4 (band 4 DN), Wetness, SI, NDSI, and Fe2O3 (composite indices), were determined as discriminating variables, and two canonical discriminant functions, y(1) and y(2), were obtained for the three groups using these five discriminating variables. When group centroids and individual cases were plotted on the plane made by two canonical discriminant functions, y(1) and y(2), the groups of cases were quite distinct and their centroids were well separated, which suggest that the canonical discriminant approach is promising for spatial discrimination of salt-affected soil surfaces.