Estimating Within-field Variations in Soil Properties from Airborne Hyperspectral Images

The ability of hyperspectral image (HSI) data to provide estimates of soil electrical conductivity (ECa) and soil fertility levels without requiring extensive field data collection was investigated. The relationships between HSI spectral reflectance signatures and soil properties were analyzed to evaluate the usefulness of HSI for quantifying within -field spatial variability. Bare soil images were acquired using a prism grating pushbroom scanner in April 2000 and May 2001 for a central Missouri experimental field in a minimum-tillage corn-soybean rotation. Data were converted to reflectance using chemically-treated reference tarps with eight known reflectance levels. Geometric distortions of the pushbroom sensor images were corrected with a rubber sheeting transformation. A 5 m pixel size was selected by analysis of short-range variations in five sub-field areas. Statistical analyses, including simple correlation, multiple regression (MR), and principal component analysis (PCA) were used to relate HSI data and derived Landsat-like bands to field-measured soil properties. The blue wavelengths of the HSI and Landsat-like images showed the highest correlation with ECa and soil chemical properties. With the exception of pH and P, the soil fertility data were negatively correlated to the HSI reflectance data. The highest correlations to the HSI bands were found for Mg and CEC. Stepwise multiple linear regression (SMLR) mo dels using the full HSI dataset included too many variables, which increased the danger of overfitting. MR models using Landsat-like bands may be more practical than using SMLR models for mapping soil properties. Analysis of principal components showed that PC 2 and PC 4 explained soil variability well for CEC, Mg, OM, K, and pH. Both approaches to data volume reduction, creating Landsat-like bands and PCA, showed potential for developing relationships with soil properties. HSI analysis appears promising for quantifying soil property variability.