A transfer learning approach utilizing combined artificial samples for improved robustness of model to estimate heavy metal contamination in soil

Abstract

Benefiting from the nanoscale sampling intervals and subtle spectral information in the visible and near-infrared band, hyperspectral technology is considered as an efficient means for monitoring soil heavy metal contamination whereby the good robustness of prediction model is driven by the increase to spectral dimension in model analysis. Considering the positive correlation between samples size and spectral dimension, we focuses on a novel derivation of enlarging samples size in this study to improve model performance by i) preparing artificial samples taking into account of flexibility and control over the laboratory environment compared with collecting wild samples, and ii) using transfer learning method called transfer component analysis (TCA) for reducing spectral feature differences caused by soil heterogeneity to train model in the same data distribution. The proposed approach was tested on three heavy metals, namely copper (Cu), cadmium (Cd) and lead (Pb), collected in the mining area located in the Xiangjiang Basin, Hunan Province, China. The experiments showed that the initial model constructed by a small number of wild samples performed strong prediction sensitivity as the training samples change. In contrast, a modified model with TCA could showed good robustness with excellent predicted ability, the average prediction accuracy of the determinable coefficient (R2) and the ratio of prediction to deviation (RPD) improved to 0.73 and 1.90, 0.74 and 1.92, 0.72 and 1.73, respectively. The results illustrated there was a more reliable modeling method in potential to predict soil heavy metals based on hyperspectral analysis at low cost.