Prediction and measurement update of fungal toxin geospatial uncertainty using a Stacked Gaussian process

The paper develops a stacked Gaussian process using both field and wet-lab measurements to predict fungal toxin (aflatoxin) concentrations in corn in South Carolina. While most of the aflatoxin contamination issues associated with the post-harvest period in the U.S. can be controlled with expensive testing, a systematic and economical approach is lacking to determine how the pre-harvest aflatoxin risk adversely affects crop producers as aflatoxin is virtually unobservable on a geographical and temporal scale. This information gap carries significant cost burdens for grain producers and it is filled by the proposed stacked Gaussian process. The novelty of the paper is twofold. First, the aflatoxin probabilistic maps are obtained using an analytical scheme to propagate the uncertainty through the stacked Gaussian process. The model predictions are validated both at the Gaussian process component level and at the system level for the entire stacked Gaussian process using historical field data. Second, a novel derivation is introduced to calculate the analytical covariance of aflatoxin production at two geographical locations. This is used to predict aflatoxin at unobserved locations using measurements at nearby locations but with the prior mean and covariance provided by the stacked Gaussian process. As field measurements arrive, this measurement update scheme may be used in targeted field inspections to warn farmers of emerging aflatoxin contaminations.