The change detection module 124 is used to detect changes in a field's crop health condition using the imagery products derived from the image processing module 123. Change detection can examine either positive change or negative change. Positive change looks for increases in normalized VI values between image pairs and can be useful for locating areas of plant growth, which could be indicative of weed growth in a field. Negative change looks for decreases in normalized VI values between image pairs and can be useful for locating areas where the relative crop condition is declining due to various crop ailments such as disease, weather damage, pest damage, poor nutrient content, and so on. The change detection process is the same for either positive or negative change; only the specific parameters and thresholds utilized may change.

FIG. 3 illustrates the process for detecting crop condition change in an agricultural field. The change detection process 300 is executed by the change detection module 124 for a specific image in a sequence of filtered images over a specific agricultural field. This can be the most recent filtered image, or any filtered image in the sequence of filtered images (hereafter referred to as the image stack), or the process can be run sequentially on every image in the stack. Most typically the process will be run sequentially through the image stack within a specified time of interest (i.e., from the beginning of the crop season to the most recent image date), beginning with the oldest image in the stack and proceeding until the most recent image is processed.