While increases and decreases in VI values in an agricultural field may indicate deleterious effects warranting the attention of the grower, there are other potential causes that need not trigger an alert to be generated. As an example, consider the seasonal growth pattern of a typical agricultural crop. Following planting, a plant will germinate and grow during the course of the season, increasing in both biomass and photosynthetic activity (green-up phase) before reaching a plateau (peak phase), followed by a gradual yellowing of the plants prior to harvest (senescence phase). FIG. 2 is a graph 200 which illustrates a generalized growth curve for an exemplar crop as expressed through vegetation index values. The green-up phase 202 is typified by a continuous increase in VI values, while the peak phase 204 sees a leveling off of the VI values, and finally the senescence phase 206 is marked by a gradual decrease in VI values over time. These seasonal increases and decreases are part of the regular plant growth cycle and are not of any particular concern to growers; however, direct change detection between VI images computed during the green-up or senescence phases may trigger an alert to be generated. There are other potential causes of increases/decreases in VI values not directly related to changes in crop health condition. As mentioned previously, differences in atmospheric constituents from one day to another can cause changes in band reflectance values and consequently VI values. While some level of correction of these effects is possible, it is difficult to fully correct, especially in an automated fashion. Finally, if different imaging platforms are used (i.e., different satellites in a constellation), there may be differences in calibration between them that cause differences in reflectance values, and consequently the VI values between images acquired by each platform.