It is important to monitor a crop throughout the season, but accurate data comparison is only possible with a radiometrically calibrated sensor. Calibration means the effects of varying sunlight conditions are compensated for, allowing growers to compare captures from different flights in the same season, or even compare datasets from different seasons to evaluate the results of fertilizer and treatment applications or changes in farming practices. For example, if three flights were taken over a field in the span of a month, and they were done on both cloudy and sunny days, calibration ensures that the differences in the data are not due to the brightness of the sun and rather to the differences in the plant reflectance itself.