NDVI (normalized difference vegetation index) uses false colours to show differences in crop growth & crop health.  Generally, red areas are thin crop or unhealthy crop.  But that is not always the case, so NDVI is a tool that complements ground truthing by an agronomist.

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Canola in particular can give some strange anomalies, with timing of imagery being important to understanding the NDVI values.  Want more info?  Come see LandView at the north end of the FCC tent or in the UAV demo area in the far Northeast corner next to Kubota.