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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In these particular plots, there are several anomalies that become immediately apparent ... flowering canola at this particular stage appears to be creating low NDVI values.