Images are taken after the fact. Make sure you look at past tension data when analyzing an NDVI map. The impact of high tension may take a while to be noticeable on an NDVI map. NDVI will let us know about the health of a crop. But as you know, agriculture is complex. Water is not the only variables at play in the health of a plan. NDVI values obtained with satellite data with high temporal resolution have a strong correlation with crop phenological stages (emerged, maturity, harvest). However, there are certain limitations. The NDVI may saturate at later stages, when the crops reach canopy closure, and produce inaccurate results. Crop type, crop age, row width will have an impact on the color you see on the map. Your grower could have a field that shows up mostly as dark orange for a field with healty 1st year leaf trees. This also means the NDVI will vary throughout the season.