What is the NDVI index?
NDVI stands for “Normalized difference vegetation index.” This index quantifies the vegetation by measuring the difference between near-infrared (which vegetation strongly reflects) and the red light (which vegetation absorbs). Overall, NDVI is a standardized way to measure healthy vegetation. The higher the value, the healthier the vegetation.
NDVI values range from +1 to -1 depending on the density of the vegetation. Water, snow, rocks usually show extremely low NDVI values, scarce vegetation like shrubs and grasslands or senescing crops may result in moderate NDVI values and high NDVI values correspond to dense vegetation such as that found in temperate and tropical forests or crops at their peak growth stage.
Importance of NDVI values for the farmer
NDVI values can be averaged over time to establish "normal" growing conditions in a region for a given time of year. When analyzed through time, NDVI can reveal where vegetation is thriving and where it is under stress. This is useful particularly to farmers as they can detect problematic areas and act accordingly to save the crop.
How to access and read NDVI chart
With the AgroCares portal you can access to the NDVI values from your field (historical and current). Moreover, you can make a chart with historical NDVI values and display NDVI images for each field.
On the main menu, you can find the ‘field’ tab. Place the cursor on top of the field to see the latest NDVI value entered. If you click on the field, you will be able to access the NDVI chart with a timeline on top of the screen. The dates that appear on the timeline, are the days that the NDVI values are available, and the cloud icon indicates the dates with no NDVI available value. You can also see the NDVI chart icon on the right side of the portal.
Initially, you can only see the latest NDVI value, but if you want the values for a specific date to be added to your chart, you can go to back to the map and select in the timeline (for instance, 2nd of July, 20th of July and 9th of August). Simultaneously, the NDVI image appears on the map. You can place the cursor over the field to see the NDVI differences within the field. To display the NDVI chart you can click again in its icon where you can see now the NDVI values for the three dates that you just selected.
You can find additional information and instructions on the portal itself on the bottom part of the chart.