Growers know when strong winds or hail pass through their fields that there's a chance their fields have suffered damage. While there's nothing you can do to prevent these events, TerrAvion can help you calculate how many acres were affected by the storm and determine how bad the damage is across your fields.
When plants are damaged by weather related events such as a hail storm or extreme wind, they become stressed, and this stress is recognized as low vigor in NDVI imagery. To identify crop damage resulting from a weather related event, growers can compare their most recent pre-storm imagery to their first post-storm images.
Identifying Weather Related Crop Damage with NDVI Imagery:
Identifying and quantifying crop damage in 3 steps:
Identify Areas in the Field with Damage:
1. Before you go to a field with damage (or after you visit the field and realize it was affected) pull up the NDVI/Vigor image for the field.
2. Compare your most recent pre-storm and post-storm imagery.
3. In your most recent post-storm imagery, identify the areas where vigor has decreased. Notice the different levels of vigor variability in the NDVI imagery, which will likely correlate to the severity of crop damage.
If you’re using the TerrAvion OverView Mobile app on iOS--or the TerrAvion OverView Beta on Android--the color scale uses grey for the lowest NDVI value, then red, orange, light green, and dark green for the highest value.
4. The imagery can help direct you on where to scout and provide a reference for your notes later.
Make Notes on the Extent of the Damage in Each Area.
Use the TerrAvion Zoning Tool to Determine How Many Acres Were Affected:
Get set up
1. To quantify the scale of your crop damage, use the TerrAvion web app
2. Find the field you scouted and select the post-wind or hail image (the same one you used to scout the field)
3. Choose the same image type and color scale you used to scout the field. If you’re using the new mobile app, its the dynamic vigor map with the NDVI_2 color scale
Use the Zone Creation Tool:
1. Click on the grid icon on the lower-right of the screen
2. Pick a number of zones that makes sense
The goal is to get the zone preview image to match the areas and severity of damage in the field.
In the example before, we saw areas with stand reduction of 60%, 30% and <10%. For this, we might choose 3 zones (one for each) or we might only be interested in areas with >30% stand reduction, and just choose two
3. For our example, we’ll choose 2 zones
4. Use your notes to adjust the zone cutoff(s) the preview matches what you saw on the ground.
Use the sliders to adjust the NDVI ranges
Click All to turn on the map preview and see the number of acres in each zone
You can also hover your mouse over an area of the image to get the specific NDVI value for that area, e.g. “Red areas have an NDVI value below 0.486”. You can enter this value into the Cutoff box.
5. Click the box next to Zone 1 to assure that your zoning map accurately represents the crop damage you observed in your field. Adjust the zoning tool NDVI histogram if you would like to alter the range of your zoning map.
6. When you are satisfied, note the acres under the Area column for Zone 1. This number will give you general idea of how many acres of your field were affected by storm damage.
7. To act on this information by replanting, making nutrient applications, etc., follow these steps on how to complete your NDVI zoning map.