What is the Plant Wetness Variability map?
The Plant Wetness Variability map shows the plant’s water potential (the amount of water in the plant), and provides an indication for the irrigation’s Distribution Uniformity (DU) and in plants’ water uptake across the field. The map uses a scale of ‘Dry’ to ‘Wet’, where ‘Dry’ is the lowest level of plant water potential value in the specific field and date, and ‘Wet’ is the highest plant water potential value in these field and date. This means that the scale changes from image to image to indicate the plant water potential uniformity in the field:
Image 1: Plant Wetness Variability Map.
Red areas represent the ‘driest’ areas and blue areas represent the ‘wettest’ areas of the field.
While other layers show potential problems in the field which can be caused by several reasons (disease, nutrition, irrigation etc.), the Plant Wetness Variability map provides an indication for vegetation inconsistency related to water only, as it is monitoring the amount of water in the plant.
How is it being calculated?
Wet plants (with higher water potential in them) reflect sunlight differently than dry plants. Using spectral indices that apply mathematical manipulation on the satellite’s SWIR bands, the system assigns a “relative wetness score” for every pixel, and then paints them accordingly.
How to use the Plant Wetness Variability map?
Start by comparing the Plant Wetness Map of a specific date to the Vegetation Variability image of the same date. Normally, you will see one of the following patters:
- Correlation between Plant Wetness and Vegetation Variability:
If the patterns in the Plant Wetness map match the patterns in the Vegetation Variability map, and they appear in a clear geometric shape, this may be an indication of irrigation system issue. Check the relevant irrigation zone for faults such as a broken valve or a clogged filter. Note that the same symptom can appear when some zones in the field were irrigated and other were not yet irrigated:
Image 2: Dry geometric shape may indicate irrigation system issue
If the patterns in the Plant Wetness map match the patterns in the Vegetation Variability map, but do not appear in a clear geometric shape, this may be an indication of plant uptake issue. This may be caused by salinity, soil type and other field parameters:
Image 3: Correlation between Plant Wetness and Vegetation Variability maps
- Non-correlation between Plant Wetness and Vegetation Variability:
When there is no correlation between the Plant Wetness and the Vegetation Variability maps, this can indicate an issue in the field which is not related to irrigation.
If the Plant Wetness indicates the crop to have high water potential but the vegetation in the Vegetation Variability map seems low in areas of the field, this may be due to crop protection issue:
Image 4: Non-correlation between Wetness and Vegetation.
The yellow spot in the Vegetation Variability map may indicate the development of a disease, as the water distribution in the field is uniform.
Another scenario when such non-correlation may happen is when the field has poor water drainage conditions. In this case, standing water may cause the plants to have high water potential, but on the same time suffocate them and decrease the vegetation over time:
Image 5: Poor drainage, early in the season. Vegetation and water potential are high
Image 6: Same field, later in the season. Standing water caused damage to the vegetation
- Early detection of irrigation problems:
Another reason for non-correlation between the Plant Wetness and Vegetation maps, is that the Plant Wetness map can help with early detection of irrigation problems as early as one month before they are apparent in the field. This will normally happen in ‘mild’ irrigation problems which develop over time, such as pressure issues:
Animation 1: Early detection of irrigation problem
When to use the Plant Wetness map?
Since the Plant Wetness maps present the water potential in the plants, they provide accurate indication only when the NDVI values are at medium-high levels (between 0.45 and 1). View the Wetness Maps with extra cautions when the vegetation in the field is low (emergence in row crops, right after bud break, very young trees etc.), as the indication may be misleading.
How to find the Wetness Variability map in the system?
The Wetness Variability map can be found in the Crop Monitoring tab. Note that the Wetness Variability map is produced using data sources which are only available in some of the constellations of satellites used by Manna, so the map will not be available for all images’ dates. Browse the Layers or the Dates selection menus in the Crop Monitoring tab to display these images when available.
We are currently working on adding this unique layer to all of our satellite images dates.