Satellite imagery is available in the UK for all plots that have a completed sowing operation.
1. Go to a plot in the farm map and click on the satellite icon. This takes you to the satellite archive for that plot. An example can be seen below, where NDVI, IRECI and Ground cover are available indices. The median value is displayed for each image in the image selector and the smoothed value is shown in the charted field progress. Viewing the satellite imagery on the map helps you understand the context of the crop and if any external factors are affecting the growth e.g. treelines or waterways.
2. Satellite insights are also shown on the activity timeline (web and mobile), where a new event will be created each time new imagery is available for a plot. Here we display the same information as above, plus how the index has changed since the last image for that plot. This helps you to understand if a plot is going in the direction you would expect or whether it requires a field visit or treatment. Click or tap on the card to compare the indexed image against the visual image.
Interpreting changes in the median index value
In the activity timeline, you will see that we display the change in a plots index value since the last time we had a reliable image for that plot.
This is to help you understand the performance of your crop, and should be used in conjunction with your crop knowledge. A decrease in NDVI, IRECI or Ground cover values will not always be a cause for concern. Sometimes it will be expected, such as with crop senescence, winter die-back or ripening, and these changes can be used to help detect the onset of these events. Whether there has been an increase or a decrease, the timeline events help you understand the progress of your crop. The images themselves may be visually compared to understand which parts of the field may need attention.
All three indexed images are derived from a visual RGB (red, green, blue) image, which is shown alongside for visual comparison. Each indexed image uses a colour scale of red through yellow to green, where red denotes a low value and green a high value. Red areas in all 3 indices denote poor or non existent crop growth, either at the beginning of the season, or in an otherwise green area may indicate poor performance. Resolution of each "square" in the imagery is 10m by 10m and imagery is provided by the Sentinel 2 satellite.
The Normalized Difference Vegetation Index (NDVI) gives an indication of chlorophyll activity in a given area, and ranges from -1 to 1. The closer to 1 the index values get, the more active chlorophyll is present within a given area. Expected values are somewhere between 0 - 0.2 for bare soil, up to 0.7 - 0.9 for full canopy coverage. In season, NDVI discrepancies can highlight underperforming regions in a given plot.
The Inverted Red Edge Chlorophyll Index (IRECI) is more closely linked with chlorophyll activity in the canopy, though is only available at a lower resolution. IRECI values will range from 0 - 0.2 for bare soil, up to 2.5 for full canopy coverage. IRECI discrepancies provide similar information to that of NDVI, but offer more accurate estimates at the cost of resolution.
Ground cover data is only available for potato crops and is shown as a percentage between 0 and 100, denoting the proportion of the soil surface covered by crop.