GeoSmart's Crop Health Maps are designed to identify areas within agricultural fields that are under stressed conditions. The maps, generated at 10m resolution (enhanced to 3m resolution) are generated every 5 days for anywhere on the Earth's surface. The Crop Health Maps is a fundamental component of GeoSmart's Crop Condition Monitoring System (CCMS), which helps producers (farmers) to detect problems in cash crop fields, orchards and vineyards at an early stage to reduce their impact on yields and crop quality.
More about the science behind the Crop Health Maps
Vegetation indices, such as the normalised difference vegetation index (NDVI), have traditionally been employed to monitor vegetation vigour using satellite imagery. The NDVI makes use of the relationship between the low reflectance of red light and high reflectance of near-infrared (NIR) radiation by plants duding photosynthesis. Healthy crops generally have high NDVI values, whereas stressed crops have noticeably lower values. The NDVI is thus an effective index for monitoring crop condition. Smaller plants of the same species also have lower NDVI responses compared to larger plants, which means it can also be used to monitor growth. This relationship is (in very simple terms) illustrated in the figure below.
NDVI values should consequently always be interpreted within the context of the specific crop type and growth stage. For instance, NDVI values of a young maize field with low canopy cover should not be compared to a field with mature (full canopy) wheat as the exposed soil in the maize field will substantially reduce NDVI values (even if the maize crops are healthy and the wheat fields are in their early scenesense stage). Mature crops should also not be compared to young crops. NDVI values should rather be used to identify problems within a particular field (planted with the same crop, at the same time).
NDVI values normally range from -1 to 1, but the CCMS uses an adjusted version of the NDVI, namely the soil adjusted vegetation index (SAVI), which has been shown to be more effective than the original NDVI for agricultural applications. SAVI values range from -1.27 to 1.27. The figure below shows an example of GeoSmart's Crop Health Map (based on SAVI) of a wheat field at two different times (20 days apart).
On 9 November, the crops were small, while on the 29 November they have reached maturity. The crops on the northern half of the field were planted earlier and generally had higher SAVI values on 11 November. The southern parts of the field experienced stressed conditions on 29 November, as indicated by the relatively lower (e.g. 0.65) SAVI values compared to the mean of 1.07. The standard deviation of SAVI is an indicator of how similar (homogeneous) the SAVI values of a field are. Ideally the standard deviation should be zero. High standard deviations indicate that there are anomalies within the field. In the 29 November example above, the standard deviation is 0.07, which suggests that most (68%) of the SAVI values in the field ranged around 0.07 of the mean (i.e. from 1 to 1.14). This means that the field is relatively homogenous and that the variations are not dramatic. The fact that the standard deviation decreased from 11 November to 29 November is also a sign that the variations are on a decreasing trend.
The Crop Health Map is best used in combination of GeoSmart's Crop Moisture Map. For instance, the figure below shows a Crop Health Map (left) and a Crop Moisture Map (right) of the same field as above, for 29 November. These maps were rendered to emphasize differences within the field (called "classified maps" in the CCMS). By comparing these maps one can clearly identify management zones that require attention.
GeoSmart's Crop Condition Monitoring System (CCMS) automatically generates a Crop Health Map and Crop Moisture Map per field at a five day interval. Several variations of the maps are also generated and incorporated into a report (in PDF format) consisting of figures, graphs and maps. Large changes are highlighted in the reports to draw attention to developing problems.
|Spatial resolution||10m (enhanced to 3.3m)|
|Temporal availability||Every 5 days|
|Horizontal accuracy||Typically 10m|
|Format||PDF, JPG, TIF, IMG|