UAVs can obtain faster and more accurate NDVI than satellite imagery for more timely assessment of crop health to provide immediate feedback to the farmer to take action. Early detection, diagnosis, and corrective action, requires high resolution NDVI imagery which will detect crop stress when the problems are just emerging. High resolution UAV based NDVI imagery enables much earlier detection, diagnosis, continuous monitoring, and corrective action than low resolution satellite imagery.
It is known from prior research that field nitrogen content can vary significantly over distances of one meter. NDVI and other vegetation indices have been correlated with nitrogen content.
Modern variable rate spreaders can take advantage of high resolution data to apply fertilizer or pesticides at a one meter square level of resolution. Hence, UAV based NDVI imagery can support variable rate spreaders operating at the 1 meter squared level of resolution whereas Landsat satellite based NDVI imagery can only support variable rate spreaders operating at a 900 square meter (i.e. 30m by 30m) level of resolution.
Significant cost savings in fertilizer and pesticides are possible with higher resolution NDVI imagery and variable rate spreaders. Having the capability to vary the application of pesticide or fertilizer at the 1 meter squared level of resolution should provide cost savings over varying the application of pesticides or fertilizer at the 900 square meter level of resolution. Hence, UAV based high resolution NDVI imagery has the potential to increase cost savings compared to lower resolution satellite based NDVI imagery.
|EZ Health Imagery||Satellite Imagery|
|Frequency of Imagery||Every day or as much as farmer demands. Can be flown daily during critical periods of the growing season||On average 4 times a month. Every 16 days for Landsat 4-5 TM and Landsat -7 ETM +|
|Spatial Resolution of Airborne Data||Sub cm level. ( < 6 cm)@400ft||30 meters for Landsat 4-5 TM and Landsat-7 ETM+|
|Effects of weather||Only can’t fly in rain but obtains accurate NDVI with cloud coverage||Cannot get NDVI imagery with any cloud coverage or rain.|
|Filters||Narrowband spectral band filters||Fixed wideband spectral band filters|
Figure 1 Satellite NDVI Sample Imagery (False color Map: Red corresponds to low NDVI values, Green corresponds to high NDVI values)
Figure 2 UAV NDVI Sample Imagery (False color map: Red corresponds to high NDVI values and Black corresponds to low NDVI values)