Another Example using NDVI Index
A New Tool for Agriculture and Forestry ...
Drones can benefit the agriculture industry by delivering a high resolution imagery of refectance of an area. This capability can allow farmers to quickly identify the overall health of a field, or find problem areas early. This can result in increased yield per acre of land and also help reduce crop losses due to under / over watering, insect infestation or allow micro management of inputs such as nitrogen and minors.
One tool that can be leveraged by Ag professionals is the NDVI Index. Originally developed by a NASA scientist and used with satellite imagery, this science is a natural fit and easily applicable using UAV / drone technology. Using multi spectrum sensor to aquire bandwidth both in the visible and in the Near Infrared spectrum, we can identify the areas that contain healthy vegitation and areas devoid of or contain weak vegitation.
CDS Aviation can deliver the NDVI solution that best assist the Ag industry professional in assessing a forest / crop area. Contact us at 803-779-9237 for more details.
The example at left shows about 60 acres of mostly forested land. The tract has a mix of conifer and deciduous trees. This image is in the NDVI index color spectrum.
The regions located near the middle band are the greenest and these also correspond to the diceduous tree concentrations. Red regions show low reflectance (a pond, a field and on the perimeter, a road) and indicate a lower solar reflectance.
*This NDVI was generated in September at 34deg N. Deciduous trees still contain active leaf content.
This image shows a wheat field after 1 month of growth. The green area shows healthy plant growth, while the yellow and red areas show stressed areas.
Farmers can utiltize this information to identify regions of fields where;
1) Water needs to be added / removed.
2) Inputs need to be corrected.
3) Areas that need to be replanted.
This service is useful for large tracts in that a quick survey can allow for identifying early in the growth cycle the regions that require additional attention to adjust or recover the crop.
Various crops have different growth stages of importance. Multiple passes over a field during a season can provide invaluable insite to a farmer as to the overall health of his crop, and perhaps increase field yield by identifying problems early in a growth / developmental stage.
Agriculture: Using NDVI to Evaluate Crop Health
What is NDVI and how do we use it?
NDVI (Normalized Difference Vegitation Index) is widely used to determine health of plants. Using a special sensor attached to a UAV we collect images from an area and then stitch these into an orthomosaic representing each of three or four wavelengths. In the example above we collected imagery using three wavelengths of light; green at 560, red at 630nm and NIR at 850nm.
These are visible above are Index maps. Looking through the images you can see each has areas colored as Red - Green (and shades in between at orange and yellow). These images are scaled and broken into 5 color bands and the values associated with the color are relative indication of the refectance in each wavelength captured. In general, the green shaded area represents the strongest reflection of that wavelength and the red areas represent the lowest reflection of that wavelength.
Once we have the refectance Index for the Red and the NIR spectrums, we can also calculate the NDVI index. This is based on the formula (NIR - Red) / (NIR + Red), and the resulting calculated value will be a number between +1 and -1, and in this example color mapped into 5 bands representing Green at +1 to Red at -1.
In the NDVI Index above you can see patches of solid red. In this example we have two ponds, and these are absorbing all light wavelengths so lowest reflectance (Red). You can also see areas of strong green. These represent areas where chlorophyl is active, in this case conifer trees. Also, the grassy field at the left top is showing strong red to yellow. This indicates that the grass is dormant.
Several outside factors can influence the accuraccy of the NDVI calculation. One is the radiance level during the photography period. It is best to shoot the target area during solar maximum. Clouds can also affect the irradiance levels, so even sky is important. Partly cloudy with some images taken in the sunlight and others in the shadow of a passing cloud can affect the accuraccy of the output.
* This images were taken at solar maximum on Feb 18 (winter at location). Source property is located at 34deg N.