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NDVI

General Brochure (PDF)

Agriculture Brochure (PDF)

EagleView Software
Learn more about our proprietary software developed specifically for agriculture.

The precision agriculture application has been around for many years. The original concept was to take images from a satellite that measures the health of a field. This data is then used to create a prescription for the field that defines varying rates of application to the field. Appropriate GPS-based variable rate equipment can then automatically vary the rate of application to the field to maximize the results while minimizing the cost.

The most commonly used image is the Normalized Difference Vegetation Index (NDVI). This image is a combination of the red and infrared images and is based on the concept of healthy plants absorbing red while reflecting infrared.

The resulting value has a range from -1 to +1, +1 being the most vigorous growth. This is often converted into a colorized image to make it easier for our picture processing brains to understand the data.

Unfortunately, there are so many variables that impact the measured NDVI value. The atmosphere has a tremendous impact on the image as seen from the airborne camera. The time of year, sun angle, and position of the camera also have an impact. Further, the local environment, field history, and plant variation all have impact on the NDVI created from the images. The simplified equation of the total at-sensor solar radiation gives an idea as to how complex it is to determine an absolute NDVI.

Even the simplified text description of the simplified equation is very complex. "The total spectral radiance received by the sensor is linearly proportional to the surface diffuse reflectance modified by a multiplicative, spatially- and spectrally-variant factor that depends on the terrain shape, and an additive, spatially-invariant, spectrally-variant term due to view path scattering." Remote Sensing, Schowengerdt

The concept of the total at-sensor solar radiation is based upon three paths for the radiation from the sun making it all the way to the sensor. The first is direct radiation, that which directly reflects off of the ground to the sensor. The next is the solar radiation that is diffused by the atmosphere on the way to the ground, and the last is the radiation that is reflecting off of the atmosphere and back to the sensor.

It might be possible one day to make enough measurements with multiple sensors at the moment the image was taken to calibrate the NDVI. Unfortunately this puts us back into a situation where we have to know well in advance where the images need be taken to set up all of the sensors. Even so, significant research will be required to determine how the data measured by these sensors will impact the actual NDVI value.

The relative NDVI removes most of the variables and simplifies the concept. It still gives you a view into the relative growth vigor on a field on a particular day, but used properly, it can help identify problem areas. Most importantly, it puts the local expert back into the creation of the prescription.

But, you must keep in mind that the NDVI is just another tool for your tool box. It is not a silver bullet that will automatically solve problems. Also, the relative NDVI is not able to compare the results of different fields nor is it able to compare results taken at a different time. Further, it can require an experienced eye to properly interpret the results.

So the relative NDVI accepts the raw data from the airborne camera and then processes the data. This data is then made available to the local expert who then makes the decisions that lead to the final prescription for that field.

We are presently using piloted aircraft as the platform for the camera. This presently provides the quickest response and highest quality at the lowest price. We are constantly evaluating new options, such as UAVs (unmanned aerial vehicles). At this time, even though owning, maintaining, and operating aircraft is very expensive, the piloted aircraft is still the best option.

View these articles and brochures for more information on agriculture. Or visit the links on the left-hand side of the page.

General Brochure (PDF, 34.6 MB)

We don't just do forestry! To find out more about our other applications (like mines, agriculture, streams and more), take a look at this brochure.

Agriculture Brochure (PDF, 19.0 MB) 

Agriculture is another of our main application areas. We are able to provide color, infrared and even vegetation index images that can be used by themselves or integrated into GPS systems for precision agriculture. The possibilities are endless, and the information you can get from our images often can't be found anywhere else. Check out this brochure for details.


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