Not all NDVI is created equal
Normalized difference vegetation index (NDVI) imagery products have become increasingly common in precision agriculture applications. More companies are offering NDVI and NDVI-like products, including “Synthetic NDVI” images from drone platforms. At Sentera, it is our mission to provide you only the most valuable crop health data, which is why all of our agricultural drone sensors produce TrueNDVI output. It’s important to understand how these products are different before deciding which technology makes sense for your business.
Drone Sensors 101
The camera payloads that come standard with most consumer and professional drones, like the DJI Phantom and DJI Inspire systems, provide a phenomenal value! These cameras and integrated gimbals provide excellent stabilization and deliver smooth, high-resolution video and high-megapixel still images.
The sensors in these cameras are built specifically to be sensitive to the same frequency bands of light that the human eye sees as color — within the visual red, green, and blue (RGB) spectrum. This is how these sensors, and any other RGB camera, produce images that can recreate almost exactly what our eyes would see.
What is NDVI?
Agronomists, turf experts, and scientists have used NDVI for the last 40 years to assess the health of plants. A NDVI sensor uses wavelengths of light outside of what regular RGB cameras can detect. These wavelengths are slightly longer than those of visible light and are located in the near-infrared (NIR) band. Light reflected in the NIR band correlates to the biological processes in plant material. The combination of the non-visual NIR band and the visible red band results in a NDVI value. This value provides growers with an accurate measurement of crop vigor and allows them to zero in on problem areas that need addressing. (For more on this topic, check out our post What is NDVI?)
So, what’s the difference between TrueNDVI and Synthetic NDVI?
NDVI is based on the combination of red light and near-infrared light, period. A sensor that cannot develop a separate measurement of near-infrared light cannot produce NDVI.
An imaging product described as “False NDVI” or “Synthetic NDVI” is exactly that — not NDVI. These products are usually formed by acquiring normal RGB images and manipulating them in a way that hopes to approximate True NDVI. But if the sensor hardware can’t measure and separate near-infrared and red light, the result can never be more than an approximation. To attempt to generate NDVI from a standard RGB drone camera is like trying to figure out the color of somebody’s shirt from a black and white photo — the information just isn’t there.
NDVI was created because it provides a great measure of vegetative vigor. RGB imagery was available from the same satellites, but NDVI was created because it’s a better measurement of vigor than reflectance using any combination of RGB.
False NDVI’s and Synthetic NDVI’s only real attraction is that it’s cheap to build. It can be generated based on an RGB image taken from any camera. But it’s an inferior measure of crop health, and users should expect that analytics and prescriptions generating using inferior data to yield inferior advice.
Will collecting TrueNDVI vs. Synthetic NDVI cost me an arm and a leg?
Sentera builds TrueNDVI sensors that are designed from the ground up to support generation of real NDVI measurements. Our low-cost sensor kits work with most popular consumer drones; alternatively, you can purchase turnkey, upgraded DJI Phantom 4 Pro or Inspire systems with NDVI sensors already integrated. For larger-scale use, the Sentera Omni and Phoenix 2, and the Lockheed Martin Indago platforms offer TrueNDVI capability integrated with available features like real-time NDVI video, longer endurance and more per-flight coverage, and multi-sensor capabilities. Sentera’s NDVI sensors are separate, so the drone’s original sensor payloads continue to function normally.
From the perspective of total cost of ownership and cost per acre surveyed, our systems provide superior, affordable solutions. And, the AgVault software provided with Sentera sensors allows for easy management and exploitation of your data and integration with other precision agriculture tools.
TrueNDVI: The Clear Choice
For those seeking the most accurate and detailed NDVI data, a Sentera sensor that collects NIR-band and TrueNDVI data is the clear choice. Available with sub-centimeter resolution, Sentera offers the most advanced sensors on the market today. They’re the smallest, lightest, and most precise sensors available anywhere. So, what are you waiting for?