Last updated: 01.12.2023

NDVI: Normalized Difference Vegetation Index

In the simplest terms possible, the Normalized Difference Vegetation Index (NDVI) measures the greenness and the density of the vegetation captured in a satellite image. Healthy vegetation has a very characteristic spectral reflectance curve which we can benefit from by calculating the difference between two bands – visible red and near-infrared. NDVI is that difference expressed as a number – ranging from -1 to 1.

Normalized Difference Vegetation Index: Change Detection

NDVI of a crop or a plant calculated regularly over periods of time can reveal a lot about the changes in their conditions. In other words, we can use NDVI to estimate plant health remotely.

A sudden drop in the NDVI values may be a symptom of crop health deterioration.

The value drop can also correspond to normal changes, such as the time of harvesting, which is why NDVI should be counter-checked against other available data. Correct NDVI values interpretation can help agronomists raise healthier yields, save money on fertilizers, and take a better care of the environment.

NDVI Calculation

NDVI is derived from satellite imagery and calculated in accordance with the formula:

where:

NIR – light reflected in the near-infrared spectrum
RED – light reflected in the red range of the spectrum

According to this formula, the density of vegetation (NDVI) at a certain point of the image is equal to the difference in the intensities of reflected light in the red and infrared range divided by the sum of these intensities.

Index Range

NDVI defines values from -1.0 to 1.0, where negative values are mainly formed from clouds, water and snow, and values close to zero are primarily formed from rocks and bare soil.

Very small values (0.1 or less) of the NDVI function correspond to empty areas of rocks, sand or snow.

Moderate values (from 0.2 to 0.3) represent shrubs and meadows, while large values (from 0.6 to 0.8) indicate temperate and tropical forests.

EOSDA Crop Monitoring successfully utilizes this scale to show farmers which parts of their fields have dense, moderate, or sparse vegetation at any given moment.

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NDVI Saturation

There are certain well-known limitations to the use of normalized difference vegetation index that should not be ignored. Namely, a phenomenon sometimes called “”saturation”” occurs when the amount of leaf pigments reaches a critical point, thus decreasing NDVI’s sensitivity.

As the reflectance in the NIR band keeps increasing at the latest stages of crop development, the RED light remains absorbed. In other words, the NIR value keeps growing, but the RED value stays the same. As a result, the NDVI values become less reliable indicators of crop health.

To solve this problem, EOSDA Crop Monitoring offers other vegetation indices that can be compared against each other to help users reach a more objective conclusion on the state of the crop.

NDVI in Remote Sensing

NDVI is probably one of the most common remote sensing indices out there. Its practical applications are incredibly diverse, including quantifying forest supply and being used as a drought indicator. Among its other uses are forecasting fire zones and desert offensive maps.

Precision agriculture platforms, like EOSDA Crop Monitoring, take advantage of NDVI to guide crop scouts to problem areas in the field and improve the precision of fertilizer application and irrigation, among other field treatment activities. NDVI is preferable for global vegetation monitoring since it helps to compensate for changes in lighting conditions, surface slope, exposure, and other external factors.

What is NDVI in Agriculture?

Put simply, normalized difference vegetation index is a measure of the state of plant health based on how the plant reflects light at certain frequencies (some waves are absorbed and others are reflected).

Chlorophyll (a health indicator pigment) strongly absorbs visible light, and the cellular structure of the leaves strongly reflects near-infrared light. When the plant becomes dehydrated, sick, afflicted with disease, etc., the spongy layer deteriorates, and the plant absorbs more of the near-infrared light, rather than reflecting it. Thus, observing how NIR changes compared to red light provides an accurate indication of the presence of chlorophyll, which correlates with plant health.

NDVI on EOSDA Crop Monitoring

EOSDA Crop Monitoring is a perfect tool for tracking the health of the crops remotely using NDVI and other vegetation indices. All you need to do is add your fields to the system, customize the NDVI settings and start receiving the notifications.

EOSDA Crop Monitoring tracks changes in the NDVI for individual fields throughout the season. This enables you to refer to the historical field’s productivity for up to 7 past years. You can monitor both the crop rotation patterns and the current vegetation rates. With the help of user-friendly graphs, the platform visualizes different types of data, including the vegetation indices, temperature, precipitation rate, growth stages, historical weather, and much more.

Another important feature of EOSDA Crop Monitoring based on NDVI measurements is VRA maps. It allows you to create special maps for variable-rate applications of seeds and fertilizers. This index helps to determine the weak and strong productivity areas across the field measured over long periods of time – Productivity maps (for sowing and K & P fertilizers). NDVI is also used to measure the variations in the crop’s needs for the N fertilizer across the field – Vegetation maps.

The way NDVI helps the scouts on EOSDA Crop Monitoring is basically guiding them to the problem areas within the fields. Much time and resources can be saved by providing the scouts with exact geo-locations of the field’s problem areas. The mobile version of the platform does this extremely well thanks to the offline maps, online reports, and the automatic notification system.

Speaking of notifications, EOSDA Crop Monitoring also employs NDVI to remotely pick up on the latest negative changes in crop development. The system notifies the user automatically about one or more of the stressed fields every time a new satellite image is available and processed with the help of NDVI. By keeping farmers, traders, insurers, and other users up to date with the state of their crops, EOSDA Crop Monitoring allows them to make the best possible decisions based on data.