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1. What is NDVI?
NDVI stands for "Normalized Difference Vegetative Index"
NDVI is the most widely used indices of relative biomass. It is obtained by comparing NIR (Near Infrared) and visible red reflectance of a designated area. This relationship between the NIR reflectance and visible red reflectance values gives us an index related to relative biomass.

NDVI=(NIR-Red)/(NIR+Red)

This index gives a value between -1 and 1, with most biomass readings in the 0.1 – 0.9 range and the higher value representing a higher relative biomass. The NDVI maps within Surety and Surety Pro multiply these decimal values by 100 to give the values a more convenient format. The values are assigned a color and then mapped to their respective square.

Download our Remote Sensing Guide for more information: Remote Sensing Intro v1

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2. What is Sentinel?
Sentinel refers to a satellite mission run by the European Space Agency (ESA). The Sentinel-2 mission contains 2 earth observing satellites developed by ESA. This mission along with 5 other Earth data collecting Sentinel missions are for the European Commission’s Copernicus program, which will use this data for different monitoring and science needs.

The Sentinel-2 satellites, known as Sentinel-2A and Sentinel-2B, are Earth observing satellites that record high-resolution optical images for land and vegetation monitoring. The two satellites in tandem will cover the earth every 5 days collecting visible and near-infrared data in swaths 290 km (180 mile) in width. This data is being made available to the public.

Download our Sentinel Tech Guide for more Information: Sentinel-2 Tech Guide

3. What product level?
2A
The Level-2A processing includes a scene classification and an atmospheric correction applied to Top-Of-Atmosphere (TOA) Level-1C orthoimage products. Level-2A main output is an orthoimage Bottom-Of-Atmosphere (BOA) corrected reflectance product.

4. What is Max NDVI?
This refers to the maximum NDVI value for each 10x10 square meter area for the growing season. Since Sentinel readings are taken every 5 days since 2018 (every 10 in 2017), we are able to search through each growing season of data and find the highest NDVI value for each 10 x 10 meter square within an area(field). This means that the Max NDVI maps have data from potentially many different dates.

5. Do NDVI maps accurately reflect yield?
NDVI maps can be used as a relative yield alternative, high biomass converts to higher yield and so on, but agronomic conditions must be kept in mind; crop, variety, weather, disease, pests etc. can change yield even when biomass seems good. A 20% decrease in NDVI does not necessarily reflect a 20% decrease in yield and so on.

6. Can I use NDVI maps for comparing fields?
If the same date and same crop (variety could cause differences), you could use NDVI as a good comparison tool for fields but beware of plant date differences.

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