original_query: What is the normalized difference vegetation index (NDVI)?
query: What is the normalized difference vegetation index (NDVI)?
answer: The normalized difference vegetation index (NDVI) is a simple graphical indicator used to analyze remote sensing measurements, assessing whether a target contains live green vegetation.  It's calculated as (NIR - Red) / (NIR + Red), where NIR is near-infrared reflectance and Red is red reflectance. NDVI values range from -1.0 to +1.0.