The most widely used vegetation index is

Correct option is B

The correct answer is (B) NDVI

Explanation:
• NDVI stands for Normalized Difference Vegetation Index. It is the most popular index used in remote sensing to monitor the health and density of vegetation.
• It is calculated using the formula: $NDVI = \frac{NIR - Red}{NIR + Red}$.
• Healthy vegetation reflects a lot of Near-Infrared (NIR) light but absorbs most of the Red light for photosynthesis. Thus, healthy plants have a high NDVI value (approaching +1).
• Bare soil, rocks, or stressed plants have low NDVI values closer to 0, while water typically has negative NDVI values.

Information Booster:
• NDVI was popularized by Rouse et al. in $1974$.
• It is widely used for yield prediction, drought monitoring, and forest management.
• One limitation of NDVI is that it can saturate over very dense canopies (tropical forests) and is sensitive to soil brightness in sparse vegetation.

Additional Knowledge:
• SAVI (Option A): Soil Adjusted Vegetation Index; it includes a correction factor (L) to minimize the influence of soil brightness in areas with low vegetation cover.
• GVI (Option C): Greenness Vegetation Index; it is part of the Tasseled Cap transformation which separates soil brightness from vegetation greenness.
• Option D: Likely refers to variations or transformations of the index for specific statistical normalizing purposes, but it is not a standard name for a widely used index.