Why does NDVI, NDBI, NDWI Ranges From -1 to 1?

Have you ever wondered how scientists monitor Earth's diverse landscapes from space? They utilize powerful tools like NDVI, NDBI, and NDWI to interpret satellite imagery. But what do these indices mean, and why do their values range from -1 to 1? Let's explore! The Normalized Difference Vegetation Index, or NDVI, is a key indicator used to assess vegetation health. It's calculated using the formula: NDVI = (NIR - Red) / (NIR + Red) Here, 'NIR' represents the reflectance in the near-infrared spectrum, and 'Red' denotes the reflectance in the red spectrum. Healthy vegetation absorbs most visible light, especially red, and reflects a significant portion of near-infrared light. This contrast results in higher NDVI values, indicating robust plant life. Next, we have the Normalized Difference Built-up Index, or NDBI, which helps identify urban and built-up areas. It's computed as: NDBI = (SWIR - NIR) / (SWIR + NIR) 'SWIR' stands for short-wave infrared reflectance. Built-up regions reflect more SWIR and less NIR, leading to positive NDBI values. Conversely, natural surfaces like vegetation reflect more NIR, resulting in negative NDBI values. Lastly, the Normalized Difference Water Index, or NDWI, is designed to highlight water bodies. It's calculated using: NDWI = (Green - NIR) / (Green + NIR) Water features absorb NIR light and reflect green light, resulting in positive NDWI values. Land areas, on the other hand, typically yield zero or negative values.