Practice question

Healthy green foliage strongly absorbs red light about 660 nm because chlorophyll pigments capture it for photosynthesis, while mesophyll cell structure highly reflects near-infrared around 800 to 850 nm. Normalized Difference Vegetation Index exploits this contrast by formula NIR minus RED divided by NIR plus RED, yielding values between minus one and one. Dense vegetation gives high positive values near zero point nine, bare soil near zero, water negative. Red-green ratio lacks physiological basis, and gamma absorption relates to nuclear physics. NIR-RED normalization corrects illumination variations for vegetation vigor mapping.