NIR
Near-Infrared. A portion of the electromagnetic spectrum (approximately 700-1400nm) not visible to the human eye. Vegetation strongly reflects NIR radiation, making it a key band for vegetation indices like NDVI. Also used to detect water bodies and distinguish soil types.
Overview
Near-Infrared (NIR) refers to the portion of the electromagnetic spectrum immediately beyond visible red light, spanning approximately 700 to 1100 nm. Invisible to the human eye, NIR radiation is critically important in Earth observation because of the dramatic spectral contrast it reveals between vegetation, water, and soil. Healthy green vegetation reflects up to 60% of incoming NIR energy while absorbing most visible red light — a contrast that forms the basis of virtually every vegetation index used in remote sensing.
How It Works
The strong NIR reflectance from vegetation occurs because of the internal cellular structure of plant leaves. The spongy mesophyll tissue — irregularly shaped cells separated by air spaces — acts as an efficient light scatterer at NIR wavelengths. Because no plant pigment absorbs NIR radiation, photons bounce between cell walls and are reflected back outward. This "red edge" — the sharp transition from low red reflectance to high NIR reflectance occurring around 700-730 nm — is a defining spectral feature of live vegetation.
Water, by contrast, strongly absorbs NIR radiation, appearing dark in NIR imagery. Soil reflectance in NIR varies with composition and moisture but is generally moderate and increases gradually with wavelength. These contrasting behaviors make NIR the most information-rich spectral region for land surface analysis.
Key Facts
- Wavelength range: approximately 700-1100 nm, just beyond visible red.
- Healthy vegetation reflects 40-60% of incoming NIR radiation — far more than visible light.
- Sentinel-2 Band 8 (842 nm, 10 m) and Band 8A (865 nm, 20 m) are the primary NIR bands.
- Landsat 8/9 Band 5 (865 nm) captures NIR at 30 m resolution.
- The "red edge" transition from low red to high NIR reflectance (~700-730 nm) is a key indicator of plant health and species.
Applications
Vegetation Index Computation
NIR is half of the NDVI equation and is used in EVI, SAVI, and most other vegetation indices.
Water Body Detection
Water absorbs NIR strongly, making it appear dark and easily distinguishable from land in NIR imagery.
Crop Health and Biomass Estimation
NIR reflectance correlates with leaf area index and biomass, enabling crop monitoring and yield estimation.
False Color Composites
NIR-Red-Green composites render vegetation as bright red, dramatically enhancing vegetation visibility and health assessment.
Limitations & Considerations
NIR reflectance alone cannot distinguish between vegetation species or stress types — it must be combined with other bands. Atmospheric scattering is less severe in NIR than visible wavelengths, but water vapor absorption exists around 940 nm. Dry or dead vegetation loses its NIR reflectance advantage over soil, reducing index sensitivity. Sensor-specific NIR band positions and widths vary, affecting cross-sensor comparisons.
History & Background
NIR imaging from space began with Landsat 1's MSS Band 7 (800-1100 nm) in 1972. The critical role of NIR in vegetation studies was recognized through the development of NDVI (Rouse et al., 1973). Each subsequent sensor generation has refined NIR band placement — Sentinel-2 provides both a broad NIR band (B8, 115 nm wide) for general use and a narrow NIR band (B8A, 20 nm wide) for applications requiring reduced atmospheric scatter.
Analyze NIR data with LYRASENSE
Use our agentic notebook environment to work with satellite data and compute indices like NIR — no setup required.