3.1. Basics of Spectral Signatures and Libraries

What is a Spectral Signature?

A spectral signature is the unique pattern of reflectance or absorption that a material exhibits across a range of wavelengths. Because different materials interact with light differently, each one has a distinct spectral fingerprint, which can be used to identify, classify, and analyse objects in hyperspectral imagery.

• Reflectance curves display how a material reflects light across the spectrum.
• These curves help differentiate between materials with similar visual appearances but different compositions (e.g., healthy vs. diseased crops, or different mineral types).

Spectral Libraries

A spectral library is a curated collection of reference spectral signatures, typically built from:

• Field measurements using spectroradiometers
• Laboratory spectrometry under controlled conditions
• Satellite or airborne data validated against ground truth

Spectral libraries are critical for:

• Material identification and classification
• Training classification algorithms
• Comparing scene spectra with known materials

Interpreting Spectral Signatures

• Identify diagnostic absorption features at specific wavelengths.
• Consider external factors: moisture content, surface roughness, and atmospheric effects.
• Use spectral indices (e.g., NDVI, chlorophyll indices) to enhance interpretation.