Spectral Signature

Spectral Signature

1. Spectral signatures
Spectral signatures are the specific combination of emitted, reflected or absorbed electromagnetic
radiation (EM) at varying wavelengths which can uniquely identify an object. The spectral signature of
stars indicates the composition of the stellar atmosphere.
 It is the idea that a given material has a spectral reflectance/emissivity which distinguishes it from
other materials.
 Spectral reflectance is the efficiency by which a material reflects energy as a function of wavelength
 The success of our differentiation depends heavily on the sensor we use and the materials we are
distinguishing
Factors affecting Spectral Signatures
 Solar angle
 View angle
 Surface wetness
 Background and surrounding material
Example
Minerals and rocks can have distinctive spectral shapes based on their chemical makeup and water
content
Spectral Signature Limitations
A spectral signature is not always enough!
 Signature of a water absorption feature in vegetation may not indicate the desired parameter.
 Signatures are typically derived in the laboratory and the field measurements can verify the
laboratory data, so the laboratory measurements may not simulate what the satellite sensor would
see.
 Using field-based measurements only is limited by the quality of the sensors.