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Spectral Signature vs. Spectral Reflectance Curve


Spectral Signature 

A spectral signature is the unique pattern in which an object:

  • absorbs energy

  • reflects energy

  • emits energy

across different wavelengths of the electromagnetic spectrum.

✔ Key Points

  • Every natural and man-made object on Earth interacts with sunlight differently.

  • These interactions produce a distinct pattern, just like a "fingerprint".

  • Sensors on satellites record these patterns as digital numbers (DN values).

  • These patterns help to identify and differentiate objects such as vegetation, soil, water, snow, buildings, minerals, etc.

✔ Examples of Spectral Signatures

  • Healthy vegetation → High reflectance in NIR, strong absorption in red

  • Water → Strong absorption in NIR and SWIR, low reflectance

  • Dry soil → Gradual increase in reflectance from visible to NIR

  • Snow → High reflectance in visible, low in SWIR

✔ Why Spectral Signature Matters

It allows:

  • Land cover classification

  • Change detection

  • Crop health monitoring

  • Mineral mapping

  • Water quality analysis

Spectral Reflectance Curve (Graphical Representation)

A spectral reflectance curve is the graph that visually shows the spectral signature of an object.

✔ What the Curve Shows

  • X-axis (horizontal): Wavelength (μm or nm)

  • Y-axis (vertical): Reflectance (%)

✔ How to Read the Curve

  • Peaks (high points): Strong reflection

  • Valleys (low points): Strong absorption

  • Shape of the curve: Unique for each material

✔ Example Curves

  • Vegetation:

    • Low reflectance in blue and red (due to pigment absorption)

    • Very high reflectance in NIR (leaf cellular structure)

  • Water:

    • Almost no reflectance in NIR or SWIR

    • Appears dark in those bands

  • Snow:

    • Strong reflectance in visible

    • Absorbs more in SWIR

✔ Purpose of the Curve

  • Helps visually compare different materials

  • Used for classification and object identification

  • Helps understand sensor band selection for specific tasks


  • Spectral Signature = The unique way an object reflects, absorbs, or emits energy.

  • Spectral Reflectance Curve = The graph that shows this unique pattern.

The signature is the physical property.
The reflectance curve is the visual tool that helps us analyze it.


A spectral signature is the characteristic pattern of reflectance, absorption, and emission of an object across wavelengths. A spectral reflectance curve is the graphical representation of this signature, with wavelength on the x-axis and reflectance (%) on the y-axis. Each object has a unique curve shape, which helps in identification and classification in remote sensing.


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