Convert DN to Reflectance using QGIS | Radiometric Calibration for Satellite Imagery

Convert DN to Reflectance using QGIS | Radiometric Calibration for Satellite Imagery
DN is just a sensor number; reflectance represents the surface property.
So, we convert DN → reflectance to make the pixel values physically meaningful and comparable.
Key reasons
1. Remove sensor effects
DN depends on the instrument’s gain and calibration. Reflectance normalizes this.
2. Remove illumination differences
Reflectance accounts for sun angle and Earth–Sun distance, which affect the recorded signal.
3. Enable comparison across time and sensors
DN values from different dates or satellites cannot be compared directly, but reflectance can.
4. Allow correct spectral analysis
Many indices and classifications (e.g., vegetation or moisture analysis) are designed for reflectance values.
Summary
We convert DN to reflectance so that the image values represent the actual reflectivity of the Earth's surface rather than the sensor’s raw digital counts.

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