Atmospheric Based Spectral Calibration     (based on atmospheric transmission) & Star Based Radiometric Calibration

Many sensors used in an outdoor environment can be spectrally calibrated by matching their measurements with distinct atmospheric moleculor absorption features. Atmospheric spectral calibration can be used to validate and enhance laboratory spectral calibrations. The figure below shows sensor measurements that were “stretched” to match the MODTRAN atmospheric transmission under conditions similar to the actual measurements. This process often produces a better spectral calibration than can be achieved in the laboratory due to the multitude of available atmospheric lines.

Star calibration is another technique that is often performed in the field. The graph below shows field measurements of known stars that are used for radiometric calibration of the sensor. Such measurements are very useful pre- and post field tests to validate sensor calibration.

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